Journal of Human Evolution 50 (2006) 1e35

Cranial anatomy of the Paleocene plesiadapiform Carpolestessimpsoni (Mammalia, Primates) using ultra high-resolution

X-ray computed tomography, and the relationshipsof plesiadapiforms to Euprimates

Jonathan I. Bloch a,*, Mary T. Silcox b,1

a Florida Museum of Natural History, University of Florida, Gainesville, PO Box 117800, FL 32611-7800, USAb Department of Anthropology, University of Winnipeg, 515 Portage Ave, Winnipeg, Manitoba R3B 2E9, Canada

Received 13 September 2004; accepted 22 June 2005

Abstract

Central to issues surrounding the origin of euprimates, affinities of Paleocene Carpolestidae have been controversial. Carpolestids have beenclassified as plesiadapoid primates, tarsiiform euprimates, dermopterans, or the sister taxon of euprimates to the exclusion of other plesiadapi-forms, based exclusively on dental or postcranial data. Newly discovered crania of Carpolestes simpsoni from the latest Paleocene of the ClarksFork Basin, Wyoming, are the first described for the family Carpolestidae. The two best preserved skulls were studied using ultra high-resolutionX-ray computed tomography. Comparison of these specimens to those of other stem primates (Plesiadapiformes) demonstrates that the diversityof cranial morphology in this group is greater than previously thought. Carpolestes differs from euprimates and is similar to other plesiadapi-forms (Ignacius and Plesiadapis) in lacking a postorbital bar and having a relatively long rostrum. Carpolestes is similar to fossil euprimates andPlesiadapis in having a bullar morphology consistent with a petrosal origin, and differs from Ignacius, in which the bulla is composed of theentotympanic. Carpolestes differs from primitive euprimates and all other known plesiadapiforms in possessing a two-chambered auditory bulla,similar to that of modern Tarsius. However, Carpolestes had an internal carotid artery (ICA) that took a transpromontorial route from a poster-omedially positioned posterior carotid foramen (pcf), unlike Tarsius, in which this artery takes a perbullar route from an anterolaterally posi-tioned pcf. Carpolestes has clear grooves on the promontorium for both the promontorial and stapedial arteries, indicating that it had anunreduced internal carotid circulation, similar to that of early euprimates. Carpolestes differs from primitive euprimates and some specimensof Ignacius in not having bony tubes surrounding the branches of the ICA. Cladistic analysis of cranial data fails to support a close relationshipof Carpolestidae to either tarsiiform euprimates or extant Dermoptera, but suggests a close relationship between Carpolestidae, Plesiadapidae,and Euprimates.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Primates; Plesiadapiformes; Cranial anatomy; Computed tomography; Phylogeny

Introduction

The Carpolestidae were small, arboreal mammals that areknown from the early to late Paleocene of North America

* Corresponding author. Tel.: C1 352 392 1721x515.

E-mail addresses: jbloch@flmnh.ufl.edu (J.I.Bloch),m.silcox@uwinnipeg.ca

(M.T. Silcox).1 Equal contributors listed alphabetically.

0047-2484/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jhevol.2005.06.009

(Rose, 1975; Bloch et al., 2001a,b; Silcox et al., 2001; Blochand Boyer, 2002a) and the late Paleocene to early Eocene ofAsia (Beard and Wang, 1995; Smith et al., 2004). It was likelythe oddly distinctivemorphology of the posterior premolars thatled Matthew and Granger (1921: 6), in their description of thefirst known carpolestid, to conclude: ‘‘This form cannot be def-initely assigned to any family or order; it may be a primate,a menotyphlan insectivore, or neither.’’ Other early studies clas-sified carpolestids as tarsiiform euprimates (Z‘‘primates of

2 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

modern aspect,’’ or crown primates; e.g., Simpson, 1945),a view still held by some, likely based on the carpolestid-likefeatures of the euprimate Altanius from the early Eocene ofAsia (Dashzeveg and McKenna, 1977; Rose and Krause,1984; McKenna and Bell, 1997). However, most recent workershave placed Carpolestidae in the plesiadapiform superfamilyPlesiadapoidea, along with the families Plesiadapidae andSaxonellidae (e.g., Rose, 1975; Beard and Wang, 1995; Silcoxet al., 2001; Bloch et al., 2001a; Bloch and Boyer, 2003),and sometimes Paromomyidae (e.g., Gingerich, 1976; Maaset al., 1988).

Plesiadapiformes was a group of Paleocene and Eocenemammals from North America, Europe, Asia, and possiblyAfrica (Tabuce et al., 2004) that includes eleven or twelve ex-tinct families (Purgatoriidae, Micromomyidae, Microsyopidae,Picrodontidae, Picromomyidae, Paromomyidae, Plesiadapi-dae, Carpolestidae, Saxonellidae, Toliapinidae, Palaechthoni-dae, and possibly Azibiidae; Hooker et al., 1999; Tabuceet al., 2004; Silcox and Gunnell, in press). Although plesiada-piforms exhibit some common traits, such as enlarged upperand lower central incisors, several authors have consideredthe group to be non-monophyletic (Van Valen, 1994; McKennaand Bell, 1997; Hooker et al., 1999; Silcox, 2001, in press; Sil-cox and Gunnell, in press; see Clemens, 2004, for an opposingview). Even if this proves to be true, the term ‘‘plesiada-piform’’ is still a useful informal designation for members ofthese families.

Beard (1993a,b) classified all plesiadapiforms, includingCarpolestidae, in Dermoptera as the sister taxon to Euprimates(his ‘‘Primates’’). Kay et al. (1990, 1992) also argued for a closerelationship between plesiadapiforms and dermopterans, al-though they considered the plesiadapiformedermopteran cladeto be only distantly related to Euprimates. The dermopteraneplesiadapiform relationship has been seriously questioned,however (Krause, 1991; Szalay and Lucas, 1993, 1996; VanValen, 1994; Stafford and Szalay, 2000; Boyer et al., 2001;Bloch and Silcox, 2001; Sargis, 2002c; Bloch and Boyer,2002a,b, 2003; Silcox, 2003, in press), and to date no evidencespecific to carpolestids has been presented that supports thisview (Fox, 1994). Indeed, neither Beard (1993a) nor Kayet al. (1992) included any carpolestids in their analyses.More recent cladistic analyses that have included carpolestidshave placed them in Primates as either the sister taxon to Eupri-mates (Bloch and Boyer, 2002a) or as one of several taxa on theprimate stem (Silcox, 2001; Silcox et al., 2005).

A significant impediment to the study of carpolestid rela-tionships has been a lack of well-preserved cranial specimens.Here we provide the first descriptions of fairly complete carpo-lestid crania, including previously unknown details of the face,and the first detailed treatment of the basicranium (see Blochand Gingerich, 1994; Bloch, 1995; Bloch and Silcox, 2003, formore superficial discussions of the basicranium). The currentstudy also tested the hypothesis that the cranial anatomy ofplesiadapiforms supports a dermopteraneplesiadapiformgrouping (Kay et al., 1990, 1992) using cladistic analysis.

Most previous studies of the Carpolestidae focused on thedentition, the anatomical region most often preserved in fossil

collections (Matthew and Granger, 1921; Gidley, 1923;Jepsen, 1930; Simpson, 1928, 1929, 1935, 1936, 1937; Dorr,1952; Russell, 1967; Gazin, 1971; Rose, 1975, 1977, 1981;Holtzman, 1978; Krause, 1978; Gingerich, 1980; Fox, 1984,1994, 2002; Biknevicius, 1986; Beard and Wang, 1995; Blochand Gingerich, 1998; Beard, 2000; Bloch et al., 2001b; Silcoxet al., 2001; Smith et al., 2004). In the dentition, carpolestidsare characterized by an unusually enlarged, multicuspate P4with correlated specializations of P3e4, and a reduced anteriordentition, but with an enlarged and procumbent I1 (Rose,1975). Prior to the discovery of the first known carpolestidskeleton (Bloch and Boyer, 2001, 2002a), the postcranium ofthis family was represented only by a fragment of a humerus(Beard, 1989) and a femur (Bloch and Gingerich, 1994, 1998).The skeleton of the late Paleocene carpolestid Carpolestessimpsoni demonstrates features that are surprising in light oftheir absence in plesiadapids. In particular, C. simpsoni shareswith euprimates an opposable hallux bearing a nail and otherfeatures of the digits of the hands and feet associated withstrong grasping capabilities (Bloch and Boyer, 2002a, 2003).When these data were included in a cladistic analysis usingpostcranial characters only, carpolestids did not group withother plesiadapoids, but were the sister group to euprimates(Bloch and Boyer, 2002a). In light of this result, the cranialmaterial of this familydparticularly of this speciesdtakeson a new importance (Kirk et al., 2003; Bloch and Boyer,2003; Bloch et al., 2004).

As for most plesiadapiforms, previous work on carpolestidcranial anatomy has been limited by a lack of material.Jepsen (1930) described the first known fossil preserving as-pects of carpolestid cranial anatomy, a maxillary fragment ofCarpolestes dubius. He described the following characteris-tics: (1) large infraorbital foramen above P3, (2) zygomaticprocess of the maxilla originating from a small area directlyabove M2, (3) M3 rooted in a round and prominent posteriortuberosity of the maxilla, (4) suture between the maxilla andthe palatal division of the palatine extending forward close tothe lingual margins of M2-3 and then further extendingobliquely and anteromedially, and (5) moderately archedand perforated palate (Jepsen, 1930). Regarding the lastpoint, he (Jepsen, 1930: 523) noted: ‘‘The anterior wall ofa large foramen is at a place opposite the middle of P3.This foramen is possibly confluent with a foramen whoseback margin aligns with the anterior edge of M1, or theremay have been a bridge between these two limits, dividingthe opening into two foramina.’’ Jepsen (1930) refrainedfrom any comparisons or phylogenetic discussions of the cra-nial anatomy he described.

Rose (1975) made a composite reconstruction of the rostralportion of the skull from new, fragmentary specimens of Car-polestes dubius, including a partially crushed snout. This re-construction is in broad agreement with the interpretationsof Jepsen (1930), although Rose was more definitive aboutthe relationships of carpolestids; he considered Carpolestesto be a primate related to Plesiadapis. Rose noted the follow-ing characteristics: (1) maxilla with a relatively large contribu-tion to the face (more than in Plesiadapis), (2) zygomatic

3J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

portion of the zygomatic arch robust (as in Plesiadapis), (3)horizontally oriented zygomaticomaxillary suture extendingfrom above M2 to above the mesial part of P4, (4) premaxillarelatively small (compared to that of Plesiadapis), and (5)small foramen (possibly an emissary) present on the anterolat-eral portion of the frontal near, but external to, the orbital mar-gin (Rose, 1975). Rose (1975) also discussed the palatalfenestrae in C. dubius, observing: ‘‘Their occurrence in carpo-lestids is unique among primates, and their function is unclear’’(p. 49). In a reconstruction of the palate of Carpodaptes ston-leyi (originally identified as C. cygneus; see Fox, 2002),Krause (1978) illustrated a single, large, undivided palatal fe-nestra. This description differed from the interpretations ofboth Jepsen (1930) and Rose (1975), according to whom C.dubius had either 2 or 4 palatal fenestrae (neither authorclaimed that one interpretation was necessarily better sup-ported than the other), with both the lateral and medial wallsof the anterior fenestrae bounded by the maxilla.

Gingerich (1987) included a photograph of the first knownrelatively complete skull of a carpolestid, although he provid-ed no anatomical description (this specimen is included in thecurrent study and is the holotype of Carpolestes simpsoniBloch and Gingerich, 1998). Bloch and Gingerich (1998) pro-vided a composite reconstruction of the palate in Carpolestessimpsoni that is similar to that provided by Krause (1978) forC. stonleyi, with the large palatal fenestration appearing to bedivided down the midline by the vomer. There is no division ofthis opening by the maxilla, and the apparent division by thevomer is likely a consequence of the dorsoventral crushingof the specimen, upon which this illustration was primarilybased (UM 101963). Bloch and Gingerich (1998) noted: (1)the posterior margin of the palate is nearly straight and but-tressed by a strong, rounded postpalatine torus, with wings ex-tending posteriorly onto the basicranium (similar to thecondition in Leptictis and Ignacius), and (2) moderately sizedincisive foramina are present at the anterior contact betweenthe premaxilla and maxilla. As should be clear from this sum-mary, apart from a few details of the anterior facial and palatalanatomy, carpolestid cranial morphology has previously beenlargely unknown.

In addition to providing the first comprehensive descriptionsof carpolestid cranial anatomy, we also compared these newskulls to others that are known for plesiadapiforms. Well-pre-served cranial material has long been known for plesiadapids(Simpson, 1935; Russell, 1959, 1964; Gingerich, 1976; Mac-Phee et al., 1983), although one of the best preserved speci-mens has never been formally described (Plesiadapis cookei;but see Gunnell and Gingerich, 1987; Gunnell, 1989; Gingerichand Gunnell, 1992; Bloch and Silcox, 2001). Microsyopids arealso known from multiple cranial specimens (Szalay, 1969;MacPhee et al., 1983, 1988, 1989; Gunnell, 1989). MacPheeet al. (1988, 1989) alluded to a Microsyops partial cranium(UW 12362), which may be the best preserved microsyopidspecimen known. This skull has never been fully described,although it is currently under study by M. Novacek (personalcommunication). The only other plesiadapiform family thatis well known from cranial material is the Paromomyidae,

for which multiple specimens are known, although their inter-pretation has varied over time (Simpson, 1955; Szalay, 1972;Rose and Gingerich, 1976; MacPhee et al., 1983; Kay et al.,1990, 1992; Bloch and Silcox, 2001; Silcox, 2003).

Two isolated cranial fragments have been attributed to themicromomyid species Tinimomys graybulliensis (Gunnell,1989; MacPhee et al., 1995). The details of the morphologypreserved in these specimens are quite different, indicatingthat they likely do not belong to the same species. In lightof the incomplete nature of these specimens, and the diffi-culties inherent in their identification, Tinimomys graybul-liensis was not included in the cladistic analysis presentedhere. A fairly complete specimen of a micromomyid isnow known, and is currently under study (Bloch, 2001; Sil-cox and Bloch, 2004; Bloch and Boyer, in press), but wasnot included here, as it remains undescribed. Fragmentarycranial specimens are also known for a palaechthonid (Pa-laechthon nacimienti; Kay and Cartmill, 1977) and a picro-dontid (Zanycteris paleocenus; Matthew, 1917). The latterlacks most of the phylogenetically informative cranial re-gions, and was not included here. The specimen of P. naci-mienti lacks the basicranium, but does provide someinformation about the anterior part of the skull, and was in-cluded in the cladistic analysis.

X-ray computed tomography is rapidly becoming a criticaltool in the study of non-human primate fossil skulls (e.g., Spoor,1996; Spoor et al., 1998; Seiffert et al., 1999; Rasmussen,2002; Rae et al., 2002; Rossie et al., 2002; Rossie, 2005;Bush et al., 2004a,b; Rae and Koppe, 2004). Ultra high-resolution X-ray computed tomography (also known as‘‘microCT’’ or uhrCT) is particularly valuable for studyingsmall skulls, since slice thicknesses and pixel sizes are smallerthan in traditional ‘‘medical’’ CT (i.e., substantially smallerthan 1 mm), so even minute structures can be visualized. Pre-vious analysis of a uhrCT data set of the paromomyid Ignaciusgraybullianus (Silcox, 2003) provided strong support for a con-troversial anatomical interpretation (the presence of an ento-tympanic bulla; Kay et al., 1990, 1992; Bloch and Silcox,2001), and revealed a completely unsuspected anatomical fea-ture (a bony tube for the internal carotid nerves and/or artery).In this study we use uhrCT data to help form a basic under-standing of Carpolestes’ cranial anatomy, and to reveal fea-tures that are not otherwise visible.

