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A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France
A RE-EVALUATION OF LATE JURASSIC (KIMMERIDGIAN) REPTI!,E EUPOSAURUS (REPTILIA : LEPIDOSAURIA) FROM CERIN, FRANCE SUSAN E. EVANS EVANS S.E. 1994. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia : Lepidosauria) from Cerin, France). [Une reevaluation du reptile Euposaurus (Reptilia: Lepidosauria) du Jurassique superieur de Cerin, France]. GEOBIOS, 27, 5 : 621-631. Villeurbanne le 31.10.1993. Manuscrit d@os6 le 10.08.1993 ; accept6 d6finitivement le 11.10.1993.
ABSTRACT Reexamination of the supposed acrodont lizard Euposaurus from the Lithographic Limestones (late Jurassic, Kimmeridgian) of Cerin (Ain), France, has shown that the three referred specimens belong to different genera. Euposaurus thiolleri, the type species, is a juvenile pleurodont lepidosaur which is probably, but not certainly, a lizard. It has no characters which suggest that it is an iguanian and is here designated Lepidosauria incertae sedis. The remaining two specimens have an acrodont dentition and are juvenile rhynchocephalians. One is referable to Homoeosaurus ; the other appears to belong to the group currently represented by Sapheosaurus, Kallimodon, Piocorrnus arid Leptosaurus although the latter two may not be valid genera. KEY-WORDS : REPTILIA,LEPIDOSAURIA,SQUAMATA,RHYNCHOCEPHALIA,FRANCE. RESUMe, Un reexamen d'Euposaurus, un reptile du Jurassique superieur (Kimmeridgian) de Cerin (/kin), France, que l'on suppose ~tre un lacertilien acrodonte, avait montr6 que chacun des 6chantillons 6tudi6s appartiennent ~ des genres diff6rents. Euposaurus thiolleri, l'esp~ce-type, est un lepidosaurien pleurodonte juv6nile, probablement, mais pas certainement, un lacertilien. I1 n'a aucun des caract6res iguaniens et est ici design6 comme Lepidosauria incertae sedis. Les deux autres 6chantillons ont une dentition acrodonte et sont des Rhynchocephales juveniles. L'un peut ~tre rapport6 ~ Homoeosaurus ; l'autre appartient, probablement, au groupe de Sapheosaurus, KaIIimodon, Piocormsts et Leptosaurus, mais il est possible que Piocormus et Leptosaurus ne soient pas des genres valides. MOTS-CLI~S : REPTILIA,LEPIDOSAURIA,SQUAMATA,RHYNCHOCEPHALIA,FRANCE.
INTRODUCTION The late Kimmeridgian Lithographic Limestones of Cerin (Ain), France have yielded an assemblage of vertebrate, invertebrate and plant material which rivals t h a t of Solnhofen (Germany) in its diversity and state of preservation (Bernier et al. 1992). Like the slightly younger Solnhofen assemblage (basal Tithonian), the Cerin assemblage has yielded a diversity of lepidosaurian reptiles including six n a m e d genera of rhynchocephalians (sensu G a u t h i e r et al. 1988) - Sapheosaurus (including Sauranodon), Homoeosaurus, Piocormus, Leptosaurus, Kallimodon and the aquatic Pleurosaurus, and one possible lizard -
Euposaurus.
The genus Euposaurus was named by J o u r d a n (1862), but the first comprehensive description was t h a t of Lortet (1892) who placed it into the Rhynchocephalia. Boulenger (1893), however, considered the teeth to be pleurodont and therefore classified Euposaurus as a lizard (Anguimorpha), an interpretation accepted by Camp (1923) who created the family Euposauridae. Cocude-Michel (1963) agreed t h a t Euposaurus was a lizard, but interpreted the dentition as acrodont. Since the only living lizards with this implantation are the acrodont iguanians, Cocude-Michel referred Euposaurus to this group, as did both Hoffstetter (1964) and Estes (1983a). In contrast, Moody
622 Figure 1 - The three Cerin reptiles referred to the genus Eup o s a u r u s . A, MHNL 15.681, the lectotype of E. c i r i n e n s i s LORTET, 1892 ; B, MHNL 15.683, the holotype of t h e type species, E. t h i o l l e r i Lortet 1892 ; C, MHNL 15.682, the holotype of E. lorteti HOFFSTETTER,1964. Scale b a r = 10ram. Les trois reptiles se rapportent au genre Euposaurus.
A
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(1980), reviewing agamid relationships, considered Euposaurus to be a rhynchocephalian, as did Gauthier et al. (1988). There is thus a conflict of opinion, not only on the taxonomic position of Euposaurus but also on important details of its dentition. In an attempt to resolve the problem, the specimens were reexamined, and drawn, under high magnification using a Wild stereomicroscope equipped with a camera lucida.
THE MATERIAL The existing material of Euposaurus consists of three small specimens, M N N L 15.681, 15.682 and 15.683 (Fig. 1), in the collections of the Musee Guimet d'Histoire Naturelle, Lyon, France. The genus w a s n a m e d by J o u r d a n (1862) on the basis of specimen 15.683, but he gave no specific designation. Subsequently, Lortet (1892) divided the three specimens into two species : Euposaurus thiolleri for type specimen (15.683) and Euposaurus cirinensis for the other two (no holotype was designated). This was remedied by CocudeMichel (1963) who n a m e d specimen 15.681 as the lectotype of E. cirinensis. Hoffstetter (1964) reviewed the material and decided that the propor-
tions of the two specimens of E. cirinensis were too different to permit their inclusion in the same species. He therefore assigned 15.682 to a separate species, E. lorteti. However, although he designated 15.682 as the holotype of his new species, it is clear from his description and diagnosis t/hat the specimen he is describing is not 15.682 at all, b u t 15.681 - the smallest and most longlimbed of the specimens (Estes 1983a made the same mistake). Thus, without realising it, Hoffstetter described the lectotype of E. cirinensis as the holotype of E. lorteti. Fortunately, this is no longer relevant because it is clear (see below) that neither 15.681 nor 15.682 belong to the genus Euposaurus. Each represents a different genus of rhynchocephalian.
THE INTERRELATIONSHIPS THE THREE SPECIMENS
OF
The three specimens show very different preservation. They are small and display common features, such as the incomplete ossification of the ends of the limb bones, which suggest t h e y are all immature. 15.681 (Fig. 1A) is a complete skeleton, preserved in dorsal view. Details of the skull and dentition are clearly visible, but the postcranial skeleton is poorer. 15.682 (Fig. 1C) is
623
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preserved in impression and is the largest of the three individuals. 15.683 (Fig. 1B) is a complete >keleton but the skull is badly damaged. The skull roof, palate and jaws are crushed into a single layer which fragmented when the blocks were split. The skull is therefore very difficult to interpret (Fig. 2). The difficulty is compounded by the fact that areas have been invaded by a dark brown crystalline material which fills bone cavities and remains in position when the original bone has been lost. Lortet's (1892) original lithographs are by far the most accurate drawings of
the tooth shape and implantation, but his interpretation of the skull was optimistic. On the left side of 15.683, teeth of the maxilla and dentary lie in parallel rows, but they are damaged. The teeth look conical because only their bases are visible and the dark infilling emphasises the triangular appearance under low magnification. The teeth on the right side of the specimen are more difficult to see without high magnification. A few of the anterior maxillary or premaxillary teeth are preserved in position (Fig. 3 -
624
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Figure 3 - Euposaurus thiolleri, MHNL 15.683, C e r i n . D e t a i l of r i g h t l o w e r d e n t i tion. Scale = lmm. ?Mx t e e t h of m a x i l l a or p r e m a x i l l a .
Ddtail de la d e n t i t i o n inferieur droite. ?Mx dents du maxillaire ou premaxilIaire.
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Figure 4 - "Euposaurus cirin e n s i s " , M H N L , 15.681, Cerin. Right dentition. Scale bar = lmm. D - dentary ; N - nasal ; Pfr - postfrontal ; Prfp r e f r o n t a l . D e n t i t i o n droite. D
- dentaire ; N - n a s a l ; P f r p o s t f r o n t a l ; P r f - prefrontal.
Mx). They are slender, a pale crown surrounding the brown infilled pulp cavity. The teeth of the right dentary are equally small and slender, the brown filling more clearly visible t h a n the outer tooth (Fig. 3). The implantation is unquestionably pleurodont, with a strong supporting labial wall and a subdental shelf. The dentition of 15.681 is well-preserved (Fig. 4) and is acrodont, as is t h a t of 15.682 (seen in the orbital region, Fig. 7). From the skull and dentition (see below), it is clear t h a t these two specimens are juvenile rhynchocephalians. Euposaurus thiollieri (15.683) is not. Since 15.683 is the holotype of the type species, it m a y be concluded t h a t the genus Euposaurus is neither a rhynchocephalian nor an acrodont iguanian, and that specimens 15.681 and 15.682 must be excluded.
15.683
:
Euposaurus thiollieri.
