Fossilized Dinosaur 'Butthole' Shows How The Giant Creatures Had Sex

The first dinosaur "butthole" ever discovered has revealed how the prehistoric creatures used this multipurpose opening to defecate, urinate, copulate and extrude their offspring or eggs.

Psittacosaurus, which roamed the Earth in the Mesozoic era, was a bristly-tailed, horn-faced dinosaur about the size of a Labrador and was relative of the three-horned Triceratops. A pristine fossil of the Psittacosaurus discovered in China decades ago has allowed scientists to reconstruct its anal opening — scientifically known as a cloacal vent — into a three-dimensional model, which was published Tuesday in the journal Current Biology.

Diane Kelly, a biologist at the University of Massachusetts Amherst who specializes in the evolution of genitalia, noted that the Psittacosaurus' fossilized orifice resembles that of living crocodilians', The New York Times reported. Researchers suggested that it may have contained musk glands used for signaling during courtship.

The outer regions of the dinosaur's cloaca were covered with a dark shade of melanin, according to researchers. And although scientists have yet to confirm just what color it was, they believe it likely would have contrasted with the dinosaur's underbelly.

The distinctive pigmentation could mean that the cloaca was used to display and signal, as well as served as an opening for pooping, peeing and reproducing. This dark melanin may have also provided antimicrobial protection, according to Jakob Vinther, the study's lead researcher and a paleontologist at the University of Bristol's School of Earth Sciences.

"It's like a Swiss Army knife of excretory openings," Vinther told Live Science. "It does everything."

The multi-purpose hole has given paleontologists some insight into the Psittacosaurus' anatomy since the dinosaur's opening is considered unique compared to other creatures' rear ends.

"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 group of animals that have morphology like that," said Vinther, CNN reported.

While some paleontologists believe that dinosaurs mated by "cloacal kissing," which involves pressing together their openings, Vinther thinks the Psittacosaurus likely had a penis due to its fossilized opening's resemblance with a crocodile's. Crocodiles, as well as some birds and ostriches, also have them.

"From what we can see, this cloaca would not have been suitable for cloacal kissing," Vinther said. "It looks like it would have been penetrative sex."

The "world’s oldest known all-purpose orifice" is now being displayed at the Senckenberg Natural History Museum in Frankfurt, Germany.