NO. I THE OLDEST KNOWN REPTILE — PEABODY II 



The surface surrounding the skeleton seems devoid of structures re- 

 sembling gastralia as indicated by early descriptions. However, a 

 problematical object that may be an unidentified bone from the an- 

 terior skeleton lies just to the left of the distal tail. Possibly of more 

 importance, an enlarged view of the surfaces near the skeleton reveals 

 a number of delicate, ovoid areas with fine striae radiating from a 

 point near one border. The striated areas occur only close to the 

 skeleton ; an example of the striated areas can be seen clearly between 

 the right ribs in plate I C. It is possible that these striated areas repre- 

 sent body scales developed from the epidermis of Eosauravus. No 

 bone is indicated in the delicate impressions 



Conclusions. — It is concluded that Cope's historic specimen from 

 Linton, Ohio, is surely a reptile that has evolved beyond the sey- 

 mouriamorph level. The broad-arched, cotylosaurian vertebrae pos- 

 sess small intercentra, and the narrow space between successive pleuro- 

 centra is in decided contrast with the wide, unossified gap seen in 

 seymouriamorphs. Here, the pedicel of the neural arch has a marked 

 overhang above the intercentral gap. The tarsus has a characteristic 

 reptilian astragalus and calcaneum, with enclosed perforating foramen 

 in the usual position. The astragalus is fully developed with no 

 indication of a compound origin as in the relict Captorhinus aguti of 

 Early Permian age (Peabody, 1951). The whole structure of the 

 pes is of basic reptilian pattern except for the 6th distal tarsal or post- 

 minimus. The latter may be considered an amphibian feature rather 

 than a supernumerary element that widens the pes surface in correla- 

 tion with aquatic adaptations — an untenable point of view considering 

 the general lack of characteristics suggesting aquatic habits of 

 Eosauravus. The combination of vertebral and tarsal characteristics 

 is consonant with other features of the skeleton ; together they 

 strengthen the evidence that the astragalar bone, originating from a 

 fusion of tibiale, intermedium, and proximal centrale of the amphibian 

 foot, may be regarded as a reliable osteological indication of the at- 

 tainment of the amniote level of organization — at least until conflict- 

 ing evidence is found. 



If it be granted that Eosauravus is a reptile, there is a question as to 

 its subgroup affiliation. Current evidence strongly suggests that 

 early ophiacodont pelycosaurs and captorhinomorphs are very close 

 to the root of the reptilian stock. The tarsus of Eosauravus is exceed- 

 ingly primitive in the possession of separate median and lateral cen- 

 trale, and of the postminimus. Only early pelycosaurs have separate 

 centralia — they are fused in Captorhinus and Limnoscelis. No reptiles 



