THE ANATOMICAL RECORD 293:402–413 (2010)

The Circumorbital Bones of the Gekkota(Reptilia: Squamata)

JUAN DIEGO DAZA1* AND AARON MATTHEW BAUER2

1CONICET, Instituto de Herpetologıa, Fundacion Miguel Lillo, San Miguel de Tucuman,Argentina

2Biology Department, Villanova University, Villanova, Pennsylvania

ABSTRACTThe enormous variation of the orbit in lepidosaurs is better concep-

tualized in terms of composition and configuration. Broadly, the orbitvaries from having totally closed rim to being open posteriorly. Two proc-esses are responsible for changes in the components of the circumorbitalseries, element loss and fusion. The resulting contacts among elementsare the main factors determining orbital configuration. Here, we presenta revision of the gekkotan circumorbital bones in the general contextof the Lepidosauria. From observations of a sample of 105 species ofgekkotans prepared using different techniques, we describe the mainchanges in the orbit and corroborate the presence or absence of some ofthe ambiguous elements such as the lacrimal and the jugal. The supraor-bital bones of squamates are reviewed and some problems of homologyare evaluated using recent phylogenenetic hypothesis. Anat Rec,293:402–413, 2010. VVC 2009 Wiley-Liss, Inc.

Keywords: cranial osteology; myology; CT scan; comparativeanatomy

INTRODUCTION

The typical circumorbital series of reptiles consists offive bones: prefrontal, postfrontal, postorbital, jugal, andlacrimal (Romer, 1956, 1970; Evans, 2008). In lepido-saurs, this general orbital pattern is modified by theintegration of bones from the tooth bearing (maxilla)and longitudinal series (frontal) and the development ofneomorphic elements such as palpebral, supraorbital,and parafrontal bones (Fig. 1).

The prefrontal in lepidosaurs is the only element thatinvariably forms part of the orbital margin; the contactof this bone with the jugal excludes the maxilla from theorbit in some forms (e.g., Anolis; Fig. 1). In some casesthe lacrimal lies between these two bones producing thesame result (e.g., Tupinambis and Varanus; Fig. 1). Thefrontal generally participates in the orbit of lepidosaurs,but is secondarily excluded from the orbit by contact ofthe prefrontal with the postfrontal (or postorbitofrontal)in representatives of virtually all squamatan clades(Conrad, 2008; Conrad et al., 2008; Evans, 2008), earlyreptiliomorphs (e.g., Limnoscelis), some testudines andother archosaurians (Romer, 1956; Carroll, 1988; Ben-ton, 2005). While both the maxilla and the frontal are

sometimes excluded from the orbital margin, they partic-ipate in the wall of the orbit (eye socket).

Element loss and fusion are the two process responsi-ble for changes in presence of bones and, consequently,orbital configuration. The presence of the postfrontal,postorbital, palpebral, lacrimal, and jugal is inconstantamong lepidosaurs and this also results in differences inorbital arrangement. The configuration of orbital bonesand the resulting contacts are variable, especially alongthe posterior margin of the orbit, where lepidosaurs maypresent closed (e.g., rhynchocephalians, iguanians, somelacertoids), semiclosed (e.g., Anguis, Vanzosaura,

Grant sponsor: NSF (Phylogeny and Evolution of the Geckosof the World); Contract grant number: DEB 0515909; Grantsponsor: CONICET.

*Correspondence to: Juan Diego Daza, CONICET, Institutode Herpetologıa, FML, Miguel Lillo 251, 4000, San Miguel deTucuman, Argentina E-mail: juand.daza@gmail.com

Received 22 June 2009; Accepted 20 August 2009

DOI 10.1002/ar.21039Published online 20 November 2009 in Wiley InterScience(www.interscience.wiley.com).

VVC 2009 WILEY-LISS, INC.

varanids) or open orbits (e.g., gekkotans, and someamphisbaenians). The posterior closure of the orbit isnormally determined by variation in the shape, size, andpresence of the jugal (Kearney, 2003), although variationin the postorbital and postfrontal (or postorbitofrontalwhen fused) also affects this closure. In fossil rhineuridamphisbaenians the orbit is different and there is astrong controversy about the identity of the bones form-ing the postorbital bar (e.g., Berman, 1972, 1973; Estes,1983; Kearney, 2003; Montero and Gans, 2008).

In the Gekkota, the orbit is an important area of theskull, in some forms the orbit occupies 41% of the skulllength (e.g., Ptenopus; Fig. 1). Orbit size is related to eyesize, which in turn is correlated with parameters of be-havioral ecology; in gekkotans the eye is larger in noc-turnal than in diurnal species and in cursorial than inscansorial species (Werner and Seifan, 2006). Some gek-

kotans are lidless and the eye is covered by a fixedtransparent window or spectacle. When eyelids are pres-ent, as in the eublepharid geckos, the nictitating mem-brane shows different degrees of development amongspecies (Underwood, 1970).

