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Ancient amphibians found in Iowa.

Ancient amphibians found in Iowa

Geologists in Iowa have discovered a large fossil bed containing the oldest well-preserved land vertebrates known to exist in North America. Dated at 335 million years old, from the Carboniferous period, these fossils of early amphibians will help scientists trace the evolutionary path from water to life on land.

"I would say it's a major discovery," says John R. Bolt of Chicago's Field Museum of Natural History. Worldwide, only 22 fossil sites of comparable age are known, and most of those have yielded limited numbers of fragmentary specimens. At the Iowa site, Bolt says, "the material is quite well preserved." He reports the find in the June 23 NATURE along with R.M. McKay and B.J. Witzke of Iowa's Geological Survey Bureau in Iowa City and M.P. McAdams of the William Penn College in Oskaloosa, Iowa.

The researchers found two types of tetrapods, or four-legged animals, that do not readily fit into any known species. These creatures reached about 3 to 5 feet in length and probably resembled giant salamanders, McKay says. While they had well-developed legs for walking on land, they apparently spent most of their time in the water. Of particular interest is an amphibian that was informally dubbed proto-anthracosaur. This newly identified animal combines advanced amphibian characteristics with features similar to those of the most primitive known tetrapods.

Paleontologists have long debated which form of fish spawned the first amphibians to crawl onto land. The proto-anthracosaur "may lead to some hypotheses as to what sort of fish ancestors we should expect for the early tetrapods," Bolt told SCIENCE NEWS.

In examining the fossil bed, the researchers also identified many fish species that may have served as food for the strong-jawed, toothy amphibians. However, McKay notes, "I don't know who was preying on whom because some of the fish were about 10 feet long. And they had big teeth."
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Author:Monastersky, Richard
Publication:Science News
Date:Jun 25, 1988
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