A descriptive catalogue of the marine reptiles of the Oxford clay. Based on the Leeds Collection in the British Museum (Natural History), London ...

Abstract

Caenivokous marine reptiles with a cetacean-like body and no visible neck ; a dorsal fin without skeletal supports, and a large vertical caudal fin, of which the lower lobe is strengthened by the downwardly-turned end of the vertebral column. A plastron of ventral ribs present, but no dermal armour. Skull large, with a more or less elongated rostrum composed mainly of the pre-maxillfe. External nares a little in front of the very large orbits, in which there is always a ring of ossified sclerotic plates. A large parietal foramen. Supratemporal fossa large, post-temporal fossa small, and lateral temporal fossa absent ; a vacuity enclosed between the quadrate and quadrato-jugal. Postorbital and postfrontal bones distinct; lachrymal and prefrontal also distinct. Quadrate immovable, being closely united below with the pterygoid, above with the squamosal and supratemporal, which remain separate. In the otic region, pro-otic and opisthotic elements distinct ; stapes (where known) short and stout, extending from basioccipital to quadrate. In the palate, pterygoids extending forwards to meet the vomers and excluding the palatines from the middle line ; an epipterygoid [columella cranii) present ; a large parasphenoid extending forwards between the pterygoids ; apparently no trausverse bone. Teeth simply conical, usually with a vertical Labyrinthodont-like folding of their walls ; restricted to the edge of the jaws ; heterodont and set in distinct sockets in some early genera (e. g. Mixosaurus) ; homodont and set in continuous dental grooves in the typical and later genera. B