This fossil reveals how dinosaurs peed, pooped and had sex
We know a lot about dinosaurs -- what they looked like, what they ate and what killed them off -- but no fossils have definitively preserved two dinosaurs in the act of mating.
However, a fossil from China of a Psittacosaurus is so well preserved that the opening the Labrador-size dinosaur used to pee, poop and reproduce is visible, allowing paleontologists to study it for the first time.
While it doesn't offer any concrete answers on how dinosaurs may have procreated, it does give some hints.
"We don't have any dinosaur fossils where you can be confident they've been caught in the act," said Jakob Vinther, a paleontologist and senior lecturer at the University of Bristol's School of Earth Sciences.
What we know is "based on natural history where we compare it to living groups of animals."
While most mammals have separate holes for bodily functions, many other animals -- including birds and reptiles -- have just one and it's known as the cloaca.
The fossilized cloaca confirms that dinosaurs had one but it doesn't look like that of any other living animals.
"It is very unique. Most cloacas form a kind of slit. Sometimes it's a vertical split, sometimes it's a smiley face, sometimes it's a sour face. This thing has a V-shaped structure with a pair of nice flaring lips and there's not a living groups of animals that have morphology like that," Vinther said. "It is somewhat similar to crocodiles but still unique."
The study, which published in the journal Current Biology on Tuesday, said that large, pigmented lobes on either side of the opening could have harbored musky scent glands, as seen in living crocodiles and alligators.
What's more, the outer margins of the cloaca are highly pigmented with melanin. While they don't know for sure what color it was, it likely would have contrasted with the dinosaur's pale underbelly, Vinther said.
This distinctive pigmentation could mean the vent was used to display and signal, similar to living baboons and some breeding salamanders.