The orbit in gekkotans is always incomplete posteri-orly and is combined in a single lateral space togetherwith the supra- and infratemporal fenestrae. Thisgreater development of the orbit produces enormouschanges in the bones of the circumorbital series. In thisarticle, we focus on two bones of controversial presencein the orbit of gekkotans, the lacrimal and jugal. Thevariation in these elements is assessed in the sevenmajor gekkotan clades (i.e., Pygopodidae, Carphodactyli-dae, Diplodactylidae, Eublepharidae, Gekkonidae, Phyl-lodactylidae, and Sphaerodactylidae; Fig. 2) byexamining museum specimens belonging to 105 extant

Fig. 1. Circumorbital bones in some lepidosaurs. (A) Sphenodonpunctatus (BMNH uncataloged), (B) Anolis cuvieri (RT uncataloged),(C) Ptenopus carpi (CAS 214548), (D) Tupinambis rufescens (FML7417), (E) Eumeces obsoletus (USNM 220269), (F) Varanus gouldii(TMM M-1295), (G) Python sebae (USNM 72032); (H) Lachesis muta

(FMNH 31178), Color coded bones, orange, frontal; red, prefrontal;pink, lacrimal; brown, maxilla; purple, jugal; blue, postorbital; yellow,postfrontal; light green, postorbitofrontal; dark green, palpebral (Vara-nus) or supraorbital (Python).

THE CIRCUMORBITAL BONES OF THE GEKKOTA 403

species. The structural role of the jugal as part of thecircumorbital series leads us to also evaluate the config-uration of other elements in the series (prefrontal, post-orbitofrontal), especially in light of recent morphologicaltreatments of exemplar gekkotans (Conrad and Norell,2006; Conrad, 2008; Conrad et al., 2008; Evans, 2008).

We acknowledge that higher order relationshipsamong squamates remain controversial and that mostdata derived from DNA (Townsend et al., 2004; Vidaland Hedges, 2004; Hugall et al., 2007; Vidal and Hedges,2009) conflict with both more traditional (Estes et al.,1988) and recent (Conrad, 2008; Conrad et al., 2008)

morphologically derived hypotheses. In this article, wefollow the higher order squamate classification of Conrad(2008) because it is the most current and comprehensivemorphological treatment of the group and facilitates theinterpretation of morphological data. We follow Gambleet al. (2008) for intra-gekkotan relationships and theallocation of species to gekkotan families.

The presence of the lacrimal is variable among squa-mates (Conrad, 2008; Fig. 2). In geckos, when present, itis very small and indefinite. Camp (1923) stated that inthe Gekkonidae, the lacrimal was crowded within theorbit and lost to view externally, an observation that has

Fig. 2. Relationships of the major extant lepidosaur clades (Conrad, 2008; Gamble et al., 2008) show-ing some of variations in the orbital bones. Abbreviations: l ¼ lacrimal; lf ¼ lacrimal foramen; pal ¼ palpe-bral; pof ¼ postorbitofrontal. þ and � symbols indicate the state of the character as present and absent,respectively in the tree topology used.

404 DAZA AND BAUER

been interpreted as a mistaken identification of areduced jugal (Stephenson and Stephenson, 1956; Evans,2008). The lacrimal has been reported as rudimentary orvery reduced in newly hatched Lygodactylus (Brock,1932), and the eublepharids Coleonyx variegatus andEublepharis macularius (Kluge, 1962; Rieppel, 1984a),where this bone shows intraspecific variation and issometimes asymmetrically present.

The jugal is usually present in lizards; its loss is arare occurrence that is known exclusively in forms withelongated bodies (e.g., Feyliniidae, Dibamidae, Serpentesand Amphisbaenia, Fig. 2). The presence of this bonehas been ambiguously interpreted for the Gekkota. Forexample, McDowell and Bogert (1954; p. 92) mistakenlydescribe the jugal as absent for geckos and pygopodids,but they label the bone in their illustrations of Aristel-liger lar, Coleonyx variegatus, Pygopus lepidopodus, Lia-lis burtonis and Aprasia repens. In the gekkotan familyPygopodidae, another group of lizards where body elon-gation and limb reduction has taken place, it has beenproposed that this bone is absent in Delma, Lialis, andPygopus (Table 1; McDowell and Bogert, 1954; Under-wood, 1957; Jollie, 1960; Kluge, 1976; Rieppel, 1984a,b;Conrad, 2008; Evans, 2008).

The postfrontal and postorbital fuse to form a singleelement in representatives of all lizards clades (Conrad,2008; Fig. 2). Apparently, this fusion also took place inthe Gekkota (Daza et al., 2008) where only one bonebounds the orbit posterodorsally (Fig. 1, see below).

In the Squamata, there are three names applied toneomorphic elements present above in the upper edge ofthe orbit (i.e., palpebral, supraorbital and parafrontalbones). Although the homology of this element has notbeen corroborated, it is very likely that these structureswere acquired independently. By definition, the palpe-bral is the neomorphic bone located above the upper eye-

lid in the anterodorsal corner of the orbit (Peters, 1964;Maisano et al., 2002). We restrict the use of palpebralfor that element that occurs discontinuously in Autarch-oglossa (pal, Fig. 2), being present in some lacertoids,cordyloids, scincoids, and anguimorphs (Estes et al.,1988; Conrad, 2008), supraorbital to the bone present inthe orbit of Loxocemus and pythonid snakes (Fig. 1), andparafrontal bones to the multiple ossifications that liebetween the prefrontal and postorbitofrontal in somegeckos; these unique structures are known only in thegekkotans Aristelliger and Teratoscincus (Bauer andRussell, 1989) and were differentiated from the osteo-derms that roof the orbit in a variety of lizards, includ-ing the gekkotan genera Geckolepis, Geckonia, andTarentola (Underwood, 1970, Bauer and Russell, 1989).

