The Dinosaurs of Wyoming - Wyoming State Geological Survey ...

112 THE DINOSAURS OF WYOMING
smaller Mesozoic mammals that J. B. Hatcher collected
from the tops of ant heaps, commonly found in sandy areas.
If no ant heaps were present Mr. Hatcher would moye an ant
colony with a shovel, returning months later to gather the
minute fossils brought to the surface by the indefatigable insects.
As flesh and blood animals these Cretaceous mammals
were tiny, mouse-like in size. There is an idea occasionally
expressed that these small mammals hastened the extinction
of the dinosaurs by feeding on the reptilian eggs. We do not
know, however, whether or not all Dinosaurs laid eggs, and
it is probable that the Upper Cretaceous mammals did not
live in the same region. These mammals were eaters of roots
and other vegetation, eaters of insects, eaters of fruits, seeds,
and some were omnivorous. Some of them lived in trees, in
holes in the ground and among the rocks. Simpson says:
"The Mesozoic mammals constituted a little world of their
own. In their society were all the fundamental adaptive types
of a recent mammalian fauna. Some were chiefly insectivorous,
others predaceous, while still others were herbivorous. It is
the latter, the Multituberculata, which ... were the most successful
of Mesozoic mammals, for, appearing as early as the
very first, they occur at every mammal-bearing horizon in the
Mesozoic and even linger into the beginning of the age of mammalian
dominance without any remarkable change. They undoubtedly
owed this longevity to their complete and successful
adaptation, and also to the fact that they alone among Mesozoic
mammals did not have to face heavy reptilian competition
for food, as did the small insectivores and carnivores. \\Then
the more progressive plant-eating mammals of the Paleocene
appeared, the days of the Multituberculates \,"ere numbered.
Yet, so perfect was their adaptation, even then they lingered
on until the very moment when the Paleocene herbivores were
themselves doomed by the invasion of the modernized mammals,
beginning in the earliest true Eocene."