One of the reasons why uhrCT scanning of the Carpolestesspecimens was so successful is the method of preparation usedin their recovery. As has been demonstrated previously (Silcox,2003), acid preparation of specimens recovered from freshwa-ter limestone (Bloch, 2001; Bloch and Bowen, 2001; Bloch andBoyer, 2001; Bowen and Bloch, 2002) can facilitate excellentvisualization of structures in uhrCT because the matrix thatfilled internal features has largely been removed. This prepara-tion regime has been central to the study of plesiadapiforms inthe past. Paromomyid and micromomyid specimens preparedfrom Eocene limestones by Peter Houde provided much ofthe material upon which debates over plesiadapiform systemat-ics have been waged (Beard, 1989, 1990, 1993a,b; Kay et al.,1990, 1992; Bloch et al., 2000; Bloch and Silcox, 2001). Other

4 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

discoveries of plesiadapiform skeletons also derive from acidpreparation from early Cenozoic limestones (Gingerich et al.,1983; Gunnell and Gingerich, 1987; Boyer and Bloch, 2000;Bloch, 2001; Bloch and Boyer, 2001, in press), and are provid-ing a rich source of data for fundamental revisions to our under-standing of this group (Bloch et al., 2001a, 2002a,b, 2004;Bloch and Boyer, 2002a,b, 2003, in press; Boyer et al., 2001;Boyer and Bloch, 2002a,b).

Institutional abbreviations

AMNH, American Museum of Natural History (New York);CM, Carnegie Museum of Natural History (Pittsburgh); CR,Cernay-les-Reims (for MNHN specimens from that locality);MNHN, Museum National d’Historie Naturelle (Paris);MPM, Milwaukee Public Museum (Milwaukee); PSU, Penn-sylvania State University Museum of Anthropology (State Col-lege); UKMNH, University of Kansas Museum of NaturalHistory (Lawrence); USNM, United States National MuseumDepartment of Paleobiology (Smithsonian Institutions, Wash-ington D.C.); USNM(MA), United States National MuseumDivision of Mammals (Smithsonian Institutions, WashingtonD.C.); UM, University of Michigan Museum of Paleontology(Ann Arbor); UMMZ, University of Michigan Museum ofZoology (Ann Arbor); UW, University of Wyoming (Laramie).

Materials and methods

Materials

Most interpretations of Carpolestes simpsoni cranial anatomywere made from two fairly complete crania prepared fromfreshwater limestones at University of Michigan locality SC-62 (Cf-2; 1335 m). These specimens, UM 101963 (Fig. 1)and USNM 482354 (Fig. 2), were prepared by J.I.B. (Blochand Boyer, 2001) and P. Houde, respectively. The type speci-men of C. simpsoni, UM 86273, includes a partial cranium(Gingerich, 1987; Bloch and Gingerich, 1998). This specimenwas prepared from freshwater limestone at University ofMichigan locality SC-29 (Cf-3; 1340 m) by P.D. Gingerich.Other fragmentary cranial specimens of C. simpsoni includedin this study are: UM 85177, UM 82670, and UM 82688dallrostra with most of the dentition from SC-62 limestonesdandUM 101923, a left palate from an SC-53 (Cf-3; 1365 m) lime-stone. All specimens (Table 1) are from the latest Paleocene(Clarkforkian North American Land Mammal Age; 55e56 Ma) Willwood Formation of the Clarks Fork Basin, ParkCounty, Wyoming; meter levels are measured from the K-Tboundary. Detailed locality information is archived at the Uni-versity of Michigan Museum of Paleontology (see also Rose,1981; Gingerich, 2001).

Fig. 1. Photographs of Carpolestes simpsoni, UM 101963. Cranium in ventral (A) and dorsal (B) views. ScaleZ 1 mm.

5J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 2. Photographs of Carpolestes simpsoni, USNM 482354. Cranium in left lateral (A), right lateral (B), dorsal (C), and ventral (D) views. ScaleZ 1 mm.

Comparisons were made to fossil specimens of Ignaciusgraybullianus (USNM 421608, 482353; UM 65569, 68006,108210), Phenacolemur jepseni (AMNH 48005), Plesiadapistricuspidens (MNHN CR-125), Plesiadapis cookei (UM87990),Microsyops knightensis (AMNH 55286),Megadelphuslundeliusi (AMNH 55284), Palaechthon nacimienti (UKMNH9557), Cantius abditus (USNM 494881), Smilodectes gracilis[UM 32773 (MPM 2612)], and Shoshonius cooperi (CM

31366, 31367, and 60494). Unpublished University of Michi-gan specimens of Microsyops sp. were also examined thanksto G.F. Gunnell. Modern taxa examined include Tupaia glis[USNM(MA) 114553, 154599, and 242241], Ptilocercus lowii[USNM(MA) 291272 and 488061], Pteropus poliocephalus[USNM(MA) 395262], Tarsius syrichta (PSU specimen), Ga-leopterus variegatus, and Cynocephalus volans [USNM(MA)83276, 84421, and 307553; UMMZ 117122].

6 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Limestone preparation

Specimens prepared at the University of Michigan Museumof Paleontology were prepared from freshwater limestone thatwas dissolved by submersion in dilute-buffered formic acid for2e3 hours at a time. To protect fossils from acid etching,a thin coating of polyvinyl acetate (PVA) was applied to thesurface of all exposed bones. Bloch and Boyer (2001) provideda more detailed description of preparation methods. Speci-mens prepared at New Mexico State University by P. Houdewere similarly prepared from freshwater limestone usingdilute-buffered acetic acid for 2 days at a time.

Ultra high-resolution X-ray computed tomography

Specimens UM 101963 and USNM 482354 were each em-bedded in a cylinder of floral foam. Floral foam, also known as‘‘oasis,’’ is a light, porous, yet stiff substance used by floristsin preparing arrangements of cut flowers. It provides a verygood substrate for safely encapsulating fragile specimens forCT analysis since it is not dense enough to interfere with the

Table 1

Cranial specimens of Carpolestes simpsoni from the Clarks Fork Basin, Will-

wood Formation, Wyoming

Specimen

no.

UM

locality

Faunal

zone

Description

UM

101963

SC-62 Cf-2 Skull, with rostrum relatively undistorted,

basicranium rotated counter-clockwise,

and compressed dorsoventrally; premaxilla

missing; palate, left orbit well-preserved;

left auditory region preserved but badly

crushed, right auditory region well-preserved

although somewhat distorted (see Fig. 1).

Associated left dentary and partial skeleton.

USNM

482354

SC-62 Cf-2 Cranium, with rostrum mediolaterally

crushed and somewhat displaced from the

back of the cranium, which is moderately

compressed dorsoventrally; neurocranium

and basicranium (including both auditory

regions) are fairly well-preserved, although

many elements are out of anatomical

position (see Fig. 2).

UM

82670

SC-62 Cf-2 Partial cranium, mediolaterally crushed;

rostrum without premaxilla, right orbit

well-preserved.

UM

85177

SC-62 Cf-2 Rostrum, mediolaterally crushed; both

premaxillae preserved, right maxilla and

orbits not preserved.

UM

82688

SC-62 Cf-2 Rostrum, only slightly mediolaterally

compressed; both premaxillae and anterior

portion of the right orbit are preserved.

Associated right dentary.

UM

101923

SC-53 Cf-3 Left maxilla, no distortion; extends to the

base of the orbit and includes the lateral

wall of the nasal cavity. Associated right

dentary.

UM

86273

SC-29 Cf-3 Cranium, mediolaterally compressed and

distorted; parts of rostrum and anterior

orbits fairly well-preserved, neurocranium

badly crushed, and auditory regions mostly

missing. Associated left dentary.

scan, yet is stiff enough that once a ‘‘pocket’’ in the foamhas been carved out to house the specimen, it will not move.The floral foam with the specimen was then placed in a plasticvial, and mounted on the OMNI-X Industrial Scanner at theCenter for Quantitative Imaging (CQI), Pennsylvania StateUniversity. The three-dimensional uhrCT data set was ac-quired in volume mode, in which 21 individual two-dimen-sional slices were created for each rotation. The axial fanangle was small enough to assume parallel beam reconstruc-tions. Each rotation consisted of 2400 views of the objectspanning 360 degrees. The post-acquisition reconstructionprocess included all 2400 views, and each individual slicewas stored as a 1024! 1024 matrix of 16 bit integers in tiffformat. For both specimens scanned, the approximate fieldof view was 43.0 mm, the reconstructed pixel size was0.042 mm, and the interslice distance was 0.04577 mm. Thesourceeobject distance was 131.4 mm and the sourceedetec-tor distance was 585.0 mm.

Images were studied using Scion Image Beta 4.02 (ScionCorporation, 2002) and ImageJ 1.27w (Rasband, 2002). Partsof the data set were cropped and stacked using the cropvoi andstrip2raw DOS programs developed by Nathan Jeffery (Uni-versity of Liverpool). Reslicing of the data in arbitrary planes,2D image linking, and 3D reconstructions were performed us-ing Voxblast for Unix (Vaytek, Inc.; http://www.vaytek.com/VBUnix.html) on an SGI Octane 2 workstation.

Terminology

Anatomical terminology follows that of McDowell (1958),Miller (1964), MacPhee (1981), and Bloch and Silcox (2001).Anatomical abbreviations are listed in Table 2.

Description of the cranial and dental anatomy ofCarpolestes

Dentition

The specimens studied (Table 1) are here referred to Carpo-lestidae because they have enlarged central incisors, reduced an-terior lower dentition (distal to I1), and plagiaulacoid structure ofP4 with correlated specializations of P3e4. They are referred toCarpolestes because P3 is polycuspate with a distinct anteroex-ternal extension and is larger than P4; P4 is high-crowned andbladelike, with 8e9 apical cusps and a talonid that mergeswith themain blade; andM1 has linearly arranged trigonid cuspsthat are of a similar height to the talonid of P4 and form part ofa continuous cutting edgewith that tooth (Rose, 1975; Silcox andGunnell, in press). At the species level, the material best fits thediagnosis of Carpolestes simpsoni because of its reduced dentalformula (lacking P3); small body size (ca. 100 g); P3 that differsfrom Carpolestes nigridens in having a narrower anterolateralextension, in being smaller overall, and in being shorter relativeto its breadth, with amore hourglass shape; and P4 that is smallerand lower crowned than inCarpolestes nigridens (see Bloch andGingerich, 1998, for a complete diagnosis and full description ofthe teeth of C. simpsoni).

7J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Table 2

Abbreviations used in text and figures

as alisphenoid

ac anterior chamber

asc anterior semicircular canal

at auditory tube (Zpharyngotympanic tube)

bo basioccipital

bs basisphenoid

Cf Clarkforkian Land Mammal Age; divisions of the Clarkforkian

LMA are indicated by the abbreviation Cf followed by the

appropriate number (see Gingerich, 2001)

CI consistency index (Kluge and Farris, 1969)

eam external auditory meatus

ec ectotympanic

er epitympanic recess

feo fenestra ovale

fer fenestra rotunda

fm foramen magnum

fo foramen ovale

fr foramen rotundum

frt frontal

hf hypoglossal foramen

if incisive foramen

ioc infraorbital canal

iof infraorbital foramen

jf jugular foramen

la lacrimal

lf lacrimal foramen

lt lacrimal tubercle

lpet left petrosal

lpl left platform bone

ma mastoid

mx maxilla

na nasal

oc occipital condyle

of optic foramen

ofs sphenorbital fissure

pa parietal

pal palatine

pc posterior chamber

pcl promontory canal

pf palatal fenestra

pgf postglenoid foramen

pgp postglenoid process

pl platform bone

pmx premaxilla

pr promontorium

pt palatine torus

ptc palatine canal

pp pterygoid plate

RI retention index (Farris, 1989)

rpet right petrosal

rpl right platform bone

SC Sand Couleedfor University of Michigan localities in the

Polecat BencheSand Coulee area of the Clarks Fork and

Bighorn Basins (see Gingerich and Clyde, 2001)

scl stapedial canal

smf stylomastoid foramen

sq squamosal

sqf subsquamosal foramen

tc tubal canal (external opening in the bulla for the auditory tube)

v vomer

Face and orbit

The face and orbit of Carpolestes simpsoni are preserved inseveral specimens (Table 1, Figs. 1e8), allowing for a fairlydetailed reconstruction of this region (Fig. 9).

Carpolestes simpsoni has an elongate snout that tapers ros-trally, with long nasals that taper posteriorly to form a narrowcontact with the frontals at their caudal margin. This contact iscaudal to the anteriormost aspect of the orbital rim and themaxillofrontal suture (Fig. 3). Along their anterolateral mar-gins, the nasals contact the premaxillae, terminating rostrallycaudal to the rostral extent of the premaxillae such that thenasals do not overhang the margin of I1. The contact betweenthe prexaxillae and the maxillae is complex. Mesially, the pre-maxilla is clearly external to the maxilla. However, distally themaxilla cups the distal edge of the premaxilla so that the max-illa overlaps onto the premaxilla (Fig. 10). When the craniumis viewed laterally, this creates the impression that the thirdtooth in the upper jaw is rooted partially in the maxilla andpartially in the premaxilla. However, in palatal view, the threeanteriormost teeth appear to be rooted in the premaxilla (Blochand Gingerich, 1998: Figure 3). The uhrCT data show thatthere is no premaxillaryemaxillary suture along the medialor caudal wall of the I3 alveolus (Fig. 4), supporting the inter-pretation that all three anteriormost teeth are rooted in the pre-maxilla. There is no evidence for a premaxillaefrontalcontact.

The maxilla contacts the premaxilla anteriorly, the nasaldorsally, the lacrimal and frontal posterodorsally (Fig. 3),and the palatine (Fig. 5) and zygomatic anteroventrally. Themaxilla makes a broad contribution to the orbital margin androstral wall. A large infraorbital foramen is located above P4

(Fig. 6; Appendix 1), extending into a wide canal for the in-fraorbital branches of the maxillary nerve and vessels (Miller,1964). This canal runs caudally through the maxilla and opensinto the anterior part of the orbit, where it continues caudallyas a wide groove that extends for most of the length of theorbit.

One specimen (UM 101923; Fig. 5) reveals a parasagittalsection of the left maxilla. In medial and palatal views, a frac-tion of the anterior part of the palatine is visible, with a well-defined palatineemaxillary suture. A portion of the cribriformplate of the ethmoid, penetrated by tiny foramina that servedfor the transmission of olfactory nerve bundles (Miller,1964), is located caudal to the olfactory chamber. The nasalcavity is divided into upper and lower portions by a crest on themaxilla for the attachment of the maxilloturbinal (Zinferiornasal concha of humans; Fig. 7).

Anteriorly, the frontal bone contacts the nasal, maxilla, andlacrimal (Fig. 3). Within the orbit, the contacts of the frontalare not entirely clear; in some cases, they are obscured bypreservation-related fractures in even the best preserved speci-mens. Caudally, the frontal contacts the parietal, and rostrally,the lacrimal and maxilla within the boundaries of the orbit. Itis unclear whether the frontal extends ventrally to contact thesphenoid or palatine. There is no evidence of ethmoid expo-sure within the orbit (the ‘‘os planum’’). The sphenoid

8 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 3. Rostrum of Carpolestes simpsoni. UM 101963 in dorsal view (A) and USNM 482354 in left lateral view (B). Note that the nasals taper distally at their

contact with the frontal. Abbreviations as in Table 2. Dashed lines indicate sutures. Scale Z 1 mm.

contribution to the orbit is not clearly demarcated by sutures,although in UM 82670, both the optic foramen and sphenorbi-tal fissure, located in the sphenoid, are visible in the posterioraspect of the orbit (Fig. 8). A small foramen is located belowthe ventral extent of the orbit (as defined by the dorsal edge ofthe zygomatic), possibly leading to the palatine canal, whichwould have transmitted the major palatine artery, vein, andnerve (Miller, 1964). There is no evidence of a postorbital pro-cess of either the frontal or the zygomatic, indicating that theorbit was open caudally. The orbits appear to face mostly lat-erally, although this has not yet been rigorously quantified.

