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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.
Tetrapod-like vertebrates first appeared in the Early Devonian period, and species with limbs and digits were around by the Late Devonian. [63] These early "stem-tetrapods" included animals such as Ichthyostega, [2] with legs and lungs as well as gills, but still primarily aquatic and poorly adapted for life on land.
Tulerpeton is considered one of the first "tetrapods" (in the broad sense of the word) to have evolved.It is known from a fragmented skull, the left side of the pectoral girdle, and the entire right forelimb and right hindlimb along with a few belly scales.
In January 2010, a group of paleontologists published a paper which showed that the first tetrapods appeared long before any known fossils of Tiktaalik or other elpistostegids. [2] This paper was accompanied by extensive supplementary material [3] and also discussed in a Nature documentary on the origin of tetrapods.
The fins evolved into the legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. The braincase of lobe-finned fish primitively has a hinge line, but this is lost in tetrapods and lungfish.
“The early story of the first tetrapods is much more complex than we thought,” said co-author Claudia Marsicano at the University of Buenos Aires, who was part of the research.
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 .
Innovations conventionally associated with terrestrially first appeared in aquatic elpistostegalians such as Panderichthys rhombolepis, Elpistostege watsoni, and Tiktaalik roseae. Phylogenetic analyses distribute the features that developed along the tetrapod stem and display a stepwise process of character acquisition, rather than abrupt. [1]