A
difference of elevation would, in such a world, make a great
difference in temperature and moisture.
Let us examine the animal record, however, before we come to any
conclusion. The chronicle of the later Cretaceous is a story of
devastation. The reduction of the cyeads is insignificant beside
the reduction or annihilation of the great animals of the
Mesozoic world. The skeletons of the Deinosaurs become fewer and
fewer as we ascend the upper Cretaceous strata. In the uppermost
layer (Laramie) we find traces of a last curious expansion--the
group of horned reptiles, of the Triceratops type, which we
described as the last of the great reptiles. The Ichthyosaurs and
Plesiosaurs vanish from the waters. The "sea-serpents"
(Mososaurs) pass away without a survivor. The flying dragons,
large and small, become entirely extinct. Only crocodiles,
lizards, turtle, and snakes cross the threshold of the Tertiary
Era. In one single region of America (Puerco beds) some of the
great reptiles seem to be making a last stand against the
advancing enemy in the dawn of the Tertiary Era, but the exact
date of the beds is disputed, and in any case their fight is soon
over.
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