Most of the lacrimal is bordered by the maxilla, with a smalllacrimalefrontal contact within the orbit. The lacrimal formsa broad contribution to the anterior aspect of the orbit(Fig. 6), and has a small facial exposure. A large lacrimal fo-ramen is located on the rim of the orbit, with a small tubercle

dorsal to this opening (Fig. 6). The zygomatic flares postero-laterally from the maxillary contribution to the zygomaticarch, and contacts the squamosal caudally.

Palatal anatomy

Several specimens of Carpolestes simpsoni (UM 82688,101923, 101963) preserve most of the hard palate (Figs. 7,10). The palatine of C. simpsoni (for a detailed reconstructionof the hard palate of this taxon, see Bloch and Gingerich,1998: Figure 3) is restricted to an approximately triangularlamina of bone, located posterior and medial to the molars.The contact between the palatine and the maxilla is manifestedin a distinct, jagged suture. At the contact between the rightand left palatines, the posterior margin of the palate is nearlystraight and is buttressed by a strong, rounded postpalatine

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Fig. 4. Left lateral view of a 3D reconstruction based on uhrCT data of Carpolestes simpsoni, USNM 482354. The reconstruction has been sliced along an oblique

parasagittal plane to reveal the alveoli of the upper incisors (compare with Fig. 2A). This view reveals that all three alveoli for the upper anterior teeth are rooted in

the premaxilla. It is possible to see, for example, that the back wall of the I3 alveolus is part of the premaxilla, lying just anterior to the premaxillaryemaxillary

suture. This supports previous reconstructions (i.e., Fox, 1984, 1994; Bloch and Gingerich, 1998) of the upper dental formula in carpolestids as including three

incisors. Scale Z 1 mm.

torus, the wings of which extend posteriorly onto the basicra-nium. The postpalatine torus is located at the posterior marginof, or just posterior to, M3, and there is no broad extension ofthe palate into the mesocranial region (between the auditorybulla and the back of the palate) behind M3. The area anteriorto the palatine contact is open, forming a large palatal fenestrathat is divided by a thin process of bone, interpreted here to bethe vomer. As indicated in the introduction, the position of thisbone is likely influenced by the dorsoventral crushing of thebest preserved skull (UM 101963), and it is unlikely that it ac-tually formed part of the palate. The vomer extends dorsally toform part or all of the nasal septum (Fig. 7). Anteriorly, thepalatal fenestra is closed by the contact between the left and

right maxillae. In UM 82688, there is evidence for the pres-ence of a fairly large incisive foramen at the contact betweenthe premaxilla and the maxilla (Fig. 10).

Basicranium and braincase

The basicranium of Carpolestes simpsoni is well-preservedin two specimens (Table 1, Figs. 11e17), allowing for a de-tailed reconstruction of this region (Fig. 9).

The basisphenoid (Fig. 11) contacts the pterygoid, alisphe-noid, basioccipital, and petrosal bones. Anteriorly, the narrowbasisphenoid is wedged between the two alisphenoids. An an-gular division on the anteriormost part of the basisphenoid

Fig. 5. Maxilla of Carpolestes simpsoni, UM 101923. Break reveals an approximately parasagittal section through the left maxilla in medial view. Abbreviations as

in Table 2. Dotted lines indicate sutures. ScaleZ 1 mm.

10 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 6. Orbit of Carpolestes simpsoni, UM 101963. Left orbit and rostrum in left lateral view. Note that the lacrimal tubercle is positioned dorsal to the lacrimal

foramen on the anterior orbital margin. A large infraorbital foramen is located above P4. Abbreviations as in Table 2. Dashed lines indicate sutures. Scale Z 1 mm.

may be the contact between the basiphenoid and the presphe-noid, although no specimen preserves this region sufficientlyintact to be sure. As the basisphenoid extends posteriorly, itmay contribute to the right and left bullae, although it is im-possible to definitively establish which fragments of bullarfloor are basisphenoid, and which are petrosal, basioccipital,or entotympanic in origin (see below). In UM 101963, a brokenridge runs down the midline of the anterior portion of the basi-sphenoid. This structure could be the posterior extension of thepresphenoid, a part of the basisphenoid, or a portion of the vo-mer (Fig. 11). The fact that this ridge does not appear to beanteriorly continuous with what would be the presphenoid(or the vomer) lends support for an interpretation of its originas basisphenoid. The contact between the basisphenoid and thebasioccipital is clearly discernable in UM 101963, with the ba-sioccipital being displaced slightly dorsally at the suture be-tween these two bones (Fig. 11).

In ventral view, the alisphenoid (Fig. 11) appears to contactthe palatine, basisphenoid, and squamosal, and extends dorsallyinto the orbit. The alisphenoid contains two foramina openinginto the braincase from the basicranium. The anterior foramenis large and round and interpreted to be the foramen rotundum,which transmitted the maxillary division of the trigeminalnerve. The posterior foramen is interpreted to be the foramenovale, through which the mandibular division of the trigeminalnerve passed.

The squamosal is triangular in outline with a moderate zygo-matic process that curves anteriorly and connects with the zygo-matic bone to form the zygomatic arch (Figs. 11, 12). Anterior

to the zygomatic process, in ventral view, is a broad, gently con-cave glenoid fossa that ends caudally in a strong postglenoidprocess. A large postglenoid foramen opens on the caudalaspect of the postglenoid process. On the lateral side of theskull, a small but distinct subsquamosal foramen is present atthe caudal end of the zygomatic arch (Figs. 13, 14). The caudal-most part of the squamosal forms the rostral border of the exter-nal auditory meatus (EAM), and the squamosal may contributeto the lateral wall of the auditory bulla. The EAM is not tubularin form, contrary to previous interpretations of these specimens(Silcox, 2001). The source of confusion was the identificationof a piece of bone that is out of place in the right side ofUSNM 482354, which was considered a possible candidatefor a tubular ectotypmanic (labeled ‘‘ec?’’ in Figs. 12, 13).Although this is indeed a fragment of bulla, the fact that thehomologous bone is preserved in place on the left side of thisspecimen allows the identification of this fragment as the outeredge of the auditory bulla and the lip of the EAM, rather than asa tubular ectotympanic (Fig. 14). In no specimen is the earregion well-enough preserved to demonstrate conclusively theform of the ectotympanic, although the displaced fragment ofbulla mentioned above may have a ring supported by strutson its inner surface (see Fig. 13). However, in the absence ofa more nearly complete specimen, we are not confident ofthis identification, and the apparent ring could just be the innerwall of a slightly pneumatized edge to the lateral opening ofthe EAM.

Fragments of the tympanic floor are preserved on the rightand left sides of both UM 101963 and USNM 482354

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(labeled ‘‘rpet?’’ and ‘‘lpet?’’ in Figs. 11, 12). As notedabove, it is difficult to tell which bones may have contributedto the auditory bulla. Although there is no positive evidencefor an entotympanic, the presence of this bone cannot beruled out. The basisphenoid may contribute to the bulla,and the squamosal may form part of the lateral wall. Thereis no evidence for a suture between the promontorium(formed by the petrosal) and the remnants of the bulla.This morphology is consistent with the interpretation thatthe bulla was formed in whole or in part by the petrosal. Al-ternatively, a suture with the petrosal may simply have

Fig. 7. Palate of Carpolestes simpsoni, UM 101963. 3D reconstruction based

on uhrCT data in ventral view (A), and 2D coronal CT slice through the ros-

trum (B). The dashed white arrow connects corresponding points on the 2D

coronal CT slice and the 3D reconstruction. Ventral is towards the top of

the page for the 2D view. Note the large palatal fenestrae. The bone visible

in this opening is likely the vomer, which can be seen to divide the nasal cavity

in the 2D slice. Also note the well-demarcated palatine torus in the 3D view,

and the very large infraorbital foramen, which is visible at its opening on the

left side of the specimen in the 2D view. Abbreviations as in Table 2.

ScaleZ 1 mm.

become obscured (although there is absolutely no evidencefor this interpretation on either the surface of the bones orin the uhrCT data; see discussion below).

The promontorium (Fig. 11) bears two clearly visible open-ings: a laterally placed fenestra ovale (Zfenestra vestibuli)and a posterolaterally positioned fenestra rotunda (Zcochlearwindow, fenestra cochleae). A septum ventral to the fenestraovale curls posteroventrally from the promontorium to connectto the back of the bulla, forming an overhanging wall that‘‘shields’’ the fenestra rotunda. A foramen on the posterome-dial aspect of the auditory bulla in UM 101963 is probablythe entrance for the internal carotid artery (labeled ‘‘pcf’’ inFig. 11). A distinct groove runs rostrolaterally across thepromontorium from this opening. This groove divides intoa large branch that extends to the fenestra ovale and a smallerbranch proceeding rostrally (Fig. 15). These grooves are inter-preted to mark the course of the stapedial and promontorialbranches of the internal carotid artery (ICA), respectively,and are clearly present in all specimens for which this regionis known (i.e., UM 101963 and USNM 482354). No othergrooves are observed on the promontorium, and there is no ev-idence that the branches of the ICAwere ever encased in bonytubes (although this does not rule out the possibility that thesetubes might have originally been presentdsee Silcox, 2003).No specimen is sufficiently intact to indicate the position ofthe anterior carotid foramen.

Posterolaterally, the petrosal forms the mastoid process andencloses a single stylomastoid foramen, through which the fa-cial nerve exited (Figs. 11, 12). This foramen was identifiedbased on its position, and on the presence of a facial canal lead-ing to this opening, which can be traced in the uhrCT data. Thestylomastoid foramen is notable in being quite large. Immedi-ately lateral to the fenestra ovale is a large epitympanic recess(Fig. 11) that would have housed the articulations of the incusand the malleus. In UM 101963, there is a process medial tothe epitympanic recess that may be part of the petrosal, whichcontinues to form a V-shaped structure (labeled ‘‘pl’’ inFig. 11). This structure is rostral to the promontorium, forminga large platform dividing the auditory bulla into two chambers(Fig. 16). Due to the nature of the damage to the two best pre-served specimens, it is unclear whether this division was partialor complete (i.e., how extensive the connection between the twochambers was originally). The promontorium is located in thelarger, more posterior chamber, while there is a smaller cham-ber in a more anteroventral position that is roofed by the V-shaped ‘‘platform bone.’’ This bone continues posterolaterallyto form a spur that contacts the face of the promontorium inUM 101963, just anterior to the fenstra ovale. The outer edgeof the platform bone is rounded and appears to conform tothe inner morphology of the auditory bullar wall. On the bullaraspect of the spur that contacts the promontorium, are twosmall, but very distinct grooves that are oriented dorsoventrally.

It is possible that this ‘‘platform bone’’ is part of the bullarfloor that has been pushed up into the bulla in UM 101963.However, the presence of this unusual configuration on boththe right and left sides of this specimen supports the interpre-tation that it is a real structure that divided the middle ear into

12 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 8. Orbit of Carpolestes simpsoni, UM 82670. Enlarged (A), and unenlarged right lateral view of the right orbit (B). Rostral is to the right, dorsal towards the

top of the page. The enlarged view in (A) is oriented slightly obliquely relative to the view in (B) to expose the sphenorbital fissure. Note the very small optic

foramen (see Fig. 20). Abbreviations as in Table 2. For (A), scaleZ 1 mm.

two chambers. It seems unlikely that a piece of bulla of pre-cisely the same size and shape would have been pusheddown into the hypotympanic cavity on both the right andleft sides of this specimen, particularly since the two sideshave suffered rather different types of damage. This structureis also identifiable in USNM 482354. On the right side ofUSNM 482354, the ‘‘platform bone’’ (labeled ‘‘Rpl’’ inFig. 11) also has the same V-shape that is seen in UM101963. On the left side, the ‘‘platform bone’’ (labeled‘‘Lpl’’ in Fig. 12) is identifiable in a position that likely corre-sponds closely to the original position with respect to the bul-lar floor. On the left side of USNM 482354, this structure isclearly positioned anteroventral to the promontorium and un-der the remnants of the auditory bulla (Fig. 12).

The uhrCT data reveal the presence of a tube passingthrough a remnant of bone that formed the lateral side of theauditory bulla in USNM 482354 (Fig. 17). Parts of a homolo-gous tube are also present in the broken edges of the bullae inUM 101963 (Fig. 11, labeled ‘‘at’’), and are present in theform of the aforementioned grooves on the bullar aspect ofthe spur of the platform bone. This tube appears to extendfrom the middle ear cavity caudally (although the precise po-sition of the intratympanic opening is not preserved), throughthe wall of the bulla, to terminate rostrally at an opening in therostral wall of the bulla (labeled ‘‘tc’’ in Fig. 9). This openingis just caudal to an indentation located medial to the foramenovale, which is in the expected position of the gutter for theauditory tube (MacPhee and Cartmill, 1986; Kay et al.,1992). Together, the evidence suggests that an auditory tuberan through the lateral wall of the bulla on the way to its typ-ical position in a gutter on the medial basicranium.

The basioccipital bone appears to contact the basisphenoid andsquamosal bones inventral view (Fig. 11).A large foramen locatedat the contact between the posterior wall of the auditory bulla andthe basioccipital is identified as the jugular foramen, throughwhich the jugular vein exited the cranium. A smaller foramen

located lateral to the ventralmost part of the occipital condyle isthe hypoglossal foramen, through which the hypoglossal nerveexited.

The braincase of Carpolestes simpsoni has a distinct post-orbital constriction across the posterior margin of the frontalbones, while caudal to this point the neurocranium expandsoutward (Fig. 9). Distinct temporal lines are present on thefrontal, dorsal to the orbit, and these join caudally in a weaksagittal crest that originates near the contact between the fron-tal and parietal bones. Caudally, the sagittal crest merges withwell-defined nuchal crests, which extend ventrolaterally ontothe nuchal surface of the mastoids. The foramen magnum isoval in shape and faces directly posteriorly (Fig. 11).

Comparative anatomy and interpretation

Face and orbit

The uhrCT data presented here put to rest the debate overwhether or not Carpolestes simpsoni had three upper incisors(Bloch and Gingerich, 1998), since all three anteriormost teethare rooted in the premaxilla (Fig. 4). The presence of threeupper incisors has been reconstructed for some other carpoles-tids (Fox, 1984, 1994; although see Rose, 1981), but this con-dition is not seen in any other plesiadapiforms for which therelevant region is preserved (e.g., Megadelphus and Plesiada-pis). It is worth noting that the premaxilla of Purgatorius,which retains three lower incisors (Clemens, 2004), is currentlyunknown.

Carpolestes had a relatively longer snout than typicallyseen in Euprimates; it is similar in this respect to Scandentia,Dermoptera, Chiroptera, and most known plesiadapiforms(Fig. 18). However, it is of some interest that the most prim-itive euprimate included in our analysis of relative snoutlength, Cantius abditus, also had a relatively long snout, in

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the range of the rest of Euarchonta (ZDermopteraC Scan-dentiaC Primates), and distinctly unlike that of later, morederived euprimates such as Smilodectes and Shoshonius.This result could be interpreted to suggest that the decreasein relative snout length postdated the origin of Euprimates.Based on an estimate of snout length provided by X. Ni forTeilhardina asiatica (5.1e5.2 mm), it appears that this spe-cies was similar to other omomyids in having a very shortsnout.