This small skeleton (66 m m total length) is preserved in dorsal view although, as explained above, the skull is badly damaged and affords little detail (Fig. 2). The state of ossification of the postcranial skeleton (see below) suggests a juvenile no more t h a n a few weeks posthatchling. At this stage of development, a lizard or sphenodonrid skull is not yet fully ossified (Rieppel 1992a,b,c) : the frontal and parietal m a y be separated and only partially formed. This complicates interpretation even further. As preserved, the specimen (Fig. 2) suggests large orbits ~separated by narrow frontals (probably paired), a broader parietal (probably unpaired), and a narrow quadrate. The large hole in
625
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Figure 5 - Euposaurus thiolleri, MHNL 15.683, Cerin, Postcranium. A, cervical vertebrae ; B, anterior dorsal vertebrae ; C, caudal vertebrae ; D, right ankle region. Scale bar = lmm. A - astragalus ; a.s - autotomy septum ; C - calcaneum ; Dr4 - distal tarsal 4 ; F - fibula ; ha - haemal arch ; Mt5 - metatarsal 5 ; rb - rib ; T - tibia ; ?tr.pr - ?transverse process. Squelette p o s t c r d n i e n . A , v e r t ~ b r e s c e r v i c a l e s ; B , v e r t ~ b r e s a n t d r i e u r e s d u t r o n c ; C, vert~bres c a u d a l e s ; D , rdgion t a r s a l e & droite. A a s t r a g a l e ; a . s - f i s s u r e d ' a u t o t o m i e ; C - c a l e a n e u m ; D r 4 - t a r s i e n d i s t a l 4 ; F - p d r o n g ; h a - arc h e m a l M r 5 - .,ndtatarsien 5 ; r b cdte ; T - t i b i a ; ? t r . p r - ?processus t r a n s v e r s e .
the rear of the skull is irregular and unnatural (it passes through more than one layer). Nothing suggests it is a parietal foramen of iguanid type (as interpreted, for example, by Estes 1983a). The right lower j a w is preserved in medial view. It bears at least 26 positions for small, sharp pleurodont teeth. The labial wall is high and a subdental shelf is retained above what appears to be an open Meckelian groove. No details of the p o s t d e n t a r y bones can be seen except the slender triangular retroarticular process of the articular. The postcranial skeleton is better preserved. The vertebrae are short and delicately built. Under high magnification, the neural arches appear incompletely developed and unfused in the dorsal midline (Fig. 5B). The atlanto-occipital region is crushed, b u t a vertebral count suggests 7/8 cervicals and 19/20 t r u n k vertebrae, making a total of 27/28 presacrals (higher t h a n previous estimates, e.g. 25 - Estes 1983a). It is impossible to deter-
mine whether the centra were amphicoelous or procoelous. The cervical vertebrae are very short and bear either short transverse processes (Fig. 5A) or small ribs, from the second cervical onwards. The vertebrae lengthen a little in the trunk. There are two sacrals with simple, unfianged ribs (which m a y not be coossified with the vertebral bodies) and more than 30 caudals. The first seven bear strong transverse processes. Contrary to Cocude-Michel (1963), the more posterior caudals are autotomous (Fig. 5C) and bear small haemal arches. The ribs appear to be single-headed throughout the trunk and were borne on all dorsal vertebrae except, perhaps, the last one or two. Between the ribs, there are additional elements (represented by fine grooves). These are probably the ventral cartilaginous components of the ribs (as seen, for example, in the Solnhofen genus Bavarisaurus), but they could also be gastralia.
626 The pectoral girdle is fragmentary and, except for the slender undilated clavicle, provides no information. The forelimbs are represented by all elements except the distal components of the hand. The h u m e r u s shows no trace of either an ectepicondylar or an entepicondylar foramen, but the preservation is not sufficiently good to be certain that neither was present. The left hand is missing ; on the right, only the metacarpals are preserved.
the middle Jurassic of Britain and late Jurassic of Portugal demonstrates that there were still survivors of more primitive lineages at this time. Euposaurus shares several features with squamates, including the fully pleurodont teeth, slender quadrate, relatively short jaw, narrow pubes and gracile form of the skeleton. However, there is some uncertainty with respect to the presence of gastralia and in the unusual form of the cervical vertebrae.
The component parts of the pelvis remain separate. The ilia and parts of the pubes are visible; the ischia are obscured by the sacral ribs. The iliac blades are longer t h a n those of con temporary rhynchocephalians and extend back to the level of the first caudal transverse process. The pubes appear slender and there was a thyroid fenestra. The hindlimb is longer than the forelimb (FIJHL:0.58), b u t the femur is comparatively short (Table 1). The astragalus is well-ossified and geometrical in shape. It extends partway below the fibula where it abuts against a circular calcaneum (Fig. 5D). Distal to the astragalus, and lying against the head of the hooked fifth metatarsal, there is a smaller circular bone which is best interpreted as distal tarsal four. The foot is long (2.3x femur) and gracile, with a phalangeal formula of 2:3:4:5:4.
If Euposaurus is a squamate, it differs in its dentition, build, and vertebral count from the Solnhofen genera Eichstaettisaurus, Ardeosaurus and Bavarisaurus. Palaeolacerta has yet to be reexamined ; it is a juvenile of similar size to Euposaurus, but no details of its dentition are available and the skull is difficult to compare with that of the French form. With respect its dentition, subdental shelf and open Meckelian groove, Euposaurus most closely resembles some of the simpler toothed paramacellodid (Scincomorpha) genera described from the British Purbeck (Hoffstetter 1967 ; Estes 1983a), although the j a w is proportionally longer and narrower. For the present, it seems preferable to retain Euposaurus as Lepidosauria incertae sedis. Excavations began again at Cerin in 1975 (Bernier et al. 1992) and have yielded an additional rhynchocephalian specimen. A second, adult, Euposaurus specimen is needed to resolve its taxonomic position.
The state of ossification of the vertebral column, limb bones and tarsus all suggest that this specimen of Euposaurus was a very young individual, probably recently hatched (Rieppel 1992a,b). Rieppel (pers.comm.1993) reports that neural arches remain unfused in hatchlings of Sphenodon and some lizards (e.g. Lacerta vivipara). According to Andrews (1982), a hatchling of this size (66 m m total length) might be expected to grow into an adult about three times larger (250 mm total length or 125 mm snout-vent length).
THE TAXONOMIC P O S I T I O N OF EUPOSAURUS The preservation of the skull and the immature condition of the skeleton makes a firm determination of the taxonomic position of this little reptile impossible. The hooked fifth metatarsal, single headed-ribs, pleurodont teeth and caudal fracture planes place Euposaurus firmly within Lepidosauria. It lacks the acrodont dentition of contemporaneous rhynchocephalians and differs from t h e m in the proportions of its limbs, the length of t h e iliac blade, and the form of its sacrum. However, this does not automatically make Euposaurus a lizard. The presence of the gracile lepidosauromorph Marmoretta (Evans 1991) in
S P E C I M E N 15.681 This small reptile (total length 48 mm) resembles
Euposaurus only in its size and delicate build. The skull is preserved in dorsal view and most of its structure can be seen clearly (Fig. 6). The nasals are small, the frontals narrow and the parietals relatively broad with an irregular unossified region surrounding the parietal foramen. The parietals lack posterolateral processes. Instead, the squamosal bears an elongated medial process which is received into a facet on the dorsal surface of the parietal (as Cocude-Michel 1963, described). There is no supratemporal and the squamosal retains a ventral process. The postfrontal and postorbital are large and separate. The postorbital bears a rather short posterior~squamosal process ; ventrally it meets a jugal which seems to lack a posterior process. Behind the parietals, there is a broad, poorly ossified region which is probably the braincase. Both maxillae have fallen outwards so that their facial processes lie lateral to their tooth rows. The premaxillae are obscured. The teeth of the lower jaws lie medial to those of the maxillae, which are also partly obscured. There are about 10 teeth, most small and
627 6 - "Euposaurus ciriMHNL 15.681, Cerin. Skull in dorsal view. Scale bar = lmm. ?Br unossified braincase ; D - dentary ; J jugal ; Mx - maxilla ; Rap retroarticul~tr process ; Sq squamosal. CrCme, r u e d o r Figure
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triangular, but not conical (i.e. they are laterally compressed). There is no sign of a caniniform tooth, but there are two or three large teeth at the rear of tlhe tooth row which could be taken as the first of the additional series (following the terminology of Robinson 1976). The appearance of these broad teeth, which have crinkled enamel, suggests that this specimen m a y not be a hatchling b u t corresponds to a stage represented by the living Sphenodon at a few weeks posthatching. The skull is followed by 23/24 poorly ossified vertebrae. These have broad zygapophyses, low neural spines (but this m a y be immaturity) and short arches. Ribs begin on the third or fourth cervical and m a y be double-headed anteriorly. It is not possible to determine the form of the second sacral, nor to determine whether or not the
caudals had fracture planes. Of the 30 caudals, up to 14 bear well-developed transverse processes. The pectoral girdle is represented by slender clavicles and fragments of the scapulocoracoid region. The pelvis provides little information except that the iliac blade is shorter than that of Euposaurus, reaching only to the level of the second sacral. None of the limb bones have completed joint surfaces, the carpus and tarsus are weakly ossified and the phalangeal formulae are indeterminate. The humerus appears to contain two distal foramina. The fii~h metatarsal is hooked. The most notable features of this specimen are its proportions (Fig. 1A) - the relatively large size of the head (a juvenile trait) and the length of its limbs in relation to the t r u n k (Table 1). It was
628
Head/S-V FL/S-V HL/S-V PH/Head FL/HL H/Fe RU/TF Hand/Foot RU/H TF/Fe Hand/head Foot/Fe Foot/SV H/head Fe/head Foot/head FL/trunk H/trunk RU/trunk Hand/trunk HL/trunk Fe/trunk TF/trunk Foot/trunk Head/trunk Trunk/S-V
15.681 0.31 0.46 0.64 0.93 0.72 0.69 0.64 0.67 0.76 0.81 1.12 1.15 0.24 0.47 0.69 0.79 1.00 0.34 0.25 0.34 1.39 0.46 0.38 0.53 0.68 0.46
15.682 0.26 0.28* 0.52 0.74 0.56* 0.72 0.65 0.57* 0.78 0.87 0.80* 1.01" 0.17" 0.48 0.68 0.67 0.50 0.22 0.17 0.17 0.91 0.30 0.26 0.30 0.46 0.57
15.683 0.25 0.30* 0.52 0.72 0.58* 0.83 0.70 0.32* 0.76 0.90 0.88* 2.30 0.29 0.42 0.50 1.15 0.53 0.44 0.14 0.16 0.92 0.23 0.20 0.51 0.44 0.56
15.642 15.645 --0.19 0.41 0.34 0.62 0.54 --0.63 0.67 0.59 0.75 0.68 0.77 0.67 0.56 0.48 0.80 0.74 0.78 0.75 1.17 1.03 1.55 1.45 0.29 0.25 --0.36 --0.53 --0.77 0.65 0.53 0.22 0.19 0.18 0.14 0.26 0.20 0.97 0.91 0.29 0.29 0.23 0.21 0.45 0.41 --0.32 0.64 0.60
these characters that Hoffstetter (1964) used to diagnose his new species of Euposaurus, E. lorteti, attributing the features to the wrong specimen, 15.682.
