Reptiles are cold-blooded, air-breathing vertebrates, a group that includes snakes, lizards, turtles, tortoises, crocodiles, and alligators. Most hatch from eggs. Many scientists believe that both mammals and birds evolved from this class of animals, and all three are part of a group called Amniota, which have been the dominant land vertebrates for over 340 million years, since the Carboniferous era. The evolution of the amniote egg was a critical innovation that allowed animals to travel substantial distances from water for the first time in planetary history. As adults, reptiles are typically protected by scales.
The first reptile is believed to be the Hylonomus (“forest mouse”), which lived 315 million years ago in what is now eastern Canada. It was small, about 8 to 12 inches (20 to 30 cm) in length, and consumed insects. Around 230 million years ago, during the Triassic period, new, larger animals — the first dinosaurs — evolved, and these would go on to dominate terrestrial ecosystems for 160 million years, until they were wiped out during the Cretaceous-Tertiary extinction event 65 million years ago. Because of their dominance during this time, the Mesozoic Era is often called “the Age of Reptiles”.
During this period, the group set various impressive records:
- Largest carnivore — Spinosaurus, 60 ft (18 m) long, 9.9 short tons (9 metric tons);
- Longest animal ever — Amphicoelias fragillimus, 200 ft (62 m);
- Heaviest animal ever — Bruhathkayosaurus, 242.5 short tons (220 metric tons).
Being cold-blooded, reptile metabolism is dependent on the temperature of the environment, and snakes and lizards will often be seen sunning themselves on rocks or in trees. On the plus side, these animals require less food than others, and some can go weeks without a meal. Many are omnivores, eating anything they can find, while others focus on insects, and others, like crocodiles, are generalized carnivores.
Today, the Earth’s ecosystems are dominated by animals rather than reptiles, although the latter are still common. One reptile, the tortoise, is among the longest-living vertebrates ever, with a record of 188 years old. This is only surpassed by the Koi fish, which can live as long as 226 years. Another reptile, the crocodile, is one of the largest living animals, with a record length of 28.2 feet (8.6 meters).