Professor Owen on BritUh Fosnl Bep tiles, 81 



themselves to siicli an li ypothesis ; for the remains of the Strep- 

 tospondylus occur likewise in the Whitby lias, which is the 

 earliest formation characterized by remains of the Teleosau- 

 rus ; and the modifications of the vertebral structure, by which 

 the S(repto8pondylu8 differs from its ancient contemporary, 

 and which it retains unaltered throughout the whole series of 

 oolitic strata, is no approximation to the ball and socket struc- 

 ture of modern crocodiles, which first appears in the Mosasau- 

 ru8 and the Eocene crocodiles, but is the very reverse. As 

 reasonably might we infer that the Teleosaur was an inter- 

 mediate form between the Streptospondylus and modern cro- 

 codiles, and that the anterior ball had first subsided, and a sub- 

 biconcave type of vertebrae had been produted before the pos- 

 terior ball, which characterizes the vertebrae of recent croco- 

 diles, was finally developed. 



If the present species of animals had resulted from progres- 

 sive development and transmutation of former species, each 

 class ought now to present its typical characters under their 

 highest recognized conditions of organization ; but the review 

 of the characters of fossil reptiles, taken in the present Report, 

 proves that this is not the case. 



No reptile now exists which combines a complicated and 

 thecodont dentition with limbs so proportionally large and 

 strong, having such well-developed marrow bones, and sus- 

 taining the weight of the trunk by synchondrosis or anchy- 

 losis to so long and complicated a sacrum, as in the order JH- 

 nosauria. 



The Megalosaurs and Iguanodons, rejoicing in these unde- 

 niably most perfect modifications of the reptilian type, attained 

 the greatest bulk, and must have played the most conspicuous 

 parts, in their respective characters as devourers of animals 

 and feeders upon vegetables, that this eai'th has ever witnessed 

 in oviparous and cold-blooded creatures. They were as supe- 

 rior in organization and in bulk to the crocodiles that preceded 

 them as to those which came after them. 



There is not the slightest ground for affirming that the pro- 

 coelian Gavial of the present day is in any respect more high- 

 ly organized than the opisthoccelian Gavial of the oldest lias. 

 If the differences of vertebral structiure ia thes© crocodilian* 



VOL. XXXin. NO. LXV. — /VI.Y 1842. » 



