PRESENT PROBLEMS OF PALEONTOLOGY. 237 



(Metopias) as between the existing stag of Europe and the wapiti deer. 

 Which branch of these primordial amphibians gave rise to the modern 

 frogs and salamanders we do not know. This and hundreds of similar 

 facts suggest the vital importance of paleogeography. 



As regards paleogeography, the great induction can be made that, 

 throughout the whole period of vertebrate evolution and until compara- 

 tively recent times, Europe, Asia and North America constituted one 

 continent and one life region, or Arctogsea (Huxley 1868, Blanford 

 1890), with which the continents of the southern hemisphere, namely, 

 Africa, South America and Australia, were intermittently, but not 

 continuously connected by land. A great southerly continent, Notogsea 

 (Huxley 1868), connected with a south polar Antarctica, now sub- 

 merged, is a theory very widely supported by zoologists and, I believe, 

 by botanists, although its existence is still denied by certain geographers 

 (Murray). We find Permian, Jurassic, late Cretaceous and early Ter- 

 tiary proofs of Antarctica in the fresh-water crustaceans (Ortmann), 

 in fresh- water fishes (Gill), in littoral mollusca (Ortmann), in rep- 

 tiles (Smith Woodward and Osborn), in birds (Forbes and Milne 

 Edwards), in worms (Beddard), in the Australian animals (Spencer), 

 in the fossil mollusca of Patagonia (Ortmann) and in the fossil mam- 

 mals of Patagonia (Ameghino). To marshal and critically examine 

 all this evidence and convert this most convenient Antarctic hypothesis 

 into an established working theory I consider one of the most pressing 

 problems of the day. 



Problem of the Source of the Reptiles and Mammals. 

 Pieturning from this geographical detour to paleontology as history, 

 we should first note that already in the Permian there was developed 

 such an astonishing variety and differentiation of the reptiles that we 

 must look to future discoveries in the Carboniferous to find the actual 

 points of descent of reptiles from the amphibia. These Permian and 

 Lower Triassic reptiles are of three kinds, comparable to a parent 

 (Cotylosauria) and two offspring (Anomodontia and Diaptosauria). 

 In the parent group (the Cotylosauria, or solid-skulled reptiles,) we 

 find so many fundamental similarities to the Stegocephalia, or solid- 

 skulled amphibia, that only by the possession of many parts of the body 

 can we surely ditinguish reptile from amphibian remains. The pri- 

 mordial reptile was probably altogether a land animal continuously using 

 its limbs in awkward progression, bringing forth its young by land-laid 

 eggs and probably possessing gills only as vestiges. These cotylosaurs 

 show very wide geographical distribution, South Africa, Siberia, Great 

 Britain and North America, and equally remarkable adaptive radia- 

 tions of habit into small and large, horned and hornless types, some 

 of which were certainly dying out branches, while others led into the 

 two offspring groups. 



