Water Reptiles of the Past and Present

PARASUCHIA

The first known specimen of the order of reptiles now generally known as the Parasuchia was found in Würtemberg, Germany, in 1826 and very briefly and inadequately described[4] two years later by Professor George Jaeger. The specimen was a sorry one, and was sadly misinterpreted by Jaeger. It consisted chiefly of casts of the alveoli or sockets of a number of teeth, more or less connected by corroded or decomposed portions of the jaws. He recognized the casts as teeth of a peculiar reptile, but mistook the roots for crowns, and, naturally concluding that such obtuse teeth would be of use only for the mastication of vegetable food—about the last kind of food to which the phytosaurs were addicted—called the animal Phytosaurus, meaning plant saurian. Because of differences he observed in the shapes of the teeth he thought that they belonged to two distinct species, which he called cylindricodon and cubicodon; but the differences were due simply to the different positions they held in the jaws.

Fourteen years later Hermann von Meyer, the renowned German paleontologist, described and figured other remains of the same or an allied reptile under the name Belodon plieningeri. In subsequent papers during the next twenty-three years von Meyer very fully described and beautifully illustrated the skulls and other remains of this and other species, all of which he referred to the genus Belodon, the name by which for many years the animals were generally known in scientific literature. Von Meyer thought that he recognized in Belodon kapfii, the species most often figured in textbooks, the same animal that Jaeger had previously described.

Von Meyer was not at all certain about the relationships of his Belodon, though he recognized its affinity with the crocodiles. It was Huxley who, in a famous paper on the evolution of the crocodiles, published in 1875, united Belodon and another genus from the Trias of Scotland, which he called Stagonolepis, with the Crocodilia as representatives of the suborder Parasuchia, one of the three into which he divided the order. Huxley admitted that the relationships between the Parasuchia and the Mesosuchia or Eusuchia, the other suborders which he proposed, were not as intimate as those between the latter two, which were separated solely on the structure of the palate and vertebrae, as has been explained in chap. xv. As early as 1869 the late Professor Cope recognized certain forms which had been previously described from Carolina as belonging to the group, calling them Belodon, but it was not until 1896 that E. Fraas separated Belodon planirostris of von Meyer as a member of a distinct genus, to which he gave the name Mystriosuchus.

Here, as a part of the order Crocodilia, the phytosaurs remained till within very recent years, though there have been some mild protests against the association, especially by Marsh, Zittel, and Baur. The famous English paleontologist, Richard Owen, located the “Belodontia,” as the phytosaurs were often called, in his order Thecodontia, based chiefly upon the manner of the insertion of the teeth in sockets. But this has long since been shown to have little value in the classification of reptiles. Various authors have written about the phytosaurs in later years, notably Cope, Fraas, Huene, and Jaekel, but it was J. H. McGregor who first definitely separated the phytosaurs into a distinct order, in a careful revision of the American forms. He called the order Parasuchia, after Huxley, dividing into two suborders, the Phytosauria, after Jaeger, and the Aetosauria, a group which, for lack of a better place, had previously been classed with the Crocodilia, either as a member of the Parasuchia or as an independent suborder by Zittel (the Pseudosuchia). More recently Huene has shown that certain African reptiles from the Lower Trias had certain very definite characters entitling them to an independent position, for which he proposed the order Pelycosimia. Upon the whole, however, these characters seem to be primitive parasuchian, and the group may provisionally be placed in the order Parasuchia, as a third suborder, the Pelycosimia. The order Parasuchia, then, until we know much more about the latter two groups, may be conveniently divided into three suborders, the Phytosauria, Aetosauria or Pseudosuchia, and the Pelycosimia, all of Triassic age.

