DENVER A rock that sat untouched in a Pennsylvania museum's fossil collection for years has rare full-body imprints of not just one but three ancient amphibians.
Researchers found the imprints in sandstone rocks taken from the Mauch Chunk Formation in eastern Pennsylvania decades ago and stored in the Reading Public Museum. The body impressions of the salamander-like creatures are estimated to be 330 million years old, or about 100 million years before the first dinosaurs appeared.
Many ancient footprints have been found, but a full-body animal impression is unusual. The three impressions show the foot-long temnospondyls had webbed feet and smooth skin similar to modern-day amphibians, rather than armored bodies.
"The most remarkable thing about these is they exist at all. This is a very rare preservation," said John Bolt, curator of fossil amphibians and reptiles at The Field Museum in Chicago.
Research by Spencer G. Lucas, interim executive director of the New Mexico Museum of Natural History and Science, and others on the discovery was presented recently at The Geological Society of America's annual meeting in Denver.
"They're really some of the oldest body imprints of land-living amphibians," Lucas said. "They show you what the shape of the body was, they show you what the texture of the skin was like. These are things we don't know from bones. They're giving us new information about the anatomy of these long-extinct amphibians."
Two of the impressions, one larger than the other, were made next to each other, head to tail. Lucas speculated that could indicate social behavior or even courtship. The impressions also could have been made at different times, Lucas said.
"The real question is why do you have three close together on a rock," Lucas said.
David Fillmore, a retiree doing postgraduate work with Kutztown University geology professor Edward Simpson, found the impressions two years ago when the two were studying Mauch Chunk Formation footprints in a fossil collection at the Reading Public Museum.
"We looked at each other and were speechless. It's way beyond anything we could imagine finding," Fillmore said.