SPECIMEN
15.682
The skull has a rounded muzzle formed by the premaxillae and maxillae. The orbits are large b u t the frontals which separate t h e m are rather broader than those in 15.681 (Fig. 7). This is true also of the squamosals, but the parietal is somew h a t narrower. Details of the postorbital and supratemporal bars are a little confused, but the postorbital is relatively larger and has a longer posterior process t h a n that of 15.681. Part of the lower dentition is visible in the orbit. It is acrodont, b u t there is not enough to make a meaningful comparison with 15.681. The vertebrae show no significant differences from those of 15.681, b u t the second sacral appears to have the bifurcated, flanged rib found in most of the contemporaneous rhynchocephalians. The vertebral count gives around 23 presacrals. More t h a n 20 caudals are preserved, but the remainder of the tail has been lost and it is not possible to determine w h e t h e r or not the vertebrae were autotomous.
15.677 15.671 15.674 0.24 0.49 0.77 0.65 0.64 0.72 0.67 0.47 0.81 0.89 1.06 1.36 0.32 0.70 0.96 1.29 1.15 0.40 0.33 0.43 1.80 0.55 0.49 0.75 0.58 0~42
0.23 0.36 ---
0.17 0.36 0.46
0.55
0.67
---
0.71
0.73
0.77
----0.77 --1.09 ---
0.68 0.68 0.75 0.85 1.13 1.25
--0.55 0.75 --0.59 0.21 0.16 0.23 ---
0.19 0.67 0.87 1.08 0.52 0.18 0.14 0.20 0.73*
0.28 ---- -
O. 24 0.20 O. 2 8 *
O. 38 O. 60
O. 28* 0.62
Table 1 -
R e l a t i v e b o d y proportions in C e r i n l e p i d o s a u r s . Key: S - V = S n o u t to v e n t l e n g t h ; FL=forelimb ; HL=hindlimb ; It=humerus ; RU=radius and u l n a ; F e = f e m u r ; PI-I=width of p o s t e r i o r h e a d ; T F = t i b i a a n d fibula ; t r u n k is t h e l e n g t h from t h e clavicle to s a c r a l 1. * indicates an estimate, and the lower v a l u e m a y n o t be significant. 15.642 a n d 15.645 (Sapheosaurus) ; 15.677 (Homoeosaurus) ; 15.671 a n d 15.674 C L e p t o s a u r u s " ) . Proportions relatives du corps dans les lepidosauriens de Cerin. Cle : S-V= longueur nasocloacale ; F L = m e m b r e anterieur ; H L = m e m b r e posterieur ; H=humerus ; RU=radius/cubitus ; Fe=femur ; PH=largeur du crdne postgrieure ; TF=tibia/p~rond ; le tronc est la longueur de la clavicule & la vertebre sacr~e ; * indique une estimation, la diffgrence peut-etre n'est pas significative.
Of the pectoral girdle, only the slender clavicle is visible. In the pelvis, the iliac blade is short (not reaching beyond the second sacral) and the pubis has the waisted appearance typical of contemporaneous rhynchocephalians. The limbs are wellbuilt but the ends of the long bones remain unossifted and the extremities are poorly preserved. The proportions of the limbs to one another and to the t r u n k are different from those of 15.681, being shorter in relation to the t r u n k so that the hands do not approach the femora (Table 1).
THE TAXONOMIC POSITIONS OF 15.681 A N D 15.682 The form of the teeth, and the structure of the skull and pelvic regions show that, unlike 15.683, both 15.681 and 15.682 are rhynchocephalians (sensu stricto, Gauthier et al. 1988). The condition of their skeletons, particularly the ossification of the limbs, is an indication that both were young, but the differences between t h e m in their limb proportions and, more subtlely, in the skull (even allowing for growth changes) suggests that they are juveniles of different genera. Determining which genera is more difficult because the sphenodontian genera of Cerin (like those of Solnhofen) are in need of revision.
629
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F i g u r e 7 - " E u p o s a u r u s lorteti", M t t N L 15.682, C e r i n . S k u l l . A, a s p r e s e r v e d i n i m p r e s s i o n ; B , t h e s a m e , p o s i t i v e . S c a l e b a r = l m m . D t - d e n t a r y t e e t h ; P f r - p o s t f r o n t a l ; P o - p o s t o r b i t a l ; P r f - p r e f r o n t a l ; S q - s q u a m o s a l . A, comme prdservg, en impression ; B, le m~me, positif. D t - dents du dentaire ; P f r - postfrontal ; P o - postorbital ; P r f - prefrontal.
Six rhynchocephalian genera have been described from Cerin - Sapheosaurus (including Saurano-
don), Piocormus, Leptosaurus, Homoeosaurus, Kallimodon and the long-bodied aquatic Pleurosaurus. Of these, the independent status of Piocormus is questionable (it is very similar to Sapheosaurus) while Cocude-Michel (1963) has suggested that Leptosaurus is the same as Kallimodon (assuming that the two specimens of Leptosaurus represent the same taxon. Even allowing for allometry, the specialised structure of Pleurosaurus excludes it from consideration. Sapheosaurus, Leptosaurus, Kallimodon and Piocormus are genera with long, narrow parietals and relatively short forelimbs in relation to the trunk. The condition of the parietals can be misleading, however. The parietal is narrow in the adult Sphenodon, but it is of comparatively normal width in the hatchling (Schauinsland 1903 ; Rieppel 1992c). In Leptosaurus, the dentary teeth are simple, acrodont cones, quite different from those of 15.681. Sap~eosaurus has been described as too-
thless, but examination of the specimens suggests that a typically acrodont dentition has been worn down. Unfortunately, we do not know what the juvenile condition would have been like. In general, the dentition of 15.681, as preserved, is closest to that of Homoeosaurus, although the maxillary teeth are partially obscured and it is not possible to determine whether the characteristic flanges of Homoeosaurus were present. The dentition, in combination with the short broad parietals and limbs that are long in relation to the trunk (Table 1) supports the conclusion that 15.681 m a y be a juvenile of Homoeosaurus. 15.682 is more like Sapheosaurus, Piocormus, Leptosaurus and Kallimodon in its limb proportions (Table 1), in the broader frontal and in the shape and configuration of the postorbital and squamosal. The relatively broad parietal m a y be a juvenile feature. The teeth of 15.682 do not permit close comparison with those of other genera except that they appear compressed rather than conical (contra Leptosaurus). Anteriorly, the prefrontals are narrow but prominent, a feature seen also in Piocormus. Postcranially, these four gene-
630 r a are, at l e a s t superficially, v e r y similar a n d not h i n g v a l u a b l e is g a i n e d b y comparison. A detailed revision of t h e i r r e l a t i o n s h i p s m i g h t m a y m a k e t h e r e l a t i o n s h i p s of 15.682 clearer. For t h e p r e s e n t , it s e e m s r e a s o n a b l e to conclude t h a t its affinities lie w i t h i n t h e t a x o n o m i c a s s e m b l a g e c u r r e n t l y r e p r e s e n t e d b y Sapheosaurus, Piocormus, Kallimodon and, if it is distinct, Leptosau-
A c k n o w l e d g m e n t s - I would like to thank the staff of the Musee Guimet, Lyon, and particularly to M. Michel Philippe, for permitting me to work on the Euposaurus material. Dr Olivier Rieppel, Field Museum of Natural History, Chicago, was kind enough to provide information on vertebral development in hatchling lepidosaurs.
r/t8.