Our intention is not to discuss all the soft parts associ-ated with the bones from the circumorbital series in theGekkota, but we do mention pertinent structures, in par-ticular those that vary across gekkotans and distinguishthem from other lizard clades.

MATERIALS AND METHODS

One hundred and five species of gekkotans were exam-ined from nine institutions (Appendix). We reviewed thecircumorbital bones in 211 specimens represented by dif-ferent preparations (skeletonized [Sk], cleared andstained [C&S], high resolution X-ray computed tomogra-phy scans [CT], fluid preserved specimens [Et]). The CTscans were available for 27 gekkotans and were per-formed at the University of Texas High-Resolution X-rayCT Facility. For this preparation the heads of fluid pre-served specimens were scanned by means of CT slicestaken along the coronal or transverse axis with variableslice thickness and interslice across the different scans.The field of reconstruction is 30 mm with an image

TABLE 1. Interpretation of presence (1) or absence (2) of the jugal bone in some papers dealing withosteology of the Pygopodidae

Taxon/authorMcDowell andBogert, 1954

Underwood,1957

Jollie,1960

Stephenson,1962

Kluge,1976

Rieppel,1984a,b

Conrad,2008

Evans,2008

Aprasia � þAprasia aurita þ þAprasia parapulchella þ þAprasia pseudopulchella þ þAprasia pulchella þ þ þ þAprasia repens þ þ þ þ þ þAprasia striolata þ þDelma australis þ þDelma butleri � þDelma concinna þ þDelma fraseri � � þ þ � þDelma impar þ þDelma inornata þ þDelma molleri þ þDelma nasuta þ þDelma tincta þ þ þLialis burtonis þ � � � � �Lialis jicari ? þ þ þOphidiocephalus taeniatus þ þParadelma orientalis þ þPletholax gracilis þ þ þ þ þPygopus lepidopodus þ þ þ þ þ þ þPygopus nigriceps � þ þ þ þQuestion mark indicates ambiguous interpretation.

THE CIRCUMORBITAL BONES OF THE GEKKOTA 405

resolution of 1024 � 1024 pixels, resulting in an inter-pixel spacing of 29.3 lm. The files contained QuickTimeslice-by-slice animations, QuickTime animations of 3Drotations and QuickTime animations of 3D cutawaysalong the three orthogonal axes. Additional to thecleared and stained material available in the collections,we prepared additional species following the techniqueof Hanken and Wassersug (1981). Illustrations were pro-duced with a camera lucida mounted on a dissectingmicroscope, and all figures were refined and assembledin AdobeVR IllustratorV

R

CS3 13.0.2. A list of specimensreviewed is provided in Appendix. Myological gross dis-sections were performed using the technique of Bockand Shear (1972).

RESULTSLacrimal

This bone is absent in most of the gekkotans exam-ined, but when present is difficult to distinguish andmay be overlooked. This element is easiest to see in CTscans and cleared and stained preparations. We corrobo-rated its presence in both Eublepharis macularius(JFBM 15831 and CM 67524, Fig. 3A–C) and Coleonyxvariegatus (YPM 14383, Fig. 3D). The lacrimal is moreprominent in E. macularius, where it is broad and flat,lying on top of the maxilla and contacting the jugal lat-

erally. In E. macularius it bounds the posterior edge ofthe lacrimal foramen (Fig. 3A–C) while in C. variegatusthe bone is reduced and occupies only the lateral cornerof this foramen, contacting the jugal anterodorsally (Fig.3D). In Pachydactylus bicolor (CAS 223912, Fig. 3E) wefound two small ossifications in the right orbit, adjacentto the lacrimal foramen. One of these ossifications con-tacts the maxilla and the other the ectopterygoid (ect,Fig. 3E). This bone is broader anteriorly relative to itsleft counterpart and fails to contact the palatine anteriorto the suborbital fenestra. It also presents a sinuousmedial edge instead of smooth one. These two small ossi-fications of P. bicolor seem to be the result of an asym-metrical and irregular development of the rightectopterygoid, as these structures do not resemble thelacrimal seen in the other species.

Supraorbital Ossifications

Among gekkotans, the sphaerodactylids Aristelligerand Teratoscincus possess parafrontal bones or ossa par-afrontalia, which are different from integumentaryosteoderms present in many lizards (Bauer and Russell,1989; Fig. 4). These supraorbital elements are a series ofsmall ossifications lying at the same depth as the frontalbone between the prefrontal and the postorbitofrontal.In both position and configuration they are quite

Fig. 3. Lacrimal bone in Eublepharis macularius: (A, B) (CM 67524),(C) (JFBM 15831) and Coleonyx variegatus: (D) (YPM 14383). (E),Pachydactylus bicolor (CAS 223912). Abbreviations: cor ¼ coronoid;

d ¼ dentary; f ¼ frontal; j ¼ jugal; l ¼ lacrimal; mx ¼ maxilla; n ¼nasal; pa ¼ palatine; pof ¼ postorbitofrontal; prf ¼ prefrontal; pt ¼pterygoid; sp ¼ splenial.

406 DAZA AND BAUER

different from the osteoderms. In position, these bonesdiffer from osteoderms because they lie beneath the der-mis in the plane of the frontal bone. In shape, they areirregular and lack correspondence with overlying epider-mal scales.

