Proc. Natl. Acad. Sci. USAVol. 91, pp. 9946-9950, October 1994Anthropology

A remarkable cranium of Plesiopithecus teras (Primates, Prosimii)from the Eocene of Egypt

(LorIformes/primate evolutlon/cranial morphology)

ELWYN L. SIMONS* AND D. TAB RASMUSSENt*Department of Biological Anthropology and Anatomy, Duke University, Durham, NC 27705; and tDepartment of Anthropology, Washington University, St.Louis, MO 63130

Contributed by Elwyn L. Simons, May 18, 1994

ABSTRACT Between 1991 and 1993 seimens ofa highlydistinctive primate, named Pksiopithecus teras [Simons, E. L.(1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747], werefound at site L-41 in late Eocene deposits of the FayumDepression, Egypt. The most important of these specimensconsists of a nearly complete skull, which facilitates the eval-uation of affinities ofthis primate. Characteristics ofthe knownmaterial now demonstrate that Plesiopithecus is a prosimian,although mandibular molar morphology, in particular, bearssimilarity to that in molars of archaic members of Anthro-poidea. Plsiopithecus has a postorbital bar but lacks postor-bital closure, it has upper molars without hypocones, and itmay retain four lower premolars. Its familial rank was con-sidered incertae sedis by Simons [Simons, E. L. (192) Proc.Nall. Acad. Sci. USA 89,10743-10747]; it can now be demon-strated that Plsiwpithecus justifies establishment of a newfamily and superfamily. The new superfamily apparently liescloser to the toothcomb prosimians (streprhines) than to anyother known primate group. Under this interpretation theenlarged, procumbent tooth in the jaw of Plesiopithecus ishomologous to either the lateral incisor or the canine of theprosimian toothcomb.

In papers published in this journal in 1989 and 1992, one ofus(E.L.S.) described several new primates from an AfricanEocene locality (site L-41) in Fayum Province, Egypt (1, 2).This Fayum site is remarkable for the diversity of primatesthat it contains. The majority of species (Arsinoea kallimos,Serapia eocaena, Catopithecus browni, Proteopithecussylviae) belong to the higher primate suborder Anthropoidea(1-4). It is possible that these four primates may belong inseparate families. The fifth species, now identified and heredescribed in detail, demonstrates the early occurrence ofanother major group of prosimians. Another undescribedprosimian recently recovered from L41 may be ranked as acercamoniine adapid (5), a group otherwise known fromEurope, North America, and Eurasia. At another earlyFayum site (locality E) an omomyid prosimian occurs, and inthe upper sequence of the Fayum there are also a tarsier anda loris (6). This great diversity of primates still provides thebest evidence that Anthropoidea, and perhaps even Primatesas an order, arose in Africa, in spite ofrecent assertions to thecontrary by Beard etal. (7). The "simian" described from thelatter fauna is not an early anthropoidean.Quarry L-41 is also of interest because the primates that

occur in it are quite distinct from most of those occurringhigher in the stratigraphic section (in what appear to beearly Oligocene deposits). This suggests that there was notonly a temporal difference of considerable magnitude butalso possible environmental differences as well that af-fected the faunal composition. Most striking is the extraor-

dinary abundance of fossil hyracoids at this site (8). Theseherbivores represent a diverse radiation with extremes ofsize and adaptation never seen elsewhere in this order.Other unusual faunal elements are abundant small cre-odonts and rodents, elephant shrews of several differentsorts, and a wide variety of water birds. Lithologically thissite is also unusual in that it is a greenish clay deposit in astratigraphic setting where sands of various degrees ofcoarseness are the normal regimen. The fime clay accountsfor preservation in great detail of many specimens, andthere is a much higher incidence of complete skulls andpartial skeletal associations than is typical of most earlyTertiary fossil sites. Because of such occurrences, this verylarge locality holds great potential for further finds of skullsand skeletal remains that will illuminate the evolutionaryhistory of primates.Kappelman et al. (9) presented paleomagnetic reversal

