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Ichthyostega (from Greek: ἰχθῦς ikhthûs, 'fish' and Greek: στέγη stégē, 'roof') is an extinct genus of limbed tetrapodomorphs from the Late Devonian of what is now Greenland. It was among the earliest four-limbed vertebrates ever in the fossil record and was one of the first with weight-bearing adaptations for terrestrial locomotion.
The order Ichthyostegalia was erected for Ichthyostega, and contained until the 1980s only three genera (Ichthyostega, Acanthostega and Tulerpeton).While Ichthyostegalia in principle contain the most basal of animals with toes rather than fins, Clack and Ahlberg uses it for all finds more advanced than Tiktaalik (the closest relative of tetrapods known to have retained paired fins rather than ...
The mandibles were also unique in the fact that they possessed a single elongated hole along their inner surface, known as an exomeckelian foramen (or a meckelian fenestra). Earlier stegocephalians like Ichthyostega possessed a subtle slit in the mandible, while most later groups had a series of smaller, well-defined holes. [1]
Ichthyostega (hindleg) 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 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 oldest near-complete tetrapod fossils, Acanthostega and Ichthyostega, date from the second half of the Fammennian. [56] [57] Although both were essentially four-footed fish, Ichthyostega is the earliest known tetrapod that may have had the ability to pull itself onto land and drag itself forward with its forelimbs. There is no evidence that ...
Ichthyostegalia, the primarily aquatic primitive labyrinthodonts such as Acanthostega, Ichthyostega, Tulerpeton, and probably loxommatids. [1] Both Ichthyostegalia and Labyrinthodontia constitute paraphyletic evolutionary grades rather than clades, with amniotes and modern amphibians branching off at some point from the latter.
Ichthyostega and Acanthostega had paddle-like polydactyl feet with stout bony toes that also would have enabled them to drag themselves across land. The aquatic ichthyostegalians flourished in tidal channels and swampland through the remainder of the Devonian, only to disappear from the fossil record at the transition to the Carboniferous .