Quedenfeldtia trachyblephara possesses a continuousmesenchymal sheet, which in position is comparable tothe parafrontal bones. This has been interpreted as aputative synapomorphy of a clade of nonminiaturizedsphaerodactylids (Daza et al., 2008). This structure dif-fers from the thickened skin of the upper surface of thehead that roofs the orbit and fills the gap between theprefrontal and the postfrontal bones in other lizards(Underwood, 1970).

Postorbitofrontal

Virtually in all species reviewed, there is a single boneat the posterodorsal corner of the orbit. This bone variesin shape among species, and when present it clasps themesokinetic frontoparietal suture. Typically, its shape isangulated with a lateral vertex from where the anteriorand posterior processes depart, but in Coleodactylus,Tarentola, Ptyodactylus, Thecadactylus, Goggia, Hemi-dactylus, Stenodactylus, and Tropiocolotes this bone isrounded laterally, these processes being less distinct. Inthe Gekkota the orbit is incomplete posteriorly, because

Fig. 4. Parafrontal bones of Aristelliger georgeensis (CAS 176485)and Teratoscincus przewalskii (CAS 171013). Abbreviations: f ¼ frontal;j ¼ jugal; mx ¼ maxilla; pof ¼ postorbitofrontal; pfb ¼ parafrontalbones; prf ¼ prefrontal.

Fig. 5. Orbits from four geckos. (A) Saltuarius cornutus (FMNH57503); (B) Rhacodactylus ciliatus (JFBM 15825); (C) Rhacodactylusleachianus (CAS 165890); (D) Rhacodactylus auriculatus (CAS165891). Abbreviations: cor ¼ coronoid; pof ¼ postorbitofrontal.

Fig. 6. Orbit posterior closure by the jaw musculature and postorbi-tal tendon. (A) Pristurus carteri: (CAS 225349). (B) Lialis burtonis(FMNH 166958). (C) Uroplatus fimbriatus (BMNH 61.3.20.9). Abbrevia-tions: A2-SUPj ¼ m. adductor mandibulae superficialis jugalis; A2-SUPm ¼ m. adductor mandibulae superficialis mandibularis; DM ¼ m.depressor mandibulae; SC ¼ spinalis capitis muscles; pot ¼ postorbi-tal tendon; PTM ¼ m. pterygomandibularis; RP ¼ rictal plate.

THE CIRCUMORBITAL BONES OF THE GEKKOTA 407

the postorbital bar typically complete in squamates andformed by the postorbital and/or jugal bar, is missing. Insome diplodactylids and carphodactylids the ventral pro-cess of the postorbitofrontal and the dorsal process ofthe coronoid (Fig. 5; Bauer, 1990) are enlarged and comeinto close approximation when the jaw is closed and indry skeletal preparations of Rhachodactylus auriculatusthese two bones may even contact one another. In othergeckos the posterior border of the orbit is completed by apostocular tendon (Stephenson and Stephenson, 1956),

and the adductor mandibulae superficialis jugalis (A2-Supj, Fig. 6A,B).

The postorbitofrontal is hypertrophied in Aristelliger(POF, Fig. 4A) and absent in Lygodactylus. In pygopo-dids the postorbitofrontal contacts or approaches theprefrontal, excluding or limiting participation of thefrontal in the orbital margin (Fig. 7A–C; Boulenger,1885). The only geckos where a contact between prefron-tal and postorbitofrontal has been found are Phelsumalineata (Fig. 7D) and P. madagascarensis (Evans, 2008).The postorbitofrontal of Pygopus, Delma and Lialis ispierced by one or two foramina (Stephenson, 1962;Kluge, 1976) and this has been postulated as indicativeof its compound origin (Evans, 2008).

In Chondrodactylus bibronii (Rieppel, 1984a) andAiluronyx seychellensis, the postorbitofrontal contactsthe squamosal, forming a secondarily developed uppertemporal arch, with no supra-temporal fenestra due tothe apposition of these two bones against the parietal.

Jugal

In the Gekkota, this bone is much reduced in lengthand the postorbital process is missing (Fig. 1), neverthe-less its complete absence was not corroborated in any ofthe specimens examined. In the genus Homonota andsome miniaturized sphaerodactylids this bone is minus-cule. In limbed gekkotans, this bone always contacts themaxilla either ventrally (most geckos) or laterally (euble-pharids, Pseudogonatodes, Lepidoblepharis, and Coleo-dactylus). There have been contradictory reportsconcerning the presence of the jugal in some pygopodids.From our review of papers dealing with cranial osteologyof this group, we found that the confusion lies in theidentification of this bone in Delma and Lialis burtonis(Table 1). Two factors that might contribute to this con-fusion are the higher propensity for the dry skulls of

Fig. 7. Dorsal view of right orbit. (A) Delma molleri (AMNHR-24852). (B) Pygopus lepidopodus (AMNH R-140843). (C) Delmaborea (USNM 128679). (D) Phelsuma lineata (FMNH 260100). Abbrevi-ations: f ¼ frontal; pof ¼ postorbitofrontal; pof-f ¼ foramen postorbito-frontal; prf ¼ prefrontal; par ¼ parietal.

Fig. 8. Presence of jugal in: (A) Delma borea (USNM 128679) and Lialis burtonis, (B) JFBM 15829, and(C–E) FMNH 166958. Abbreviations: ect ¼ ectopterygoid; j ¼ jugal; max ¼ maxilla; pof ¼ postorbitofron-tal; ps, putative suture; pt ¼ pterygoid.

