T
his chapter examines the evolution of the dinosaurs and of the continents
during the Tr iassic period.The Triassic, from 250 to 210 million years
ago, marks the beginning of the Mesozoic era.The period was named for
a sequence of redbed and limestone strata in central Germany. All continents
joined into a single great continent called Pangaea,which supported a distinc-
tive suite of terrestrial plants and animals. In North America, continental sedi-
ments and redbeds add to the rugged beauty of Wyoming, Colorado, and Utah
(Fig. 130).At the end of the period,Pangaea began rifting apart into the present-
day continents, and massive amounts of basalt spilled onto the landscape.
During the late Triassic, large families of terrestrial animals died off in
record numbers.The extinction spanned a period of less than a million years
and was responsible for killing nearly half the reptile families. The dying out
of species forever changed the character of life on Earth and initiated the rise
of the dinosaurs (Fig. 131), one of biology’s greatest success stories.
THE DINOSAUR ERA
At the beginning of the Mesozoic, the continents consolidated into a super-
continent; at midpoint, they began to rift apart; and at the end, they were well
TRIASSIC DINOSAURS
THE AGE OF BIG BEASTS