REFERENCES
DISCUSSION P r e v i o u s w o r k e r s h a v e differed in t h e i r assessm e n t of t h e position a n d s t a t u s of Euposaurus, a n d it is now clear w h y t h e "genus" p r o v e d so problematic. Euposaurus, as originally defined, was a n a s s e m b l a g e of v e r y y o u n g lepidosaurs u n i t e d b y little e x c e p t t h e i r small size and weakly ossified limbs. T h e g e n u s Euposaurus is r e p r e s e n t e d b y a single, r e l a t i v e l y poorly p r e s e r v e d s p e c i m e n of a v e r y y o u n g ( h a t c h l i n g or s h o r t l y posthatchling) lepidos a u r (hooked fifth m e t a t a r s a l , caudal autotomy). T h e d e e p l y p l e u r o d o n t d e n t i t i o n shows t h a t it is not a r h y n c h o c e p h a l i a n a n d it is probably, but not certainly, a lizard. H o w e v e r , if Euposaurus is a lizard, it is not a n a c r o d o n t iguanian. This rem o v e s t h e one possible record of a i g u a n i a n liz a r d f r o m t h e J u r a s s i c of L a u r a s i a ; all k n o w n Jurassic a n d e a r l y C r e t a c e o u s g e n e r a can be assig n e d to t h e Scleroglossa (Gekkota, S c i n c o m o r p h a a n d A n g u i m o r p h a ) ( E v a n s 1993a,b,c). I f c u r r e n t t a x o n o m i c h y p o t h e s e s are correct, i g u a n i a n liz a r d s b r a n c h e d from t h e lizard s t e m prior to t h e r a d i a t i o n of scleroglossans. T h e y m u s t t h e r e f o r e h a v e b e e n in e x i s t a n c e b y at least t h e middle J u rassic (because a n g u i m o r p h s , scincomorphs and, possibly, g e k k o t a n s are k n o w n f r o m the Bathonian, E v a n s 1993 ; 1994a,b ; E v a n s & Milner 1991). T h e fact t h a t all c u r r e n t l y k n o w n J u r a s s i c l i z a r d a s s e m b l a g e s are L a u r a s i a n ( N o r t h America, B r i t a i n , P o r t u g a l , F r a n c e , G e r m a n y , Kaz a c h s t a n - t h e C h i n e s e Yabeinosaurus is p r o b a b l y of e a r l y C r e t a c e o u s age) u n d o u b t e d l y distorts this picture. T h e J u r a s s i c l i z a r d a s s e m b l a g e s of Laur a s i a are d o m i n a t e d b y p a r a m a c e l l o d i d scincom o r p h s a n d a n g a i m o r p h s , w i t h possible gekkot a n s in G e r m a n y (Eichstaettisaurus) a n d B r i t a i n (Evans, 1994a,b). It is possible, as E s t e s (1983b) s u g g e s t e d , t h a t i g u a n i a n lizards evolved a n d rad i a t e d in G o n d w a n a l a n d , only l a t e r i n v a d i n g N o r t h e r n continents. U n t i l t h e r e are c o m p a r a b l e small vertebrate assemblages from the Jurassic of S o u t h America, Africa a n d t h e I n d i a n subcontin e n t (the K o t a F o r m a t i o n has potential), we can only speculate.
ANDREWS R.M. 1982 - Patterns of growth in reptiles. In GANS C. & POUGH F.H. (eds.) : Biology of the Reptilia. Academic Press, London & New York, 13 : 273-320. BERNIER P., BARALEJ.-P., BUFFETAUTE., GAILLARDC., GALL J.-C. & WENZ S. 1992 - The paleoecological excavations at Cerin (Southern French Jura Mountains), results and interpretation. Geobios, M.S. 16: 1-35. BOULENGERG. 1893 - On some newly described Jurassic and Cretaceous lizards and rhynchocephalians. Annals & Magazine of Natural History, 11 : 204210. CAMP C. 1923 - Classification of the lizards. Bulletin of the American Museum of Natural History, 48 : 289481. COCUDE-MICHEL M. 1963 - Les Rhynchocephales et les Sauriens des calcaires lithographiques (Jurassique Superieur) d'Europe occidentale. Nouvelles Archives Musee d'histoire naturelle, Lyon, 7 : 187p. ESTES R. 1983a - Sauria Terrestria, Amphisbaenia. In WELLNHOFER P. (ed.) : Encyclopedia of Paleoherpetology. Gustav Fischer Verlag, Stuttgart, 10A : 249 p. ESTES R. 1983b - The fossil record and early distribution of lizards. In RHODIN A. & MIYATA K. (eds.) : Advances in Herpetology and Evolutionary Biology, Essays in honor of E.E. Williams. Museum of Comparative Zoology, Harvard University : 365-398. EVANS S.E. 1991 - A new lizard-like reptile (Diapsida : Lepidosauromorpha) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, 103 : 391-412. EVANS S.E. 1993 - Jurassic lizard assemblages. In BUFFETAUT E. & MAZIN J.-M. (eds.) : Proceedings of the Second Georges Cuvier Symposium. Revue de Paleobiologie, Vol. sp~c. 7 : 55-65. EVANS S.E. 1994a - The Solnhofen (Jurassic : Tithonian) lizard genus Bavarisaurus : new skull material and a reinterpretation. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 192 : 37-52. EvANs S.E. 1994b - A new anguimorph lizard from the Jurassic and early Cretaceous of England. Palaeontology, 37 : 33-49. EVANS S.E. & MILNER A.R. 1991 - Middle Jurassic microvertebrate faunas from the British Isles. In KIELAN-JAWOROWSKA Z., HEINTZ N. & NAKREM H.-A. (eds.) : Fifth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Contributions to the Palaeontological Museum, University of Oslo, 364 : 21-
22. GAUTHIER J.-P., ESTES R. & DE QUEIROZ K. 1988 - A phylogenetic analysis of the Lepidosauromorpha. In ESTES R. & PREGILL G. (eds.) : Phylogenetic Rela-
631
tionships of the Lizard Families, Essays commemorating Charles L. Camp. Stanford U n i v e r s i t y Press, C a l i f o r n i a : 15-98. HOFFSTETTEI~',R. 1964 - Les S a n r i a du J u r a s s i q u e super i e u r et s p e c i a l e m e n t les Gekkota de Baviere et de Mandchourie. Senckenberger Biologie, 45 : 281-324. HOFFSTETTER R. 1967 - Coup d'oeil s u r les S a u r i e n s (= lacertiliens) des couches de Purbeck (Jurassique sup e r i e u r d'Augleterre. Resume d ' u n Memoire). Collo-
ques Internationaux du Centre National de la Recherche Scientifique, 163 : 349-371. JOURDAN C. 1862 - Les t e r r a i n s siderolitiques. Revue Socidtd Say. (Paris), 1 : 130-133. LORTET M. 1892 - Les reptiles fossiles du Bassin du Rhone. Archives du Musdem d'Histoire naturelle, Lyon, 5 : 1-139. MOODY S.M. 1980 - Phylogenetic a n d historical biogeographical :relationships of the genera i n the family A g a m i d a e (Reptilia : Lacertilia). Ph. D Thesis, University of Michigan : 373p. RIEPPEL O. 1992a - Studies on skeleton formation in reptiles, i : The postembryonic development of the skeleton i n Cyrtodactylus pubisulcus (Reptilia : Gekkonidae). Journal of Zoology (London), 227 : 87-100.
RIEPPEL O. 1992b - Studies on skeleton formation in reptiles, 3 : P a t t e r n s of ossification i n the skeleton of Lacerta vivipara JACQUIN (Repti]ia : Squamata). Fieldiana (n.s.), 68 : 1-25. RIEPPEL O. 1992c - The skull in a hatchling of Sphenodon punctatus. Journal of Herpetology, 26 : 80-84. ROBINSON P.L. 1976 - How Sphenodon and Uromastyx grow their teeth a n d use them. I n BELLAIRS A.d'A. & C.B. Cox (eds.) : Morphology and Biology of Reptiles. L i n n e a n Society Symposium Series. Academic Press, London & New York, 3 : 43-64. SCHAUINSLAND H. 1903 - Beitrage zur Entwicklungsgeschichte u n d Anatomie der Wirbeltiere, 1 : Sphenodon, Callorhynchus, Chamaeleo. Zoologica, 39 : 1-98.