408 DAZA AND BAUER

pygopodids to disarticulate, compared with those ofgeckos, and the topographic position of this bone. Pygo-podids differ from fully limbed gekkotans in that the ju-gal does not approach the anterior margin of the orbit(Evans, 2008), being located more posteriorly andsqueezed anteriorly between the maxilla and the ectop-terygoid. In Delma borea (USNM 128679, Fig. 8), thejugal is present and firmly contacts the ectopterygoidmedially, forming a lateral elevated flange to the flatectoperygoid. In Delma as in the rest of gekkotans, theectoperygoid is flat. The ectopterygoid in Lialis burtonis(FMNH 166958) presents an elevated lateral wall, andin this specimen the jugal appears to be absent (Fig.8B,E). A closer look at the digital sections of the ectop-terygoid in both sagittal and lateral planes revealed alengthwise putative suture, which in some places createsa hollow space (Fig. 8C). On the surface of the ectoptery-goid of a skeletonized specimen (JFBM 15829) a longitu-dinal mark that may indicate a close contact suturebetween the ectopterygoid and the jugal is clearly visible(Fig. 9). The complex shape of the ectopterygoid in L.burtonis and the presence of a putative suture stronglysuggest that in this species, the jugal is not lost, butinstead is fused to the ectopterygoid. A detail of the

articulation of the ectopterygoid and pterygoid is pro-vided with our interpretation of the portion that corre-sponds to the jugal (Fig. 8). Additional evidence for thepresence of the jugal in Lialis is provided by the muscleadductor mandibulae superficialis jugalis (A2-Supj, Fig.6). This muscle is attached to the jugal bone in gekko-tans (Daza, 2005). In limbed gekkotans, it is immedi-ately behind the eye, bordering the orbit posteriorly(Fig. 6A). In Lialis, this muscle is attached to the lateralflange of the ectopterygoid. A space between the eye andthis muscle indicates that the muscle has been displacedposteriorly in association with the relative developmentof the jugal in pygopodids.

DISCUSSION

Apparently, the Eublepharidae, uniquely among gek-kotans, retain a discrete and unambiguously identifiablelacrimal. Although we did not find it in other species inour sample (the ossifications in P. bicolor are probablyan abnormal structural development, see above), it ispossible that this element is easily lost during tradi-tional dermestid prepared specimens that comprise themajority of specimens reviewed. The lack of lacrimal in

Fig. 9. Close up of the inferior orbital bones in Lialis burtonis (JFBM 15829) in dorsal (A), lateral (B),ventrodorsal (C). (D) Detail of the articulation of the pterygoid and ectopterygoid þ jugal. Abbreviations:ect ¼ ectopterygoid; j ¼ jugal; max ¼ maxilla; pa ¼ palatine; pof ¼ postorbitofrontal; ps, putative suture;pt ¼ pterygoid.

THE CIRCUMORBITAL BONES OF THE GEKKOTA 409

the majority of gekkotans, together with the inconsistentcontact of the jugal and the prefrontal generates varia-tion in the configuration of the lacrimal foramen amonggekkotans. This does not affect the anterior pathway ofthe lacrimal duct from the lower posterior side of thelower lid (eublepharids) or spectacle (spectacled gekko-tans) toward the palate.

The presence of a palpebral has been proposed by Con-rad (2008) as a synapomorphy for Scincogekkonomorpha.This is due to his scoring of palpebral presence in thefossil taxa Ardeosaurus and Bavarisaurus, which he con-sidered basal members of this clade. However, this boneis not present in either Ardeosaurus or Bavarisaurus(Camp, 1923; Cocude-Michel, 1961; Hoffstetter, 1964;Mateer, 1982; Evans, 2003, 2008) being restricted mostlyto autarchoglossans. The only scincogekkonomorphs thatpresent comparable structures are members of thesphaerodactylid subclade of crown gekkotans, whichpresent the parafrontal bones. In these taxa, the struc-ture and organization of parafrontal bones differs consid-erably with the single palpebral bone (Bauer andRussell, 1989). By position and structure, these bonesare not homologous, which falsifies this character as asynapomorphy for Scincogekkonomorpha.

The postorbitofrontal is present in almost all gekko-tans and can be hypertrophied (e.g., Aristelliger) orreduced (e.g., Lialis), being lost only in Lygodactylus ofthe taxa examined to date. Evans (2008) concluded thatthe single ossification in the dorsoposterior corner of theorbit in ‘‘geckos’’ is the postfrontal and that in pygopo-dids it is a compound bone formed by postfrontal andpostorbital. She used two arguments for considering thebone of pygopodids as compound, the observation of twoelements in Lialis jicari (Rieppel, 1984a) and the pres-ence of one or more foramina in this bone in some spe-cies of Delma, Lialis and Pygopus. Since pygopodids arenested within limbed geckos, we believe that these argu-ments might apply to the whole clade and we recom-mend that the term postorbitofrontal also be applied tothis bone in limbed gekkotans.

The postorbitofrontal resembles the postfrontal ofsome squamates in which the two elements are present(e.g., Iguania, Anolis occultus, gobiguanians; autarcho-glossans, Cordylus giganteus; teiioids; the fossil gekko-nomorph AMNH FR 21444; Conrad and Norell, 2006)and to the element remaining in some other squamatesgenerally regarded as lacking a postorbital (e.g., Lantha-notus borneensis, Acontias meleagris) (J. Conrad, perso-nal communication). However, the identity of this boneis open to discussion and the terms postorbital or post-frontal have been used interchangeably in gekkotanosteology (see discussion in Daza et al., 2008), and weconsider that the term postorbitofrontal reflects the mostconservative interpretation of the element as it does notimply the loss of either element.

