270 



PROE. OWEN ON THE SKELETON OE 



Discussion. 



Mr. Httlke asked if the lateral view of the pelvis of Platypodo- 

 saurus really bore out the view of the author as to its remarkable 

 Mammalian affinities, and especially whether the acetabulum is in 

 front of or behind the vertical of the sacro-iliac junction. He further 

 remarked that most reptiles have not one but many series of teeth ; 

 aud such would seem to have been necessary for carnivorous animals, 

 in which the teeth are continually liable to damage. He stated that 

 the canine described in this specimen seemed different from what had 

 been described as characteristic of the order Theriodontia. 



Prof. Seeley inquired whether the ilium of Platypodosaurus re- 

 sembled that of a Seal. So far as he could judge from the single 

 diagram, the whole pelvis closely resembled that of Dicynodon ; and 

 if so, its affinities with other orders of fossil reptiles were more im- 

 portant than its presumed analogies with the Mammalia. This type 

 of pelvis was approximated to by certain Dinosaurs, and, but for 

 their prolonged iliac bones, was even more closely paralleled by the 

 pelvis of some Solenhofen Pterodactyles. Even should the marsu- 

 pial bones suspected by Prof. Owen have existed, the character 

 need not be mammalian, since it is well developed in the Pterodac- 

 tyle group. 



With regard to the Theriodontia, he was unable to admit the 

 importance of the characters and presumed characters on which 

 the order was founded. The teeth of existing Lizards would, by 

 the variety of types which they present, as well sanction ordinal 

 subdivisions as the Anomodontia. The Dinosaurs also, with their 

 carnivorous and herbivorous types of teeth, presented greater variety 

 among themselves than that which was held to separate the fossil 

 described from its Anomodont allies. He could not see how the 

 circumstance of the so-called canine tooth being better nourished 

 and growing larger could in these animals be an ordinal character. 

 He thought it premature to infer the absence of successional teeth 

 as an ordinal character — because the animals described were mature, 

 and succession of teeth may well have occurred in early life. Not 

 only were there no such characters dividing these animals from 

 Anomodonts as separate Crocodiles from Lizards or Turtles from 

 Crocodiles, but there was absolutely no important difference of plan 

 in the structure of the skulls of Anomodonts and the so-called 

 Theriodonts. Prof. Owen had long ago classed these animals as 

 Cynodontia, forming a family of the Anomodonts ; that classification 

 he thought excellent, but he could not accept the family as an order 

 or adopt its new name. 



Mr. Twelvetrees had just returned from the district of widely 

 spread Permian deposits of Kussia. So far as he knew, these rocks 

 had only exhibited two types of Reptilian structure, the Labyrintho- 

 dontia and the Theriodontia. He asked for information as to the re- 

 lations between the latter and several genera described by Prof. Cope. 



Prof. Owen said that the sacrum of the Dinosaurs approached 

 that of birds rather than that of mammals. He was not aware of 



