A dark sliver of rock extracted from an Oklahoma limestone quarry holds the distinction of being the oldest-known fossilized skin, dating back almost 290 million years. This remarkable find belongs to an early member of the amniotes, a group that encompasses reptiles, birds, and mammals, originating from amphibians. Published in Current Biology on January 11, researchers state that this discovery surpasses the age of the only other documented fossilized skin from the Paleozoic Era, a period spanning 541 million to 252 million years ago when animals transitioned to land.
Paleontologist Ethan Mooney from the University of Toronto Mississauga describes this fossil as definitively the oldest mummified skin, contributing to the broader narrative of the first animals transitioning from water to land. Discovered by fossil collectors Bill and Julie May in an ancient limestone cave system known as Richards Spur, the fossils benefited from unique cave conditions. The fine sediments in which the corpses were buried excluded oxygen, slowing decay, and exposure to iron-rich groundwater aided in tissue preservation. Additionally, the site was an ancient oil seep, with petroleum and tar sealing and staining the remains.
Analyses of cast cross sections revealed a thickened outer skin layer, or epidermis, indicating a robust protection mechanism for early amniotes against the elements while retaining water. The skin samples exhibit nonoverlapping scales of varying sizes, distributions, and abundances, likely originating from different parts of the amniote body and possibly different animals.
Mooney’s team suggests that this tough and bumpy amniote skin represents the initial stage, eventually leading to the development of bird feathers and mammalian hair follicles. This discovery sheds light on the evolutionary journey of animals from water to land. The study, published online on January 11, 2024, in Current Biology, is supported by readers’ contributions to quality science journalism.
