The period between the end of the Triassic and the beginning of the
Jurassic was one of the most exciting times in the history of land vertebrates.
In the late Triassic, all the continents were joined only at their western ends
with Laurasia in the north and Gondwana in the south. Nonetheless, animal
life on Laurasia was becoming distinct from that on Gondwana. A land bridge
connecting Laurasia to the Indochina microcontinent might have been the
last link, enabling the migration of animals when the two blocks collided as
the Triassic drew to a close.
At the end of the Triassic, about 210 million years ago, a huge mete-
orite slammed into Earth, creating the 60-mile-wide Manicouagan impact
structure in Quebec, Canada (Fig. 140). The gigantic explosion appears to
have coincided with a mass extinction over a period of less than a million
years that killed off 20 percent or more of all families of animals, including
nearly half the reptile families. In the ocean, ammonoids and bivalves were
decimated, and the conodonts completely disappeared. The extinction for-
ever changed the character of life on Earth and paved the way for the rise
of the dinosaurs.
Almost all modern animal groups, including amphibians, reptiles, and
mammals, made their debut on the evolutionary stage at this time. This was
also when the dinosaurs achieved dominance over Earth and held their
ground for the next 145 million years. Afterward, another large meteorite
Figure 140The
Manicouagan impact
structure, Quebec,Canada.
(Photo courtesy NASA)TRIASSIC DINOSAURS