reared up on their hind legs.Although most reptiles walked or ran on all fours,
by the late Permian, some smaller reptiles often stood on their hind legs when
they required speed and agility. The body pivoted at the hips, and a long tail
counterbalanced the nearly erect trunk. This stance freed the forelimbs for
attacking small prey and completing other useful tasks.
Reptiles have scales that retain the animal’s bodily fluids. In contrast,
amphibians have a permeable skin that must be moistened frequently.Another
major advancement over the amphibians was the reptiles’ mode of reproduc-
tion. Like fish, amphibians laid their eggs in water. After hatching, the young
fended for themselves, often becoming prey for predators. The reptiles’ eggs
had hard, watertight shells so they could be laid onto dry land. Reptiles belong
to a group known as amniotes, which also includes birds and mammals.
Amniotes are animals with complex eggs that evolved from the amphibians.
Reptile parents protected their young, which gave them a better chance of
survival, contributing to reptiles’ great success in populating the land.
Like fish and amphibians, reptiles are cold-blooded, a term that is mis-
leading since they draw heat from the environment. Therefore, the blood of a
reptile sunning on a rock can actually be warmer than that of a warm-blooded
mammal.A high body temperature is as important to a reptile as it is to a mam-
mal to achieve maximum metabolic efficiency. On cold mornings, reptiles are
sluggish and vulnerable to predators. They bask in the sun until their bodies
warm and their metabolism can operate at peak performance.
Reptiles require only about one-tenth the amount of food mammals need
to survive because mammals use most of their calories to maintain a high body
temperature. The total energy consumption of mammals is 10 to 30 times and
the oxygen intake is about 20 times that of reptiles the same weight. Conse-
quently, reptiles can live in deserts and other desolate places and flourish on small
quantities of food that would quickly starve a mammal of the same size.The gen-
erally warm climate of the Mesozoic was very advantageous to the reptiles and
aided them in colonizing the land. In contrast, the amphibians, which avoided
direct sunlight and were relatively cold and slow moving, were at a disadvantage.
Many early reptiles evolved into some of the most bizarre creatures. Per-
haps the strangest reptile that ever lived was Tanystropheus ,dubbed the “giraffe-
neck saurian.”The animal measured as much as 15 feet from head to tail and is
famous for its absurdly long neck, which was more than twice the length of the
trunk.As it matured, its neck grew at a much faster rate than the rest of its body.
Apparently, the reptile was aquatic because it could not possibly have supported
the weight of such a lengthy neck while on land.Tanystropheus probably
stretched its neck downward to scavenge bottom sediments for food.
The phytosaurs were large, heavily armored predatory reptiles with
sharp teeth.They resembled crocodiles with their elongated snouts, short legs,
and long tails but were not closely related to them.They evolved from the the-Historical Geology