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M.S.Y. LEE AND J.D. SCANLON 



Table 2. Measurements of Mesoleptos zertdrinii holotype (based on 

 Cornalia and Chiozza, 1852: pi. 3), for comparison with data in Table 1. 

 The vertebrae are numbered from the first preserved rib. 



Vertebra no. 



Centrum length 



Greatest width 



Rib length 



1 

 2 

 2 



- 



- 



45 



_ 



_ 



75 



4 



12 



- 



90 



5 



13 



- 



116 



6 



12 



- 



120 



7 



12 



18 



125 



8 



12 



20 



119+ 



9 



20* 



23 



124+ 



10 



15 



24 



120+ 



11 



15 



25 



120+ 



12 



15 



22 



114 



* there may be inaccuracies with the outlines of some vertebrae in the original 

 figure, or this anomalous high value could reflect longitudinal separation of two 

 adjacent vertebrae during partial disarticulation of the skeleton before fossilisation. 



but in any case most of the vertebrae are bisected by the broken 

 surface of the slab and are thus seen as cross-sections at various 

 levels. The intervertebral articulations are not clearly exposed, and 

 Cornalia found no indication that the vertebrae were procoelous, 

 though Gorjanovic-Kramberger (1892) and later authors assumed 

 that they must have been similar to the specimen in the Novak 

 collection (discussed below). The type specimen could not be 

 located in recent times: Calligaris (1988) was unable to confirm it 

 was still in the Museo Civico di Storia Naturale de Milano (Milan). 

 The most anterior parts preserved of the type are strongly curved 

 ribs which probably contacted the sternum, and the first vertebral 

 fragments are associated with the fourth visible rib. Some small 

 elements and fragments visible between the anterior ribs may include 

 parts of the shoulder girdle and/or forelimb. Apart from the first few, 

 the ribs are weakly curved proximally and nearly straight for the 

 distal two-thirds of their length. The ribs are widest at the proximal 

 articulation and are otherwise slender, with no trace of thickening 

 (pachyostosis) more distally. Ribs in the posterior half of the trunk 

 are displaced to point anteriorly, corresponding to bloating and 

 maceration of the carcass proceeding most rapidly in the area of the 

 viscera, and the most posterior ribs are either lost or not exposed. 

 The outlines of the first 12 preserved vertebrae are nearly triangular, 

 indicating that they are split horizontally through the middle or 

 lower part of the centrum. From about the 1 3th preserved vertebra 

 the outlines of the trunk vertebrae are expanded posteriorly as well 

 as anteriorly and the neural canal is exposed, indicating a more 

 dorsal position of the break; after the 22nd there is not much visible 

 of the vertebral centra themselves. Prominent transverse processes 

 are visible on vertebrae 24-27, and transverse grooves on the 24th 

 and 26th vertebrae resemble lymph channels seen on the ventral 

 surface of the sacral and anterior caudal vertebrae in Varanus, 

 suggesting that the skeleton is exposed ventrally, and that the 24th 

 and 25th preserved vertebrae are the sacrals. After the first two 

 caudals (26-27), represented by broad transverse processes of one 

 side, there are indeterminate fragments of two more vertebrae, then 

 indications of four vertebrae in lateral view showing elongate, near- 

 vertical chevrons and a tall but antero-posteriorly narrow, slightly 

 back-sloping neural spine. Traces of longitudinal elements under the 

 transverse processes of the 25th-26th probably represent the ilium, 

 slightly displaced posteriorly, medially and (if the orientation is 

 correct) dorsally from its natural position. The femur is level with 

 the probable sacrals; the tibia and fibula are articulated, but incom- 

 plete distally. 



The two referred specimens consist of HUJ-PAL EJ699 and 

 another specimen in the Museo Civico di Storia Naturale. Trieste 

 (MCSNT 9962: locality and other collection details undetermined). 

 The latter consists of a shorter but similar section of the skeleton to 

 that in the type, exposed dorsally (Calligaris. 1988). Comparisons of 

 the vertebrae are difficult due to the different parts and orientations 

 of the skeleton in the different specimens, but all three specimens 

 might share the derived character of unusually long, and posteriorly 

 tapering, trunk centra. The shape of the centrum in the type can be 

 inferred from the cross-sectional views of the vertebrae, which in 

 some parts of the trunk show a similar outline to the ventral views in 

 HUJ-PAL EJ699, being wide across the transverse processes and 

 narrowing steeply behind them to be almost parallel-sided posteriorly. 

 In MCSNT 9962, where only the upper part of the neural arch and 

 postzygapophyses are visible, the vertebrae are about 3/4 as long 

 (between successive neural arches) as wide (across 

 postzygapophyses), which is similar to proportions in the more 

 posterior part of HUJ-PAL EJ699. 



All three specimens share a distinctive feature of the ribs in that 

 the distal portion, representing most of their length, is nearly straight. 

 This is interpreted as a derived condition corresponding to lateral 

 compression of the trunk region, as in the pachyophiids and some 

 other groups of thoroughly aquatic snakes. All three specimens also 

 exhibit, as far as can be seen, complete but small girdles and limbs. 

 The development of the forelimb and shoulder girdle in the current 

 specimen matches the development of the pelvis and hindlimb in the 

 type and MCSNT specimens of Mesoleptos. The shoulder girdle and 

 forelimb in HUJ-PAL EJ699 are relatively small, but complete in 

 that all major elements are present. All ossified shoulder girdle 

 elements except the interclavicle are preserved, while (based on the 

 size and ossification of the humerus) most of the distal forelimb 

 bones were present. This is consistent with the small but well 

 developed (though incompletely preserved) sacrum, pelvis and 

 hindlimb in the two previously known specimens of Mesoleptos. 

 The observation that the shoulder girdle and forelimb in HUJ-PAL 

 EJ699 are both reduced in size but complete, as is the pelvis and 

 hindlimb in Mesoleptos, further suggests they are the same or 

 closely related species. 



Thus, HUJ-PAL EJ699 can be associated with the two known 

 specimens of Mesoleptos because ( 1 ) they exhibit no significant 

 differences from each other, though they all differ from all other 

 squamates, (2) they have derived similarities in the ribs (otherwise 

 found only in very different forms) and, less certainly, in the 

 vertebrae and limbs. 



'Mesoleptos' cf.zendrinii 



Gorjanovic-Kramberger ( 1 892: pi. Ill, fig. 4) reported a specimen in 

 I. Novak's collection showing several articulated vertebrae with 

 ribs, and fragments of some other elements, which he referred to 

 Mesoleptos, close to M. zendrinii. The collection consisted of 

 material from Cretaceous deposits of Isola di Lesina (Italian name 

 for Hvar Island), Croatia (Gorjanovic-Kramberger, 1 892). This was 

 held after his death by his widow Antonia Novak (Kornhuber, 1 90 1 : 

 19) but the present location of this material is unknown (Calligaris, 

 1988). Gorjanovic-Kramberger interpreted the specimen as exposed 

 ventrally, but the shape of contacts between condyles and cotyles 

 visible in his figure suggest that the vertebra may actually be 

 exposed in dorsal view but sectioned horizontally at the base of the 

 neural canal; this would invalidate comparisons based on the sup- 

 posed ventral surface, though not the overall outline, of the centrum. 

 The shape of the centrum in the most complete vertebra is very 

 similar to vertebrae 9-13 of HUJ-PAL EJ699. The elongate and 





