PRESENT PROBLEMS OF PALEONTOLOGY. 239 



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 diapto- 

 saurs, we find them embracing (with the exception of the Testudinata 

 and plesiosaurs) not only vast reptilian armies, marshaling into thir- 

 teen orders, mastering the distinctive Age of Eeptiles (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 con- 

 ception of the connection between these thirteen highly diversified 

 orders and a simple ancestral form of diaptosaur, typified by the Per- 

 mian Palceoliatteria 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 recon- 

 structed 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 Eeptiles in the Mesozoic as a whole is again of radiations and 

 subradiations from central forms and the frequent independent evolu- 

 tion 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 Ehyn- 

 chocephalia), 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 similari- 

 ties of analogous habit from the similarities of real kinship. 



The most conservative members of this second branch are the 