An alternative explanation for an apparently long snout inCantius is that cranial length decreased in Euprimates relativeto the primitive condition as a result of a change in the propor-tions of the neurocranium associated with increasing brainsize. Coordinated reductions in both snout and cranial lengthwould result in an apparently primitive relative snoutlength since the basic proportions of the skull (measured in

Fig. 9. Reconstruction of the cranium of Carpolestes simpsoni based on UM

101963 and USNM 482354. Cranium rostral to the rectangle is reconstructed

in dorsal view, while the area within the rectangle is rotated 180 degrees into

ventral view. Dotted line with arrow indicates the path of the auditory tube.

Reconstruction by D. Boyer. Abbreviations as in Table 2. Scale Z 1 mm.

length) would remain the same. If this were the case, a reduc-tion of absolute snout length would not be reflected in a plot ofsnout length to cranial length. Further study of the relative pro-portions of the different parts of the skull in fossil and extanteuprimates might test these competing hypotheses, but isbeyond the scope of the current paper.

Fig. 10. Part of the anterior palate of Carpolestes simpsoni, UM 82688, in ven-

tral view. Note moderately sized incisive foramina at the contact between the

premaxilla and the maxilla. Abbreviations (except standard dental abbrevia-

tions) as in Table 2. Dashed lines delimit inferred boundaries of the incisive

foramina, and indicate the observed premaxillaryemaxillary suture. Solid

lines indicate observed boundaries of the incisive foramina. ScaleZ 1 mm.

Fig. 11. Basicranium of Carpolestes simpsoni, UM 101963, in ventral view.

Note that this specimen is compressed dorsoventrally and some structures

are out of place with cavities partially collapsed. Abbreviations as in Table 2.

ScaleZ 1 mm.

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Carpolestes is similar to Plesiadapis but differs from Igna-cius, Palaechthon, Microsyops, and Megadelphus in the shapeof the nasals, and in the nature of their contact with the frontal.In both Carpolestes and Plesiadapis, the nasals are narrowcaudally, forming a narrow articulation with the frontals, whilenon-plesiadapoid plesiadapiforms have nasals that widen dis-tally, forming a wide articulation. Rose and Gingerich(1976) stated that the nasals narrow caudally in Ignacius gray-bullianus based on a fragmentary rostrumdin fact, the speci-men they examined is damaged in this area, and the shape ofthe caudal part of the nasals is difficult to assess. A much bet-ter preserved specimen (USNM 421608) reveals that the nasalswiden caudally in I. graybullianus (Kay et al., 1992). The phy-logenetic significance of this feature is thrown into doubt bythe observation that the caudal width of the nasals variesamong species of primitive euprimates.

Unlike Plesiadapis, but similar to Microsyops, there is noevidence of a premaxillaryefrontal contact in C. simpsoni.Like Plesiadapis and Microsyops, but unlike many extant eu-primates, including Tarsius (Cartmill, 1978; Wible and Co-vert, 1987), there is no evidence of an ethmoid exposure(Zos planum) in the orbit of C. simpsoni. A broad contribu-tion of the maxilla to the rostral wall of the orbit and a maxil-lary contact with both the frontal and lacrimal are featuresshared by Plesiadapis, C. simpsoni, and euprimates, that arenot present in Megadelphus (Wible and Covert, 1987). No pa-romomyid specimens are well enough preserved to

Fig. 12. Basicranium of Carpolestes simpsoni, USNM 482354, in ventral view.

Note that this specimen has been compressed mediolaterally and has under-

gone some crushing and damage. Identification of structures is based on com-

parison to UM 101963, and to less damaged plesiadapiform and euprimate

skulls (see list in Materials and methods). Abbreviations as in Table 2.

ScaleZ 1 mm.

Fig. 13. 3D reconstruction based on uhrCT data of the skull ofCarpolestes simp-

soni, USNM482354, in oblique lateral view (A), with a coronal 2DCT slice (B).

Ventral is towards the top of the page for the 2D view. This 3D reconstruction has

been sliced open to reveal a displaced fragment of the external auditory meatus

on the right side of this specimen. The dashedwhite arrow connects this structure

to the corresponding structure in the 2D slice. Note the doubled outer edge of this

bone in the 2D view, which would have formed the outermargin of a non-tubular

EAM or, alternatively, could represent an ectotympanic ring supported by struts

to the inner wall of the bulla. Abbreviations as in Table 2. ScaleZ 1 mm.

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Fig. 14. Left lateral view of a 3D reconstruction based on uhrCT data ofCarpolestes simpsoni, USNM482354 (A), and enlarged view of the opening to the middle ear

(B). Although this region is damaged, a piece of bone representing the outermost edge of the external auditory meatus (EAM) is preserved in place. This bone is not

expanded into a tube, indicating that C. simpsoni had a non-tubular EAM. The structure indicated with an asterisk in the enlargement (B) is a sharp crest located just

inside the entrance to the EAM. It can be alternatively interpreted as the crista tympani, for the attachment of the tympanic membrane, or an annular bridge, which

would have articulated with an ectotympanic ring. The identification of this crest remains equivocal in the absence of an intact ectotympanic. Abbreviations as in

Table 2. Scale Z 1 mm.

demonstrate the composition of the orbital mosaic (Kay et al.,1992), although in Ignacius, the maxilla does form part of therostral wall of the orbit, and thus it probably did contact thefrontal, as in Carpolestes.

Carpolestes is similar to Plesiadapis and paromomyids inlacking any evidence for a postorbital bar or process. This fea-ture contrasts with the presence of a complete postorbital barin all specimens of fossil euprimates for which this region isknown (also present in all extant scandentians and certain chi-ropterans); it also contrasts with the combination of a postor-bital bar and partial postorbital plate in Tarsius. Megadelphusand Palaechthon both have a postorbital process of the frontalthat is not expanded into a complete bar (McKenna, 1966;Szalay, 1969; Kay and Cartmill, 1977), similar to the conditionin dermopterans and some chiropterans. As for other plesiada-piforms for which this region is known (i.e., Ignacius, Plesia-dapis, Megadelphus, and Palaechthon), C. simpsoni has orbitsthat face mostly laterally. One admittedly crude measure of or-bital orientation is interorbital breadth (‘‘the smallest breadthbetween the medial walls of the orbits at their entrances’’;Schultz, 1962, cited in Cartmill, 1970: 61). Euprimates typi-cally have a narrower interorbital breadth than other mam-mals, associated with their more convergent orbits(Fig. 19A). Carpolestes simpsoni lies on the regression linefor Scandentia, near Ptilocercus lowii, rather than with extanteuprimates, indicating a much greater interorbital breadth thanis typical for an extant primate of comparable size.

As in other plesiadapiforms (Kay and Cartmill, 1977; Maaset al., 1988; i.e., Plesiadapis tricuspidens, Palaechthon naci-mienti, Phenacolemur jepseni, Carpolestes dubius), Carpo-lestes simpsoni has very small orbits relative to its craniallength compared to a broad array of extant euprimate and

non-euprimate mammals (Fig. 19B). The significance of thisfinding for the reconstruction of activity period for C. simpsoniis complicated. In modern primates, smaller orbits are consis-tently associated with diurnality at smaller cranial lengths(Kay and Cartmill, 1977; Kay and Kirk, 2000; Heesy andRoss, 2001; Ni et al., 2004). However, small, nocturnal non-euprimate mammals also typically have small orbits (Kay andCartmill, 1977), begging the question of whether the orbits ofa primate as primitive as Carpolestes would be expected toscale as in euprimates. In discussing the similarly small orbitsof P. nacimienti, Kay and Cartmill (1977) cautiously leaned to-ward an interpretation of this species as nocturnal, althoughthey noted similarities to the orbital size of diurnal mongooses(e.g., Helogale). Maas et al. (1988) interpreted small orbits inplesiadapoids as indicating nocturnality. Both Kay and Cartmill(1977) andMaas et al. (1988) presented data on orbital diameterand cranial length using polygons to encompass the ranges ofmammals having similar activity periods. In the case of Maaset al. (1988: Figure 11), the individual data points were leftoff their graph, leading to a substantial over-simplification ofthe true situation. In fact, the data ranges almost totally overlapfor the nocturnal and diurnal non-euprimate mammals mea-sured by Cartmill (1970), and regression lines fitted throughthese data for ln (orbital diameter) on ln (cranial length) are sta-tistically indistinguishable (see Fig. 19B). This result indicatesthat, for non-euprimates, relative orbital size cannot be used asa clear indicator of activity pattern.

If Carpolestes had orbits that did not scale as in euprimates,as its position outside the range of modern primates suggests,then this measure also cannot provide an unequivocal answeras to whether Carpolestes simpsoni was nocturnal or diurnal.Since it is unclear at which phylogenetic node the orbits of

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Fig. 15. Internal carotid circulation of Carpolestes simpsoni, USNM 482354. Cranium in ventral view (A), enlargement of the right promontorium (B), and en-

largement of the right promontorium with the grooves marking the course of the promontorial and stapedial branches of the internal carotid artery (ICA), demar-

cated by dashed black lines (C). Note that the grooves are well defined and that the stapedial groove is of greater width than the promontorial groove, unlike that of

extant haplorhines, in which the stapedial branch is reduced or absent. The groove for the ICA stem, before the branching of the promontorial and stapedial arteries,

is wide and in the range of extant mammals with a fully functional ICA (Fig. 21). For (A), scaleZ 1 mm.

extinct euprimates began scaling as they do in modern eupri-mates, similar caution is needed in interpreting the relevanceof orbital size near the base of the euprimate tree in the ab-sence of other evidence (see below). This caveat applies par-ticularly to Teilhardina asiatica, a taxon recently describedas diurnal on the basis of its small orbits. We included T. asi-atica in Fig. 19B, which differs from the data portrayed by Niet al. (2004: Figure 4) in including both non-primates andlarge-bodied extant euprimates. With the inclusion of large-bodied forms in the diurnal euprimate regression, T. asiaticais substantially below the diurnal euprimate line (i.e., it hasmuch smaller orbits than would be predicted for a diurnal eu-primate of its cranial length). Teilhardina asiatica is actuallylocated closer to the diurnal and nocturnal non-euprimate linesthan it is to the diurnal euprimate line. This result suggests thatthe orbits in T. asiatica, as for C. simpsoni, were not scaled asis typical of modern euprimates. As such, the activity period ofT. asiatica also remains equivocal (Martin, 2004). Problemswith extrapolating data beyond the range of modern primates,highlighted by Martin (2004), also mandate caution in accept-ing Ni et al.’s (2004) conclusion of a diurnal activity period for

T. asiatica. This is not as much of a problem for C. simpsoni,as several euprimates of similar cranial length are included inthe analysis.

Another line of evidence that has been investigated for itsrelevance to reconstructing activity period is relative opticforamen size (Kay and Kirk, 2000; Kirk and Kay, 2004).The basis upon which this variable might have some relevanceto activity period has to do with the relationship between thesize of the optic nerve (and its proxy, the optic foramen) andthe degree of retinal summation present for a given animal.Retinal summation can be defined as ‘‘a condition in whichmore than one photoreceptor cell can interact with a singleganglion cell via vertical pathways’’ (Kay and Kirk, 2000:238). High degrees of retinal summation increase visual sensi-tivity since the response produced by light in one photorecep-tor cell is summed with that of other cells before the data arepassed on to a ganglion cell. Lower levels of summation implysmaller receptive field centers in the eye (Kay and Kirk, 2000).This means that a given area of the retina is effectively moreextensively subdivided, and thus the brain receives more in-puts from a given area than in a higher summation eye. This

17J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 16. 3D reconstruction based on uhrCT data of the basicranium of Carpolestes simpsoni, UM 101963, in ventral view oriented with rostral towards the top of the

page (A), and three coronal 2D CT slices oriented with ventral towards the top of the page (B). Dashed white arrows connect corresponding points on the 3D

reconstruction and the 2D views. Bone appears as brighter, lighter shades of gray, whereas matrix is dark gray in color in the 2D CT slices. These images dem-

onstrate the presence of the posterior chamber (pc) overlying the platform bone (indicated with the solid white arrows), which would have roofed the anterior

chamber (ac). Although this specimen is crushed dorsoventrally, and the posterior chamber is partly filled with matrix, these images demonstrate that the middle

ear of C. simpsoni was divided into two distinct chambers. Abbreviations as in Table 2. Scale Z 1 mm.

implies that the brain is more likely to receive separate inputsfrom neighboring perceived items, so it is better able to dis-criminate between them. Thus, lower degrees of summationproduce higher levels of visual acuity, allowing for better dis-crimination between closely spaced objects. It is to be ex-pected that nocturnal animals will be selected for sensitivityover visual acuity, while diurnal animals with no shortage ofavailable illumination will select for acuity over sensitivity(Kay and Kirk, 2000; Kirk and Kay, 2004). Because high de-grees of retinal summation necessitate fewer ganglion cells,and thus presumably smaller optic nerves, one proxy for de-gree of retinal summation may be the relative size of the opticforamen.

Kay and Kirk (2000) and Kirk and Kay (2004) developedtwo metrics for comparing optic foramen size among eupri-mates (Fig. 20). The optic foramen index (OFI) is a measureof optic foramen size relative to an estimate of orbital area.These authors found that a slightly more complicated measure,optic foramen quotient (OFQ), better represented variation inprimates by taking into consideration differences in the pro-portion of the eye relative to the orbit between euprimatetaxa. For both OFI and OFQ, diurnal haplorhines were foundto have relatively high values (i.e., large optic foramina), con-sistent with a lesser degree of retinal summation and greaterlevel of visual acuity. Calculation of OFQ allowed for a finerteasing apart of the rest of the euprimate sample than possiblewith OFI, with diurnal and cathemeral strepsirrhines havinghigher average values of OFQ than nocturnal primates,

although with some overlap in the ranges. While overlap be-tween the ranges complicates attempts to use OFQ alone to re-construct activity period for fossil primates, the observedranges of OFQ in combination with orbital size can allowa prediction of activity pattern. In the case of C. simpsoni, ifit has small orbits because it is diurnal, it should also have rel-atively large optic foramina. Alternatively, if it has small orbitsbecause it is nocturnal, it should have relatively small opticforamina.

The values of the OFI and OFQ for Carpolestes simpsoniare exceptionally low (Fig. 20; Appendix 4). In fact, this taxonhas an optic foramen that is small not only relative to all mea-sured extant primates, but also to various other archontans. In-terestingly, scandentians show a pattern similar to primates inthat nocturnal Ptilocercus lowii has a substantially lower OFIand OFQ than diurnal Tupaia glis, which suggests that a com-parable relationship may exist within this group. Of the arch-ontans measured by Kay and Kirk (2000) and in this study, thenext lowest values for OFI and OFQ are in the nocturnal der-mopterans. These various lines of evidence suggest that the or-bits of Carpolestes are small because it was a non-visuallydirected nocturnal mammal, not because it was a visually di-rected diurnal animal like a modern diurnal euprimate. Theonly apparent case of a diurnal euprimate with a small opticforamen, Adapis (Kay and Kirk, 2000), was found to havea larger optic foramen, in the range of modern diurnal strepsir-rhines, with the measurement of better preserved specimens(Kirk and Kay, 2004).

18 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 17. 3D reconstruction based on uhrCT data of the neurocranium of Carpolestes simpsoni, USNM 482354, in left lateral view oriented with rostral towards the

left (A), and three coronal 2D CT slices oriented with dorsal towards the top of the page (B). The 3D view has been sliced open along a parasagittal plane, revealing

a tube running through part of the wall of the bulla. The dashed white arrows connect corresponding structures on the 2D images, demonstrating the continuous

lumen of the tube. Based on comparison to Tarsius, the lumen is interpreted as marking the course of the auditory tube running through the wall of the bulla to

bypass the anterior chamber. Scale Z 1 mm.