Contact between the postorbitofrontal and the prefron-tal, a condition described by Boulenger (1885), is a fea-ture that distinguishes pygopodids from other geckos.McDowell and Bogert (1954) contended that this obser-vation did not apply to Aristelliger (and possibly othergeckos). In this particular case, we think that McDowelland Bogert were referring to the bridge between thesetwo elements formed by the parafrontal bones (labeledby them as palpebral bones). In this species, the prefron-tal and postorbitofrontal are separated and the parafron-

tal bones create the illusion of a continuous structure.The only geckos where a contact between prefrontal andpostorbitofrontal has been found are Phelsuma lineataand P. madagascarensis and is very likely to be wide-spread across Phelsuma. The fact that Phelsuma andLygodactylus (a genus without postorbitofrontal) are sis-ter taxa (Kluge and Nussbaum, 1995; Kruger, 2001; Aus-tin et al., 2004; Han et al., 2004; Feng et al., 2007;Raxworthy et al., 2007) demonstrates the variability ofthe circumorbital bones, even among closely relatedtaxa.

The approximation of the ventral process of the postor-bitofrontal and the coronoid process in Rhacodactylusproduces an incomplete bony bar in the posterior borderof the orbit. This should be not considered as a second-ary formed postorbital bar because it involves an ele-ment from the mandible, but it does provide a partialskeletal separation of the eye and the jaw musculaturein these geckos.

In related gekkonomorphs where the orbit is complete(e.g., AMNH FR 21444; Conrad and Norell, 2006) ornearly complete (e.g., Ardeosaurus brevipes; Camp, 1923;Cocude-Michel, 1961; Hoffstetter, 1964; Mateer, 1982;Evans, 2003, 2008), the jugal forms most of the postorbi-tal bar. The reduction in the size of the jugal, is themain feature responsible for an incomplete orbit in theGekkota (Evans, 2008). With the data from dissectionsand high resolution X-ray computed tomographies wedemonstrated that this element is present in all gekko-tans examined, and that in Lialis burtonis it is fused tothe ectopterygoid. We based this identification in the to-pology criterion (principe des connexions, GeoffroySaint-Hilaire, 1818) and the criterion of special quality.The portion of the ectopterygoid that we homologizewith the jugal fulfills the properties of this bone in allsquamates (Rieppel and Kearney, 2002) in having a rela-tively slender, three-dimensional structure, and havingits anterior end taper off along the dorsomedial surfaceof the maxilla (unless participating in a well defined con-tact between the maxilla, lacrimal and prefrontal). Thejugal is crucial for gekkotans and possibly varanids,because it serves as an anchor point for the postorbitaltendon and the muscle adductor mandibulae superficia-lis jugalis (A2-Supj, Fig. 4A,B), which extends betweenthe jugal and the postobitofrontal. An alternative inter-pretation would be the migration of the attachment toan adjacent point onto a contiguous element (e.g., theectopterygoid) in association with the decrease in sizeand eventual loss of the jugal. We favor the first expla-nation given the distinct morphology of the ectoperygoidin Lialis and the presence of putative sutures and hol-low space, easily seen with the different preparations.For this reason we suspect that this presents a mechani-cal restriction that prevents this element from beinglost. This hypothesis predicts that the loss of the jugal inother taxa should only occur if the muscle is not present.For the sake of this argument, we can conclude that inall lizards where this muscle has been identified(Agama, Uromastyx, gekkotans, Xantusiidae and Varani-dae) the jugal is present, and in the taxa where the jugalis lost, this muscle is absent.

The orbit of the gekkotans is highly modifiedcompared with the rest of Lepidosauria. Our survey ofgekkotan circumorbital bones has allowed us to identifysome discrepancies with previous morphological analyses

410 DAZA AND BAUER

attributable to overlooked bones or differences in theinterpretation among authors.

The phylogenetic implications of this are important foroptimization of morphological characters in future clad-istic analysis. The results from this analysis imply thatsupraorbital ossifications do not support the Scincogek-konomorpha and that special attention to this ossifica-tion across the Squamata is required in order todetermine its homology. The retention of the jugal is uni-versal among gekkotans, although it is often muchreduced and may be fused to the ectopterygoid in somepygopodids. Pygopods also exhibit a derived condition inthe contact of the prefrontal and postorbitofrontal. Thepresence of a lacrimal occurs in only some eublepharidgeckos and is absent in all examined representatives ofother gekkotan families. Neither the limbed Pacificgeckos (Diplodactylidae and Carphodactylidae) nor thehighly diverse and species rich ‘‘modern’’ gekkotans(Sphaerodactylidae þ Phyllodactylidae þ Gekkonidae)are diagnosable by features of the orbital rim, but char-acters of this portion of the skull do support the mono-phyly of particular genera (e.g., Phelsuma, Lygodactylus)and may yet prove informative at the intergeneric level.

