These saurians (which until the discovery of the Archegosaurus in the coal were the most ancient examples of fossil reptiles) are all distinguished by having the teeth implanted deeply in the jaw-bone, and in distinct sockets, instead of being soldered, as in frogs, to a simple alveolar parapet. In the dolomitic conglomerate near Bristol the remains of species of two distinct genera have been found, called Thecodontosaurus and Palæosaurus by Dr. Riley and Mr. Stutchbury[306-A]; the teeth of which are conical, compressed, and with finely serrated edges ([figs. 348] and [349.]).
Fig. 348.
Tooth of Palæosaurus platyodon, nat. size.
Fig. 349.
Tooth of Thecodontosaurus, 3 times magnified.
In Russia, also, Thecodont saurians occur, in beds of the Permian age, of several genera, while others named Protorosaurus are met with in the Zechstein of Thuringia. This family of reptiles is allied to the living monitor, and its appearance in a primary or paleozoic formation, observes Mr. Owen, is opposed to the doctrine of the progressive development of reptiles from fish, or from simpler to more complex forms; for, if they existed at the present day, these monitors would take rank at the head of the Lacertian order.[306-B]