Reptilia
Classification and Evolution
The class Reptilia, also known as reptiles, is a group of cold-blooded vertebrates that includes turtles, lizards, snakes, alligators, and crocodiles. This class is characterized by their dry scaly skin and their ability to lay hard-shelled eggs on land. The evolution of reptiles dates back to about 310-320 million years ago during the Carboniferous Period.
Characteristics
Reptiles are tetrapods, meaning they have four limbs, with the exception of snakes. They have a strong, bony skeleton and their skin is covered in scales or scutes, which are made of keratin. Reptiles are ectothermic, meaning they rely on the environment to regulate their body temperature. They have a three-chambered heart, with the exception of crocodilians which have a four-chambered heart.
Reproduction
Reptiles reproduce sexually, with internal fertilization. Most reptiles lay eggs (oviparous) but some give live birth (viviparous). The eggs of reptiles are covered in a protective shell and are usually laid in a nest. The sex of the offspring in some species is determined by the temperature at which the eggs are incubated, a phenomenon known as temperature-dependent sex determination.
Diversity and Distribution
Reptiles are found in a wide range of habitats, from deserts to oceans, and on every continent except Antarctica. They are most diverse in the tropics and subtropics. There are over 10,000 species of reptiles, making them the second most diverse group of vertebrates after birds.
Conservation
Many species of reptiles are threatened by habitat loss, pollution, climate change, and overexploitation. Conservation efforts for reptiles include habitat protection, captive breeding programs, and legislation to protect endangered species.