MESOLEPTOS AND THE ORIGIN OF SNAKES 



135 



posteriorly narrow centra have been regarded as diagnostic of 

 Mesoleptos, and are not found in any other limbed squamates, 

 though a similarly shaped centrum is present in some primitive 

 snakes (e.g. Lapparentophis, Hoffstetter. 1960; Patagoniophis, 

 Scanlon, 1993; Coniophis, Gardner and Cifelli, 1999). 



Girdle and limb elements are also present in the Novak specimen; 

 Gorjanovic-Kramberger (1892: 99) describes 'indistinct impres- 

 sions' of the humerus, radius, ulna and two metacarpals, altogether 

 measuring 93.3 mm in length. This must be less than the total length 

 of the forelimb, because the elements are incompletely represented 

 (the ends of the long bones are obscured and the humerus can not be 

 compared in detail with HUJ-PAL EJ699), but it can be concluded 

 that a forelimb was present and equivalent in length to between three 

 and four thoracic vertebrae, just as in the HUJ specimen. Plate-like 

 structures are also shown just anterior to the supposed humerus in 

 Gorjanovic-Kramberger's figure, suggesting the posterior margins 

 of a scapula and coracoid like those of the HUJ specimen, although 

 no useful details can be compared. 



On the other hand the ribs, although long, are curved throughout 

 their length. While the centrum length of the one well-preserved 

 vertebra is about 3 1 .5 mm, the length of the most complete rib 

 (belonging to the preceding vertebra) is over 90 mm (Gorjanovic- 

 Kramberger, 1892). These proportions seem to indicate a position 

 deep within the dorsal region. In HUJ-PAL EJ699, curved ribs only 

 occur up to the anterior dorsal region while more posterior ribs are 

 straight. Thus the Novak specimen apparently lacks this apomorphy 

 shared by the type of Mesoleptos zendrinii with the MCSNT and 

 HUJ specimens (neither Gorjanovic-Kramberger nor subsequent 

 writers have commented on this difference). It should therefore not 

 be referred to Mesoleptos, but might possibly represent a species 

 closely related to either Mesoleptos or the Mesoleptos-smxke clade 

 (see below). 



Adriosaurus, Acteosaurus 



Adhosaunis suessi Seeley, 1881 (Lee and Caldwell, 2000) and 

 Acteosaurus tommasinii von Meyer, 1860 (considered identical by 

 Nopcsa, 1 923) are small marine lizards with distally straight ribs and 

 thus, laterally compressed bodies. Adriosaurus is known from two 

 specimens, from Upper Cretaceous deposits of Comen. Slovenia 

 and Lesina (=Hvar), Croatia, while Acteosaurus is known from a 

 single specimen from Comen. However, they both differ from 

 Mesoleptos in lacking the distinctly small cervicals (relative to 

 dorsals), in possessing proportionally larger limbs, proportionally 

 shorter and wider dorsal vertebrae, and in exhibiting heavy 

 pachyostosis of both dorsal vertebrae and ribs. They are also much 

 smaller than Mesoleptos. 



Eidolosaurus trauthii 



Nopcsa (1923) described Eidolosaurus trauthii from a near-com- 

 plete skeletal impression found during the demolition of a house in 

 the Istrian region, i.e. in the same general region as Comen, but 

 possibly within the present borders of either Slovenia, Croatia, or 

 Italy (more precise locality details were not provided). This speci- 

 men is currently housed in the Geologische Staatsanstalt, Vienna but 

 has yet to be completely prepared. Fragments of the skull are present 

 in articulation with the vertebral column, so that the total number of 

 presacral vertebrae can be determined as 34. Short, slender ribs were 

 present on at least three posterior cervicals, but on the basis of a 

 sharp increase in length and thickness between adjacent ribs (as 

 there is no trace of the sternum), Nopcsa counted 1 1 cervical and 23 

 dorsal vertebrae. Two sacral and 48 or more postsacral vertebrae 

 were also present. Nopcsa interpreted the type of Mesoleptos zendrinii 



as also having 23 dorsal vertebrae. The numbers of cervical and 

 trunk vertebrae in Mesoleptos and Eidolosaurus are therefore com- 

 parable. The relative femur length is similar in both, corresponding 

 to the length of three middle dorsal vertebrae. However, there are 

 also considerable differences: in Eidolosaurus the centra of trunk 

 vertebrae are as wide as long, with no indication of a posterior taper; 

