Prof. Owen on the genus Dicynodon. 'J'J 



Summary. 



In reviewing the relations of the Dicynodonts to other Reptiles, recent and ex- 

 tinct, which have been elicited by the examinations and comparisons of the fossils 

 described in the foregoing pages, the result may be generally summed up as proving 

 the cranium, in this peculiar extinct genus or family, to have been organized ac- 

 cording to a type essentially Lacertian, but with Crocodilian and Chelonian modi- 

 fications, and with very peculiar dicynodontal characters engrafted on that compo- 

 site basis. 



The CrocodiUan structure is chiefly manifested in the occipital region of the skull, 

 and gives place to the Lacertian characters in the upper and fore-part ; but in regard 

 to these deviations it must be remembered, that the distinctive features of the Cro- 

 codiUan type are most broadly manifested in the existing representatives of the order, 

 and are modified and rendered less salient in the more numerous and varied extinct 

 members. Thus in the Teleosauri, the partial bony roof of the temporal fossae, formed 

 by the union of the post-frontal and mastoid, loses its broad development, and is re- 

 duced to the form of a slender column, which with the intermediate cranium is pro- 

 portionally longer than in the Gavials. This region of the skull is still longer in 

 the Pistosaurus, in which the parietal is perforated as in the Dicynodon and many 

 Lizards. The traces of the normal separate nasal apertures still exist in the Teleo- 

 sauri, at the point of convergence of the pre-frontal, lachrymal and superior maxil- 

 lary bones. In the Plesiosaurus the Lacertian character of the cranial bones, as a 

 decussating columnar framework, is more extensively displayed, and the two distinct 

 nostrils alone exist at the situation which I have termed ' normal ' in reference to 

 the great Saurian division of the Reptilian class, because of its prevalence in the 

 majority of the existing members, forming the Lacertian group of Sauria, and also 

 in the majority of the extinct members, which in other parts of their organization 

 are more nearly allied to the modern Loricata or Crocodiles. 



It is necessary to bear in mind this tendency to the amalgamation of Crocodihan 

 and Lacertian characters in the older Loricata, in order to form a right estimate of 

 the value of those correspondences with the cranial peculiarities of the existing 

 Lacertians which have before been detailed. 



Nevertheless, the characters of the occipital condyle, the position and division of 

 the nostrils, and above all, the condition and form of the intermaxillary bone, jus- 

 tify the conclusion, that the general type of cranial organization manifested by 

 modern Lizards was that on which the peculiar modifications of the Dicynodon 

 have been superinduced. It is not, however, amongst the modern Lizards that we 

 find the nearest approximation to the Dicynodon. For this we must go as far 

 back into the period of Reptilian existence as the epoch of the new red sand- 



VOL. VII. SECOND SERIES. M 