ACKNOWLEDGMENTS

The authors thank K. de Queiroz from the NationalMuseum of Natural History (Smithsonian Institution)for suggestions to earlier versions of this article andaccess to specimens. Jack Conrad from the AmericanMuseum of Natural History in New York and an anony-mous referee provided interesting comments thatimproved the article. The authors also thank C. McCar-thy from Natural History Museum in London, D. Frostand D. Kizirian from the American Museum of NaturalHistory in New York, R. Thomas from the University ofPuerto Rico, and T. Gamble from the James Ford BellMuseum, University of Minnesota (Saint Paul, USA) foraccess to specimens and equipment; L. Benavides and G.Hormiga for access to the photographic facilities at theGeorge Washington University; and finally, A. Herrerafrom the same institution for discussing her ideas aboutthe homology of the circumorbital bones in some atypicalfossil lizards.

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APPENDIX

Institution Acronyms

AMNH, American Museum of Natural History (NewYork, USA); BMNH, British Museum (Natural History,London, England); CAS, California Academy of Sciences(San Francisco, USA); CM, Carnegie Museum of NaturalHistory (Pittsburgh, USA); FMNH, The Field Museum(Natural History) (Chicago, USA); JFBM, James Ford

Bell Museum, University of Minnesota (Saint Paul,USA); MZSP, Museu de Zoologia da Universidade de SaoPaulo (Sao Paulo, Brazil); USNM, United StatesNational Museum of Natural History (Washington,USA); YPM, Yale Peabody Museum of Natural History(New Haven, USA).

Specimens Examined

Diplodactylidae. Hoplodactylus cf. maculatus: AMNHR-31547 [Sk]; Hoplodacylus duvaucelii: BMNH 62.9.2.18[Sk], BMNH uncataloged [Sk], Oedura tryoni: BMNH96.7.1.6 [Sk]; Rhacodactylus auriculatus: BMNH86.3.11.10 [Sk], CAS 165891 [Sk]; CAS 205486 [CT];Rhacodactylus ciliatus: BMNH 85.11.16.7 [Sk], JFBM15825 [Sk]; Rhacodactylus leachianus: CAS 165890;Rhacodactylus trachyrhynchus: BMNH 86.3.11.4 [Sk];Strophurus ciliaris: FMNH 215488 [CT].Carphodactylidae. Nephrurus levis: BMNH1908.5.28.24, 1910.5.28.2 [Sk], AMNH R-86394 [Sk];Nephrurus milii: AMNH R-5085 [C&S], BMNH1904.10.7.35, 5.10.16.106 [Sk]; Saltuarius cornutus:FMNH 57503 [CT].Pygopodidae. Delma borea: USNM 128679 [CT], Delmamolleri: AMNH R-24850, 24852 [Sk]; Lialis burtonis:AMNH R-103872, 20883, 57894 [Sk], FMNH 166958[CT], JFBM 15829 [Sk]. AMNH R-111673 [Et]; Pygopuscf lepidopodus: AMNH R-140843 [Sk]; Pygopus nigri-ceps: AMNH R-24915, 32851[Sk].Eublepharidae. Aeluroscalabotes felinus: FMNH146141[CT]; Coleonyx variegatus: AMNH R-141105,69090, 74613, 89271 [Sk], 8994, 144405 [C&S], YPM14383 [CT]; Coleonyx variegatus abbotti: BMNH 2040[Sk]; Coleonyx variegatus bogerti: AMNH R-2541,2541[C&S]; Eublepharis macularius: AMNH R-89837-89838 [Sk], BMNH 87.11.2.3 [Sk], JFBM 15831[Sk] CM67524 [CT]; Goniurosaurus araneus: JFBM 15830 [Sk];Hemitheconyx caudicinctus: AMNH R-104409 [Sk],BMNH 1911.7.11.1 [Sk], Hemitheconyx taylori: BMNH1937.12.5.373 [Sk].Sphaerodactylidae. Aristelliger georgeensis: CAS176485 [CT]; Aristelliger lar: AMNH R-50272 [Sk]; Aris-telliger praesignis: BMNH 1964.1812, 86.4.15.4 [Sk];Aristelliger praesignis nelsoni: AMNH R-146747-146748[C&S]; Aristelliger praesignis praesignis: AMNH R-71593, 71595 [Sk]; Coleodactylus brachystoma: MZUSPuncataloged [C&S]; Gonatodes albogularis [CT]; Gonato-des albogularis notatus: AMNH R-71594 [Sk]; Gonatodesantillensis: AMNH R-72642 [Sk]; Gonatodes atricuculla-ris: AMNH R-144391-144394, 146762-146768 [C&S];Gonatodes cf. annularis: AMNH R-2713 [C&S]; Gonato-des sp: AMNH R-146758-146759 [C&S]; Lepidoblepharisxanthostigma: AMNH R-144541 [C&S]; Pristurus carteri:BMNH 1971.44 [Sk]; CAS 225349[CT]; Pristurus insig-nis: BMNH 1953.1.7.73 [Sk]; Pristurus sp. AMNH R-20032, 20056, 20071[C&S]; Pseudogonatodes barbouri:AMNH R-144395-144396, 146746, 146752-146757 [C&S];Quedenfeldtia trachyblephara: FMNH 197682 [C&S];Saurodactylus mauritanicus: BMNH 87.10.6.1.6 [Sk];Sphaerodactylus cinereus cinereus: AMNH R-49566[C&S]; Sphaerodactylus difficilis: AMNH R-144413-144435 [C&S]; Sphaerodactylus gossei: BMNH1964.1801-2 [Sk]; Sphaerodactylus macrolepis: AMNHR-12984, 13197 [C&S]; Sphaerodactylus molei: AMNHR-15616-15621 [C&S]; Sphaerodactylus nigropunctatus

