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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.
The tetrapods, including all large- and medium-sized land animals, have been among the best understood animals since earliest times. By Aristotle 's time, the basic division between mammals, birds and egg-laying tetrapods (the " herptiles ") was well known, and the inclusion of the legless snakes into this group was likewise recognized. [ 28 ]
Though stem-tetrapods originated in the preceding Devonian, it was in the earliest Carboniferous that the first crown tetrapods appeared, with full scaleless skin and five digits. During this time, amphibians (including many extinct groups unrelated to modern forms, referred to as "basal tetrapods") were the predominant tetrapods, and included ...
The traits enabled animals to check area on land for safe spots if being chased by a predator in water, as well as being useful for searching for prey items above the water. The water-based lateral line system was used substantially by these aquatic tetrapods to detect danger from predators. [ 2 ]
The first tetrapods are four-legged, air-breathing, terrestrial animals from which the land vertebrates descended, including humans. They evolved from lobe-finned fish of the clade Sarcopterygii , appearing in coastal water in the middle Devonian, and giving rise to the first amphibians .
The vomeronasal organ is found in many living tetrapods but not any fish, suggesting it originated in tetrapods only. Similarly, all tetrapods have parathyroid glands which other animals don't. Depending on the water depth at which a species lives, the visual perception of many aquatic species is better suited to darker environments than those ...
In animals such as the actinopterygian cavefish, the alternating footfalls and general layout of the ancient trackways was readily reproduced. [5] Similarly, modern lungfish, a sarcopterygian fish, were shown to be able to produce somewhat similar trackways through axial flexing rather than limb driven locomotion. [ 6 ]
Stegocephalians include both the modern lineage of limbed vertebrates (the crown group tetrapods, including modern amphibians, reptiles, birds and mammals) as well as a portion of the stem group, the earliest limbed tetrapodomorphs such as Ichthyostega and Acanthostega, which evolved in the Devonian period long before the origin of the crown group.