analyses of sediments in the Jebel Qatrani Formation thatsuggest the L-41 beds were deposited during chron C15r,which has been dated to 35.6-35.9 million years (My). Theseresults are based on preliminary sampling of Fayum sedi-ments and may be subject to further refinement with futurework. This date ranks the fauna of L-41 in the late Eocene asindicated by recent geological research (10, 11). Faunalcorrelations also support an Eocene age for the locality (12)and faunal comparisons suggest to us that this site is olderthan Algerian sites reported to be of middle Eocene age (13,14). Site L-41 is older than Omani sites that have also yieldedearly anthropoid primates (15). The site of Chambi, Tunisia,may be of similar or greater antiquity than site L-41 (16).Although Plesiopithecus is not an early anthropoidean, it iscontemporary with Catopithecus and other earliest demon-strable simians at L-41. Eosimias recently described byBeard et al. (7) from 45-My-old deposits near Shanghuang,China, is not a simian (=anthropoidean) and may not even bea primate.

Abbreviations used in the text: CGM, Cairo GeologicalMuseum; DPC, Duke University Primate Center; YPM, YalePeabody Museum.

SYSTEMATICS

Order Primates Lineus, 1758; Suborder Prosimi , hIger,1811; Infraorder cf. Lrisiformes; SuperfamilyPleskolteaodea, new; Family Plpithecdae, new; genusPlesiopithecus Simons, 1992.

Type species. Plesiopithecus teras Simons, 1992.Revised diagnosis. Can be distinguished from Anthro-

poidea by the absence of postorbital closure and from allother primates in showing the following combination: largeorbits with the lacrimal foramen at the margin of the orbit;an upper dental formula of (?0-2)-1-3-3 and lower dentalformula of 0-1-4-3 or 1-1-3-3; enlarged procumbent lower

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FIG. 1. Lateral view of right and left sides of the cranium of P. teras (DPC 12393).

canine or lateral incisor and enlarged, vertical upper canine;molar trigonids short mesiodistally with paraconid reducedto shelf-like crest; slight metastylids present; hypoconesabsent.

P. teras Simons, 1992

Holotype. CGM 42291, right mandible with C, P2-4, M1-3.

Type locality. Quarry L-41, Jebel Qatrani Formation,Fayum Province, Egypt.Referred material. DPC 12393, a crushed but nearly com-

plete cranium with maxillary dentition (Figs. 1 and 2); DPC11636, left mandible with C, P1-4, M1-3 (Fig. 3); DPC 13607,left mandible with C, P2, P4, M1-3.Diagnosis. As for genus.Measurements. Table 1.

FIG. 2. Crown view of the palate and upper teeth of P. teras (DPC 12393).

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FIG. 3. Medial view of the mandible of P. teras (DPC 11636).

DESCRIFIONThe known cranium (DPC 12393) is nearly complete, butmuch of it is badly crushed in the sagittal plane (Fig. 1). Partsof all the maxillary teeth are present; the preillae andincisors, ifany, are missing. Some features ofthe face, orbits,zygoma, cranial vault, and basicranium can be determined,and these are described in sections below. The postcaninedentition and snout are about the size of those in Nycticebuscoucang, but brain volume was clearly smaller and therostrum was unusually deep.

Maxillary Dentition. The canines are large and verticallyimplanted, with big roots extending upward into the face (Fig.1). In shape, the canines are buccolingually compressed(Table 1), forming distinct mesial and distal edges. There isa small occlusal wear facet at the tip of the unbroken leftcanine and evidence of wear on the distal edges of bothcanines.The upper teeth are illustrated in Figs. 1 and 2. P1 is

bilaterally absent. P2 is the smallest maxillary tooth; it issimple in structure with one primary cusp and with small nubsor cuspules on the mesial and distal borders. The tooth isbilaterally compressed. P3 is also single-cusped, but it has asmall lobe extending lingually from the cusp. The lobe doesnot bear a separate cusp. P4 is much larger than the otherpremolars and it is more complex in shape. In outline thetooth is mesiodistally short but buccolingually broad. It hastwo distinct cusps, one buccal and one lingual (see dimen-sions in Table 1).The three molars are all fairly simple, three-cusped

