PROTOROSAURUS
The genus Protorosaurus is of peculiar interest, as one of the first, if not the first, known fossil reptiles, described by Spener as long ago as 1710 as a crocodile, from fragmentary remains found in 1706 in the Permian deposits of Thuringia. Numerous other skeletons or parts of skeletons attracted the attention of naturalists of the eighteenth century, but were very imperfectly described. No name was given to the animal represented by the various specimens until 1840, when Herman von Meyer restudied all the known material and described it under the name Protorosaurus speneri. The position of the genus among reptiles always has been and yet is uncertain, for the reason that the structure of the skull, and especially the structure of the temporal region, has never been satisfactorily determined. Seeley, in 1887, described more fully the original specimen of Spener, now preserved in the museum of the College of Surgeons of London, and because of certain peculiarities which it showed proposed for its reception the order Protorosauria. He thought that he detected an upper temporal vacuity, like that of lizards, but was very uncertain about the structure of the lower part of the temporal region. The writer, who has examined this type specimen, must admit that the structure of the region here is very doubtful. Under the general assumption, however, that all old reptiles must be related to Sphenodon, the Protorosauria have generally been classified as a suborder of the Rhynchocephalia. It is merely another instance of the proclivity we all have to propose hypotheses, and then, speedily forgetting that they are hypotheses, to accept them as facts.
Protorosaurus was long supposed to be an aquatic reptile, but we now know that it was a strictly terrestrial one, probably with climbing habits; and the genus concerns us only by reason of its possible relationships to distinctly aquatic reptiles of a later age.
Fig. 62.—Life restoration of Araeoscelis.
A few years ago the writer described a very slender, lizard-like reptile about two feet in length from the Permian of Texas under the name Araeoscelis, so named because of its slender legs. The structure of both the skull and the skeleton of this reptile is now quite satisfactorily known, so well known indeed that the accompanying restoration ([Fig. 62]) has little that is conjectural about it, at least so far as the form is concerned. The skull has a single, upper temporal opening, quite like that of lizards, but the quadrate is not loose below. And this is really what we should expect in the ancestral lizards; and everything else of the skeleton, except perhaps one character, is what would be expected. That one character is the elongation of the cervical vertebrae, which are about twice the length of the dorsal vertebrae following them. The cervical ribs are very slender bones, articulating by a single head with the centrum only. In these and other characters, so far as they are known, Araeoscelis seems to agree with Protorosaurus, and both have very hollow bones.
Fig. 63.—Skeleton of Pleurosaurus.
(After Lortet)
PLEUROSAURUS
We may for the present be justified in maintaining the order Protorosauria for those reptiles having a single, typically upper temporal opening on each side, with a fixed quadrate, not including the ichthyosaurs. It is not improbable, however, that when more is known of the ancestors of the lizards, the whole group will find its most natural place among the Squamata. This definition will include a peculiar aquatic reptile that has been known for many years, but which has been wrongly classed in the same family as Sphenodon, on the purely gratuitous assumption that it has two temporal openings on each side; we now know that it has but one. This reptile, known scientifically as Pleurosaurus, was described originally by H. von Meyer in 1843, but we are indebted to M. Lortet for a more precise knowledge of the animal, and for the figure ([Fig. 63]) which is here given of the skeleton. Not a few excellent skeletons are preserved in the museums at Lyons and Munich. The specimen here figured, as actually preserved, measures about three feet in length; a part of the tail is missing, which is known from other specimens to have been remarkably long.