S.E. E V A N S
Department of Anatomy and Development Biology University College London Gower Street London WCIE 6BT, England
ABSTRACT Reexamination of the supposed acrodont lizard Euposaurus from the Lithographic Limestones (late Jurassic, Kimmeridgian) of Cerin (Ain), France, has shown that the three referred specimens belong to different genera. Euposaurus thiolleri, the type species, is a juvenile pleurodont lepidosaur which is probably, but not certainly, a lizard. It has no characters which suggest that it is an iguanian and is here designated Lepidosauria incertae sedis. The remaining two specimens have an acrodont dentition and are juvenile rhynchocephalians. One is referable to Homoeosaurus ; the other appears to belong to the group currently represented by Sapheosaurus, Kallimodon, Piocorrnus arid Leptosaurus although the latter two may not be valid genera. KEY-WORDS : REPTILIA,LEPIDOSAURIA,SQUAMATA,RHYNCHOCEPHALIA,FRANCE. RESUMe, Un reexamen d'Euposaurus, un reptile du Jurassique superieur (Kimmeridgian) de Cerin (/kin), France, que l'on suppose ~tre un lacertilien acrodonte, avait montr6 que chacun des 6chantillons 6tudi6s appartiennent ~ des genres diff6rents. Euposaurus thiolleri, l'esp~ce-type, est un lepidosaurien pleurodonte juv6nile, probablement, mais pas certainement, un lacertilien. I1 n'a aucun des caract6res iguaniens et est ici design6 comme Lepidosauria incertae sedis. Les deux autres 6chantillons ont une dentition acrodonte et sont des Rhynchocephales juveniles. L'un peut ~tre rapport6 ~ Homoeosaurus ; l'autre appartient, probablement, au groupe de Sapheosaurus, KaIIimodon, Piocormsts et Leptosaurus, mais il est possible que Piocormus et Leptosaurus ne soient pas des genres valides. MOTS-CLI~S : REPTILIA,LEPIDOSAURIA,SQUAMATA,RHYNCHOCEPHALIA,FRANCE.
INTRODUCTION The late Kimmeridgian Lithographic Limestones of Cerin (Ain), France have yielded an assemblage of vertebrate, invertebrate and plant material which rivals t h a t of Solnhofen (Germany) in its diversity and state of preservation (Bernier et al. 1992). Like the slightly younger Solnhofen assemblage (basal Tithonian), the Cerin assemblage has yielded a diversity of lepidosaurian reptiles including six n a m e d genera of rhynchocephalians (sensu G a u t h i e r et al. 1988) - Sapheosaurus (including Sauranodon), Homoeosaurus, Piocormus, Leptosaurus, Kallimodon and the aquatic Pleurosaurus, and one possible lizard -
Euposaurus.
The genus Euposaurus was named by J o u r d a n (1862), but the first comprehensive description was t h a t of Lortet (1892) who placed it into the Rhynchocephalia. Boulenger (1893), however, considered the teeth to be pleurodont and therefore classified Euposaurus as a lizard (Anguimorpha), an interpretation accepted by Camp (1923) who created the family Euposauridae. Cocude-Michel (1963) agreed t h a t Euposaurus was a lizard, but interpreted the dentition as acrodont. Since the only living lizards with this implantation are the acrodont iguanians, Cocude-Michel referred Euposaurus to this group, as did both Hoffstetter (1964) and Estes (1983a). In contrast, Moody
622 Figure 1 - The three Cerin reptiles referred to the genus Eup o s a u r u s . A, MHNL 15.681, the lectotype of E. c i r i n e n s i s LORTET, 1892 ; B, MHNL 15.683, the holotype of t h e type species, E. t h i o l l e r i Lortet 1892 ; C, MHNL 15.682, the holotype of E. lorteti HOFFSTETTER,1964. Scale b a r = 10ram. Les trois reptiles se rapportent au genre Euposaurus.
A
\
\ J
J
(1980), reviewing agamid relationships, considered Euposaurus to be a rhynchocephalian, as did Gauthier et al. (1988). There is thus a conflict of opinion, not only on the taxonomic position of Euposaurus but also on important details of its dentition. In an attempt to resolve the problem, the specimens were reexamined, and drawn, under high magnification using a Wild stereomicroscope equipped with a camera lucida.
THE MATERIAL The existing material of Euposaurus consists of three small specimens, M N N L 15.681, 15.682 and 15.683 (Fig. 1), in the collections of the Musee Guimet d'Histoire Naturelle, Lyon, France. The genus w a s n a m e d by J o u r d a n (1862) on the basis of specimen 15.683, but he gave no specific designation. Subsequently, Lortet (1892) divided the three specimens into two species : Euposaurus thiolleri for type specimen (15.683) and Euposaurus cirinensis for the other two (no holotype was designated). This was remedied by CocudeMichel (1963) who n a m e d specimen 15.681 as the lectotype of E. cirinensis. Hoffstetter (1964) reviewed the material and decided that the propor-
tions of the two specimens of E. cirinensis were too different to permit their inclusion in the same species. He therefore assigned 15.682 to a separate species, E. lorteti. However, although he designated 15.682 as the holotype of his new species, it is clear from his description and diagnosis t/hat the specimen he is describing is not 15.682 at all, b u t 15.681 - the smallest and most longlimbed of the specimens (Estes 1983a made the same mistake). Thus, without realising it, Hoffstetter described the lectotype of E. cirinensis as the holotype of E. lorteti. Fortunately, this is no longer relevant because it is clear (see below) that neither 15.681 nor 15.682 belong to the genus Euposaurus. Each represents a different genus of rhynchocephalian.
THE INTERRELATIONSHIPS THE THREE SPECIMENS
OF
The three specimens show very different preservation. They are small and display common features, such as the incomplete ossification of the ends of the limb bones, which suggest t h e y are all immature. 15.681 (Fig. 1A) is a complete skeleton, preserved in dorsal view. Details of the skull and dentition are clearly visible, but the postcranial skeleton is poorer. 15.682 (Fig. 1C) is
623
,.
Fi gu re 2 Euposaurus thiolleri, . U t l N I , 15.683. Cer",~, S k u l l ~ , a h , h:~r = l m m . B r - b r a i n { ' . s o . I . D - l{'Ct d e n -
~+61..__RM x
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1~' ; LMx left m a x i l l a : Q qua(Irate ~ lid H g h t (ionia ry; R M x right maxilla Crdne. Br - boite cra~lienm, LD - dentaire gauche ; LMx maxillaire gauche ; Q - carre RD - dentaire droit ; RMx maxillaire droit.
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preserved in impression and is the largest of the three individuals. 15.683 (Fig. 1B) is a complete >keleton but the skull is badly damaged. The skull roof, palate and jaws are crushed into a single layer which fragmented when the blocks were split. The skull is therefore very difficult to interpret (Fig. 2). The difficulty is compounded by the fact that areas have been invaded by a dark brown crystalline material which fills bone cavities and remains in position when the original bone has been lost. Lortet's (1892) original lithographs are by far the most accurate drawings of
the tooth shape and implantation, but his interpretation of the skull was optimistic. On the left side of 15.683, teeth of the maxilla and dentary lie in parallel rows, but they are damaged. The teeth look conical because only their bases are visible and the dark infilling emphasises the triangular appearance under low magnification. The teeth on the right side of the specimen are more difficult to see without high magnification. A few of the anterior maxillary or premaxillary teeth are preserved in position (Fig. 3 -
624
?M×
Figure 3 - Euposaurus thiolleri, MHNL 15.683, C e r i n . D e t a i l of r i g h t l o w e r d e n t i tion. Scale = lmm. ?Mx t e e t h of m a x i l l a or p r e m a x i l l a .
Ddtail de la d e n t i t i o n inferieur droite. ?Mx dents du maxillaire ou premaxilIaire.
I
I
Figure 4 - "Euposaurus cirin e n s i s " , M H N L , 15.681, Cerin. Right dentition. Scale bar = lmm. D - dentary ; N - nasal ; Pfr - postfrontal ; Prfp r e f r o n t a l . D e n t i t i o n droite. D
- dentaire ; N - n a s a l ; P f r p o s t f r o n t a l ; P r f - prefrontal.
Mx). They are slender, a pale crown surrounding the brown infilled pulp cavity. The teeth of the right dentary are equally small and slender, the brown filling more clearly visible t h a n the outer tooth (Fig. 3). The implantation is unquestionably pleurodont, with a strong supporting labial wall and a subdental shelf. The dentition of 15.681 is well-preserved (Fig. 4) and is acrodont, as is t h a t of 15.682 (seen in the orbital region, Fig. 7). From the skull and dentition (see below), it is clear t h a t these two specimens are juvenile rhynchocephalians. Euposaurus thiollieri (15.683) is not. Since 15.683 is the holotype of the type species, it m a y be concluded t h a t the genus Euposaurus is neither a rhynchocephalian nor an acrodont iguanian, and that specimens 15.681 and 15.682 must be excluded.
15.683
:
Euposaurus thiollieri.