teeth-no hypocones are present. They decrease in size fromfront to back. Ml has a pronounced lingual cingulum bearingsmall beaded cuspules. The protocone is the largest cusp;there are slight but distinct paraconule and larger meta-conule. M2 is slightly smaller than Ml and has a basalcingulum running around the protocone and along the distalborder ofthe tooth. As in a lorisoid upper molar (YPM 23987)

from quarry I (6), the basal cingulum is not distinct on theanterior border, nor is it clear on the buccal side of the tooth.The M2 of the new L-41 primate further resembles YPM23987 in having relatively small paracone and metaconeplaced close together (the latter smaller than the former) anda much larger protocone placed relatively far lingually. Theresemblances between the Plesiopithecus M2 and YPM23987 suggest the latter may be an M2, rather than an M3, asoriginally reported (6). M3 is small and simple in structure,exhibiting only the three main cusps.

Facial Sleton. The orbits are clearly quite large andalmost certainly imply a nocturnal adaptation (Fig. 4). Theright orbit appears to have been increased in size by distor-ton, whereas that of the left side is decreased (Fig. 1). Skulllength (about 52-54 mm) is similar to that ofN. coucang, andit appears that the orbits (14.0-17.6 mm) were comparablylarge. When these estimated sizes are ranked with compar-ative primate data (17), Plesiopithecus falls within the noc-turnal range, near Avahi and Nycticebus.On the right side of the skull, a small lacrimal foramen is

clearly present at the margin ofthe orbit. This differs from thefacial position of this foramen in lemurs and from the intraor-bital position in anthropoids. The orbital rim passes directlyacross the foramen, as in Nycticebus. There also appears tobe a suborbital fissure open on the anterior floor of the orbit.

Presumably, a postorbital bar encircled the side of theorbit. The frontal process of this bar is preserved on eachside. As in Nycticebus, the dorsal root of the postorbital barhas three surfaces (it is trianlar in section): an orbital face,a temporal face, and a dorsal face.The facial exposure of the maxilla is short and deep. It

appears that small, vertically oriented premaxillae possiblycontaining incisors have detached from the front of the face.The upper canines, in spite of sagittal crushing, are separatedfrom each other. In life, there would have been a gap of6mmor more, unlike the lower canines, which are in contact. Faceshape has probably been somewhat distorted by crushing

Table 1. Dental measurements (in mm) of P. teras showing mesiodistal length (1) and buccolingual width (w) of the four known specimens

DPC C P2 P3 P4 Ml M2 M3no. I w 1 w 1 w w 1 w I w I w

Upper dentition12393 4.5 2.5 2.4 1.7 2.6 2.4 2.7 3.9 4.2 4.8 3.0 4.3 1.9 3.1

Lower dentitionType 3.8 1.9 2.6 1.4 2.5 1.8 2.9 2.3 3.5 3.0 3.3 2.7 3.3 2.411636* 3.6 2.1 2.7 1.4 2.9 1.7 3.1 2.2 3.5 2.9 3.1 2.8 3.2 2.313607 4.0 2.1 3.5 2.9 3.4 2.9*Lower P1 in DPC 11636, the only specimen preserving this tooth has a mesiodistal length of 2.7 and buccolingual width of 1.0 mm.

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..--- -- \X *s~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~......

1 !

2cm

FIG. 4. Drawing of a reconstructed lateral view of the skull andmandible of P. teras, based on material described in this report.

together from side to side, but it seems clear that the face wasvery deep above the premolars. The anterior edge ofthe orbitruns forward to align just above the P4. The infraorbitalforamen sits fairly low on the face, away from the orbitalmargin, and a short distance above the P3. The zygomaticarch is lightly built but is badly damaged so few details canbe discerned.

Basicranium. The glenoid surface of the temporomandib-ular joint is visible on the left side. It is relatively flat andbroad, unlike the guttered fossa of tarsioids (18, 19). Thepterygoid plates are damaged and compressed together. Onthe left side the mastoid is crushed and distorted in shape. Onthe right side the mastoid has been broken open (Fig. 1). Thebroken rim suggests that the mastoid may have been large andinflated like those of lorisoids. The wall enclosing whatappears to be the mastoid air space is relatively thick. Theoccipital condyles are both present and are about the samesize as in typical N. coucang or Galago crassicaudatus.

