Page:The Osteology of the Reptiles.pdf/229

Rh 1. SYNAPSIDA. A single temporal opening, primitively below the postorbito-squamosal arch; two coracoids.

1. Theromorpha. Skeleton primitive; vertebrae notochordal with persistent dorsal intercentra; teeth on palate bones; phalangeal formula primitive; propodials horizontal in locomotion.

1. . Carnivorous; teeth strongly anisodont with diastema; dorsal spines more or less elongated; interparietal and tabulars present. Lower Permian.

2. . Malacophagous; teeth small, isodont. Dorsal spines elongate, with bars; interparietal and tabulars present. Lower Permian.

3. . Insectivorous; teeth small, conical, subisodont; dorsal spines not elongate. Lower Permian.

4. . Malacophagous; teeth small, isodont; dorsal spines short. Lower Permian.

2. Therapsida. Skeleton less primitive; vertebrae amphicoelous, rarely notochordal; dorsal intercentra absent or unknown; phalangeal formula often reduced; propodials turned more or less downward in locomotion.

1. . Skull massive; no secondary palate; quadrate large, temporal opening surrounded by postorbital and squamosal; phalangeal formula primitive [?]. Upper Permian.

2. . Dentition subisodont or absent; no secondary palate; phalangeal formula 2, 3, 3, 3, 3. Permian.

3. . Edentulous or with long canine, or canine and molars; a rudimentary secondary palate; an acromion; phalangeal formula 2, 3, 3, 3, 3. Upper Permian, Triassic.

4. . Carnivorous; dentition more or less heterodont, at least one pair of caniniform teeth; phalanges and teeth variable. Temporal opening extending to parietal in later forms. Triassic.

2. SYNAPTOSAURIA. A single temporal opening bounded below by postorbito-squamosal arch; no supratemporal, interparietal or tabulars. A single coracoid (? Placodontia).

1. Sauropterygia. Vertebrae platycoelous; no dorsal intercentra; dorsal ribs single-headed, articulating with diapophysis; no teeth on palate. Neck more or less elongated.

1. . Amphibious; feet webbed; phalangeal formula primitive; no interpterygoidal opening in palate. Middle and Upper Triassic.

2. . Marine; limbs paddle-like, the propodials long; hyperphalangic; palate with openings. Triassic to close of Cretaceous.

2. Placodontia. Jaws and closed palate with heavy pavement teeth; vertebrae deeply amphicoelous; dorsal ribs double-headed; body with dermal bones; coracoids and feet unknown. Upper Triassic.