FAUNAL RELATIONS OF EARLY VERTEBRATES 399 
New Jersey and Judith River faunas, we get some notable, though 
very dilatory appearances of European forms, the first land scaled 
reptiles, the first salamanders, and, with them, the first of the modern 
type of crocodiles, allied to the Borneo gavials. And with them also, 
the very much belated long-headed crocodiles of ancient type gave 
up the ghost, while the duck-billed and horned dinosaurs and the 
marine turtles, all distinctively American forms, the most distinctive 
of American Mesozoic vertebrates save thalattosaurs that we have, 
waxed and grew mighty. A new type for America of terrestrial 
turtles appeared. The polacanthid dinosaurs, long since unknown 
in Europe, continued to the very close (Paleoscincus). The mosa- 
saurs present a European genus (Mosasaurus), but one that was 
most certainly developed here in America, and emigrated. Finally 
at the close a new type of reptiles (Choristodera), with marked rhyn- 
chocephalian affinities, appears both here and in Europe, continuing 
on into the Tertiary, in forms almost generically identical; and the 
same may be said of the American crocodiles (Thoracosaurus) which 
reappear in Europe in the early Tertiary, with scarcely any differences. 
And all these facts indicate conclusively a continued intermigration 
between the eastern and western continents of land animals, with 
possibly some less freedom during late Cretaceous times. 
To summarize: ‘The Pennsylvanian fauna has nothing distinctive, 
at least till near the close; there must have been a continuous and 
free interchange of land animals with the eastern continent till near 
the close. Before its close, it had already diverged and certain true 
reptiles had appeared. Before the beginning of Permian times an 
interruption of migration occurred, producing a complete and con- 
tinuous isolation of the Permian American fauna. With the close 
of these times a long interval elapsed, during which physical condi- 
tions were almost uniform over a large part of the Rocky Mountain 
area at least; during which interval we have no records of land or 
freshwater life, but which is represented in part by marine forms of 
remarkable character, possibly in part derived from American ances- 
tors. With the reappearance of land forms in the Upper Trias we 
find certain evidence of free migrations again, with the closest rela- 
tionships between eastern and western forms, none of which could 
have been derived, immediately at least, from the known American 
