Water Reptiles of the Past and Present

by Samuel Wendell Williston

The Pelycosimia of Huene are very interesting as showing apparently primitive forms with which the true phytosaurs may have been intimately related ancestrally. They, too, have a rather short skull with the nostrils in front, and were not at all aquatic in habit. Not much is known about the single genus that is located in the group, aside from the skull and a few limb bones.

PHYTOSAURIA

The Phytosauria, so far as known, were all reptiles of considerable size, greatly resembling the crocodiles, and especially the gavials in form and habit, but differing very greatly in having the external nostrils situated far back near the eyes; in having no false palate so characteristic of the Crocodilia; in having a more primitive shoulder-girdle, consisting of a short coracoid, interclavicle, and clavicles; and in having the ordinary type of pelvis, that is, with the pubis entering into the acetabular articulation for the femur. They were all, like the crocodiles, covered more or less by a bony armor; there are two openings on each side of the temporal region; there is no pineal opening; the vertebrae are gently biconcave, precisely like those of the early or mesosuchian crocodiles; there is always an opening of considerable size, called the preorbital foramen, in front of the eyes, as in some crocodiles, many dinosaurs, and most pterodactyls; there is also an opening through the back part of the mandibles as in crocodiles; and the double-headed ribs are attached exclusively to the transverse process of the arch, precisely as in the crocodiles, dinosaurs, and pterodactyls. From all these it is evident that the phytosaurs are related most nearly to the crocodiles and dinosaurs, and are probably an early branch of the stem from which they, the pterodactyls and the birds, arose, a branch that persisted only a short time, geologically speaking, and went entirely out of existence at the close of Triassic times, leaving no descendants behind. Nevertheless, in this comparatively brief life-span they developed not a few distinctive forms and became widely distributed over the earth. Their remains are known from the Upper Trias of Germany, England, and Scotland, India, South Africa, and from Massachusetts, North and South Carolina, and many places in the Rocky Mountains. No true phytosaurs are yet known from South America, but in all probability they will be discovered there when the Triassic deposits of that continent have been better explored for fossils. In the Rocky Mountains, especially, their remains are widely scattered, they have been found in many localities in Wyoming, Colorado, Oklahoma, Utah, and New Mexico. Though for the most part their known remains from these localities are yet fragmentary, not less than four distinct genera have been described from these regions: “Belodon,” Angistorhinus, Paleorhinus, and Episcoposaurus. From the Carolinas and Massachusetts a single genus, though described under numerous names, has been made known, originally called by Emmons Rutiodon (Rhytidodon). And from Europe and India at least as many more different genera are known. All these genera are, however, so closely allied that they are placed in the single family Belodontidae.

Fig. 92.—Restoration of Mystriosuchus,
an Upper Triassic phytosaur.

Fig. 93.—Skull of Mystriosuchus, a phytosaur: pm, premaxilla; m, maxilla; na, nasal; f, frontal; p, prefrontal; l, lacrimal; pf, postfrontal; po, postorbital; pa, parietal; sg, squamosal; qj, quadratojugal; pl, palatine; t, transverse; in, internal nares; en, external nares; pt, pterygoid; bs, basisphenoid; eo, exoccipital. (After McGregor.)

Fig. 94.—Dorsal vertebrae
of phytosaur: az, anterior zygapophysis;
pz, posterior zygapophysis; d,
c, articulations of rib.