This discussion is relevant to the issue of the ancestralactivity period for Euprimates. In light of the cautionsraised here (see also Martin, 2004), the small orbits of Teil-hardina asiatica are unconvincing as evidence of a diurnalorigin for the group. Heesy and Ross (2001) used an argu-ment based on character optimization to reconstruct the ac-tivity period of the basal euprimate as nocturnal. However,their tree did not include any plesiadapiforms. As stem pri-mates, plesiadapiforms are the most relevant taxa for recon-structing states at the basal euprimate node (Silcox, 2001, inpress). Nonetheless, the suggestion presented here of a noc-turnal activity pattern for Carpolestes simpsoni is supportive

of their conclusion, providing additional evidence in favorof the common ancestor of Euprimates having beennocturnal.

While the infraorbital foramen is reduced in many eupri-mates, some plesiomorphic taxa (e.g., Cantius and Shosho-nius) have a relatively large infraorbital foramen, whichcan be hypothesized as the primitive condition for the clade(Kay et al., 1992). All plesiadapiforms for which this regionis known, including Carpolestes simpsoni, also have rela-tively large infraorbital foramina, suggesting that tactile vi-brissae may have been present (Kay and Cartmill, 1974,1977).

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Fig. 18. Bivariate plot of relative snout length for a variety of extant and fossil mammals (A), and bar graph of the residuals plotted in increasing order (B). Data

(measured in millimeters) are from individuals (see Appendix 3). Snout length was measured from the base of the anterior surface of the root of the zygomatic arch

to the front of the specimen, as figured. Cranial length was measured as a maximum length. The line plotted is a least-squares regression of the natural logarithm of

snout length on the natural logarithm of cranial length (yZ 1.606x � 3.51; r2 Z 0.79; p ! 0.001). Note that Carpolestes simpsoni falls on the line, near individ-

uals of Ptilocercus lowii. The low residual for Carpolestes simpsoni indicates a snout length close to that generally predicted for a mammal of the same cranial

length, contrasting substantially with the very negative residuals (implying a substantially reduced snout length) for the fossil euprimates Smilodectes and Shosh-

onius. Double-headed arrows indicate ranges of snout length residuals in Primates and Euprimates (dashed line indicates the maximum for Euprimates) included in

this analysis.

The lacrimal foramen is located on the face in Carpo-lestes simpsoni, similar to the condition in Plesiadapis andMegadelphus. Unlike in these taxa, however, the lacrimalforamen is positioned closer to the orbital rim in C. simp-soni, more like that of Palaechthon nacimienti. Similarly,certain primitive euprimates (e.g., Cantius, Shoshonius, andNotharctus) have an extra-orbital lacrimal foramen. In con-trast, the lacrimal foramen is located inside the orbit inIgnacius (Rose and Gingerich, 1976). Carpolestes hasa small tubercle associated with the lacrimal foramen, a con-dition similar to that of Palaechthon, Ignacius, and certaineuprimates, but different from Megadelphus and Plesiadapis,which lack this tubercle.

Palatal anatomy

As observed for the carpolestids Carpolestes dubius(Jepsen, 1930; Rose, 1975) and Carpodaptes cygneus(Krause, 1978), Carpolestes simpsoni has a large fenestra-tion in the palate (Bloch and Gingerich, 1998). This featureis not seen in other plesiadapiforms or euprimates for whichthe relevant region is known. Unlike the reconstruction ofthis feature in C. cygneus, in C. simpsoni this fenestra is di-vided by a vertical lamina of bone interpreted to be the vo-mer (Fig. 8; Bloch and Gingerich, 1998), although, as notedabove, dorsoventral crushing has likely influenced the posi-tion of this bone.

20 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 19. Bivariate plots of the natural logarithm of interorbital breadth on the natural logarithm of cranial length (A), and the natural logarithm of orbital diameter

on the natural logarithm of cranial length (B). Data for (A) in part from Cartmill (1970) and for (B) in part from Cartmill (1970), Kay and Kirk (2000), and Ni et al.

(2004). Interorbital breadth was measured as ‘‘the smallest breadth between the medial walls of the orbits at their entrances’’ Schultz, 1962, cited in Cartmill, 1970:

61), cranial length was measured from prosthion to inion, and orbital diameter was measured from dorsal to ventral extents of the orbit (Cartmill, 1970). Data are

species means. Least-squares regression lines are fitted through the data for each order in (A). Note that, in (A), Carpolestes simpsoni lies approximately on the line

for Scandentia, near Ptilocercus lowii, with a much greater interorbital breadth than would be predicted for a modern primate of its cranial length. Least-squares

regression lines were fitted through the data for each group identified in the legend in (B). Note that, in (B), C. simpsoni has smaller orbits than would be expected

not only for a euprimate, but also for a non-euprimate mammal with the same cranial length. Although it is true that nocturnal and cathemeral euprimates generally

have larger orbits than diurnal euprimates, this relationship is reversed in Scandentia, in which diurnal Tupaia minor has larger orbits than the similarly sized

nocturnal Ptilocercus lowii. This reflects the fact that smaller orbits are not generally indicative of diurnality in non-euprimate mammals. Contrary to the conclu-

sion of Ni et al. (2004), Teilhardina asiatica plots closer to both the nocturnal and diurnal non-euprimate lines than to the diurnal euprimate line in this analysis,

suggesting that its activity pattern is equivocal and that the primitive euprimate condition remains unresolved.

The position of the caudal midsagittal margin of the hardpalate is similar in most plesiadapiforms and euprimates, lo-cated near the level of a line drawn between the distal edgesof the right and left M3s. The one exception to this is foundin paromomyids, in which the caudal midsagittal margin ofthe palate extends significantly posterior to the level of M3,much further caudally than in Carpolestes. It is not clearwhat the significance of this unusual characteristic of paromo-myids (also seen in some bats) might be. Plesiadapiforms,

including Carpolestes simpsoni, possess a thickening at thecaudal margin of the palate (Zpostpalatine torus), althoughthis feature is not expanded into a thick, barlike structure, asseen in some insectivores (e.g., erinaceomorphs).

Basicranium and braincase

Two foramina in the alisphenoid ofCarpolestes simpsoni havebeen interpreted here as the foramen rotundumand foramen ovale

21J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

(Fig. 11). This identification is complicated by disagreementsabout the identification of similarly placed openings in Plesiada-pis tricuspidens. The foramen rotundum is the passageway forcranial nerve V2 (maxillary branch of the trigeminal) to exit theneurocranium. In many mammals, this nerve passes through thesphenorbital fissure, and the foramen rotundum is consideredto be confluent with this opening (so it is therefore ‘‘absent’’).Muller (1934) and Kielan-Jaworowska (1981) argued that thiswas the primitive state for Eutheria, as seen in Asioryctes(Kielan-Jaworowska, 1981) and Leptictidae (Novacek, 1986).However, various mammals, including marsupials, carnivorans,rodents, some euprimates (e.g., Tarsius), and some scandentians(e.g., Tupaia glis), do have a separate foramen rotundum(Cartmill and MacPhee, 1980).

Determining the presence or absence of the foramen ro-tundum is related to debates over the presence of the subop-tic foramen. The suboptic foramen is variably positionedand carries a vein communicating between the ophthalmic

Fig. 20. Box plots for optic foramen index (OFI) (A) and optic foramen quo-

tient (OFQ) (B) for Carpolestes simpsoni and selected extant archontans. OFI

and OFQ calculated following Kay and Kirk (2000). Note that C. simpsoni has

very low OFI and OFQ (i.e., a very small optic foramen), suggesting high de-

grees of retinal summation and a nocturnal activity period. Data from both Kay

and Kirk (2000) and this study (Appendix 4).

veins in the two orbits (Butler, 1948). Identifications ofthe suboptic foramen and the foramen rotundum are interde-pendent because they are often either associated with oneanother (and therefore are easily confused), or are confluentwith the sphenorbital fissure (Zfissura sphenoidalis ofGingerich, 1976; foramen lacerum anterius of McDowell,1958; superior orbital fissure of White, 1991), and arethus part of this structure and not distinguishable. The sphe-norbital fissure is always present since it carries at least cra-nial nerves III, IV, V1, and VI. A suboptic foramen, distinctfrom the sphenorbital fissure, is found in a few eutheriangroups (Cartmill and MacPhee, 1980; Novacek, 1986), in-cluding a number of bats (Kay et al., 1992). Cartmill andMacPhee (1980) noted the presence of a distinct subopticforamen in some scandentians (Dendrogale and some speci-mens of Tupaia tana). This foramen is missing in mostarchontans, however, including dermopterans, euprimates,many scandentians (e.g., Ptilocercus lowii), and many bats(Cartmill and MacPhee, 1980; Kay et al., 1992), makingthe identification of a suboptic foramen in Plesiadapis byKay et al. (1992) somewhat surprising.

The basis for the identification of a suboptic foramen inPlesiadapis is rather confusing. Kay et al. (1992: 480) stated:‘‘A foramen rotundum has been described for Plesiadapis(Russell, 1964) but we believe that this foramen in Plesiada-pis (MNHN CR 965) is more likely the suboptic foramen.’’ Inthe appendix giving their character descriptions, however,they made the following statement: ‘‘A suboptic foramen ispresent in Plesiadapis tricuspidens (MNHN CR 965) butwas labeled ‘t.d.a.’ by Russell (1964: fig. 19)’’ (Kay et al.,1992: 497). Examination of Fig. 19 in Russell (1964) revealsthat there are separate foramina labeled ‘‘t.r.’’(Z‘‘trou rond,’’foramen rotundum) and ‘‘t.d.a.’’ (Z‘‘trou dechire anterieur,’’sphenorbital fissure). From the conflicting statements givenabove, it is not clear which of these two openings Kayet al. considered the suboptic foramen. If P. tricuspidensdoes have a suboptic foramen, whichever opening is not thesuboptic foramen must be the sphenorbital fissure ratherthan the foramen rotundum since all mammals have a sphe-norbital fissure, while only some have a foramen rotundumas well. Kay et al. (1992) coded Plesiadapis as having no fo-ramen rotundum.

The potential foramen rotundum in Plesiadapis tricuspi-dens (‘‘trou rond’’ of Russell, 1964) opens into the neurocra-nium and is shifted towards the cranial base, as would beexpected for a foramen rotundum. This orientation and posi-tion would not be expected for a suboptic foramen or sphe-norbital fissure, both of which one would expect to find inthe orbit, close to the optic foramen. The ‘‘t.d.a’’ of Russell(1964) could more plausibly be considered a suboptic fora-men since it is actually located in the medial wall of theorbit, in approximately the expected anatomical position.There are two problems with this interpretation, however.First, the medial walls of the orbits, and the optic foramina,are well separated in Plesiadapis, unlike the situation inscandentians that have a suboptic foramen, making it veryunlikely that there was a connection between the two orbits.

22 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Second, this interpretation would require the supposed fora-men rotundum to be the sphenorbital fissure, which is gener-ally located more ventrally than this opening, at least basedon its position in the best preserved skull of P. tricuspidens(MNHN Cr-125). In other words, if the foramen labeled‘‘t.d.a.’’ is the suboptic foramen, then there is no openingpresent as a plausible candidate for the sphenorbital fissure,which is impossible if P. tricuspidens had functional eyes.Following this line of reasoning, Russell’s original (1964)identification of a foramen rotundum in Plesiadapis seemsmore plausible than Kay et al.’s (1992) contrary interpreta-tion, and is followed here.

Carpolestes simpsoni is similar to Plesiadapis in the pres-ence of two foramina that are located in the alisphenoid, ros-tral to the auditory bulla. As noted above, the sphenorbitalfissure has already been identified as an additional openingon the medial orbital wall in C. simpsonidthis identificationshould be uncontroversial since this opening is in the expectedposition, near the optic foramen (Fig. 8). The more caudal fo-ramen in the alisphenoid is in the expected position for the fo-ramen ovale, directly rostral to the auditory bulla, making itsinterpretation similarly uncontroversial. This leaves the morerostral foramen in the alisphenoid unidentified.

A possible interpretation for this more rostral opening isthat it is a middle lacerate foramen for entry of an enlargedascending pharyngeal artery (as had been erroneously identi-fied for Ignacius; MacPhee et al., 1983; but see Szalay et al.,1987; Kay et al., 1992). This is unlikely, however, since thereis good evidence that a significant portion of the blood sup-ply to the brain traveled through the middle ear (see below).This more rostral opening is directed into the neurocraniumand is ventrally situated, so it is unlikely to be a suboptic fo-ramen. This orientation is also not consistent with it beingassociated with an alisphenoid or alar canal, which wouldbe oriented rostrocaudally rather than dorsoventrally. Com-parisons with taxa that have a patent foramen rotundum sug-gest that this identification is the most likely. In MNHNCr-125, the foramen considered by Russell (1964) to be a fo-ramen rotundum in Plesiadapis is separated from the fora-men ovale by a wider section of bone than separates theseapparently homologous openings in Carpolestes simpsoni.The relatively longer mesocranial region in the former taxonplausibly explains this contrast. As such, the evidence sug-gests that both Plesiadapis tricuspidens and C. simpsonieach possess a distinct foramen rotundum and no subopticforamen. Although the presence or absence of a suboptic fo-ramen is unknown for Ignacius (because of damage to the or-bit in all known specimens), the evidence currently availablesuggests that a distinct foramen rotundum was absent. Thereis no opening rostral to the foramen ovale in Ignacius, mak-ing it unlike Carpolestes and Plesiadapis. The relevant regionis not well-enough preserved in Palaechthon or in any micro-syopid to determine whether or not a separate foramen rotun-dum was present.

As in euprimates and other plesiadapiforms, Carpolestessimpsoni has a well-demarcated postglenoid foramen, unlikedermopterans, in which it is absent. A small but distinct

subsquamosal foramen is present in C. simpsoni. This is in-terpreted to be homologous to the opening referred to byKay et al. (1992) in Ignacius as a suprameatal foramen.Beard and MacPhee (1994) documented the variable useof this term, and suggested that ‘‘suprameatal foramen’’be restricted to the opening in the side of the skull of Tar-sius that allows for an anastomosis between the intracranialstapedial (middle meningeal) and posterior auricular arteries(see MacPhee and Cartmill, 1986). In Tarsius this ‘‘true’’suprameatal foramen is located directly above the externalauditory meatus, caudal to the end of the zygomatic arch,in a position quite different from the foramen in Ignaciusand Carpolestes. The foramen located at the base of the zy-gomatic arch has been called a ‘‘subsquamosal foramen’’ byvarious authors (Gregory, 1920; Butler, 1956), and this termseems more appropriate for the opening in question. Whenthis opening is very large, it can carry a vein connectingthe superior petrosal sinus with the external jugular vein(Novacek, 1986)dthis condition was likely the case inAsioryctes and leptictids. In plesiadapiforms this openingis never as large as in more primitive eutherians, and a func-tional vein may or may not have been present inCarpolestes.

The evidence indicates that Carpolestes simpsoni did nothave a tubular external auditory meatus (Fig. 14). This con-trasts with the situation in Plesiadapis, paromomyids, and Tar-sius, and is more similar to the situation in microsyopids andsome primitive euprimates, including adapids and Shoshonius(Beard and MacPhee, 1994).

Homology of the bones forming the auditory bulla in ple-siadapiforms has been a topic of considerable controversybecause the presence of a petrosal bulla has long been re-garded as one of the key euprimate synapomorphies (e.g.,Cartmill, 1972). Several lines of evidence suggest that Igna-cius did not have a petrosal bulla, but rather possessed themore primitive condition of an expanded entotympanic ele-ment that is separated by sutures from the petrosal, basisphe-noid, and basioccipital (Kay et al., 1990, 1992; Bloch andSilcox, 2001; Silcox, 2003). Reinterpretation of the morphol-ogy in Phenacolemur suggests a similar condition (Bloch andSilcox, 2001), implying that this was likely typical forparomomyids.

