With respect to the affinities of Hyperodapedon, there can be no doubt that it is very closely allied to the genus Rhyncosaurus, established by Prof. Owen upon a fossil skeleton from the Trias of Shropshire. But Rhynchosaurus has shown no trace of teeth in either upper or under jaw, and seems to differ from Hyperodapedon as Oudenodon does from Dicynodon. There is a certain analogy with another Triassic genus, Placodus, in the dentigerous roof of the palate of Hyperodapedon ; but too little is known of the rest of the organization of Placodus to test the value of this analogy.
I do not find grounds for assuming any special affinity between Hyperodapedon and Telerpeton ; nor has Hyperodapedon anything to do with the Thecodonts, Crocodilian or otherwise, which abound in the Trias.
But it is a very remarkable circumstance that it is nearly allied to an anomalous lizard, Sphenodon (Hatteria), which still lives in New Zealand. Professor Owen first directed attention to some similarities in the construction of the skull between Sphenodon (under the name of Rhynchocephalus) and Rhyncosaurus. A short time since, however, the new-Zealand lizard furnished to Dr. Gunther, F.R.S., the subject for an excellent memoir now published in the ' Philosophical Transactions,' in which the many anatomical peculiarities of this singular saurian were first indicated; and on perusing this memoir, I was at once struck with the resemblance in the arrangement and wear of the teeth, as described by Dr. Gunther in Sphenodon, to that which I had become acquainted with in the fossil lizard.
I have since had the opportunity, by Dr. Gunther's kindness, of inspecting his osteological and other preparations, and I have satisfied myself that Sphenodon is the nearest ally to Hyperodapedon of all recent or fossil reptilia, except Rhynchosaurus.
Both Sphenodon and Hyperodapedon have amphicoelous vertebrae (those of the ancient reptile being far less fish-like than those of the modern one, be it noted); both have beak-like praemaxillae, not anchylosed together ; both have the inferior zygoma complete ; both have similarly formed lower jaws; in each, a single row of teeth in the mandible bites between two rows of teeth fixed to a plate which is formed by a union of the maxilla with the palatine bone — a structure which is quite anomalous among Lacertians ; and, finally, in both, these teeth wear down to the bone of the jaw by the effect of masticatory attrition.
I now proceed to offer to the notice of the Society a few general considerations which arise out of the facts just detailed.
With respect to the habits of life of Hyperodapedon, I see no reason to doubt that it may have been a purely terrestrial animal— though it is a very hard matter, from the structure of a Lacertian, to say whether it is entirely terrestrial or largely aquatic. Consider, for example, how nearly the aquatic and terrestrial Varani resemble one another, and how slight is the difference between that species of Amblyrhynchus in the Galapagos Islands which cannot be driven
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