NO. I THE OLDEST KNOWN REPTILE — PEABODY 7 



distinct outline than is warranted. A thin plate lying anterior to the 

 head of the right femur may represent the left ilium broken over to 

 the right. Although the thin plate may be regarded as a patch of over- 

 lying matrix such as obscures the centrale of the left tarsus (see be- 

 low), there is a definite anterior border that looks much like the an- 

 terior edge of an iliac blade. Nowhere is there evidence of a long 

 posterior process of the ilium like that of Eogyrinus. 



The anterior 4 or 5 caudal vertebrae are associated with 3 pairs of 

 sharply curved ribs. In addition, there are short structures faintly 

 shown on the left side that are not curved and probably represent short 

 haemal spines nearly in the correct position. Also, there is a distinct 

 haemal wedge between the 3d and 4th caudal centra. Certainly there 

 is enough evidence to question seriously earlier observations (Cope, 

 1897, p. 89; Romer, 1950, p. 641) that there are no haemal spines in 

 the tail. 



The caudal series becomes twisted, possibly 180 degrees, at the posi- 

 tion of the 7th vertebra, which appears to be lying on its left side. 

 Posteriorly the series is oriented with ventral side down — an unusual 

 position if neural and haemal arches were at all well developed here, 

 or if there was any lateral compression of the centra. Under these 

 conditions the vertebrae would be almost certainly lying on one side 

 or the other as in the anterior column. However, the caudal centra 

 appear broader than high, and occasional fusion of neighboring centra 

 seems to have occurred. All features of the tail, including the orienta- 

 tion, suggest some specialized function — perhaps a prehensile action 

 in the dorsoventral plane. A special aquatic function does not seem 

 possible, insofar as a lateral sculling motion is concerned, although 

 the fused vertebrae may suggest a stiffened axis serving as the founda- 

 tion for a rudder. 



Part of the left manus (omitted in Cope's figure, 1897, pi. 3) lies 

 disarticulated near the anterior end of the vertebral column. Enough 

 is shown to indicate that the carpus was definitely as fully ossified as 

 the tarsus, and less surely that the phalangeal formula was comparable 

 to the reptilian count in the pes. 



Both limbs are complete except for the loss of some terminal 

 phalanges on the left side. The left femur is preserved with the dorsal 

 surface uppermost — the right femur with the ventral surface upper- 

 most. Thus the whole contour of the bone can be recognized in com- 

 posite. The femoral head, internal trochanter, adductor fossa, and 

 distally the tibial and fibular condyles resemble those of primitive 

 reptiles such as ophiacodonts and captorhinids. The trochanter is 



