BOSTON, Massachusetts -- Prehistoric aquatic amphibians developed the ability to feed on land well before they became terrestrial reports a new study in the early online edition of Proceedings of the National Academy of Sciences (PNAS).
The research, conducted by Harvard University biologists Molly J. Markey and Charles R. Marshall, is based on analysis of 375-million-year-old skulls of the first amphibians and their fish ancestors. The researchers say the "shapes of the junctions between adjacent skull bones" reveal how these extinct animals captured prey.
"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," said Markey. "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."
Markey and Marshall say their work shows that "in one key transitional species, the aquatic amphibian Acanthostega, the shapes of the junctions between adjacent skull bones are consistent with biting prey," suggesting that the species may have attacked 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 said. "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."
"The analysis suggests that amphibians evolved a bite before emerging onto land as fully terrestrial animals," she added.
CITATION: Molly J. Markey and Charles R. Marshall (2007). Terrestrial-style feeding in a very early aquatic tetrapod is supported by evidence from experimental analysis of suture morphology. PNAS Online Early Edition for the week of April 16-20, 2007. www.pnas.orgcgidoi10.1073pnas.0611256104
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