This small skeleton (66 m m total length) is preserved in dorsal view although, as explained above, the skull is badly damaged and affords little detail (Fig. 2). The state of ossification of the postcranial skeleton (see below) suggests a juvenile no more t h a n a few weeks posthatchling. At this stage of development, a lizard or sphenodonrid skull is not yet fully ossified (Rieppel 1992a,b,c) : the frontal and parietal m a y be separated and only partially formed. This complicates interpretation even further. As preserved, the specimen (Fig. 2) suggests large orbits ~separated by narrow frontals (probably paired), a broader parietal (probably unpaired), and a narrow quadrate. The large hole in
625
B
A
?tr.pr~
C~
Dr4. Mt5 -8.$
Figure 5 - Euposaurus thiolleri, MHNL 15.683, Cerin, Postcranium. A, cervical vertebrae ; B, anterior dorsal vertebrae ; C, caudal vertebrae ; D, right ankle region. Scale bar = lmm. A - astragalus ; a.s - autotomy septum ; C - calcaneum ; Dr4 - distal tarsal 4 ; F - fibula ; ha - haemal arch ; Mt5 - metatarsal 5 ; rb - rib ; T - tibia ; ?tr.pr - ?transverse process. Squelette p o s t c r d n i e n . A , v e r t ~ b r e s c e r v i c a l e s ; B , v e r t ~ b r e s a n t d r i e u r e s d u t r o n c ; C, vert~bres c a u d a l e s ; D , rdgion t a r s a l e & droite. A a s t r a g a l e ; a . s - f i s s u r e d ' a u t o t o m i e ; C - c a l e a n e u m ; D r 4 - t a r s i e n d i s t a l 4 ; F - p d r o n g ; h a - arc h e m a l M r 5 - .,ndtatarsien 5 ; r b cdte ; T - t i b i a ; ? t r . p r - ?processus t r a n s v e r s e .
the rear of the skull is irregular and unnatural (it passes through more than one layer). Nothing suggests it is a parietal foramen of iguanid type (as interpreted, for example, by Estes 1983a). The right lower j a w is preserved in medial view. It bears at least 26 positions for small, sharp pleurodont teeth. The labial wall is high and a subdental shelf is retained above what appears to be an open Meckelian groove. No details of the p o s t d e n t a r y bones can be seen except the slender triangular retroarticular process of the articular. The postcranial skeleton is better preserved. The vertebrae are short and delicately built. Under high magnification, the neural arches appear incompletely developed and unfused in the dorsal midline (Fig. 5B). The atlanto-occipital region is crushed, b u t a vertebral count suggests 7/8 cervicals and 19/20 t r u n k vertebrae, making a total of 27/28 presacrals (higher t h a n previous estimates, e.g. 25 - Estes 1983a). It is impossible to deter-
mine whether the centra were amphicoelous or procoelous. The cervical vertebrae are very short and bear either short transverse processes (Fig. 5A) or small ribs, from the second cervical onwards. The vertebrae lengthen a little in the trunk. There are two sacrals with simple, unfianged ribs (which m a y not be coossified with the vertebral bodies) and more than 30 caudals. The first seven bear strong transverse processes. Contrary to Cocude-Michel (1963), the more posterior caudals are autotomous (Fig. 5C) and bear small haemal arches. The ribs appear to be single-headed throughout the trunk and were borne on all dorsal vertebrae except, perhaps, the last one or two. Between the ribs, there are additional elements (represented by fine grooves). These are probably the ventral cartilaginous components of the ribs (as seen, for example, in the Solnhofen genus Bavarisaurus), but they could also be gastralia.
626 The pectoral girdle is fragmentary and, except for the slender undilated clavicle, provides no information. The forelimbs are represented by all elements except the distal components of the hand. The h u m e r u s shows no trace of either an ectepicondylar or an entepicondylar foramen, but the preservation is not sufficiently good to be certain that neither was present. The left hand is missing ; on the right, only the metacarpals are preserved.
the middle Jurassic of Britain and late Jurassic of Portugal demonstrates that there were still survivors of more primitive lineages at this time. Euposaurus shares several features with squamates, including the fully pleurodont teeth, slender quadrate, relatively short jaw, narrow pubes and gracile form of the skeleton. However, there is some uncertainty with respect to the presence of gastralia and in the unusual form of the cervical vertebrae.
The component parts of the pelvis remain separate. The ilia and parts of the pubes are visible; the ischia are obscured by the sacral ribs. The iliac blades are longer t h a n those of con temporary rhynchocephalians and extend back to the level of the first caudal transverse process. The pubes appear slender and there was a thyroid fenestra. The hindlimb is longer than the forelimb (FIJHL:0.58), b u t the femur is comparatively short (Table 1). The astragalus is well-ossified and geometrical in shape. It extends partway below the fibula where it abuts against a circular calcaneum (Fig. 5D). Distal to the astragalus, and lying against the head of the hooked fifth metatarsal, there is a smaller circular bone which is best interpreted as distal tarsal four. The foot is long (2.3x femur) and gracile, with a phalangeal formula of 2:3:4:5:4.
If Euposaurus is a squamate, it differs in its dentition, build, and vertebral count from the Solnhofen genera Eichstaettisaurus, Ardeosaurus and Bavarisaurus. Palaeolacerta has yet to be reexamined ; it is a juvenile of similar size to Euposaurus, but no details of its dentition are available and the skull is difficult to compare with that of the French form. With respect its dentition, subdental shelf and open Meckelian groove, Euposaurus most closely resembles some of the simpler toothed paramacellodid (Scincomorpha) genera described from the British Purbeck (Hoffstetter 1967 ; Estes 1983a), although the j a w is proportionally longer and narrower. For the present, it seems preferable to retain Euposaurus as Lepidosauria incertae sedis. Excavations began again at Cerin in 1975 (Bernier et al. 1992) and have yielded an additional rhynchocephalian specimen. A second, adult, Euposaurus specimen is needed to resolve its taxonomic position.
The state of ossification of the vertebral column, limb bones and tarsus all suggest that this specimen of Euposaurus was a very young individual, probably recently hatched (Rieppel 1992a,b). Rieppel (pers.comm.1993) reports that neural arches remain unfused in hatchlings of Sphenodon and some lizards (e.g. Lacerta vivipara). According to Andrews (1982), a hatchling of this size (66 m m total length) might be expected to grow into an adult about three times larger (250 mm total length or 125 mm snout-vent length).
THE TAXONOMIC P O S I T I O N OF EUPOSAURUS The preservation of the skull and the immature condition of the skeleton makes a firm determination of the taxonomic position of this little reptile impossible. The hooked fifth metatarsal, single headed-ribs, pleurodont teeth and caudal fracture planes place Euposaurus firmly within Lepidosauria. It lacks the acrodont dentition of contemporaneous rhynchocephalians and differs from t h e m in the proportions of its limbs, the length of t h e iliac blade, and the form of its sacrum. However, this does not automatically make Euposaurus a lizard. The presence of the gracile lepidosauromorph Marmoretta (Evans 1991) in
S P E C I M E N 15.681 This small reptile (total length 48 mm) resembles
Euposaurus only in its size and delicate build. The skull is preserved in dorsal view and most of its structure can be seen clearly (Fig. 6). The nasals are small, the frontals narrow and the parietals relatively broad with an irregular unossified region surrounding the parietal foramen. The parietals lack posterolateral processes. Instead, the squamosal bears an elongated medial process which is received into a facet on the dorsal surface of the parietal (as Cocude-Michel 1963, described). There is no supratemporal and the squamosal retains a ventral process. The postfrontal and postorbital are large and separate. The postorbital bears a rather short posterior~squamosal process ; ventrally it meets a jugal which seems to lack a posterior process. Behind the parietals, there is a broad, poorly ossified region which is probably the braincase. Both maxillae have fallen outwards so that their facial processes lie lateral to their tooth rows. The premaxillae are obscured. The teeth of the lower jaws lie medial to those of the maxillae, which are also partly obscured. There are about 10 teeth, most small and
627 6 - "Euposaurus ciriMHNL 15.681, Cerin. Skull in dorsal view. Scale bar = lmm. ?Br unossified braincase ; D - dentary ; J jugal ; Mx - maxilla ; Rap retroarticul~tr process ; Sq squamosal. CrCme, r u e d o r Figure
nensis",
i_.."
"-% "'7
---'Mx
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sale. ? B r - b o i t e c r C m i e n n e ; D - d e n t a i r e ; J~ j u g a l ; M x maxillaire ; Rap - processus rdtroarticulaire ; Sq - squamo-
sal.
mSq
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..