Determining the composition of the auditory bulla for mi-crosyopids is complicated. There is no specimen that hasbeen described for the family that includes an intact auditorybulla. McKenna (1966) suggested that the presence of a ru-gose area on the ventromedial side of the petrosal in Micro-syops knightensis indicates a contact with an entotympanicelement, either ossified or cartilaginous. However, McKenna(1966: 15) also noted that ‘‘additional material is necessaryto determine the exact nature of the microsyopid entotym-panic.’’ Not only could the microsyopid bulla have been anossified or cartilaginous entotympanic, but it is also possiblethat this taxon had a significantly larger ectotympanic ele-ment than seen in other plesiadapiforms, forming part, orall, of the bulla (e.g., as in Cynocephalus; MacPhee et al.,1983, 1988, 1989). Only two definite conclusions currently

23J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

can be reached about the composition of the microsyopid bul-la. First, there is no evidence for a suture comparable to thatseen in Ignacius, so the relationship between the bullar roofand the promontorium was not precisely the same as in thattaxon. Second, the absence of significant petrosal processessuggests that the bulla cannot have been petrosal in origin(MacPhee et al., 1983, 1988, 1989). In this way, microsyo-pids also differ from Plesiadapis and Carpolestes, whichmay have significant petrosal processes. Both Plesiadapisand Carpolestes also lack the rugosity on the promontoriumobserved in Microsyops.

The continuity between the promontorium and bulla inPlesiadapis has been interpreted by some authors as indicat-ing that the auditory bulla was petrosal in origin, a derivedcharacteristic shared with euprimates (Russell, 1959; Szalay,1972; Szalay et al., 1987). While it has since been demon-strated that paromomyid plesiadapiforms had a non-petrosalcomponent to their bulla (Kay et al., 1990, 1992; Blochand Silcox, 2001; Silcox, 2003), Carpolestes lacks any evi-dence for the ‘‘apronlike’’ suture separating the promonto-rium from the bulla that is characteristic of even fully adultparomomyids (Kay et al., 1992; Bloch and Silcox, 2001),making it identical in this respect to Plesiadapis and eupri-mates. Thus, the presence of an entotympanic in paromo-myids should not be used as evidence of an entotympanicin other plesiadapiforms, including Carpolestes. Some extantrodents develop a morphology comparable to that observed inPlesiadapis tricuspidens and euprimates as a result of ontoge-netic obliteration of the suture between their ectotympanicbulla and the petrosal elements of the middle ear; it hasbeen suggested that Plesiadapis might have had a similarcondition (MacPhee et al., 1983; MacPhee and Cartmill,1986; Beard and MacPhee, 1994). Regarding this argument,we agree with Szalay et al. (1987) on the following three crit-ical points. First, the lack of a petrosal bulla in primitive ple-siadapiforms such as microsyopids does not argue against thepresence of a petrosal bulla in the more derived plesiadapoidprimates. Most recent phylogenetic analyses have found thatPlesiadapiformes is not a monophyletic group, even if theirviews differ on other details of the relationships within thisgroup (Gunnell, 1989; Beard, 1993a; Hooker et al., 1999;Silcox, 2001, in press; Bloch and Boyer, 2002a, 2003; Silcoxet al., 2005; but see Kay et al., 1992; Clemens, 2004). Thisimplies that the state of this character in one plesiadapiformcannot be assumed to apply to another plesiadapiform. Sec-ond, given the regrettable absence of a complete ontogeneticsequence for the cranium of both Plesiadapis and Carpo-lestes, the hypothesis that a suture was present but has be-come ontogenetically obliterated (the ‘‘suture hypothesis’’;MacPhee et al., 1983; MacPhee and Cartmill, 1986) is impos-sible to definitively falsify. However, these data are also com-pletely lacking for almost all other late Paleocene and earlyEocene mammals (including the most primitive known eupri-mates Cantius, Donrussellia, and Teilhardina), and the ab-sence of such data is not itself a valid falsification of thehypothesis that plesiadapoids had a petrosal bulla, which isthe view most consistent with the available anatomy.

Parsimony arguments (e.g., Wible and Covert, 1987) arealso incapable of falsifying this hypothesis, since they are de-pendent on a pattern of relationships that is a hypothesis, notevidence, rather than on any positive anatomical data. Third,the ‘‘suture hypothesis’’ predicts that immature specimens ofPlesiadapis should have a suture. In fact, a cranium of an im-mature Plesadapis lacks a suture (Szalay et al., 1987), sup-porting the presence of a petrosal bulla in this taxon. Thecranium of an immature specimen of Nannodectes presentsadditional evidence for a petrosal origin of the bulla in ple-siadapids (Boyer et al., 2004). As it stands, we interpret theanatomy of C. simpsoni to be most consistent with the pres-ence of a petrosal bulla. In fact, our phylogenetic analysissuggests that a petrosal bulla may have been inherited fromthe common ancestor of plesiadapoids and Euprimates (seebelow).

An unusual feature of Carpolestes is the presence of a sep-tum of bone on the promontorium that ‘‘shields’’ the fenestrarotunda. A similar ‘‘shielding’’ of this opening exists in ple-siadapids, but is missing in known microsyopids. In Tupaiaglis (but not Ptilocercus lowii), at least one specimen of Igna-cius graybullianus (Silcox, 2003), and some euprimates, thefenestra rotunda is similarly shielded, but this is accomplishedby the passage of an arterial tube across the promontorium,suggesting that this may not be a homologous configuration.

Carpolestes simpsoni is most similar to Microsyops (andpossibly Tinimomys graybulliensis; Gunnell, 1989; but seeMacPhee et al., 1995) among plesiadapiforms in possessingfairly wide grooves on the promontorium for the stapedialand promontory branches of the ICA (Fig. 15). When meas-urements of bony proxies for the size of the ICA are plottedwith extant taxa that have functional and non-functional inter-nal carotid arteries, C. simpsoni is clearly positioned with taxahaving a functional ICA (Fig. 21). Unlike extant haplorhines,including Tarsius, evidence for the stapedial artery is not onlypresent, but this vessel appears to have been larger than thepromontory artery (Appendix 1). Presence of these well-demarcated arterial grooves contrasts with the situation inPlesiadapis, which has only shallow, inconsistently placedgrooves on the promontorium that probably transmitted nervesrather than arteries (Saban, 1963; Gingerich, 1976; MacPheeet al., 1983; Bloch and Silcox, 2001; but see Szalay et al.,1987). Paromomyids appear to have had a reduced internalcarotid artery (Kay et al., 1992), although a groove is presentin one specimen (Bloch and Silcox, 2001), and a bony tube inanother (Silcox, 2003), each of which likely carried a remnantof the promontory artery in addition to the internal carotidnerves. Carpolestes also differs from paromomyids in themore medial course of the internal carotid artery, extendingrostrolaterally from a medially positioned posterior carotid fo-ramen (pcf; Fig. 9). In paromomyids this vessel runs across thelateral face of the promontorium from a laterally positionedpcf (Kay et al., 1992; Wible, 1993; Bloch and Silcox, 2001;Silcox, 2003), which is a condition also exhibited by adapidsand one omomyid (Shoshonius cooperi; Beard and MacPhee,1994), suggesting that this may be the primitive euprimatecourse (Bloch and Silcox, 2001). Based on the position of

24 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 21. Bivariate plot of the logarithm of the posterior carotid foramen (pcf) diameter on the logarithm of cranial length. Pcf diameter was estimated for Carpo-

lestes simpsoni using the groove for the ICA on the promontorium, before it divides into the promontorial and stapedial branches, averaged in UM 101963 and

USNM 482354 (Appendix 1). Carpolestes simpsoni clearly plots with modern taxa that have a functional ICA. Data in part from Kay et al. (1992).

the posterior carotid foramen in the one plesiadapid for whichit can be identified (Gingerich, 1976), it appears that this familywas somewhat intermediate, with a more lateral position forthe pcf than in Carpolestes, but a more medial position thanin paromomyids.

An unusual feature of the ear region in Carpolestes is thedivision of the auditory cavity into two chambers. This fea-ture is not seen in any other plesiadapiforms or primitive eu-primates for which the anatomy is known. However, extantTarsius does possess an auditory cavity with two chambers.This is of particular interest because of the hypothesis thatcarpolestids are tarsiiform euprimates (McKenna and Bell,1997). In this extant genus (and in anthropoids), an anterioraccessory cavity is located rostromedially to the middle earcavity proper, originating from a rostrally located point ofpneumatization, near the opening of the auditory tube intothe hypotympanic sinus (MacPhee and Cartmill, 1986). InTarsius, this extra cavity necessitates an unusual route forthe auditory tube, which travels through part of the lateralwall and roof of the bulla in the process of bypassing the an-terior accessory cavity (Fig. 22; MacPhee and Cartmill,1986). The auditory tube seems to have taken a similar routein Carpolestes, with remnants of it preserved in parts of thewall of the bulla (Fig. 17).

In spite of these similarities, there are some significant dif-ferences between the configuration of the ear in Carpolestesand that observed in Tarsius. The posterior chamber in Car-polestes extends much further rostrally than in Tarsius, so itis captured in cross-sections extending most of the lengthof the ‘‘platform bone’’ that roofs the anterior chamber(Fig. 16). In Tarsius, there is much less extensive overlap,so anterior slices through the basicranium include only theanterior accessory cavity (Fig. 22). In addition, the anterioraccessory cavity of Tarsius is located more medially relativeto the middle ear cavity proper than is the case in

Carpolestes, in which the two cavities are stacked on topof one another. This suggests that the accessory chamber inCarpolestes may have arisen from a point of pneumatizationlocated more caudally and laterally than in Tarsius. The con-figuration is also quite different from the multiple accessorycavities arising from pneumatization near the epitympanic re-cess in lorises (MacPhee and Cartmill, 1986). Indeed, the

Fig. 22. Ultra high-resolution X-ray CT slice from a skull of extant Tarsius

syrichta (PSU specimen). In this coronal view, ventral is towards the top of

the page. This slice is fairly far anterior, so the large cavity is the anterior ac-

cessory cavity (labeled ac), rather than the middle ear cavity proper (Zhypo-

tympanic sinus); compare to MacPhee and Cartmill (1986: Figure 3D) for the

purposes of orientation. This figure demonstrates the bony canal for the prom-

ontory artery (pcl) running in a perbullar position. Adjacent to this canal is the

passageway for the auditory (pharyngotympanic) tube, passing through the

roof and lateral wall of the bulla, bypassing the anterior accessory cavity. Ab-

breviations as in Table 2. Scale Z 1 mm.

25J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

subdivision of the tympanic cavity in Carpolestes is quite un-like that seen in any other primate clade. Nonetheless, it is ofinterest adaptively. In anthropoids, the double-chambered earcavity may be related to improvements in hearing both highand low frequency sounds, with a trough in the audiogram(representing reduced ability to hear) in mid-frequency rangesounds (Coleman and Ross, 2004). Huang et al. (2000) founda similar phenomenon in their study of cats with multi-cham-bered ears, which they suggested might be associated withavoiding deficiencies in hearing at higher frequencies thatcould interfere with the use of sound for localization ofprey. Although it is unlikely that cats make a good behavioralmodel for carpolestids, it seems clear from these preliminaryindications that a better understanding of the functional basisof this feature may aid in future efforts to paint a more com-plete picture of the adaptive repertoire of Carpolestessimpsoni.

Even more significantly, Tarsius and Carpolestes differ inthe position of the internal carotid artery relative to the ear cav-ities. In Carpolestes, the internal carotid artery takes the moreprimitive transpromontorial route through the middle ear cavityproper, leaving grooves on the promontorium. In Tarsius (andother haplorhines), the internal carotid artery takes a perbullarroute, bypassing both the middle ear cavity proper and the an-terior accessory cavity (Fig. 22; MacPhee and Cartmill, 1986).

The postorbital constriction seen in Carpolestes is alsoa characteristic feature of the skull of other plesiadapiforms(e.g., Ignacius, Megadelphus, Plesiadapis, and Palaechthon);this feature is typically less marked in primitive euprimates.

Phylogenetic analysis

To examine the phylogenetic implications of the cranialanatomy of Carpolestes simpsoni, we included it in a cladisticanalysis with all the other plesiadapiform groups known frominformative cranial material, as well as primitive euprimates,extant Tarsius, and dermopterans. Ptilocercus lowii was

chosen to represent Scandentia based on evidence that thisspecies is the most primitive member of the order (Sargis,2002a,b,c,d, 2004, in press; Olson et al., 2005). Leptictidswere chosen as the outgroup because many features of theskeleton and dentition suggest they are plesiomorphic (Rose,1999), and their cranial anatomy is very well known (Novacek,1986). Chiroptera was not included in the analysis. Althoughbats have been linked to dermopterans in some morphologicalstudies (e.g., McKenna, 1975; Szalay, 1977; Novacek andWyss, 1986), in molecular analyses, Chiroptera usually formsa clade with carnivores and ungulates (e.g., Miyamoto et al.,2000; Liu et al., 2001; Murphy et al., 2001a,b; Springeret al., 2003), and never forms part of a group with Euarchonta,suggesting that they are only distantly related to this clade.

Twenty-four characters of the cranium were scored for 11mammalian taxa (Table 3). A description of these charactersis given in Appendix 2. All characters were unordered andequally weighted; multi-state characters were interpreted aspolymorphic. An exhaustive search using parsimony was per-formed in PAUP 4.0b10 (Swofford, 2002).

Results

The cladistic analysis yielded three most parsimonious cla-dograms (lengthZ 60 steps, CIZ 0.633, and RIZ 0.607; treestatistics calculated in PAUP). The three most parsimonouscladograms are shown in Fig. 23AeC. A strict consensustree was calculated in PAUP from these trees, and this isshown in Fig. 23D. In the consensus tree, Carpolestes simp-soni is part of a trichotomy with Plesiadapidae andEuprimates.

Discussion

This analysis reached a different conclusion from a previ-ous cladistic analysis of cranial characteristics in plesiadapi-forms (Kay et al., 1992) by failing to find a close

Table 3

Data matrix for cladistic analysis1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Leptictidae2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Ptilocercus lowii 0 0 0 0 1 0 1 0 0 0 2 1 1 0 1 1 1 0 1 1 0 2 0 0

Cynocephalidae3 0 2 1 1 2 0 1 0 0 0 1 0 1 1 0 0 0 0 1 1 0 0 0 0

Tarsius syrichta 1 1 1 1 1 2 1 1 1 1 2 1 0,1 0 1 1 0 2 1 2 1 1 0 1

Shoshonius cooperi 1 1 0 0 1 1 1 1 1 1 2 1 0 0 1 1 1 ? 0 2 ? 1 1 0

Adapidae4 1 1 0 0 1 1 1 1 0 1 2 0 0 0,1 1 0 0,1 1 0 2 ? 1 1 0

Palaechthon nacimienti ? ? ? ? ? ? ? 0 ? 0 1 ? ? 0 1 0 1 ? 0 0 ? 2 ? ?

Microsyopidae5 0 ? 0 ? 0 0 1 0 0 0 1 0 0 0 1 0 1 0 1 ? ? 1 0 0

Paromomyidae6 0 2 1 0 0,1 1 1 1 0 0 0 0 0 2 1 0 1 ? 0 0 0 0 1,2 0

Plesiadapidae7 1 ? 1 0 2 0 1 1 0 0 0 0 0 0 1 1 1 1 1 0 1 1 2 0

Carpolestes simpsoni 1 ? 0 ? 0 0 1 1 0 0 0 0 0 0 1 1 1 1 0 0 1 2 2 1

1 See Appendix 2 for character descriptions.2 Leptictidae coded based on Palaeictops bicuspis (Novacek, 1986: Figure 3) when preserved, and otherwise from Leptictis dakotensis.3 Cynocephalidae coded as a composite from Cynocephalus volans and Galeopterus variegatus.4 Adapidae coded as a composite based on Cantius abditus and Smilodectes gracilis.5 Microsyopidae coded from a composite of Megadelphus lundeliusi and Microsyops latidens.6 Paromomyidae coded as a composite from Ignacius graybullianus and Phenacolemur jepseni.7 Plesiadapidae coded from Plesiadapis tricuspidens, Plesiadapis cookei, and Nannodectes gidleyi.

