In the rocks of the next great time division, the Mississippian, as we call it in America, corresponding more or less closely with the Lower or Subcarboniferous of other parts of the world, numerous footprints of amphibians have been discovered, but no fossil remains except a few from near its close in Scotland. From the Upper Carboniferous, or Pennsylvanian, however, not only numerous footprints but the actual skeletons, or impressions of skeletons, have long been known in Europe and America. Until recently all these footprints and skeletons were supposed to be exclusively amphibian. We are now almost sure that some of them belonged to reptiles of lowly type, the earliest coming from near the middle of the Pennsylvanian of Linton, Ohio. The amphibians of this period were, for the most part, salamander-like creatures of from a few inches to two or three feet in length. They all belong to the group collectively known as the Stegocephalia, except that very near the close of the period there appeared small, slender, small-legged aquatic forms which seem to be the ancient representatives of the real salamanders of modern times. Some of the Stegocephalians had become greatly specialized as legless, snake-like, or eel-like creatures.
Fig. 25.—Restoration of Seymouria, the most primitive of known cotylosaur reptiles. From the Permian of Texas, about two feet long.
By the beginning of Permian times tremendous changes had taken place in the land life. The small amphibians of the Carboniferous types dwindled away, soon to disappear, and their places were taken by others of peculiar types, for the most part larger; and by many and diverse kinds of reptiles—water reptiles, marsh reptiles, land reptiles, and even climbing tree reptiles. From the uppermost Carboniferous and Lower Permian rocks of the United States more than fifty genera and twice that many species of amphibians and reptiles have been made known in recent years, and doubtless as many more will be discovered in the future. From other parts of the world the history of reptiles of the Lower Permian is yet scanty, two or three forms from South America, as many more from Africa, and a half-dozen or so from Europe are all; and of these very few are known at all well.
Fig. 26.—Captorhinus, a cotylosaur reptile from Texas.
We classify all the known forms of reptiles from the Lower Permian under three or four orders, the Cotylosauria, Theromorpha or Pelycosauria, Proganosauria, and possibly the Protorosauria, but the classification is yet provisional, representing merely the present stage of our knowledge. The Proganosauria and Protorosauria, including distinctively aquatic reptiles, will be more fully described in the following pages. To give even a brief description of the more terrestrial reptiles of this, the earliest known reptilian fauna, would be beyond our purpose; the accompanying life restorations by the author of some of the more typical and better known forms, based upon nearly perfect skeletons, will suffice.
From the reptiles and amphibians of the Lower Permian of Texas and New Mexico to the ichthyosaurs of the Middle Triassic of California there is a complete gap in the records of the land life of North America. We do not know what became of all the remarkable animals of the Permian. There are few traces of their descendants elsewhere known, unless it be in South Africa. From the Middle and Upper Permian of South Africa and Russia, a marvelous reptilian fauna has been made known in recent years. More than a hundred species of six or seven groups, and at least two orders have been described. Of these the Cotylosauria are the continuation of the American order, but include more specialized forms, the Pareiasauria and the Procolophonia, all of them, like the more primitive American forms, characterized by the imperforate temporal region. The Therapsida, likewise, seem to be the continuation of the American Theromorpha, so closely allied to them that it is difficult to draw a distinguishing line between them. On the other hand, these African reptiles merge through the Theriodontia into the mammals in the Triassic. They are all terrestrial, crawling reptiles, except a few which are described on a later page under the Anomodontia.
Fig. 27.—Restoration of Labidosaurus, a cotylosaur reptile from Texas, about three feet long.