CROSSING A CLIMATE THRESHHOLD
Mysterious Fossil Mammals
The most remarkable thing about this greenhouse era in North America was
the sudden diversification of modern mammals from just a few predecessors.
Ancestors of today's barnyard residents-cows, pigs, and sheep-roamed among
tropical ferns and palm trees, along with the early relatives of deer,
camels, and hippos. Rhinos and miniature horses galloped across the
landscape. And cat-sized primates with large eyes and long tails jumped
from tree to tree catching insects.
Paleontologists had long wondered whether climatic changes led to this
flourishing menagerie. Now Koch and Zachos have evidence implying that the
new mammals were ushered into North America by a quick pulse of high
temperatures in the already warm world. To get that evidence, the pair had
to connect clues from land and sea...