This 294-Million-Year-Old Fossil Preserved Something Scientists Almost Never Find

It’s a big year for the do-it-all butthole known as the cloaca: the all-purpose pee, poop, and reproductive chute found in birds, reptiles, amphibians, and even a few mammals. Earlier this year, researchers identified what appears to be the first fossilized imprint of a reptilian cloaca. Now, according to a new study published in iScience and reported by IFLScience, researchers have found evidence of another cloaca, this one belonging to a 294-million-year-old relative of mammals.

Scientists from Berlin’s Museum für Naturkunde were studying fossilized footprints and a tail drag left behind by Dimetropus, an ancient synapsid that lived long before the dinosaurs. They noticed two rows of raised scales near the base of the tail that surrounded what looks like the imprint of a cloaca.

This appears to be the oldest known evidence of a cloaca in the mammalian lineage, and the first found in a synapsid trace fossil.

Or, to put it another way, it’s the earliest known evidence of a mammal having a multipurpose butthole.

What Makes This Fossilized Cloaca Find So Impressive

Scientifically speaking, the finding also suggests that early tetrapods may have had vertically oriented cloacas instead of the horizontal arrangement seen in many modern animals. As for why its spectacularly useful butthole was up ways instead of sideways, scientists aren’t quite sure, but they have some theories. Maybe it had something to do with their reproductive anatomy, or maybe it was influenced by its environment, or maybe it had something to do with regulating body temperature through moisture loss. A lot of ideas but nothing definitive yet.

The find is especially impressive since soft tissues rarely fossilize, but we are also in a golden age of researchers finding fossilized soft tissue, as just a few weeks ago it was announced that paleontologists from the University of Oklahoma found a “one in a million” 450 million-year-old fossil that had some of its soft tissue preserved.

In the case of the Dimetropus, mud preserved the impression it left behind, letting the researchers reconstruct its anatomy, which would normally have disappeared way before fossilization occurred.

We’re still discovering new things about the butts of creatures that died hundreds of millions of years ago. Ah, the wonders of paleontology.