McGregor was quite right in retaining for the suborder the name Phytosauria, suggested by Jaeger in 1828, inappropriate as the word is etymologically, but was hardly justified in substituting the generic name Phytosaurus for the long and well-known Belodon, because it is quite impossible to say that Jaeger’s very fragmentary specimen upon which he based the genus Phytosaurus really is the same as Belodon. Professor Fraas very kindly showed the writer the original type-specimen of Jaeger, now preserved in the Stuttgart Museum, and both are agreed that it is impossible to prove the identity of Belodon and Phytosaurus from the very fragmentary and imperfect specimen. It is quite as probable, for instance, that Phytosaurus and Mystriosuchus are identical as that Phytosaurus and Belodon are. Unfortunately, this is not the only case in vertebrate paleontology where the fragmentary specimens to which names have been given are inadequate to determine the species, or genus, or even the family to which they belong; there have been very many such instances. The pioneers in paleontology were often justified in naming small and obscure fragments of bones, or single bones. One would be justified even yet in giving a name to an indeterminable fragment of a bird bone from the Triassic formation, because the discovery of a bird of any kind in that formation would be very important for science, even if its precise kind might never be recognized from the specimen. Nevertheless, the custom is a very reprehensible one when indiscriminately followed. For these reasons the writer disagrees with McGregor in substituting the inappropriate name Phytosaurus for Belodon, the name by which the most typical forms were so long known.

The Aetosauria, which have long been known from a marvelous specimen found in Würtemberg many years ago and described by the elder Fraas, need not detain us long. They were relatively small reptiles about two feet long, almost completely incased in a bony armor, and purely terrestrial in habit. The skull even yet is not perfectly known, and it is possible that when it is the group may have to be dissociated from the phytosaurs. The nostrils were not posterior, and the skull is short. Other specimens of the same group have been described from the Upper Triassic rocks of Massachusetts.

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.

In Belodon (Fig. 96), the earliest known and most typical genus, perhaps, the moderately elongated face has a high crest reaching nearly to its front end, and this type is known both from Europe and from New Mexico. Others have the face long and slender, even longer and more slender than in the ancient teleosaur crocodiles or the modern gavials. In some forms the teeth are cylindrical and slender throughout, and there may be as many as fifty on each jaw, or two hundred in all; while in others only the anterior teeth are cylindrical and the posterior teeth are flattened and serrate along their cutting edges. In the body not very great differences have been observed. Some are more slender than others, and there are minor differences in the shapes and sizes and numbers of the bony scutes along the back and on the throat.

But they are all alike in their essential characters, a very long beak with numerous teeth; the foremost ones on the expanded, more or less spoon-shaped front extremity, are more or less, sometimes greatly, elongated. The jaws may be likened to a long and slender pair of tongs with nipping teeth at the front end. The strong, long, and flattened tail is sufficient evidence that the phytosaurs were excellent swimmers, but, aside from that and the posterior location of the external nostrils, directly over the internal, few other aquatic adaptations are observed in the skeleton. There are no sclerotic bony plates about the eyes, or at least none have so far been discovered, although among the numerous known specimens they would confidently be expected were they really present in the skeleton; and the presence of bony armor negatives markedly aquatic habits.

Doubtless on the whole the habits of the phytosaurs were not very unlike those of the modern gavials, which they so strongly resemble in form, size, and general characters. But they differ very greatly from the gavials in the extreme posterior position of the nostrils, and in the greatly elongated teeth of the front end of the beak, teeth which must have had some especial and peculiar use. Nor is the position of the nares to be accounted for satisfactorily by reference to aquatic habits. It has been suggested that the creatures used the very long and slender beak in prodding and probing in the sand and mud for soft-bodied invertebrates, worms and the like, for which the teeth would be especially fitted; and that the posterior position of the nostrils may be in part, perhaps wholly, accounted for by this habit, which permitted the reptiles to breathe without extricating the beak from the mud or shallow waters. That the animals were wholly and intensely carnivorous in habit is attested by their teeth; although they are called “plant saurians,” they never had anything to do with plants in the way of food. Unfortunately so far no specimens have ever been found showing the remains of stomach contents, nor have any been found showing impressions of the form of the body or of any of its parts. Until such specimens are found, as they doubtless will be eventually, one can be less sure of the precise details in their life reconstructions. However, the skeleton is now known nearly completely, and this suffices to give a very approximately correct idea of what the animals were like when alive.