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The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus) [41] but this is a great deal smaller than the largest amphibian that ever existed—the extinct 9 m (30 ft) Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. [42]
Most scientists have concluded that all of the primary groups of modern amphibians—frogs, salamanders and caecilians—are closely related. Some writers have argued that the early Permian dissorophoid Gerobatrachus hottoni is a lissamphibian. [ 2 ]
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
Most labyrinthodonts had special sense organs in the skin, forming a lateral line organ for perception of water flow and pressure, like those found in fish and a number of modern amphibians. [10] This would enable them to pick up the vibration of their prey and other waterborne sounds while hunting in murky, weed filled waters.
Temnospondyli (from Greek τέμνειν, temnein 'to cut' and σπόνδυλος, spondylos 'vertebra') or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent.
Amphibians are notable as remnants of the first vertebrates capable of surviving in both aquatic and terrestrial environments. [1] The embryonic development of tailless amphibians is presented below using the African clawed frog ( Xenopus laevis ) and the northern leopard frog (Lithobates pipiens ) as examples.
The eyes of most frogs are located on either side of the head near the top and project outwards as hemispherical bulges. They provide binocular vision over a field of 100° to the front and a total visual field of almost 360°. [83] They may be the only part of an otherwise submerged frog to protrude from the water.
Most amniotes still require regular access to drinking water for rehydration, like the semiaquatic amphibians do. They have better homeostasis in drier environments, and more efficient non-aquatic gas exchange to power terrestrial locomotion , which is facilitated by their astragalus.