FAUNAL RELATIONS OF EARLY VERTEBRATES 169 



America, during these and later times, it is impossible to say just what 

 became of it, but certainly, with the close of the Permian time, so far 

 as our knowledge yet goes, it was completely blotted out of our records. 



How much longer this Permian isolation continued it is of course 

 impossible yet to say, since the gap in our records to the Upper Trias- 

 sic is complete and absolute, at least so far as distinctively land forms 

 are concerned. Dr. Merriam has brought to light within recent 

 years from the Pacific regions a comparatively rich and varied marine 

 vertebrate fauna of the Middle and Upper Trias, but it does not throw 

 much light on continental faunal conditions. The remarkable 

 demonstration of evolutional characters presented by the numerous 

 ichthyosaurs which he has discovered indicates, it seems to me, a 

 dispersal center of these animals, a group which must have been 

 derived from the most primitive of reptiles, such indeed as the Per- 

 mian fauna of x'Vmerica presents; and they may have been the direct 

 descendants of that fauna. With them, moreover, is associated a 

 remarkable new group of reptiles, the thalattosaurs, of almost sub- 

 terrestrial type, unknown elsewhere in the world, a form which may 

 have arisen from Lower Triassic land reptiles of true rhyncho- 

 cephalian afitinities, the first indication of this type, I believe, in 

 America. Where their ancestors came from we cannot say, but I 

 believe that they were immigrants, since we know of nothing that 

 could have been their progenitors from the Permian of America. 



With the land fauna of the Upper Trias of America we have again 

 the most astonishing proofs of an intermingling of European and 

 American faunas, an opening-up of some broad land connection which 

 had been interrupted during Permian times. In the phytosaurs 

 and the nearly contemporaneous thalattosaurs of the Pacific Triassic 

 we have the first definite indication of the great archosaurian group 

 of reptiles, already represented since early Permian times in Europe. 

 Both they and the associated labyrinthodonts, which had been wholly 

 absent since Carboniferous times, show the most intimate affinities 

 with the European types, proving beyond doubt the equivalency 

 of the deposits yielding them with the Keuper of Europe. And, also 

 associated with them, are true dicynodonts — of this I have no doubt — 

 forms intimately allied to those of similar age in the Trias of South 

 Africa, the first representatives in America of another great group 