412 DAZA AND BAUER

decoratus: AMNH R-71550 [Sk]; Sphaerodactylus sp.:AMNH R-144544 [C&S]; Teratoscincus microlepis:AMNH R-88524 [Sk]; BMNH 1934.10.9.14 [Sk]; Terato-scincus przewalskii: CAS 171013 [CT]; Teratoscincusscincus: BMNH 92.11.28.1 [Sk].Gekkonidae. Ailuronyx seychellensis: BMNH 69.5.14.49[Sk]; Afroedura karroica: CAS 198274 [CT]; Afroeduratransvaalica: BMNH 1960.1.7.6 [Sk]; Agamura persica:BMNH 86.9.21.16 [Sk], CAS 140562 [CT]; Calodactylodesaureus: BMNH 7.4.29.1166 [Sk]; Cyrtodactylus ayeyarwa-dyensis: CAS 2211985 [CT]; Cyrtodactylus consobrinus:BMNH 1904.7.19.48 [Sk]; Gehyra marginata: BMNH1910.4.26.9 [Sk]; Gehyra mutilata: JFBM 15819 [Sk];Gehyra oceanica: AMNH R-27048 [Sk]; Gehyra sp.:AMNH R-144406 [C&S]; Gekko gecko: AMNH 118697,140786-140787, 141109, 141120 [Sk], FMNH 186818 [CT];Gekko smithii: BMNH 1964.1792 [Sk]; Gekko vittatus:AMNH R-144494 [C&S]; Goggia lineata: CAS 193627[CT];Hemidactylus agrius: AMNH R-144518 [C&S]; Hemidac-tylus cf. bowringii: AMNH R-77529 [Sk]; Hemidactylusangulatus: BMNH 1978.1472 [Sk]; Hemidactylus fascia-tus: 1911.5.291 [Sk]; Hemidactylus frenatus: AMNH R-71551, 71589 [Sk], CAS 215743 [CT];Hemidactylus gigan-teus: 1908.1.29.6 [Sk]; Hemidactylus lemurinus: BMNH1977.99 [Sk]; Hemidactylus mabouia: AMNH R-102426[Sk]; Hemidactylus turcicus: AMNH R-144436 [C&S],AMNH R-153733[Sk]; Hemidactylus sp.: AMNH R-146749-146751, 75973 [C&S]; Lygodactylus picturatus:JFBM 15818 [Sk]; Narudasia festiva: CAS 186278 [CT];Pachydactylus bicolor: CAS 223912 [CT]; Chondrodacty-lus bribonii: BMNH 1910.4.20.9 [Sk]; Pachydactylus mac-ulatus: AMNH R-8946 [C&S]; Phelsuma cepediana:

AMNH R-141104 [Sk]; Phelsuma lineata: FMNH 260100[CT]; Ptenopus carpi: CAS 214548 [CT]; Rhoptropus afer:BMNH 1937.12.3.60 [Sk]; Stenodactylus arabicus: BMNH1978.1349 [Sk]; Stenodactylus dorae: BMNH 1971.1191[Sk]; Stenodactylus khobarensis: BMNH 171.1733 [Sk];Stenodactylus petrii: BMNH 1917.3.31.1[Sk]; Tropioco-lotes tripolitanus: BMNH 97.10.28.7 [Sk]; Uroplatus fim-briatus: AMNH R-2235 [Sk]; BMNH 1964.181, 61.3.20.9[Sk]; CAS-SU 13469 [CT].Phyllodactylidae. Asaccus elisae: BMNH Uncataloged[Sk]; Homonota fasciata: JFBM 15827 [Sk]; Phyllodacty-lus lanei: AMNH R-144517 [C&S]; Phyllodactylus mura-lis: AMNH R-19368 [C&S]; Phyllodactylus muralisisthmus: AMNH R-15934 [C&S]; Phyllodactylus tubercu-losus: BMNH 1906.6.1.220 [Sk]; Phyllodactylus tubercu-losus magnus: AMNH R-15953 [Sk]; Phyllodactylustuberculosus saxatilis: AMNH R-63647 [C&S]; AMNH R-78765 [C&S]; Phyllodactylus xanti: AMNH R-141106[Sk]; Phyllodactylus xanti zweifeli: AMNH R-7394[C&S]; Phyllopezus pollicaris: JFBM 15822 [Sk]; Phyllo-dactylus sp.: AMNH R-144397-144398, 146760-146761[C&S]; Ptyodactylus hasselquistii: BMNH1900.9.22.15 [Sk]; Tarentola americana: AMNH R-17726[Sk], AMNH R-22727 [C&S]; Tarentola annularis:BMNH 1920.1.20.1875 [Sk]; Tarentola delandii gigas:BMNH 1906.3.30.31 [Sk]; Tarentola mauritanica:AMNH R-144407-144410 [C&S], AMNH R-71591 [Sk],BMNH 1913.7.3.36 [Sk]; Tarentola sp.: AMNH R-144519-144520 [C&S]; Thecadactylus rapicauda: BMNH39.9.6.436 [Sk]; Thecadactylus rapicauda: AMNH R-59722, 75824, 85312 [Sk]; Thecadactylus sp.: AMNH R-144516 [C&S].

THE CIRCUMORBITAL BONES OF THE GEKKOTA 413