Cranial Vault. Remains of a nuchal crest are evident. Thevault carries distinct temporal lines that converge and, atleast toward the back ofthe vault, form a sagittal crest. Thereis no evidence of a metopic suture. On the frontal bone,between the internal and dorsal margins of the orbit and thetemporal lines, is a flattened, diamond-shaped area, some-what depressed, which is similar to this region of the skull inlorisoids.

Mandible. The holotype mandible and dentition were de-scribed and illustrated elsewhere (1, 4). In this section, wedescribe additional details of tooth andjaw structure evidenton the two additional mandibles. In DPC 11636 the angle ofthe mandible is extended backward a considerable distancebut it is increasingly damaged posteriorly, so that its fulllength is uncertain (Fig. 3). The mandibular condyle is wellpreserved on this specimen and shows a broad, relatively flathead, unlike those of tarsioid primates. This specimen alsopossesses a first lower premolar (Fig. 3), a tooth absent fromthe other two specimens (perhaps due to postmortem loss orvariability). This tooth might also be the lateral caninederived from a toothcomb. The P1 is only about half the sizeofP2 and is single-rooted with a crown that is angled forwardand flange-like, reaching over the distal base ofthe canine. Inall three specimens of P. teras the lower canine is greatlyelongated and strikingly compressed from side to side. Thereis a wear facet on the mesial side indicating contact with theopposite canine. It is clear from all three specimens that thesymphysis is unfused and that no lower incisors could havebeen present. However, the canine is generally reminiscentof the tooth that forms the lateral tine of the toothcomb inextant Lemuriformes and Lorisiformes (Fig. 5). The upper

FIG. 5. Comparison of the crown views of the right mandible inP. teras (the holotype, CGM 2291) and N. coucang.

canine appears to come to a rounded point, with only theslightest evidence of apical wear. From the apex a wear facetruns down the posterior side of the tooth, but less than halfway. The lack of any wear surface reaching down to the baseof the tooth implies that, unlike in the modern strepsirhines,there was no occluding anterior lower premolar. The lowermolars are highly distinctive from those of extant strep-sirhines, notably in the highly rounded talonid basin, thelingually shifted protoconid, and the extensive buccal slopeof the tooth.

DISCUSSION AND CONCLUSIONSOriginally, Simons (1) reported Plesiopithecus as havingaffinities with anthropoids, even though he pointed out thatits ranking with any known family was very dubious andplacement should await further finds. The molars of the typemandible showed a decrease in size posteriorly similar to thatseen in Catopithecus and Proteopithecus. Also, unlikelorisoids, the molar talonids are broader and the molar outlineis rounded, unlike the waisted outline of most prosimianmolars. Moreover, the loss of permanent lower incisors andappressed lower canines appeared to be a shared specializa-tion found otherwise only in Parapithecus. In addition, theholotype did not show the P1 and therefore the lower dentalformula appeared to be the same as in Parapithecus. For

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these reasons, the resemblances to lorisids did not appear tobe compelling evidence for affinity.The cranium and upper dentition make it clear that Ple-

siopithecus is not an anthropoid. The cranium unambigu-ously lacks postorbital closure. A postorbital bar is present.The similarities between Plesiopithecus and Parapithecus inthe anterior lower dentition are clearly convergent becauseparapithecids are undoubted anthropoids with postorbitalclosure and a whole series of other cranial and postcranialanthropoid features (20, 21). Other features ofPlesiopithecusthat stand in contrast to most other Fayum anthropoidsinclude lack ofhypocones on upper molars, lacrimal foramenon rim of orbit, lack of symphyseal fusion, possession of P1,and elongated and compressed lower front teeth (resemblingenlarged toothcomb teeth).There are no characters specifically resembling either

