on their way to their present-day locations. The breakup of Pangaea created
three new bodies of water, including the Atlantic, Arctic, and Indian Oceans.
The climate was exceptionally mild for an unusually long time. One particu-
lar group of animals that excelled during these extraordinary conditions were
the reptiles. Besides conquering the land, some species went to sea and others
took to the air,occupying nearly every corner of the globe. Forests were also
extensive and covered large parts of the world with lush vegetation. In Ari-
zona’s Petrified Forest lie the fossilized remains of primitive Triassic-age
conifers (Fig. 132) that once flourished in the upland regions.
Early in the Triassic, Earth was recovering from a major ice age and an
extinction event that took the lives of more than 95 percent of all species.
Thus, the start of the Mesozoic marked a rebirth of life, and 450 new families
of plants and animals came into existence. However, instead of inventing
entirely new body plans as happened during the Cambrian explosion at the
beginning of the Paleozoic,species developed new variations on already estab-
lished themes.Therefore, fewer experimental organisms arose, and many lines
of today’s species evolved. Several major groups of terrestrial vertebrates made
their debut.These comprised the direct ancestors of modern animals, includ-Figure 130Triassic and
Jurassic beds at Silver Falls
Creek,Circle Cliffs region,
Garfield County, Utah.
(Photo by R. G. Luedke,
courtesy USGS)
Historical Geology