PRESENT PROBLEMS 581 



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) l 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 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 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. 2 The bold con- 

 ception of the connection between these thirteen highly diversified 

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

 Permian Palceohatteria or the surviving Hatteria (tuatera of New 

 Zealand) we owe chiefly to the genius of Baur, 3 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 is 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 (Ich- 

 thyosauria, Mosasauria, Crocodilia). 4 In the Jurassic period there 



1 H. F. Osborn, Reclassification of the Reptilia, American Naturalist, Feb. 1904, 

 pp. 93-115. For the Diaptosauria, see Osborn on The Reptilian Subclasses Dia- 

 psida and Synapsida, Memoirs, American Museum of Natural History, vol. i, pt. 

 vin, Nov. 1903, p. 467 et seq. 



2 H. F. Osborn, Reconsideration of the Evidence for a Common Dinosaur-Avian 

 Stem in the Permian, American Naturalist, vol. xxxiv, no. 406, Oct. 1900, pp. 

 777-799. 



3 G. Baur, On the Phylogenetic Arrangement of the Sauropsida, Journal of Mor- 

 phology, vol. i, Sept. 1887, pp. 99-100. 



4 E. Fraas, Die Meer-Crocodilier (Thalattosuchia) des oberen Jura, Paleontogra- 

 phica, Bd. XLIX, Stuttgart, 1902. 



