What are amphibians? (with photos)

Amphibians, like tree frogs, are cold-blooded, non-amniotic tetrapods that spend at least part of their lives on land.

An amphibian is any cold-blooded, non-amniotic (no eggs in shell) tetrapod animal that spends at least part of its time on land. Living examples include toads, frogs, salamanders, newts, and caecilians. There are only about 6,200 living species described by science, but there are many extinct amphibians in the fossil record. Of the three amphibian subclasses (Labyrinthodonti, Lepospondyli, Lissamphibia), only one, Lissamphibia, exists. Amphibians are far less successful today than in the geological past, having been overtaken by reptiles and mammals.

A salamander is an amphibian.

Amphibians are animals that enter and exit the water. Without scales like reptiles, they are more prone to drying out and therefore most species require frequent dips to stay moist. With the exception of a few species of frogs, these animals rely on freshwater puddles to lay their eggs. These eggs stay in the water, with some entering into symbiotic relationships with single-celled algae. After a few days, these eggs hatch into tadpoles, the larval form of frogs, which swim through the water, eating debris. Through a process called metamorphosis, these tadpoles transform into adult frogs.

Salamanders are a type of amphibian.

These animals are most closely related to mammals that are still in the larval stage. Other tetrapods go through their larval stage in the egg or uterus and emerge as small versions of the adult form. This can be seen in some tropical frogs, which lay their eggs on the forest floor and hatch into a miniature adult form.

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The first amphibian was also the first tetrapod. An animal that lived about 365 million years ago, the Acanthostega, is often cited, although there were several early tetrapods that lived around the same time. Acanthostega looked like a salamander, with eight digits on each limb. It is thought that the limbs initially evolved to traverse root-choked swamps and eventually became strong enough to be used in incursions on land. For their combination of characteristics of fish and tetrapods, some of the first land animals were called fishapods. For about 25 million years, amphibians were the only terrestrial tetrapods and vertebrates, until the evolution of amniotes (reptiles) with animals like Casineria, which lived 340 million years ago.

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