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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.
Pederpes, a tetrapod from the Early Carboniferous period, also has hindlimbs containing five digits that are rotated to face anteriorly. [2] Unlike previous tetrapods, who have been only partially adapted to land, Pederpes has the novel ability to bend its limbs and propel itself forwards in a terrestrial setting.
The tetrapod tongue is built from muscles that once controlled gill openings. The tongue is anchored to the hyoid bone, which was once the lower half of a pair of gill bars (the second pair after the ones that evolved into jaws). [89] [90] [91] The tongue did not evolve until the gills began to disappear.
Tiktaalik, a lobe-finned fish with some anatomical features similar to early tetrapods. It has been suggested to be a transitional species between fish and tetrapods. [81] 365 Ma Acanthostega is one of the earliest vertebrates capable of walking. [82] 363 Ma By the start of the Carboniferous Period
The first tetrapods appeared in the fossil record over a period, the beginning and end of which are marked with extinction events. This lasted until the end of the Devonian 359 mya. The ancestors of all tetrapods began adapting to walking on land, their strong pectoral and pelvic fins gradually evolved into legs (see Tiktaalik). [38]
An informal term with a broader meaning is stem tetrapod, a stem group consisting of all species more closely related to modern tetrapods than to lungfish, but excluding the crown group. This group includes both traditional "labyrinthodonts" as well as more basal tetrapodomorph fish, though its total content is a matter of some uncertainty, as ...
The other groups of tetrapods considered more closely related to amniotes are put in the superorder Reptiliomorpha. [ 6 ] The phylogenetic relationships of Paleozoic tetrapods have not yet been worked out with certainty, and the validity of Batrachomorpha as a clade depends on where other amphibians and early amniotes fit on the evolutionary tree.
Embolomeri is an order of tetrapods or stem-tetrapods, possibly members of Reptiliomorpha. Embolomeres first evolved in the Early Carboniferous (Mississippian) Period and were the largest and most successful predatory tetrapods of the Late Carboniferous (Pennsylvanian) Period. They were specialized semiaquatic predators with long bodies for eel ...