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 inhabitan