CHAPTER XII 



THE SUBCLASS DIAPSIDA 



Two temporal openings, the upper bounded by the parietal above, 

 the postorbito-squamosal arch below; the lateral by the postorbito- 

 squamosal arch above, the jugal, or jugal and quadratojugal, below. 

 A single coracoid on each side; no cleithra. Pelvis with pubo- 

 ischiatic opening. Quadrate fixed or partly movable, never strep- 

 tostylic. 



The phyletic unity of this great division of reptiles and their 

 descendants, the birds, admits of Httle or no doubt. In much prob- 

 ability they were derived from the single-arched type with the lateral 

 opening, by the simple separation of the postorbital and squamosal 

 from the parietal. Until recently it was confidently believed that the 

 most primitive and oldest representative of the subclass was Paleo- 

 hatteria, from the Lower Permian. In all probability, if not cer- 

 tainty, this form did not have the upper temporal opening, and must 

 therefore be included in the more primitive group, the Theromorpha. 

 At present the oldest known form referable to the subclass is 

 Youngina, from the Upper Permian of Africa, an intermediate type 

 peculiar in its retention of certain skull bones lost in all other mem- 

 bers. It is, however, yet very imperfectly known. Doubtless many 

 other forms from the Permian with these and yet other primitive 

 characters await discovery. 



12. ? Order Proterosuchia 



Skull elongate, with palatal teeth; an antorbital vacuity. Skull 

 only known. 



[Triassic. Proterosuchus Broom, South Africa.] 



13. Order "Eosuchia" 



Family Younginidae. Skull with interparietals and tabulars 

 (Psupratemporals). Skull short; no antorbital vacuity^; probably 

 with palatal teeth. Skeleton otherwise unknown. 



Upper Permian. Youngina Broom, South Africa, 



^ [An antorbital vacuity is present, according to Broom. — Ed.] 



