The tetrapods are a group of animals characterized by having four limbs, which used to move or manipulation, attached to the trunk.
Not all tetrapods have four limbs. Some, like whales and snakes, have lost all or part of those four limbs that their ancestors had, but are still considered tetrapods because of their kinship.
Although amphibians were the first tetrapods to begin the conquest of the terrestrial environment, reptiles were the first to become totally independent of water, since from this class of animals, their embryos are surrounded by the amnion, a membrane that protects them . of desiccation and shock, and allows the development of the embryo inside an egg outside the water.
Tetrapods can be:
- Oviparous, such as the most primitive reptiles, birds, and mammals, and the embryos develop within an egg.
- Viviparous, like the most evolved mammals, marsupials and placentals, which do so within the mother's body.
- Ovoviviparous, they develop inside an egg but inside the body of the female. For example, some sharks and reptiles.
Almost all tetrapods are vertebrate animals that live in the terrestrial environment, such as pigeons, frogs, sparrows and cats, for example, but there are also tetrapods that have returned to the marine environment, such as dolphins, whales, sea turtles, seals, and sea lions, for example.
Tetrapods are classified into four classes :