Early tetrapod likely ate on shore

From Ottawa, at a meeting of the Society of Vertebrate Paleontology

The skull structure of Acanthostega, a semiaquatic creature that lived about 365 million years ago, suggests that although the creature spent most of its time in the water, it fed on shore or in the shallows rather than in deep water.

Molly J. Markey, a paleontologist at Harvard University, examined the pattern of boundaries between skull bones in Acanthostega. The boundaries, called sutures, can have straight edges or jagged, interlocking edges.

The pattern of skull sutures in Acanthostega doesn’t match the one found in Polypterus, a modern fish that, like most fish today, captures its prey by slurping it in (SN: 4/24/04, p. 264: Hooking the Gullible), or the pattern found in Eusthenopteron, a fish that lived about 385 million years ago and seems to have been a suction feeder. Both creatures had a straight-edged suture running along the top center of its skull.

In contrast, the suture layout in Acanthostega‘s skull closely resembles the pattern found in the skull of Phonerpeton, an amphibian that lived and presumably fed on land around 300 million years ago. Markey has measured the strains across straight and jagged sutures in Polypterus skulls as the fish ate. From her results, she speculates that the Polypterus and Eusthenopteron pattern successfully resists the stresses that arise during slurping, while the Phonerpeton and Acanthostega pattern would better resist the stresses during grab-and-bite dining.

Therefore, Markey suggests that Acanthostega fed on shore or in shallow water.