CHAPTER XI 



THE SUBCLASS PARAPSIDA 

 8. ORDER PROGANOSAURIA 



Primitive, aquatic reptiles with long neck, body, and tail, two or 

 three feet in length. Structure of skull imperfectly known, probably 

 with a single, upper temporal opening on each side. Face long and 

 slender, the nostril near orbits, the premaxillae elongated. Teeth 

 numerous, long and slender; small teeth on vomers, probably also on 

 other palatal bones. Vertebrae deeply amphicoelous; intercentra 

 unknown; eleven or twelve cervicals, eighteen to twenty-two dorsals, 

 two sacrals and sixty or more caudals. Free ribs on all presacrals 

 except atlas; dorsal ribs stout, single-headed, articulating with cen- 

 tra. Numerous parasternal ribs. Scapula fan-shaped; a single cora- 

 coid; clavicular girdle primitive; pelvis with small pubo-ischiatic 

 vacuity. Humerus with entepicondylar foramen. Propodials long; 

 epipodials short, carpus and tarsus primitive; phalangeal formula of 

 pes (in Mesosaurus and Noteosaurus at least) 2, 3, 4, 5, 6, the fifth toe 

 elongate. 



These small reptiles, the first known in geological history with 

 marked aquatic adaptations, retain many primitive characters, 

 though highly speciahzed in the scapular girdle with its single cora- 

 coid, the earhest known. Aside from the Dolichosauria and certain 

 dinosaurs they are the only known aquatic reptiles with both neck 

 and tail elongated. Until the skull is better known, however, doubt 

 remains as to their relationships with other reptiles. By some they 

 have been placed with the double-arched reptiles; by others among 

 the Sauropterygia. Because of the articulation of the single-headed 

 ribs especially, and the probable possession of but a single, upper 

 temporal opening, their natural association seems to be near the 

 ichthyosaurs and lizards.^ 



1 [Much further evidence for this view is given by von Huene in his memoir Die 

 Ichthyosaurier des Lias und ihre Ziisammenhdnge, 1922, 4to, Berlin. — Ed.] 



