A piece of dark rock found in a limestone quarry in Oklahoma is the oldest fossil skin ever found in the world.
The fossils are about 290 million years old and were once early members of amniotes, a group of four-legged vertebrates that evolved from amphibians and include all reptiles, birds and mammals, researchers said on Sept. 11. January in modern biology . . This is 21 million years older than the only other recorded fossilized skin from the Paleozoic era, which spans 541-252 million years ago, when animals moved along the coast and diversified.
"This is by far the oldest [known] piece of mummified skin," says paleontologist Ethan Mooney of the University of Mississauga in Toronto. It fits into the "great story of how the first animals left the water and came onto land."
Fossil collectors Bill and Julie May found the cast along with well-preserved skin impressions in a quarry in Oklahoma, an ancient limestone cave system known as Richards Spur.
Here, a special combination of cave conditions contributed to the impressive preservation of fossils. The bodies were buried in fine sediment, which excludes oxygen and slows decomposition, and were exposed to groundwater rich in iron, an element that helps preserve tissue. In addition, there was an oil spill at this place earlier. The oil and resin seeped into the remains, protecting them from decay and causing them to turn black.
All skin specimens have scales that do not overlap, although the size, location, and number of scales vary. Mooney's team suggests that the samples were taken from different parts of the amniote's body and possibly from different animals.
Sections of the model were found to have a thickened outer layer of skin, or epidermis. The development of a durable epidermis could have protected early amniotes from the elements and also helped them retain water.
This superficial innovation eventually led to the feathers of birds and the hair follicles of mammals. The hard, lumpy amniotic skin was "stage one," Mooney says.