26 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Fig. 23. Results of cladistic analyses based on 24 cranial characters for 10 ingroup taxa (Table 3; Appendix 2). An exhaustive search in PAUP 4.0b10 (Swofford,

2002) produced three most parsimonious trees of lengthZ 60 steps, CIZ 0.633, RIZ 0.607. The three equally parsimonious trees are presented in AeC. A strict

consensus tree based on the three equally parsimonious trees was calculated in PAUP and is presented in D. Based on optimizations in MacClade, the following are

unambiguous synapomorphies supporting the listed nodes in D: 1: 7(1), 15(1), 17(1); 2: 11(1); 3: 19(1); 4: 13(1); 5: 8(1); 6: 1(1), 21(1), 22(1); 7: 2(1), 5(1), 6(1),

10(1), 11(2), 20(2), 23(1); 8: 9(1), 12(1). Note that, in the strict consensus tree, Carpoleses simpsoni and Plesiadapidae form a trichotomy with Euprimates. In

none of the most parsimonious trees are paromomyids and cynocephalids (Dermoptera) sister taxa. In fact, dermopterans are grouped with Scandentiada

conclusion in agreement with recent molecular results (Liu and Miyamoto, 1999; Liu et al., 2001; Madsen et al., 2001; Murphy et al., 2001a,b; Springer

et al., 2004).

relationship between non-microsyopid plesiadapiforms anddermopterans (i.e., Eudermoptera; Beard, 1993a). There arelikely many reasons for this, including the absence ofsome derived character states in Carpolestes that had previ-ously been thought to support this grouping [e.g., a reducedinternal carotid artery (Character 5)], as well as the reassess-ment of many characters with new morphological observa-tions (e.g., the discovery of a bony tube for the internalcarotid nerves and/or promontory artery in one specimen

of Ignacius; Silcox, 2003). There are currently no convincingcranial synapomorphies that link plesiadapiforms and der-mopterans to the exclusion of euprimates (Bloch and Silcox,2001). The shortest tree that includes this grouping is twosteps longer than the most parsimonious tree (CIZ 0.613,RIZ 0.571).

A link betweenDermoptera and Scandentia is supported in re-cent molecular phylogenetic analyses (e.g., Liu and Miyamoto,1999; Liu et al., 2001; Madsen et al., 2001; Murphy et al.,

27J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

2001a,b; Springer et al., 2004), and also appears on this tree. Theunambiguous support for this grouping is limited, however, to thepresence of dual posterior lacerate (Zjugular) foramina [Charac-ter 13(1)]. The sister taxon to PtilocercusCDermoptera is Mi-crosyopidae. Although some authors have suggested a possibledermopteranemicrosyopid relationship (i.e., Szalay et al.,1987), this tie to ScandentiaCDermoptera is surprising. Thesupport for this relationship is very weak, however, with onlyone feature [absence of a lacrimal tubercle; Character 19(1),also absent in Plesiadapidae] providing unambiguous support.In all three of the most parsimonious trees, the poorly known ple-siadapiform Palaechthon nacimienti falls out as the sister taxonto MicrosyopidaeC ScandentiaCDermoptera. This result iscontrary to hypotheses that would link palaechthonids and mi-crosyopids to the exclusion of other archontans in Microsyopoi-dea (Gunnell, 1989). However, as with the position ofMicrosyopidae, the support for this pattern of relationships isquite weak, with the relevant node being unambiguously sup-ported only by the presence of a postorbital process [Character11(1); expanded into a postorbital bar in Scandentia]. In this anal-ysis, the postorbital bar of euprimates was optimized to have aris-en independently from the postorbital bar of scandentians. This isconsistent with the apparently labile nature of this feature, as in-dicated by its widespread occurrence throughout Mammalia(Ravosa et al., 2000), suggesting that it is a character ofrelatively low phylogenetic valence (Silcox, 2003).

In keeping with the results of a phylogenetic analysis basedon postcranial characteristics (Bloch and Boyer, 2002a), ourresults based on cranial characters support the monophyly ofa clade that includes ParomomyidaeC CarpolestidaeCPlesiadapidaeC Euprimates. Support for this node includesthe presence of a narrow central stem and expansive hypotym-panic cavity (Character 8). Paromomyids also share with prim-itive euprimates a bony tube for the internal carotid nervesand/or branches of the artery, which shields the fenestra rotun-da and runs in a lateral position across the promontorium[Characters 5(1; also shared with Ptilocercus lowii; scored asvariable in paromomyids), 6(1), and 23(1; scored as variablein paromomyids)]. These features are absent, however, in ple-siadapids and Carpolestes simpsoni, so their pattern of evolu-tion remains unclear.

Plesiadapidae and Carpolestes simpsoni form a trichotomywith Euprimates in the strict consensus tree. All three treesinclude a relationship between Carpolestes simpsoni, Plesia-dapidae, and Euprimates. Among the characters supportingthe plesiadapoidC euprimate clade is the presumed presenceof a petrosal bulla, based on the absence of a suture separat-ing the bulla from the promontorium [as is found, for exam-ple, in paromomyids (Kay et al., 1992; Bloch and Silcox,2001; Silcox, 2003); Character 1(1)]. One possible criticismof these results is that they rest too heavily on a trait (thepresence of a petrosal bulla) that is still the subject of debatefor Carpolestes and plesiadapids. To assess the importance ofthis trait in the phylogenetic results, we re-ran the analysiswith Character 1 inactivated. The result was the same threemost parsimonious cladograms found in the analysis that in-cluded this trait (Fig. 23AeC; tree statistics for analysis

excluding Character 1: tree lengthZ 59 steps, CIZ 0.627,RIZ 0.577). This is a clear indication that, while the inferredpresence of a petrosal bulla in Carpolestes and plesiadapidsadds to the support for the EuprimateC PlesiadapidaeCCarpolestes simpsoni node, there is other support in thedata set for this relationship. Other traits providing unambig-uous support for this node are the presence of a foramen ro-tundum [Character 21(1)] and the presence of a lacrimalforamen that is on the face [Character 22(1); also presentin Microsyopidae and missing in Carpolestes simpsoni, whichexhibits character state 22(2)].

We ran an additional analysis that included the petrosalbulla character, and re-coded Characters 5 and 23 as non-var-iable for paromomyids [Character 5(1); Character 23(1)]. Ourreason for performing this analysis was that we consider itlikely that the apparent variation in these characters, relatingto the presence or absence of a tube for the internal carotidartery and/or nerves, likely owes more to damage to somespecimens than to the original anatomy. That is, we considerit likely that paromomyid specimens that have a groove forthese structures, rather than a tube, are damaged and original-ly had a tube. One reason for this view is the fact that thespecimens in which the groove has been documented (seeBloch and Silcox, 2001) are quite heavily damaged, moreso than the specimen in which the tube is preserved (seeSilcox, 2003). Also, the morphology of the groove itself issuggestive of its origin as the base of a tube since its sidesare quite sharp. The result of this analysis was a single mostparsimonious cladogram (lengthZ 59 steps; CIZ 0.610;RIZ 0.589) that corresponds to one of the three cladogramsfound previously (Fig. 23A). Thus, we consider this clado-gram to be the best representation of the relationships indicat-ed by the cranial data known for plesiadapiforms.

Neither Plesiadapiformes nor Primates sensu lato are sup-ported as monophyletic groups. This is probably due to thelack of data for Palaechthon nacimienti and the primitivenature of the microsyopid ear. In light of the weakness ofthe support for the reconstructed positions of P. nacimientiand Microsyopidae, these conclusions are likely to changewith the inclusion of dental data (e.g., see Silcox, 2001;Bloch and Boyer, 2003; Silcox et al., 2005; Bloch et al.in prep.).

This result does not support previous taxonomic hypoth-eses that would place carpolestids in Euprimates as tarsii-forms to the exclusion of other plesiadapiforms(Dashzeveg and McKenna, 1977; McKenna and Bell,1997). Although Carpolestes simpsoni has some tarsier-likefeatures of its ear (e.g., the presence of two chambers;Character 24), it lacks other features seen in extant haplor-hines (e.g., a reduced stapedial artery and a perbullar routefor the internal carotid artery), as well as characteristics thatare present in both tarsiers and omomyids [i.e., very largeorbits, very narrow, ‘‘peaked’’ choanae (Character 9), noclear mastoid process (Character 12)] and more general eu-primate features [i.e., reduced snout (Character 10), postor-bital bar (Character 11), large optic foramen (Character20)].

28 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Summary and conclusions

The cranial anatomy of Carpolestes simpsoni exhibitsa complicated assortment of primitive characteristics, suchas an unreduced internal carotid circulation that runs ingrooves, and more derived features, including a divided bullarchamber. Although the cladistic analysis presented in this pa-per provides support for a relationship between euprimates andsome plesiadapiforms, including Carpolestes, this taxon lacksdistinctive euprimate features of the skull that have been asso-ciated with increased brain size and enhanced visual process-ing. Particularly, Carpolestes simpsoni retains primitivefeatures, such as strong postorbital constriction of the brain-case, a long snout, no postorbital bar, a relatively small opticforamen, and lack of convergent orbits.

Previous analysis of the postcranium of Carpolestes simp-soni documented characteristics associated with graspingthat had previously been considered euprimate synapomor-phies (including an opposable hallux with a nail; Bloch andBoyer, 2002a). The lack of certain distinctive euprimate fea-tures in the skull (e.g., convergent orbits and a postorbitalbar) and the presence of others (e.g., a petrosal bulla) indicatesthat C. simpsoni exhibits a mosaic of features overall. This ob-servation is in keeping with the idea that the distinctive eupri-mate characteristics that are found in adapids and omomyidsarose in a mosaic fashiondthe earliest additions being dentaland grasping features, with derived leaping and visual charac-teristics evolving later, supporting a scenario for primate ori-gins that begins with terminal branch feeding (Bloch andBoyer, 2002a, 2003; Silcox et al., in press).

This conclusion is relevant to the recent description of Teil-hardina asiatica by Ni et al. (2004), in which they challengedthe use of a Carpolestes-based model for the ancestor of Eu-primates. Ni et al. (2004: 68) stated that the skull of T. asiatica‘‘undermines a recent hypothesis that the euprimate wasevolved from a Carpolestes-like terminal fruit-feeder in thelatest Palaeocene. The last common ancestor of stem eupri-mates, if it mirrored T. asiatica in morphology, would be por-trayed as a small, diurnal, visually oriented predator. Thiswould have positioned earliest euprimates in a very differentecological niche from that occupied by apparently more fru-givorous, less visually oriented carpolestids.’’ We disagreewith this conclusion. In their own analysis, Ni et al. (2004)found T. asiatica to be a stem haplorhine, not a stem eupri-mate, with T. asiatica at least one node removed from thebase of Euprimates. In fact, the only taxon we consider tobe a ‘‘stem euprimate’’ is Altiatlasius koulchii, which wasnot included in Ni et al.’s (2004) analysis. Furthermore, theprimitive members of the sister taxa to Euprimates (Carpo-lestes simpsoni and/or Plesiadapidae) are reconstructed as om-nivores with frugivorous specializations. For these reasons, T.asiatica does not make a good model for the ancestor of Eu-primates. Indeed, there is good reason to believe that the com-mon ancestor of Euprimates was frugivorous or omnivorous,rather than a specialized insectivore. Strait (2001) found thatmany omomyids that had long been assumed to have been in-sectivorous based on their small size and similarity to tarsiers

were, in fact, likely to have been partly or predominantly fru-givorous. Most plesiadapoids and adapids were also likely tohave been frugivorous (Rose, 1995). The oldest known eupri-mate, Altiatlasius koulchii, has extremely low-crowned, buno-dont teeth, which is inconsistent with a reconstruction of itsdiet as insectivorous, and is much more suggestive of a frugiv-orous diet. For these reasons, it is actually more parsimoniousto reconstruct the common euprimate ancestor as a frugivore,rather than a specialized visual predator.

Cladistic analysis of cranial data discussed here does notsupport a special relationship between extinct plesiadapiformsand extant dermopterans to the exclusion of other archontanmammals (Kay et al., 1990, 1992). Rather, results from thisstudy are congruent with recent cladistic analyses of postcra-nial data that ally Dermoptera with Scandentia rather thanwith paromomyids and euprimates (Bloch and Boyer, 2002a,2003; Sargis, 2002d). Results from cladistic analysis of cranialfeatures in isolation suggest a close relationship between Ple-siadapoidea (not including paromomyids; Beard and Wang,1995; Silcox et al., 2001) and Euprimates, although this anal-ysis was unable to definitively resolve the precise branchingpattern between plesiadapids, Carpolestes simpsoni, and Eu-primates. An analysis that includes multiple data partitionsis needed to help resolve these areas of disagreement (Silcox,2001; Bloch et al., 2002b, 2004; Bloch and Boyer, 2003;Silcox et al., 2005; Bloch et al., in prep.).

Acknowledgements

P. Houde collected and prepared USNM 482354. TheuhrCT scanning was performed by Ozgen Karacan (Centerfor Quantitative Imaging, Penn State University). We thankthe following people for suggestions about scanning protocolsand the interpretation of CT data: A. Grader, P. Halleck,N. Jeffrey, O. Karacan, R. Ketcham, F.S. Spoor, and A. Walk-er. A. Walker also provided generous access to resources andmuch helpful advice. This paper was improved by contribu-tions from P.D. Gingerich, G.F. Gunnell, D. Polly, andK.D. Rose. Thanks to A. Chew for taking the measurementsof skull length in Appendix 4. Thanks to X. Ni for providingunpublished data on Teilhardina asiatica. The following peo-ple provided access to specimens in their care: L. Gordon, R.Purdy, R.F. Kay, M.C. McKenna, P.D. Gingerich, G.F. Gun-nell, and K.D. Rose. Special thanks to P.D. Gingerich andG.F. Gunnell for access to unpublished material. The recon-struction in Fig. 9 was done by D. Boyer. This research wassupported by NSF grant BCS-0003920 to A. Walker, andgrants from the Wenner-Gren Foundation for AnthropologicalResearch, the Paleobiological Fund, Sigma Xi, NSF (doctoraldissertation improvement grant 9815884), NSERC and Majorand Discretionary research grants (University of Winnipeg) toMTS. Field and laboratory research were supported by grantsfrom the National Science Foundation to G.F. Gunnell, P.D.Gingerich, and JIB (BCS-0129601), and from the Scott TurnerFund (Department of Geological Sciences, University ofMichigan) to JIB.

29J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

Appendix 1. Measurements of Carpolestes simpsoni1

UM 101963 UM 101923 USNM 482354 UM 82670 UM 85177 UM 82688 UM 86273 Mean S.D.

