ing reptiles, mammals, and perhaps the predecessors of birds. (The true birds
did not appear in the fossil record for another 50 million years.)
The amphibians declined substantially when the great swamps began to
dry out toward the end of the Paleozoic. Populations of amphibians contin-
ued to fall during the Mesozoic. All large, flat-headed species became extinct
early in the Triassic. The group thereafter was represented by more modern
forms. Although the amphibians did not achieve complete dominion over the
land, their descendants the reptiles became the undisputed rulers of the world.
The reptiles were the leading form of animal life in the early Triassic.The
unusually warm climate of the Mesozoic contributed substantially to the suc-
cess of the reptiles. Not all reptiles were small creatures, however; some grew
upward of 16 feet long. The reptiles were better suited for living continuously
Figure 131Dinosaurs
were one of biology’s
greatest success stories.TRIASSIC DINOSAURS