 there is a median groove between paired ridges on the ventral 

 surface throughout the trunk (the groove further divided by a median 

 ridge in posterior vertebrae); all trunk ribs are strongly and uni- 

 formly curved and greatly thickened; and both the vertebrae and ribs 

 are pachyostotic. 



Nopcsa (1923: 107, footnote) also mentions 'An undescribed 

 fossil discovered by Professor Jakel, which came to my attention 

 while this work was in press, shows 1 8 posteriorly tapering vertebral 

 centra, which bear long, slightly curved, proximally club-shaped 

 ribs. The specimen is 28 cm long. The vertebral centra show a 

 shallow but well developed median longitudinal groove. The ante- 

 rior centra are almost triangular and wider than long. The general 

 habitus is Mesoleptos-Yike. but the ribs are somewhat pachyostotic. 

 Probably this form is related to Eidolosaurus.' 1 This may have been 

 the specimen collected by Prof. O. Jakel at Lesina which Kornhuber 

 (1901: 3) mentioned and referred to Carsosaurus. It would be 

 particularly interesting to compare this specimen with HUJ-PAL 

 EJ699, which also resembles Mesoleptos but has somewhat thick- 

 ened ribs, but no illustration was provided and again the present 

 location of the specimen is unknown (Calligaris, 1988: 117). 



Dolichosaurs: Dolichosaurus, Coniosaurus, 

 Pontosaurus 



Dolichosaurus longicollis Owen, 1850a from the English Chalk 

 (Owen, 1842, 1851; Caldwell, 2000) and Pontosaurus lesinensis 

 (Kornhuber. 1873) from Hvar. Croatia, are elongate, Cenomanian 

 marine squamates known from two or more articulated partial 

 skeletons, and are thus important for comparison with Mesoleptos. 

 They both clearly differ from HUJ-PAL EJ699 and the other 

 Mesoleptos specimens in the shape of the ribs (distally curved rather 

 than straight), the more gradual changes in rib length and vertebral 

 dimensions along the trunk, and greater number of dorsal vertebrae, 

 all of which correspond to a more slender and cylindrical body form. 

 Individual mid-trunk vertebrae of Dolichosaurus differ from those 

 of Mesoleptos in being less massive, and having proportionally 

 larger condyles and cotyles. Otherwise, they are similar in possess- 

 ing broad transverse processes, a posteriorly cylindrical centrum, 

 well-developed zygosphenes, a long neural spine, and absence of 

 pachyostosis. Vertebral morphology of Pontosaurus can not yet be 

 adequately compared because the specimens remain incompletely 

 prepared (Calligaris, 1988). Coniosaurus crassidens Owen, 1850a 

 (Coniosaurus Caldwell and Cooper, 1999, invalid emendation or 

 sustained lapse) and Coniosaurus gracilodens Caldwell, 1999, oc- 

 cur in the same deposits as D. longicollis but comparisons are more 

 problematic. Only very incomplete postcranial remains of 

 Coniosaurus are known; the vertebrae are very similar to those of 

 Dolichosaurus, and the two species are diagnosed by features of the 

 jaws and teeth unknown in Dolichosaurus. Thus, one of the species 

 of Coniosaurus might be synonymous with Dolichosaurus (Caldwell, 

 2000). 



Pachyvaranus crassispondylus 



Pachyvaranus was described from the Maastrichtian of Morocco 

 (Arambourg and Signeux, 1952: 288-91, pi. 41) based on a small 

 number of isolated vertebrae (MNHN PMC l^t) and two doubtfully 

 associated osteoderms (PMC 5-6), and originally referred to 



