It's a first for paleontology, and one that might produce a giggle. For the first time, scientists have been able to describe in fine detail a dinosaur's cloaca. If you're not familiar with that body part, CNET translates: It's essentially "a jack-of-all-trades butthole." The study published Tuesday in Current Biology concerns a dog-size herbivore that lived about 120 million years ago called Psittacosaurus. Scientists with the University of Bristol write that "it was previously noted that the cloacal region was preserved" though flattened in this fossil, found decades ago in China, but the detailed anatomy of the region hadn't been properly reconstructed. That's what they managed, via a 3D model of the opening of the orifice, which was used for defecation, urination, copulation, and birth.
The New York Times notes "cloaca" comes from the Latin word for "sewer," and it's not at all unique to dinosaurs: Some modern birds, reptiles, amphibians, and a handful of mammals have one, but to the researchers' knowledge, the cloaca isn't preserved in any other non-avian dinosaur fossil. So how does this one measure up to those we're familiar with? It's definitely in a class of its own, but most like those seen in crocodiles and alligators. While most cloacal openings, or vents, appear as slits or holes, that of the Psittacosaurus has "discrete lateral lips, but they only converge anteriorly, giving the cloaca a unique v-shape anatomy," per the study. Those lips were heavily pigmented, indicating they might have a signaling function, perhaps a sexual one; it's possible they also held musk glands. (Read more discoveries stories.)