Unveiling the Ancient Fossilized Skin: Insights into Life's Transition to Land

An ancient piece of rock extracted from a limestone quarry in Oklahoma holds the world’s most ancient fossil cast of skin.

The fossil is about 290 million years old and is known to have come from an early amniote, a branch of four-legged vertebrates that evolved from amphibians to include all birds, reptiles, and mammals. This is according to researchers who reported their results on January 11 in Current Biology. The fossil is 21 million years older than any other reported fossilized skin from the Paleozoic Era, a period ranging from 541 million to 252 million years ago marked by the diversification of onshore animal life.

“We now definitively have the oldest example of mummified skin,” says Ethan Mooney, a paleontologist from the University of Toronto Mississauga. “It provides valuable insight on how the earliest animals transitioned from water to land.”

The fossil cast, including exquisitely preserved skin impressions, was unearthed by fossil collectors Bill and Julie May at a quarry in Oklahoma, located in an ancient limestone cave system known as Richards Spur.

The fossils’ excellent state of preservation is due to the exceptional conditions in the cave. Remains were covered in fine sediments that reduced decay by excluding oxygen, and were exposed to iron-rich groundwater that helped to preserve tissues. In addition, the area was an old oil seep, allowing petroleum and tar to permeate and shield the remains from decay, while also giving them a black coloration.

The skin samples feature distinct scales of varied sizes, densities, and quantities. Mooney’s team suggests that the specimens could have originated from diverse parts of the amniote body and possibly from different animals as well.

Cross sections of the cast showed a thick outer skin layer, or epidermis. The evolution of a sturdy epidermis would have safeguarded early amniotes against environmental conditions, whilst also aiding in water retention.

Mooney says, the tough and uneven skin of ancient amniotes was "the first stage" which later led to the development of bird feathers and mammalian hair follicles.