Fossilized skin dating back approximately 290 years has been found. – He writes science news
The dark silver stone, taken from a limestone mine in Oklahoma, is the oldest skin fossil ever found in the world. The fossil is about 290 million years old and belongs to an early member of the amniotes. Amphipods are a branch of four-legged vertebrates that evolved from amphibians and include all reptiles, birds, and mammals. The researchers announced their discovery in the journal Current Biology on January 11. 21 million years ago the only fossilized skin ever reported dating from the Paleolithic period (541 million to 252 million years ago). During the Paleozoic era, animals descended to land and branched out.
Bill and Julie May, two fossil collectors, found the specimen along with other excellently preserved skin impressions in a quarry in the ancient Richard Speer limestone cave system in Oklahoma. The cave's special conditions contributed to the excellent preservation of the fossil. The bodies were buried in fine sediment, which excluded oxygen and slowed decomposition, and were exposed to iron-rich groundwater. Iron helps preserve tissue. There is also an old oil seep at the site. Oil and tar seeped through the remains, insulating them from the deteriorating conditions while they were painted black.
Skin specimens contain non-overlapping scales, although scale sizes, distribution and abundance vary. The samples are likely to come from different parts of the placenta's body, and perhaps from different animals. Cross sections of the specimen show a thick outer skin layer (epidermis). The development of strong skin protected early embryos from the elements while helping to retain water.
Surface innovation eventually led to the appearance of bird feathers and mammalian hair follicles. The first step was the bumpy foreskin.
(Source: Science News: https://www.sciencenews.org/)