New knowledge about the eating habits of ancient amphibians

ScienceDaily covers a story about a new discovery about how the ancient species evolved.

Ancient Amphibians Evolved A Bite Before Migrating To Dry Land

Ancient aquatic amphibians developed the ability to feed on land before completing the transition to terrestrial life, researchers from Harvard University report this week in the Proceedings of the National Academy of Sciences.

Their work is based on analysis of the skulls of the first amphibians, which arose 375 million years ago, and their fish ancestors. The shapes of the junctions between adjacent skull bones -- termed "sutures" -- in the tops of these fish and amphibian skulls reveal how these extinct animals captured prey, say authors Molly J. Markey and Charles R. Marshall.

"Based on experimental data obtained from living fish, we found that the shapes of sutures in the skull roof indicate whether a fish captures its prey by sucking it into the mouth -- like a goldfish -- or by biting on it directly, like a crocodile," says Markey, a postdoctoral researcher and lecturer in Harvard's Department of Earth and Planetary Sciences. "A biting or chewing motion would result in a faint pushing together of the frontal bones in the skull, while a sucking motion would pull those bones ever so slightly apart. By comparing the skull roofs of living fish to those of early amphibians and their fishy ancestors, we were able to determine whether the fossil species fed by suction or by biting."

Using this approach, Markey and Marshall found that in one key transitional species, the aquatic amphibian Acanthostega, the shapes of the junctions between adjacent skull bones are consistent with biting prey. This finding, the scientists say, suggests that the water-dwelling Acanthostega may have bitten on prey at or near the water's edge.

"Going from the aquatic realm to land involved a series of adaptations to facilitate changes in locomotion, respiration, reproduction, sensation, and feeding," Markey says. "In water, suction is an efficient method of feeding, but it does not work in the much less dense air environment. Early terrestrial inhabitants would thus have had to develop the means for chomping prey."

I am not quite clear how this change our understanding of the evolution of amphibians, as the discovery seems quite consistent with what would have been expected. On the other hand, it is always nice to have such things confirmed.