FAUNAL RELATIONS OF EARLY VERTEBRATES 395 
dence of the great phyla of archosaurian and synaptosaurian reptiles 
here, for I, for one, am pretty thoroughly convinced that the Pely- 
cosaurs have no genetic relationship with either of these groups. The 
origin of the branch leading to the mammals, so far as our knowledge 
yet goes, was in Africa; there is nothing to prove that it was in 
North America. What then became of the Permian land fauna of 
North America? Not a trace of it is found later in the Mesozoic land 
fauna of America. Until we know more of the land fauna of South 
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 America 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 affinities, 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 
