Ichthyostega(redirected from Ichthyostaga)
the most ancient and primitive genus of extinct amphibians. Ichthyostega measured approximately 1 m long. The structure of its skull as a whole was that of most labyrinthodonts, but there were characteristics typical of cross-opterygians (short snout with a rostral element, vestiges of bones of the gill cover, lateral organs enclosed in bony canals). The extremities and girdles were constructed like those of terrestrial animals, but the tail bore a fin with bony rays. Apparently Ichthyostega lived in water and never abandoned it for long. It is an important connecting link between terrestrial vertebrates and fish, and proves the origin of amphibians from crossopterygians. Remains of Ichthyostega and closely related forms have been discovered in Upper Devonian deposits of Greenland.