Reptiles are cold-blooded, air-breathing vertebrates which include snakes, lizards, turtles, tortoises, crocodiles, and alligators. Most reptiles hatch from eggs. Both mammals and birds evolved out of reptiles. 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 which allowed animals to travel substantial distances from water for the first time in planetary history. In adulthood, reptiles are protected by scales.

The first reptile was 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 reptiles – 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 the Age of Reptiles, the group set various impressive records, including largest carnivore (Spinosaurus, 18 m/60 ft long, 9 tonnes), longest animal ever (Amphicoelias fragillimus, 62 m/200 ft), and heaviest animal ever (Bruhathkayosaurus, 220 tonnes). The only real competition for the latter two is the blue whale.

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, reptiles require less food than animals, and some can go weeks without a meal. Many reptiles 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 mammals 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 8.6 meters (28.2 feet).