What animals are considered tetrapods?
Tetrapods include all land-living vertebrates, such as frogs, turtles, hawks, and lions. The group also includes a number of animals that have returned to life in the water, such as sea turtles, sea snakes, whales and dolphins, seals and sea lions, and extinct groups such as plesiosaurs, ichthyosaurs, and mosasaurs.
In a nutshell, the “fish–tetrapod transition” usually refers to the origin, from their fishy ancestors, of creatures with four legs bearing digits (fingers and toes), and with joints that permit the animals to walk on land.
Why did fish evolve to tetrapods?
Experts differ about the environmental pressures that prompted lobe-finned fish to evolve into walking, breathing tetrapods, but one theory is that the shallow lakes and rivers these fish lived in were subject to drought, favoring species that could survive in dry conditions.