,..-
,:~
,
,
Rap ?Br
triangular, but not conical (i.e. they are laterally compressed). There is no sign of a caniniform tooth, but there are two or three large teeth at the rear of tlhe tooth row which could be taken as the first of the additional series (following the terminology of Robinson 1976). The appearance of these broad teeth, which have crinkled enamel, suggests that this specimen m a y not be a hatchling b u t corresponds to a stage represented by the living Sphenodon at a few weeks posthatching. The skull is followed by 23/24 poorly ossified vertebrae. These have broad zygapophyses, low neural spines (but this m a y be immaturity) and short arches. Ribs begin on the third or fourth cervical and m a y be double-headed anteriorly. It is not possible to determine the form of the second sacral, nor to determine whether or not the
caudals had fracture planes. Of the 30 caudals, up to 14 bear well-developed transverse processes. The pectoral girdle is represented by slender clavicles and fragments of the scapulocoracoid region. The pelvis provides little information except that the iliac blade is shorter than that of Euposaurus, reaching only to the level of the second sacral. None of the limb bones have completed joint surfaces, the carpus and tarsus are weakly ossified and the phalangeal formulae are indeterminate. The humerus appears to contain two distal foramina. The fii~h metatarsal is hooked. The most notable features of this specimen are its proportions (Fig. 1A) - the relatively large size of the head (a juvenile trait) and the length of its limbs in relation to the t r u n k (Table 1). It was
628
Head/S-V FL/S-V HL/S-V PH/Head FL/HL H/Fe RU/TF Hand/Foot RU/H TF/Fe Hand/head Foot/Fe Foot/SV H/head Fe/head Foot/head FL/trunk H/trunk RU/trunk Hand/trunk HL/trunk Fe/trunk TF/trunk Foot/trunk Head/trunk Trunk/S-V
15.681 0.31 0.46 0.64 0.93 0.72 0.69 0.64 0.67 0.76 0.81 1.12 1.15 0.24 0.47 0.69 0.79 1.00 0.34 0.25 0.34 1.39 0.46 0.38 0.53 0.68 0.46
15.682 0.26 0.28* 0.52 0.74 0.56* 0.72 0.65 0.57* 0.78 0.87 0.80* 1.01" 0.17" 0.48 0.68 0.67 0.50 0.22 0.17 0.17 0.91 0.30 0.26 0.30 0.46 0.57
15.683 0.25 0.30* 0.52 0.72 0.58* 0.83 0.70 0.32* 0.76 0.90 0.88* 2.30 0.29 0.42 0.50 1.15 0.53 0.44 0.14 0.16 0.92 0.23 0.20 0.51 0.44 0.56
15.642 15.645 --0.19 0.41 0.34 0.62 0.54 --0.63 0.67 0.59 0.75 0.68 0.77 0.67 0.56 0.48 0.80 0.74 0.78 0.75 1.17 1.03 1.55 1.45 0.29 0.25 --0.36 --0.53 --0.77 0.65 0.53 0.22 0.19 0.18 0.14 0.26 0.20 0.97 0.91 0.29 0.29 0.23 0.21 0.45 0.41 --0.32 0.64 0.60
these characters that Hoffstetter (1964) used to diagnose his new species of Euposaurus, E. lorteti, attributing the features to the wrong specimen, 15.682.
SPECIMEN
15.682
The skull has a rounded muzzle formed by the premaxillae and maxillae. The orbits are large b u t the frontals which separate t h e m are rather broader than those in 15.681 (Fig. 7). This is true also of the squamosals, but the parietal is somew h a t narrower. Details of the postorbital and supratemporal bars are a little confused, but the postorbital is relatively larger and has a longer posterior process t h a n that of 15.681. Part of the lower dentition is visible in the orbit. It is acrodont, b u t there is not enough to make a meaningful comparison with 15.681. The vertebrae show no significant differences from those of 15.681, b u t the second sacral appears to have the bifurcated, flanged rib found in most of the contemporaneous rhynchocephalians. The vertebral count gives around 23 presacrals. More t h a n 20 caudals are preserved, but the remainder of the tail has been lost and it is not possible to determine w h e t h e r or not the vertebrae were autotomous.
15.677 15.671 15.674 0.24 0.49 0.77 0.65 0.64 0.72 0.67 0.47 0.81 0.89 1.06 1.36 0.32 0.70 0.96 1.29 1.15 0.40 0.33 0.43 1.80 0.55 0.49 0.75 0.58 0~42
0.23 0.36 ---
0.17 0.36 0.46
0.55
0.67
---
0.71
0.73
0.77
----0.77 --1.09 ---
0.68 0.68 0.75 0.85 1.13 1.25
--0.55 0.75 --0.59 0.21 0.16 0.23 ---
0.19 0.67 0.87 1.08 0.52 0.18 0.14 0.20 0.73*
0.28 ---- -
O. 24 0.20 O. 2 8 *
O. 38 O. 60
O. 28* 0.62
Table 1 -
R e l a t i v e b o d y proportions in C e r i n l e p i d o s a u r s . Key: S - V = S n o u t to v e n t l e n g t h ; FL=forelimb ; HL=hindlimb ; It=humerus ; RU=radius and u l n a ; F e = f e m u r ; PI-I=width of p o s t e r i o r h e a d ; T F = t i b i a a n d fibula ; t r u n k is t h e l e n g t h from t h e clavicle to s a c r a l 1. * indicates an estimate, and the lower v a l u e m a y n o t be significant. 15.642 a n d 15.645 (Sapheosaurus) ; 15.677 (Homoeosaurus) ; 15.671 a n d 15.674 C L e p t o s a u r u s " ) . Proportions relatives du corps dans les lepidosauriens de Cerin. Cle : S-V= longueur nasocloacale ; F L = m e m b r e anterieur ; H L = m e m b r e posterieur ; H=humerus ; RU=radius/cubitus ; Fe=femur ; PH=largeur du crdne postgrieure ; TF=tibia/p~rond ; le tronc est la longueur de la clavicule & la vertebre sacr~e ; * indique une estimation, la diffgrence peut-etre n'est pas significative.
Of the pectoral girdle, only the slender clavicle is visible. In the pelvis, the iliac blade is short (not reaching beyond the second sacral) and the pubis has the waisted appearance typical of contemporaneous rhynchocephalians. The limbs are wellbuilt but the ends of the long bones remain unossifted and the extremities are poorly preserved. The proportions of the limbs to one another and to the t r u n k are different from those of 15.681, being shorter in relation to the t r u n k so that the hands do not approach the femora (Table 1).
THE TAXONOMIC POSITIONS OF 15.681 A N D 15.682 The form of the teeth, and the structure of the skull and pelvic regions show that, unlike 15.683, both 15.681 and 15.682 are rhynchocephalians (sensu stricto, Gauthier et al. 1988). The condition of their skeletons, particularly the ossification of the limbs, is an indication that both were young, but the differences between t h e m in their limb proportions and, more subtlely, in the skull (even allowing for growth changes) suggests that they are juveniles of different genera. Determining which genera is more difficult because the sphenodontian genera of Cerin (like those of Solnhofen) are in need of revision.
629
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/ :
•
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F i g u r e 7 - " E u p o s a u r u s lorteti", M t t N L 15.682, C e r i n . S k u l l . A, a s p r e s e r v e d i n i m p r e s s i o n ; B , t h e s a m e , p o s i t i v e . S c a l e b a r = l m m . D t - d e n t a r y t e e t h ; P f r - p o s t f r o n t a l ; P o - p o s t o r b i t a l ; P r f - p r e f r o n t a l ; S q - s q u a m o s a l . A, comme prdservg, en impression ; B, le m~me, positif. D t - dents du dentaire ; P f r - postfrontal ; P o - postorbital ; P r f - prefrontal.
Six rhynchocephalian genera have been described from Cerin - Sapheosaurus (including Saurano-
don), Piocormus, Leptosaurus, Homoeosaurus, Kallimodon and the long-bodied aquatic Pleurosaurus. Of these, the independent status of Piocormus is questionable (it is very similar to Sapheosaurus) while Cocude-Michel (1963) has suggested that Leptosaurus is the same as Kallimodon (assuming that the two specimens of Leptosaurus represent the same taxon. Even allowing for allometry, the specialised structure of Pleurosaurus excludes it from consideration. Sapheosaurus, Leptosaurus, Kallimodon and Piocormus are genera with long, narrow parietals and relatively short forelimbs in relation to the trunk. The condition of the parietals can be misleading, however. The parietal is narrow in the adult Sphenodon, but it is of comparatively normal width in the hatchling (Schauinsland 1903 ; Rieppel 1992c). In Leptosaurus, the dentary teeth are simple, acrodont cones, quite different from those of 15.681. Sap~eosaurus has been described as too-
thless, but examination of the specimens suggests that a typically acrodont dentition has been worn down. Unfortunately, we do not know what the juvenile condition would have been like. In general, the dentition of 15.681, as preserved, is closest to that of Homoeosaurus, although the maxillary teeth are partially obscured and it is not possible to determine whether the characteristic flanges of Homoeosaurus were present. The dentition, in combination with the short broad parietals and limbs that are long in relation to the trunk (Table 1) supports the conclusion that 15.681 m a y be a juvenile of Homoeosaurus. 15.682 is more like Sapheosaurus, Piocormus, Leptosaurus and Kallimodon in its limb proportions (Table 1), in the broader frontal and in the shape and configuration of the postorbital and squamosal. The relatively broad parietal m a y be a juvenile feature. The teeth of 15.682 do not permit close comparison with those of other genera except that they appear compressed rather than conical (contra Leptosaurus). Anteriorly, the prefrontals are narrow but prominent, a feature seen also in Piocormus. Postcranially, these four gene-
630 r a are, at l e a s t superficially, v e r y similar a n d not h i n g v a l u a b l e is g a i n e d b y comparison. A detailed revision of t h e i r r e l a t i o n s h i p s m i g h t m a y m a k e t h e r e l a t i o n s h i p s of 15.682 clearer. For t h e p r e s e n t , it s e e m s r e a s o n a b l e to conclude t h a t its affinities lie w i t h i n t h e t a x o n o m i c a s s e m b l a g e c u r r e n t l y r e p r e s e n t e d b y Sapheosaurus, Piocormus, Kallimodon and, if it is distinct, Leptosau-
A c k n o w l e d g m e n t s - I would like to thank the staff of the Musee Guimet, Lyon, and particularly to M. Michel Philippe, for permitting me to work on the Euposaurus material. Dr Olivier Rieppel, Field Museum of Natural History, Chicago, was kind enough to provide information on vertebral development in hatchling lepidosaurs.
r/t8.