Cranial measurements (in mm)

Cranial length 39.56 39.56

Nasioneinion 21.48 21.48

Prosthionenasion 14.07 12.85 13.46 0.86

Orbital diameter 7.66 7.04 7.90 6.88 7.37 0.49

Interorbital breadth 10.70 10.60 11.08 10.79 0.25

Internasal suture length 12.96 12.96

Minimum width of the central stem 1.00 1.00

Dental arcade length 14.64 14.74* 15.63 15.505* 15.13 0.51

Maximum dental arcade width (including alveoli) 9.76 9.08 9.42 0.48

Palatal width at M2 not including alveoli 6.78 6.78

Length of molar toothrow (M1e3) 4.20 4.10 4.25* 4.30 4.25* 4.22 0.08

Minimum postorbital breadth 3.92 3.92

Maximum braincase breadth 12.05 12.05

Length of the sagittal crest 16.51 16.51

Arterial canal measurements (in mm)

Width of groove for stapedial a. 0.40 0.375* 0.39 0.02

Width of groove for promontorial a. 0.15 0.15 0.15 0.00

Width of groove for ICA stem 0.55 0.5* 0.53 0.04

Measurements of foramina (in mm2)

Optic foramen area 0.105 0.24 0.15 0.165 0.09

Sphenorbital fissure area 0.56 0.56

Lacrimal foramen area 1.20 0.75 0.98 0.32

Infraorbital foramen area 1.125* 1.54 0.84* 0.99 1.24* 1.15 0.27

Palatine canal area 0.20 0.20

Postglenoid foramen area 0.20 0.43* 0.32 0.16

Stylomastoid foramen area 1.13 1.13

Subsquamosal foramen area 0.24 0.17 0.25 0.22 0.04

Foramen ovale area 0.30 0.30

Foramen rotundum area 0.20 0.20

Hypoglossal foramen area 0.30 0.30

Jugular foramen area 0.84 0.84

1 All measurements in mm or mm2. Area of foramina calculated as the product of the greatest diameter of the foramen and the maximum length perpendicular to

the first measurement, following Kay et al. (1992).

* Values averaged from left and right sides.

Appendix 2. Characters used in the cladistic analysis

Sources of characters for this data set include: Szalay,1975; Wible and Covert, 1987; Kay et al., 1992; Wible,1993; Beard and MacPhee, 1994; and Silcox, 2001. This char-acter list is smaller than those used in other analyses of plesia-dapiform cranial data (e.g., Kay et al., 1992; Silcox, 2001),primarily because the taxon sampling regime employed hererendered several characters uninformative (e.g., the exclusionof Chiroptera; see the discussion in the text).

1. Structure of the auditory bulla: 0Zmembranous or bony,but non-petrosal in origin; 1Z no suture separating bullafrom petrosal (and/or no developmental evidence for addi-tional elements). This character was modified from Beardand MacPhee (1994), and is designed to employ the bestdata that are available from fossils (i.e., under this defini-tion, microsyopids can be coded in spite of the uncertaintyabout the make-up of their bullae).

2. Relations of the entotympanic: 0Z entotympanic contactsthe petrosal medially; 1Z no entotympanic is present;2Z entotympanic contacts the basioccipital medially.

This character was modified from Kay et al. (1992), andwas scored only in taxa for which an entotympanic couldbe positively identified.

3. Form of the external auditory meatus (EAM): 0Z not ex-panded into a tube; 1Z expanded into a bony tube. As de-fined here, this character does not differentiate betweentubular external auditory meati that are formed from dif-ferent bones. This reflects the difficulty of accurately re-constructing the contribution of all of the bones makingup the auditory bulla in fossils.

4. Presence of a subtympanic recess (between the tympanicring and the bulla): 0Z subtympanic recess present, andthe ectotympanic includes a ringlike element separatedby an annular bridge, with a membrane or gap between itand the bulla; 1Z subtympanic recess absent, and the ec-totympanic does not include a distinct ringlike element.In all mammals, an ectotympanic element is present witha sharp crest, the crista tympani, for attachment of the tym-panic membrane. In dermopterans, this crest is on a broadersheet of bone, so there is no ringlike element to the ecto-tympanic. In this case, there is no subtympanic recess pres-ent. When a subtympanic recess is present, and there is

30 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

a ringlike element to the ectotympanic, there are multiplepossibilities about the relationship between this ring andthe wall of the bulla. One possibility is that the recessmay be fully or partly bridged by an annular bridge. Insome euprimates, this annular bridge is interrupted bya gap, the recessus dehiscence (MacPhee, 1987). Whenpresent, the recessus dehiscence demonstrates that the an-nular bridge is petrosal in origin. However, in the absenceof a recessus dehiscence (as is the case, for example, in Ple-siadapis), it is impossible to know in the absence of devel-opmental data which bones contribute to the annular bridge(MacPhee, 1987). For this reason, we considered it inap-propriate to include a character on the presence/absenceor composition of the annular bridge in this analysis sincethese issues can be difficult or impossible to resolve withfossils (contra Beard and MacPhee, 1994). As configuredhere, this character allows the recognition of the basic sim-ilarity of a ringlike ectotympanic, even if this is all that ispreserved (i.e., as is the case for Ignacius; Bloch and Sil-cox, 2001).

5. Presence of branches of the internal carotid artery (ICA)or the internal carotid nerve: 0Z grooves for at least thepromontorial branch, no tubes; 1Z tubes present for oneor both arteries, or for the internal carotid nerves;2Z ICA absent, no tube for the internal carotid nerves.In contrast with Kay et al. (1992), the various features as-sociated with the internal carotid artery were combinedinto a single character in this analysis. In taxa in whichthe entire internal carotid artery involutes (e.g., dermop-terans), the absence of the stapedial and promontorialbranches is clearly not independent. Also, the inclusionof a separate character relating to the presence or absenceof arterial tubes ignores the fact that the absence of the in-ternal carotid artery can only be deduced in fossils fromthe absence of any evidence for its passage, such as tubes.As such, the complete absence of this vessel is essentially‘‘triply weighted’’ in Kay et al.’s (1992) data set, in whichthey subdivided this range of morphologies into three dif-ferent characters. Paromomyidae has been coded as beingpolymorphic for this character (both ‘‘0’’ and ‘‘1’’ states).This coding is based on the observation that there arespecimens of Ignacius known that exhibit a groove (e.g.,see Bloch and Silcox, 2001) and one that exhibits a tube(Silcox, 2003). However, it is possible that specimenswith a groove originally had a tube, which has brokenaway. In light of the fact that there is no way to establishthis conclusively from the current evidence, we have takenthe more conservative route and coded this character forParomomyidae based on what can be observed in theknown specimens. We did run an additional analysiswith this character coded as non-variable for paromo-myids, however, which is discussed in the text. In thisanalysis Paromomyidae was assigned the ‘‘1’’ state.

6. Posterior carotid foramen position (or the position of theentry of the internal carotid artery and/or nerves into themiddle ear): 0Z posteromedial; 1Z posterolateral. Fol-lowing a conservative path, we have chosen to code the

intermediate morphology of Plesiadapis with the primi-tive state for this character. The posterolateral positionof the foramen present in some primitive euprimates andparomomyids is rare in Eutheria (Wible, 1993), makingit likely that the posteromedial position is primitive.

7. Presence of the subsquamosal foramen: 0Z present,large; 1Z very small or absent. This feature refers to a fo-ramen located at the distal end of the zygomatic arch,making it equivalent to the opening called a suprameatalforamen by Kay et al. (1992; see discussion in Beardand MacPhee, 1994, and above).

8. Width of the central stem and relative size of the hypotym-panic sinus: 0Zbroad (hypotympanic sinus restricted);1Z narrow (hypotympanic sinus expansive). Beard andMacPhee (1994: 79) defined the central stem as ‘‘the mid-line keel of the posterior basicranium normally composedof the basisphenoid and basioccipital bones.’’ Taxa withhighly inflated bullae (i.e., an expansive hypotympanic si-nus) also by necessity have a central stem, so the expanseof the hypotympanic sinus was not included as a separatecharacter here (i.e., as employed as a character by Mac-Phee and Cartmill, 1986).

9. Choanae shape: 0Zbroad; 1Zvery narrow and ‘‘peaked.’’This character comes from Beard and MacPhee (1994),and was scored by viewing the choanae from the caudalend of the skull.

10. Cranial and snout proportions: 0Z long snout, long neu-rocranium; 1Z reduced snout, more bulbous and shorterneurocranium.

11. Presence of a postorbital bar: 0Z absent; 1Z postorbitalprocess of the frontal is present, but does not meet zygo-matic arch; 2Z complete postorbital bar present. Al-though it can be difficult to rule out the presence ofa postorbital bar in damaged specimens, the absence ofa process of either the zygomatic or the frontal can dem-onstrate that there was no complete bar.

12. Presence of a mastoid process: 0Z strong tubercle or in-flation in the mastoid region; 1Z no strong tubercle or in-flation in the mastoid region. This character was scoredsomewhat differently than in Kay et al. (1992) in that itwas considered likely that an inflated mastoid regionwas on the same morphocline as a strong tubercle, ratherthan being most similar to the complete absence of any ex-pansion of the mastoid.

13. Number of jugular (Zposterior lacerate) foramina:0Z single; 1Z dual.

14. Position of the caudal midsagittal margin of the hard pal-ate: 0Z near M3; 1Zwell rostral to M3; 2Z caudal toM3. The states for this character differ somewhat fromthose used by Kay et al. (1992), who based the characteron the small variations in the position of the midsagittalmargin of the palate. Observation of a large collectionof scandentian skulls by MTS at the National Museumof Natural History (Smithsonian Institutions) showedthat the precise position of the caudal midsagittal marginof the palate varies intraspecifically around the level ofM3, from being situated exactly at the level of the tooth,

31J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

to clearly behind it or slightly in front of it. In light of this,only extreme states were recognized for which there isconsistently evidence for a palate that ends nearer to M2

than M3 (State 1), or that is extended into the mesocranialregion by a broad sheet of bone (State 2).

15. Presence of the supraorbital foramen: 0Z present;1Z absent.

16. Shape of the nasals and width of the suture with the frontal:0Z nasals flare laterally at the caudal extent (wide contactwith frontal); 1Z nasals do not flare, narrow suture withfrontal. The coding of this character for Dermoptera differsfrom that of Novacek (1980), who considered this group toshow the derived state. In USNM(MA) 84421, a subadultGaleopterus variegatus with clearly demarcated sutures,the nasals broaden caudally, producing a wide contactwith the frontals. The coding for Leptictidae is based onthe more primitive Palaeictops bicuspis rather than themore derived Leptictis dakotensis (Novacek, 1986).

17. Diameter of the infraorbital foramen: 0Z small; 1Z large.For this analysis, twomeasurements were taken from the in-fraorbital foramen, following Kay et al. (1992): the greatestdiameter and the maximum length perpendicular to the firstmeasurement. These two measurements were then multi-plied together to give an approximation of the area of the fo-ramen. A least-squares regression analysis was performedon the infraorbital foramen area vs. the logarithm of M1

(calculated as buccal length!width). Taxa that fell outsidethe 99% confidence limit for this analysis were grouped to-gether in the ‘‘small’’ category (Silcox, 2001).

18. Contact between lacrimal and palatine in the orbit:0Z present; 1Z obscured by maxillofrontal contact;2Z obscured by ethmoid exposure in the orbit (Zosplanum).

19. Presence of a lacrimal tubercle: 0Z present; 1Z absent.20. Size of the optic foramen: 0Z small; 1Zmoderate;

2Z large. Coding for this character followed the rangesemployed by Kay et al. (1992).

21. Presence of the foramen rotundum: 0Z absent;1Z present

22. Position of the lacrimal foramen: 0Z in orbit; 1Z onface; 2Z on orbital rim. This character is clearly not inde-pendent from the presence or absence of a frontal processof the lacrimal bone, so no additional character was in-cluded to deal with variation in this feature (i.e., as wasemployed by Kay et al., 1992).

23. Presence of a shielded fenestra rotunda (Zcochlear win-dow, fenestra cochleae): 0Z absent; 1Z shielded by an ar-terial tube; 2Z shielded by a bony septum.As for Character5, this trait was coded as polymorphic for Paromomyidae. Inall known paromomyid skulls, the fenestra cochlea isshielded. In one instance, the structure that is shieldingthis opening is clearly a bony tube (Silcox, 2003). In the oth-er specimens, a tube is not clearly present, so the structureshielding the opening may be a bony septum. However, itis possible that a tube has broken away in these cases. Inlight of the fact that we cannot currently establish that thisis true, this character has been coded conservatively based

on what is observed in the relevant specimens. As notedin the text, however, we ran an additional analysis withthis character coded as non-variable for paromomyids, inwhich they were assigned the ‘‘1’’ state.

24. Auditory tube that runs through the lateral wall ofan anterior chamber: 0Z absent; 1Z present. This char-acter was designed to recognize the lack of independencebetween the presence or absence of an anterior chamber,and the necessary re-routing of the auditory tube that ac-companies the presence of an additional chamber.

Appendix 3. Data for snout and cranial length in anassortment of extant and fossil mammals (see Fig. 18)

Taxon Specimen number Cranial

length1

(mm)

Snout

length2

(mm)

Residual3

Shoshonius cooperi CM 60494 28.10 2.55 �0.91012

Shoshonius cooperi CM 31366 25.90 2.80 �0.68569

Smilodectes gracilis UM 32773 60.00 12.14 �0.56768

Megadelphus lundeliusi AMNH 55284 101.55 36.23 �0.31918

Cantius abditus USNM(VP)494881 82.00 25.84 �0.31381

Plesiadapis tricuspidens MNHN Cr126 106.14 42.72 �0.22538

Pteropus poliocephalus USNM(MA)37812 70.92 23.66 �0.16887

Cynocephalus volans USNM(MA)536048 69.02 22.87 �0.15923

Pteropus poliocephalus USNM(MA)35102 68.49 23.22 �0.13166

Pteropus poliocephalus USNM(MA)121903 67.55 23.67 �0.09028

Cynocephalus volans USNM(MA)219056 72.25 27.72 �0.04034

Ignacius graybullianus USMN 421608 47.60 14.21 �0.03852

Carpolestes simpsoni USNM 482354

(cranial length) and UM

86270 (snout length)

39.56 10.95 �0.00207

Cynocephalus volans USNM(MA) 144656 68.13 26.32 0.00211

Galeopterus variegatus USNM(MA)253411 68.38 26.80 0.01430

Cynocephalus volans USNM(MA) 144660 68.75 27.69 0.03831

Galeopterus variegatus USNM(MA)84420 76.03 33.31 0.06149

Cynocephalus volans USNM(MA) 144662 62.21 24.26 0.06657

Galeopterus variegatus USNM(MA)255716 70.16 29.98 0.08517

Ptilocercus lowii USNM(MA)112611 37.17 10.90 0.09341

Galeopterus variegatus USNM(MA)115493 69.02 30.03 0.11314

Ptilocercus lowii USNM(MA) 121855 36.06 10.60 0.11418

Ptilocercus lowii USNM(MA)488052 36.84 11.01 0.11777

Galeopterus variegatus USNM(MA)83276 60.52 24.43 0.11777

Galeopterus variegatus USNM(MA)253412 72.50 33.14 0.13271

Ptilocercus lowii USNM(MA)488061 35.76 11.08 0.17188

Leptictis dakotensis AMNH 108194 67.50 31.74 0.20428

Ptilocercus lowii USNM(MA)291272 37.05 12.44 0.23097

Tupaia glis USNM(MA)487951 51.60 22.97 0.31216

Tupaia glis USNM(MA)487952 49.58 21.81 0.32446

Tupaia glis USNM(MA)487953 51.18 23.27 0.33826

Tupaia glis USNM(MA)487950 51.06 23.81 0.36497

Tupaia glis USNM(MA)487949 50.93 23.86 0.37116

Asioryctes nemegtensis MgM-I/56 30.46 10.52 0.37777

1 Cranial length was measured as a maximum length.2 Snout length was measured from the base of the anterior surface of the root

of the zygomatic arch to the rostral edge of the specimen.3 Residuals calculated from the least-squares regression analysis of natural

logarithm of snout length on natural logarithm of cranial length

(yZ 1.606x� 3.51; r2Z 0.79; p! 0.001); see Fig. 18. Taxa listed in order

of the value of the residual.

32 J.I. Bloch, M.T. Silcox / Journal of Human Evolution 50 (2006) 1e35

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Appendix 4. Data for cranial length, orbital diameter,optic foramen area, activity pattern, OFI, and OFQ fortaxa measured in this study (see Fig. 20)1

Taxon Skull

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