Page:The Osteology of the Reptiles.pdf/231

Rh single coracoid; no cleithrum. Phalangeal formula primitive. Often reduced postaxially.

1. ? Proterosuchia. Skull elongate, with palatal teeth; an antorbital vacuity. Skull only known. Triassic.

2. ? Eosuchia. No antorbital vacuity ; interparietal and tabulars present; a parietal foramen. Only skull known. Upper Permian.

A. DIAPTOSAURIA. No antorbital foramen in skull; no supratemporal, tabulars or interparietals; palate with teeth. Vertebrae amphicoelous. Dorsal ribs articulating with intercentral space or centrum and arch, holocephalous.

1. Rhynchocephalia. Teeth protacrodont or acrodont.

1. . Skull broad, with decurved premaxillae and crushing teeth on palate. No epicondylar foramina; pubo-ischiatic opening small. Littoral reptiles. Upper Triassic.

2. . Premaxillae beak-like; pelvis with large pubo-ischiatic vacuity; an entepicondylar foramen; dorsal intercentra persistent. Littoral reptiles. Upper Jurassic to Recent.

3. . Face elongate, the nares terminal; no pubo-ischiatic vacuity; teeth labyrinthine. Subaquatic. Uppermost Cretaceous and Lowermost Eocene.

4. ? . Skull elongate, with external nares posterior. Ribs attached by single head to centrum. Limbs paddle-like. Imperfectly known. Aquatic. Triassic.

AA. ARCHOSAURIA. Dorsal ribs, anteriorly at least, articulating with arch only, dichocephalous; no teeth on palate; no parietal foramen; no supratemporal, interparietal, or tabulars; vertebrae variable; dorsal intercentra not persistent; usually an antorbital opening. Typically with large pubo-ischiatic vacuity.

1. Parasuchia. Pelvis more or less plate-like with small pubo-ischiatic vacuity; vertebrae amphicoelous; no false palate; phalanges not reduced; body with dermal scutes.

1. . External and internal nares near extremity of face; legs elongate, the epipodials long. Cursorial reptiles. Triassic.

2. . External and internal nares terminal. Legs short and stout. Terrestrial or marsh reptiles. Triassic.

3. . External and internal nares remote from extremity of slender face. Triassic.

2. Crocodilia. Pubes excluded from acetabulum, not meeting in ventral symphysis. A secondary palate. External nares terminal; vertebrae amphicoelous or procoelous; postaxial digits reduced.

1. . With dermal plates; no sclerotic plates. Amphibious. Jurassic to Recent.