Acanthostega
Clack remarks on how the lower jaw of Acanthostega shows a change from the jaws of fish. It differs in having a small number of larger teeth in the outer row and smaller teeth in the inner row. Research based on analysis of the skull suggests the species may have bitten directly on prey at or near the water's edge. Markey and Marshall compared the skull with the skulls of fish, which use suction feeding as the main way to catch prey, and creatures known to have used the direct biting typical of terrestrial animals. Their results indicate that Acanthostega was adapted for what they call terrestrial-style feeding. This strongly supports the hypothesis that the terrestrial mode of feeding first emerged in aquatic animals. If correct, this shows an animal specialized for hunting and living in shallow waters in the line between land and water. Newer research also indicates that it is possible Acanthostega evolved from an ancestor that had more terrestrial adaptations than itself.