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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.
However, most tetrapod species today are amniotes, most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous. The key innovation in amniotes over amphibians is the amnion , which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water.
Nine tetrapod trackways from three sites have been reported from the Valentia Slate Formation of Valentia Island, Ireland. [ 2 ] [ 3 ] The Valentia Slate Formation is composed mostly of purple coloured fine-grained sandstones and siltstones interpreted to represent a fluvial setting.
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]
That means tetrapods may have thrived in colder climates earlier than scientists expected, prompting more questions about how and when they took over the Earth. “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 transition from fins to limbs occurred once an endoskeleton entered the base of the fin, as seen in today's lungfish. [21] This is thought to have originated in the group Sarcopterygians, including osteolipiforms like Eusthenopteron, due to the homology of the tetrapod forelimb and the osteolepiform fin endoskeleton. [21]
Colosteus is an extinct genus of colosteid tetrapod from the Late Carboniferous (late Westphalian stage) of Ohio.Its remains have been found at the Linton site in Saline Township, Ohio, where it is one of the most common tetrapods, [1] and at the Five Points site in Mahoning County, Ohio. [2]
Colosteidae is a family of stegocephalians (stem-group tetrapods) that lived in the Carboniferous period. [1] They possessed a variety of characteristics from different tetrapod or stem-tetrapod groups, which made them historically difficult to classify.