Paleontologists say an “extremely rare” fossilized anus — preserved in remarkable detail — may provide groundbreaking insight into reptile evolution and dinosaur biology.

The specimen, belonging to a small horned dinosaur known as Psittacosaurus, features a preserved cloaca — the multi-purpose opening used by reptiles, birds and some amphibians for excretion and reproduction. Soft tissue preservation in fossils is exceptionally uncommon, making the find scientifically significant.

A Window Into Ancient Anatomy

Unlike bones, soft tissues typically decay long before fossilization can occur. In this case, however, researchers discovered detailed external features around the cloacal region, offering rare evidence of how dinosaurs’ reproductive and digestive systems may have functioned.

Scientists say the structure appears more similar to modern crocodiles than to birds, potentially reshaping assumptions about how certain dinosaurs reproduced and evolved.

Why It Matters

The cloaca is a crucial anatomical feature in reptiles, but fossil evidence of it is nearly nonexistent. By comparing the preserved structure to living species, researchers can better understand evolutionary links between ancient dinosaurs and modern reptiles and birds.

“This is the first time we’ve had this kind of preservation,” one researcher noted, calling the specimen “a once-in-a-generation discovery.”

Evolutionary Breakthrough?

While more analysis is underway, experts believe the find could help clarify long-standing debates about dinosaur reproductive biology and the evolutionary pathway that led from prehistoric reptiles to present-day species.

In paleontology, even the smallest anatomical detail can carry enormous implications. In this case, an ancient fossilized opening may help unlock millions of years of evolutionary history.