Page 62 - The Restless Earth Fossils

Marking turning points in evolution 61

the cenozoic: MaMMals (and FloWers) rule
The Cenozoic saw the rise of all the major mammal groups,
including horses, whales, monkeys, apes, and human beings.
Flowering plants (also called angiosperms)—well, they flowered!
Grasses became an increasingly important part of ecosystems. The
Cenozoic began as a warm world that gradually cooled to produce
a series of ice ages separated by minor warm spells lasting a few
millennia. Human beings are living in such a warm spell now.

important Fossil sites
A site near Darmstadt, Germany, more than 50 million years
old, yields early mammals, birds, insects, and other creatures that
lived in or near a lake in a semitropical area. Along Baltic Sea
shores in Poland, Germany, and Denmark, amber (fossilized tree
sap) contains flowers and plant parts, insects, and other arthro-
pods. The Rancho La Brea Tar Pits (11,000 to 38,000 years old)
in the center of Los Angeles, California, have trapped mammoths,
dire wolves, saber-toothed cats, and a host of other animals in the
goo of natural asphalt. In the Rocky Mountains of the American
West, fantastic tropical animals emerge from today’s oil shales.

cenozoic eden: the green river Formation
About the time the last dinosaur died, the Rocky Mountains in
the middle of North America began their slow climb skyward.
After 20 million years had passed, water drained from the high-
lands all around to create a series of lakes in what is now western
Colorado, eastern Utah, and southwestern Wyoming. Forests of
palms, alders, sycamores, and chestnut trees sheltered bats, col-
lie-sized horses, lemurlike primates, clouds of insects, horned and
tusked Uintatheres, and seven-foot-tall predatory ground birds.
Lake Uinta at times covered 24,000 square miles (62,000 square
kilometers)—bigger than Michigan’s Great Lakes—and existed for
17 million years, leaving lake deposits 7,000 feet thick in places.
In 1856, Dr. John Evans collected and described the first fossil

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