Tetrapod
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| Tetrapods Fossil range: Late Devonian to Recent |
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Tetrapods (Greek tetrapoda, Latin quadruped, "four-legged") are vertebrate animals. Tetrapods have four feet, legs or leglike appendages, for example arms or wings. Amphibians, reptiles, dinosaurs, birds, and mammals are all tetrapods. Even though snakes do not have limbs, they are tetrapods because they evolved from animals with four limbs. The earliest tetrapods evolved from the Sarcopterygii, or lobe-finned fishes, into air-breathing amphibians in the Devonian period.
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[change] Evolution
Research by Jennifer A. Clack showed that the earliest tetrapods lived entirely in water. They could not live on land. Before this, it was believed that fish had first moved onto land - either looking for food (like modern mudskippers) or to find water when the pond they lived in dried out. It was believed that they later evolved legs, lungs, and other body parts to live better on land.
The first tetrapods are now thought to have evolved in shallow and swampy freshwater habitats during a time near the end of the Devonian, a little more than 365 million years ago.
Freshwater habitats were not the only places they could be found. Swampy habitats like shallow wetlands, coastal lagoons and river deltas also existed at this time. There is much to suggest that this is the kind of environment in which the tetrapods evolved. Early fossil tetrapods have been found in marine sediments. Also, because fossils of early tetrapods are found all around the world, they must have spread by following the coastal lines. This means they could not have lived in freshwater only.
[change] Living tetrapods
There are three main groups of living ("crown group") tetrapods. Each group also includes many extinct groups:
- Amphibia
- frogs and toads, newts and salamanders, and caecilians
- Sauropsida
- birds and modern reptiles
- Synapsida
- mammals
Snakes and other legless reptiles are tetrapods because they are evolved from ancestors who had four limbs. This is also true for caecilians and aquatic mammals.
[change] Classification
A partial taxonomy of the tetrapods:
- Phylum Chordata
- Class Sarcopterygii
- Superclass Tetrapoda
- Family Elginerpetontidae
- Family Acanthostegidae
- Family Ichthyostegidae
- Hynerpeton
- Family Whatcheeriidae
- Family Crassigyrinidae
- Family Loxommatidae
- Family Colosteidae
- Batrachomorpha
- Class Amphibia - Amphibians
- Subclass Lepospondyli
- Subclass Temnospondyli
- Subclass Lissamphibia - frogs, salamanders
- Class Amphibia - Amphibians
- Reptiliomorpha
