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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 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. Acanthostega still had gills, so this would have been a later development. In an aquatically feeding animals, the ...
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]
New animals appeared in the warmer, drier regions near the equator as four-legged vertebrates called stem tetrapods evolved and split into groups that formed the basis for modern animals. But that ...
The creature existed some 40 million years before dinosaurs evolved. Researchers have long examined such ancient predators to uncover the origins of tetrapods: four-legged animals that clambered ...
Acanthostega is a partially aquatic tetrapod with developed limbs that shares features common with the earlier tetrapods, Panderichthys and Eusthenopteron. [3] Like Panderichthys , the humerus of Acanthostega is flattened dorso-ventrally, the intermedium terminates level with the radius, and the endoskeleton can be divided into stylopodium ...
The creature existed some 40 million years before dinosaurs evolved. Researchers have long examined such ancient predators to uncover the origins of tetrapods: four-legged animals that clambered onto land with fingers instead of fins and evolved to amphibians, birds and mammals including humans.
Phylogenetic analysis has shown Ichthyostega is intermediate between other primitive stegocephalian stem-tetrapods. The evolutionary tree of early stegocephalians below follows the results of one such analysis performed by Swartz in 2012. [9] Simplified phylogeny of the fish–tetrapod transition.