lemurs or tarsiers in the new material. P. teras differs fromall tarsiiform primates in its molar structure and in thenonguttered temporomandibular joint (18, 19). Nannopithexhas an enlarged anterior lower tooth but it is not laterallycompressed like the canine of Plesiopithecus, nor are thereany derived dental resemblances to it or other microchoer-ines. Although there are several intriguing similarities be-tween P. teras and extant lorisoids (Table 2, Fig. 5), it is clearthat P. teras is not closely affined to this latter group either.It lacks several shared features ofmodern lorisoids and bearsits own peculiar specializations. For example, in all extantlorisoids, upper and lower fourth premolars are fully molar-ized, the lower premolars are reduced to three in number, andall share the toothcomb adaptation. Plesiopithecus thereforefalls outside the superfamily Lorisoidea, clearly warrantingits own new superfamily. Plesiopithecus could prove to be amember of Lorisiformes, or it may eventually be seen as asister taxon to both the Lorisiformes and Lemuriformes. Thebraincase ofP. teras appears to be distinctly smaller than thatof extant lorisoids relative to size (of the face, orbits, andteeth), as would be expected for early Tertiary forms (22).The specialization of the lower canines and loss of lower

incisors set the group represented by P. teras apart from allother prosimians. Nevertheless, the compressed, forward-tilted and elongated anterior teeth of this species look as if

Table 2. Possibly derived morphological features shared by P.teras and extant lorisoid primates1. Buccolingually compressed, vertically implanted, large

upper canines2. Lower canines laterally compressed, resembling much

enlarged toothcomb canines3. Lacrimal foramen at margin of orbit4. Apparent pneumatization of the mastoid5. Obliquely oriented trigonids of lower molars, with

paraconids reduced to a shelf6. Reduced upper and lower third molars7. Upper M1-2 morphologically similar to those of lorisoids

they could have most easily been derived from a specieshaving a toothcomb, through hypertrophy of the caninescoupled with loss of the incisors. Therefore, this late Eocenespecies provides evidence that the toothcomb adaptationmight have already developed in pre-late Eocene times.

We thank F. A. Ankel-Simons, I. M. Tattersall, T. M. Bown, andP. D. Gingerich for offering their expertise on the manuscript. Thespecimens were prepared by P. S. Chatrath, F. A. Ankel-Simons,and E.L.S. Illustrations were prepared by E.L.S. and D.T.R. Theresearch was supported by grants from the National Science Foun-dation (BNS 88-09776 and BNS 91-08445). Research in Egypt wascarried out with the assistance ofthe Egyptian Geological Survey andMining Authority and the director and staff of the Cairo GeologicalMuseum. The specimens were found by E.L.S. (skull) and E.L.S.,K. C. McKinney, and P. S. Chatrath (jaws). This is Duke PrimateCenter publication no. 589.

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P. S., in Anthropoid Origins, eds. Fleagle, J. G. & Kay, R. F.(Plenum, New York), in press.

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10. Odin, G. S. & Montanari, A. (1989) C. R. Acad. Sci. Paris 309,1939-1945.

11. Prothero, D. R. & Berggren, W. A., eds. (1992) Eocene-Oli-gocene Climatic and Biotic Evolution (Princeton Univ. Press,Princeton).

12. Rasmussen, D. T., Bown, T. M. & Simons, E. L. (1992) inEocene-Oligocene Climatic and Biotic Evolution, eds. Pro-thero, D. R. & Berggren, W. A. (Princeton Univ. Press, Prince-ton), pp. 548-566.

13. Gevin, P., Feist, M. & Mongereau, N. (1974) Bull. Soc. Hist.Nat. Afir. Nord. 65, 371-375.

14. Godinot, M. & Mahboubi, M. (1992) Nature (London) 357,324-326.

15. Thomas, H., Roger, J., Sen, S., Bourdillon-de-Grissac, C. &Al-Sulaimani, Z. (1989) Geobios 22, 101-120.

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17. Rasmussen, D. T. & Simons, E. L. (1992) Int. J. Primatol. 13,477-508.

18. Simons, E. L. (1961) Bull. Br. Mus. (Nat. Hist.) Geol. 5, 45-69.19. Rosenberger, A. L. (1985) Folia Primatol. 45, 179-194.20. Fleagle, J. G. & Kay, R. F. (1987) J. Human Evol. 16,483-532.21. Simons, E. L., Am. Mus. Novit., in press.22. Le Gros Clark, W. E. (1956) Fossil Mamm. Afr. 9, 1-6.

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