REFERENCES
DISCUSSION P r e v i o u s w o r k e r s h a v e differed in t h e i r assessm e n t of t h e position a n d s t a t u s of Euposaurus, a n d it is now clear w h y t h e "genus" p r o v e d so problematic. Euposaurus, as originally defined, was a n a s s e m b l a g e of v e r y y o u n g lepidosaurs u n i t e d b y little e x c e p t t h e i r small size and weakly ossified limbs. T h e g e n u s Euposaurus is r e p r e s e n t e d b y a single, r e l a t i v e l y poorly p r e s e r v e d s p e c i m e n of a v e r y y o u n g ( h a t c h l i n g or s h o r t l y posthatchling) lepidos a u r (hooked fifth m e t a t a r s a l , caudal autotomy). T h e d e e p l y p l e u r o d o n t d e n t i t i o n shows t h a t it is not a r h y n c h o c e p h a l i a n a n d it is probably, but not certainly, a lizard. H o w e v e r , if Euposaurus is a lizard, it is not a n a c r o d o n t iguanian. This rem o v e s t h e one possible record of a i g u a n i a n liz a r d f r o m t h e J u r a s s i c of L a u r a s i a ; all k n o w n Jurassic a n d e a r l y C r e t a c e o u s g e n e r a can be assig n e d to t h e Scleroglossa (Gekkota, S c i n c o m o r p h a a n d A n g u i m o r p h a ) ( E v a n s 1993a,b,c). I f c u r r e n t t a x o n o m i c h y p o t h e s e s are correct, i g u a n i a n liz a r d s b r a n c h e d from t h e lizard s t e m prior to t h e r a d i a t i o n of scleroglossans. T h e y m u s t t h e r e f o r e h a v e b e e n in e x i s t a n c e b y at least t h e middle J u rassic (because a n g u i m o r p h s , scincomorphs and, possibly, g e k k o t a n s are k n o w n f r o m the Bathonian, E v a n s 1993 ; 1994a,b ; E v a n s & Milner 1991). T h e fact t h a t all c u r r e n t l y k n o w n J u r a s s i c l i z a r d a s s e m b l a g e s are L a u r a s i a n ( N o r t h America, B r i t a i n , P o r t u g a l , F r a n c e , G e r m a n y , Kaz a c h s t a n - t h e C h i n e s e Yabeinosaurus is p r o b a b l y of e a r l y C r e t a c e o u s age) u n d o u b t e d l y distorts this picture. T h e J u r a s s i c l i z a r d a s s e m b l a g e s of Laur a s i a are d o m i n a t e d b y p a r a m a c e l l o d i d scincom o r p h s a n d a n g a i m o r p h s , w i t h possible gekkot a n s in G e r m a n y (Eichstaettisaurus) a n d B r i t a i n (Evans, 1994a,b). It is possible, as E s t e s (1983b) s u g g e s t e d , t h a t i g u a n i a n lizards evolved a n d rad i a t e d in G o n d w a n a l a n d , only l a t e r i n v a d i n g N o r t h e r n continents. U n t i l t h e r e are c o m p a r a b l e small vertebrate assemblages from the Jurassic of S o u t h America, Africa a n d t h e I n d i a n subcontin e n t (the K o t a F o r m a t i o n has potential), we can only speculate.
ANDREWS R.M. 1982 - Patterns of growth in reptiles. In GANS C. & POUGH F.H. (eds.) : Biology of the Reptilia. Academic Press, London & New York, 13 : 273-320. BERNIER P., BARALEJ.-P., BUFFETAUTE., GAILLARDC., GALL J.-C. & WENZ S. 1992 - The paleoecological excavations at Cerin (Southern French Jura Mountains), results and interpretation. Geobios, M.S. 16: 1-35. BOULENGERG. 1893 - On some newly described Jurassic and Cretaceous lizards and rhynchocephalians. Annals & Magazine of Natural History, 11 : 204210. CAMP C. 1923 - Classification of the lizards. Bulletin of the American Museum of Natural History, 48 : 289481. COCUDE-MICHEL M. 1963 - Les Rhynchocephales et les Sauriens des calcaires lithographiques (Jurassique Superieur) d'Europe occidentale. Nouvelles Archives Musee d'histoire naturelle, Lyon, 7 : 187p. ESTES R. 1983a - Sauria Terrestria, Amphisbaenia. In WELLNHOFER P. (ed.) : Encyclopedia of Paleoherpetology. Gustav Fischer Verlag, Stuttgart, 10A : 249 p. ESTES R. 1983b - The fossil record and early distribution of lizards. In RHODIN A. & MIYATA K. (eds.) : Advances in Herpetology and Evolutionary Biology, Essays in honor of E.E. Williams. Museum of Comparative Zoology, Harvard University : 365-398. EVANS S.E. 1991 - A new lizard-like reptile (Diapsida : Lepidosauromorpha) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, 103 : 391-412. EVANS S.E. 1993 - Jurassic lizard assemblages. In BUFFETAUT E. & MAZIN J.-M. (eds.) : Proceedings of the Second Georges Cuvier Symposium. Revue de Paleobiologie, Vol. sp~c. 7 : 55-65. EVANS S.E. 1994a - The Solnhofen (Jurassic : Tithonian) lizard genus Bavarisaurus : new skull material and a reinterpretation. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 192 : 37-52. EvANs S.E. 1994b - A new anguimorph lizard from the Jurassic and early Cretaceous of England. Palaeontology, 37 : 33-49. EVANS S.E. & MILNER A.R. 1991 - Middle Jurassic microvertebrate faunas from the British Isles. In KIELAN-JAWOROWSKA Z., HEINTZ N. & NAKREM H.-A. (eds.) : Fifth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Contributions to the Palaeontological Museum, University of Oslo, 364 : 21-
22. GAUTHIER J.-P., ESTES R. & DE QUEIROZ K. 1988 - A phylogenetic analysis of the Lepidosauromorpha. In ESTES R. & PREGILL G. (eds.) : Phylogenetic Rela-
631
tionships of the Lizard Families, Essays commemorating Charles L. Camp. Stanford U n i v e r s i t y Press, C a l i f o r n i a : 15-98. HOFFSTETTEI~',R. 1964 - Les S a n r i a du J u r a s s i q u e super i e u r et s p e c i a l e m e n t les Gekkota de Baviere et de Mandchourie. Senckenberger Biologie, 45 : 281-324. HOFFSTETTER R. 1967 - Coup d'oeil s u r les S a u r i e n s (= lacertiliens) des couches de Purbeck (Jurassique sup e r i e u r d'Augleterre. Resume d ' u n Memoire). Collo-
ques Internationaux du Centre National de la Recherche Scientifique, 163 : 349-371. JOURDAN C. 1862 - Les t e r r a i n s siderolitiques. Revue Socidtd Say. (Paris), 1 : 130-133. LORTET M. 1892 - Les reptiles fossiles du Bassin du Rhone. Archives du Musdem d'Histoire naturelle, Lyon, 5 : 1-139. MOODY S.M. 1980 - Phylogenetic a n d historical biogeographical :relationships of the genera i n the family A g a m i d a e (Reptilia : Lacertilia). Ph. D Thesis, University of Michigan : 373p. RIEPPEL O. 1992a - Studies on skeleton formation in reptiles, i : The postembryonic development of the skeleton i n Cyrtodactylus pubisulcus (Reptilia : Gekkonidae). Journal of Zoology (London), 227 : 87-100.
RIEPPEL O. 1992b - Studies on skeleton formation in reptiles, 3 : P a t t e r n s of ossification i n the skeleton of Lacerta vivipara JACQUIN (Repti]ia : Squamata). Fieldiana (n.s.), 68 : 1-25. RIEPPEL O. 1992c - The skull in a hatchling of Sphenodon punctatus. Journal of Herpetology, 26 : 80-84. ROBINSON P.L. 1976 - How Sphenodon and Uromastyx grow their teeth a n d use them. I n BELLAIRS A.d'A. & C.B. Cox (eds.) : Morphology and Biology of Reptiles. L i n n e a n Society Symposium Series. Academic Press, London & New York, 3 : 43-64. SCHAUINSLAND H. 1903 - Beitrage zur Entwicklungsgeschichte u n d Anatomie der Wirbeltiere, 1 : Sphenodon, Callorhynchus, Chamaeleo. Zoologica, 39 : 1-98.
S.E. E V A N S
Department of Anatomy and Development Biology University College London Gower Street London WCIE 6BT, England