† Ichthyostegalia Säve-Söderbergh, 1932
Ichthyostegalia is an order of extinct amphibians, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade.
The group appeared in early or middle Devonian. They continued to thrive as denizens of swampland and tidal channels throughout the period. They gave rise to the Temnospondyli and then disappeared at the transition to the Carboniferous.
As first described, the order's sole member was Ichthyostega, from which the group takes its name. Ichthyostega was seen as transitional between fish and the early Stegocephalians, in that it combines a flat, heavily armoured stegocephalian skull with a fishlike tail bearing fin rays. Later work on Ichthyostega and other Devonian Labyrinthodonts shows that they also had more than 5 digits to each foot, in fact the whole foot being fin-like. Acantostega, later found in the same locations, appears to have had a soft operculum and both it and Ichthyostega possessed functional internal gills as adults.
The Ichthyostegalians were all rather large, adult size was on the order of a meter or more. Their heads were flat and massive, with a host of labyrinthodont teeth. They were carnivorous and may have fed on washed ashore carcasses of fish and other marine life, and hunted unwary arthropods and other invertebrate life along the tidal channels of the coal swamps. As adults, the animals would have been heavy and clumsy on land, and would probably appear more as fish that occasionally went ashore rather than proper land animals.
1. ^ Niedźwiedzki & al. (2010): Tetrapod trackways from the early Middle Devonian period of Poland. Nature no 463, pp 43-48 DOI: 10.1038/
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