84 A REVISION OF THE COTVLOSAURIA OF NORTH AMERICA 



RESTORATION OF DIADECTES PHASEOLINUS. (Plate 14.) 



The restoration is based on the specimen No. 4684 Am. Mus., used as the 

 basis of the foregoing description, but a few points are taken from other specimens. 

 There are lacking from the specimen, the skull, axis, and atlas, many of the bones of 

 the feet, and some of the caudal vertebrae. The teeth of the lower jaw show that the 

 animal belongs to the same species, phaseolinus, as the skull No. 4839 Am. Mus., 

 and this skull, which belonged to an animal only slightly smaller, was used in the 

 restoration. The adas and axis are restored from the individual No. 1075, in the 

 collection of the University of Chicago. The feet are conjectural; the number of 

 phalanges has been placed at the primitive formula 2, 3, 4, 5, 4-3, but it may be 

 that the formula was more simple, perhaps the 2, 3, 3, 4, 3 suggested for Pareiasaurus. 

 The number of vertebrae in the presacral series, as restored, is twenty-one, one more 

 than in the complete series in the Chicago specimen, but there seems no escape from 

 the conclusion that the first vertebra preserved is the third. 



The general form impresses one with its peculiar massiveness and clumsiness, 

 which is even more pronounced than that in Pareiasaurus as restored by Broom.* 

 The head is heavy and was held low, just clearing the ground and probably fre- 

 quently resting upon it. There was no neck, and the thoracic region was much 

 more narrow than might have been expected. The limbs were very powerful, but 

 exceedingly short, and as the motion of the humerus was closely limited to a forward 

 and backward movement in the horizontal plane, the movement of the limbs must 

 have been like that of the turtles. Viewed from the front, the heavy head and short 

 limbs, with the humeri standing almost straight out from the scapulas, give the 

 animal a very testudinate appearance. The expanded thoracic ribs and the plates 

 over the sixth, seventh, and eighth are in keeping with what seems to be a general 

 tendency in adaptation during the period. Many of the herbivorous reptiles and 

 amphibians show an expansion of the ribs with or without an accompaniment of 

 overlying plates; this was perhaps an attempt to resist the attacks of such fiercely 

 carnivorous forms as Dimetrodon, in a time before agility of body or high intelli- 

 gence had become possible adaptations. No attempt has been made to represent 

 a dorsal armor, but the character of the terminations of the neural spines, the numer- 

 ous parallel adaptations with Pareiasaurus in which such plates occur, and the 

 numerous instances of a dorsal armor in coexisting forms render it very probable 

 that there was such a protection, at least in a rudimentary state. 



The wide, short feet with the strong blunt nails suggest the land turtles more 

 than any other type. The tail resembled that of the modern Crocodilia in form 

 and proportions. In looking about for a modern reptile with which to compare it, 

 Heloderma seemed the nearest in many respects. If the limbs of this lizard were 

 shortened, the claws turned to nails, and the bulky tail fashioned into that of a croc- 

 odile the resemblance would be very exact. 



The habits of the creature are at least indicated. Herbivorous, of low brain 

 power, sluggish in action, it can only have occupied a purely defensive attitude 

 towards such animals as the carnivorous Pelycosaurs. The strong girdles, power- 

 ful limbs with well-formed articulations and especially strong rugosities for muscular 

 attachment, the closely knit and well-formed carpus and tarsus, all indicate a 

 terrestrial habit. The broad, short feet, with large spatulate terminal phalanges 

 which were covered by powerful nail-like claws, strongly resemble those of certain 

 fossorial forms, such as the gopher turtle of Florida, Gopherus polyphemus. It 

 seems probable that the foot rested fairly flat on the ground with a pad raising the 



* Annals South African Museum, vol. iv.pt. 11, 1903. 



