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| Tetrapods
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Synapsida Sauropsida Amphibia
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A tetrapod ( Greek tetrapoda, "four-legged") is a vertebrate animal having four feet, legs or leglike appendages. Since amphibians, reptiles, dinosaurs and mammals are all tetrapods, and even birds and snakes are tetrapods by descent, the term is only really useful in describing the earliest tetrapods, which radiated from the Sarcopterygii, or "lobe-finned" fishes, into air-breathing amphibians in the Devonian period.
The Latin version of "tetrapod" is " quadruped," meaning any four-legged creature.
The first tetrapods evolved in shallow and swampA swamp is a wetland that features permanent inundation of large areas of land by shallow bodies of water, generally with a substantial number of hummocks, or dry-land protrusions. Swamps usually are regarded as including a large amount of woody vegetatioy freshwater habitats, towards the end of the Devonian, a little more than 360 million years ago. By the late Devonian, land plantGreen algae land plants (embryophytes non-vascular embryophytes Hepatophyta liverworts Anthocerophyta hornworts Bryophyta mosses vascular plants (tracheophytes seedless vascular plants Lycopodiophyta clubmosses Equisetophyta horsetails Pteridophyta "true"s had stabilized freshwater habitats, allowing the first wetlandFlorida, USA, with an endangered American Crocodile. In physical geography, a wetland is an environment "at the interface between truly terrestrial ecosystems. and truly aquatic systems. making them different from each yet highly dependent on both" (Mitsc ecosystemIn ecology, an ecosystem is a community of organisms (plant, animal and other living organisms also referred as biocenose) together with their environment (or biotope), functioning as a unit. The term ecosystem first appeared in a 1935 publication by thes to develop, with increasingly complex food webs that afforded new opportunities.
Primitive tetrapods developed from an osteolepiform Sarcopterygian. The "living fossil" coelacanthLatimeria chalumnae Latimeria menadoensis Coelacanths (pronounced see-le-canth, meaning "hollow spine" in Greek), are lobe-finned fish with the pectoral and anal fins on fleshy stalks, and the tail fin divided into three lobes, the middle one of which als is a lobe-finned fish that had already developed adaptations of fins with fleshy bases and boneFor other uses of the word "bone", see bone (disambiguation). Gray's illustration of a human femur, a typically recognized bone. Bone refers either to a hardened connective tissue or to one of the individual structures, or organs, into which it is formed,s. They used these fins as paddles in shallow water habitats choked with plants and detritus. The universal tetrapod characteristics of front limbs that bend backward at the elbow and hind limbs that bend forward at the knee can plausibly be traced to early tetrapods living in shallow water.
The evolution of the air-breathing lung from the primitive swim bladder of lobe-finned fishes has not yet been worked out in detail. However, functioning internal gills were present in at least one late Devonian tetrapod, Acanthostega .
Nine genera of Devonian tetrapods have been described, several known mainly or entirely from lower jaw material. All of them were from the European-North American supercontinent that comprised Europe, North America and Greenland. The only exception is a single Gondwanan genus, Metaxygnathus , which has been found in Australia.
The first Devonian tetrapod identified from Asia, was recognized from a fossil jawbone reported in 2002. The Chinese tetrapod Sinostega pani was discovered among fossilized tropical plants and lobe-finned fish in the red sandstone sediments of the Ningxia Hui Autonomous Region of northwest China. This finding substantially extended the geographical range of these animals and has raised new questions about the worldwide distribution and great taxonomic diversity they achieved within a relatively short time.
These earliest tetrapods were not terrestrial. The earliest confirmed terrestrial forms are known from the early Carboniferous deposits, some 20 million years later. Still, they may have spent very brief periods out of water and would have used their legs to paw their way through the mud.
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