Page:Popular Science Monthly Volume 66.djvu/243

Rh reptiles will perhaps afford some consolation to those who still shrink from the ultimate consequences of Darwin's 'Descent of Man' As regards degrees of probability, it must be said that while the affiliation of the Plesiosaurs and Testudinata with the Anomodont group still requires confirmation, the connection of the mammals with certain Anomodonts (Theriodontia) is not only probable but is almost on the verge of actual demonstration, and at present it seems likely that the Karoo Desert of South Africa will enjoy the honor of yielding the final answer to the problem of the origin of mammals, which has has stirred comparative anatomists for the last sixty years.

Turning to the progeny of the other branch, the Permian diaptosaurs, we find them embracing (with the exception of the Testudinata and plesiosaurs) not only vast reptilian armies, marshaling into thirteen orders, mastering the distinctive Age of Reptiles (Triassic, Jurassic and Cretaceous), and surviving in the four existing orders of lizards, snakes, crocodiles and tuateras, but we also find them giving off the birds as their most aristocratic descendants. The bold conception of the connection between these thirteen highly diversified orders and a simple ancestral form of diaptosaur, typified by the Permian Palæoliatteria or the surviving Hatteria (tuatera of New Zealand) we owe chiefly to the genius of Baur, a Bavarian by birth, an American by adoption. Absolutely diverse as these modern and extinct orders are, whatever material for analysis we adopt, whether paleontological, anatomical or embryological, the result is always the same—the reconstructed primordial central form is always the little diaptosaurian lizard. The actual lines of connection, however, are still to be traced into the great radiations of the Mesozoic.

The chief impression derived from the survey of this second branch of the Reptiles in the Mesozoic as a whole is again of radiations and subradiations from central forms and the frequent independent evolution of analogous types. The aquatic life had been already chosen by the plesiosaurs and by some of the turtles, as well as by members of three diaptosaur orders (Proganosauria, Choristodera, certain Rhynchocephalia), two of which were surviving in Jurassic times. Yet it in independently again chosen by four distinct Triassic orders, always beginning with a fresh-water phase (Parasuchia, Crocodilia), and sometimes terminating in a high sea phase (Ichthyosauria, Mosasauria, Crocodilia). In the Jurassic period there were altogether no less than six orders of reptiles which had independently abandoned terrestrial life and acquired more or less perfect adaptation to aquatic life. Nature, limited in her resources of outfitting for aquatic life, fashioned so many of these animals into like form, it is small wonder that only within the last two years have we finally distinguished all the similarities of analogous habit from the similarities of real kinship.

The most conservative members of this second branch are the