When the dog-sized Psittacosaurus was living on Earth, it was most likely concerned with not being killed by other dinosaurs. It wouldn't have thought that scientists would be looking up its clacker 120 million years later.
In 2021, scientists published an exquisitely detailed description of a non-avian dinosaur's cloaca: the catch-all hole used for peeing, pooping, and laying eggs.
The Swiss Army knife of buttholes is common throughout the animal kingdom today. We don't know a lot about the cloacae of dinosaurs, what they looked like, and how they were used.
I noticed the cloaca several years ago after we reconstructed the color patterns of this dinosaur using a remarkable fossil on display at the Senckenberg Museum in Germany which clearly preserves its skin and color patterns.
It took a long while before we got around to finish it because no one has ever cared about comparing the exterior of cloacal openings of living animals.
The specimen of a reptile. Vinther et al., Current Biology, 2020.
The team compared the cloaca to modern cloacae.
Their specimen was the only non-avian dinosaur fossil known to have a preserved cloaca, but due to the way the fossil was positioned, the internal anatomy of this opening has not been preserved. There was a lot of information that the researchers were unable to gauge.
Diane Kelly of the University of Massachusetts said that the vent doesn't tell you much about an animal's sex in most cases.
Those distinguishing features are tucked inside the cloaca, but they are not preserved in the fossil.
There are some pretty interesting clues as to what some dinosaur cloacae looked like, and how they were used.
The team was able to identify several features in common with crocodiles and alligators, despite the fact that the dinosaur's cloaca is unlike any other modern animal.
There was a rounded swelling near the cloaca, similar to the one seen in birds, but without the internal structure.
The cloaca had lips on either side of the opening. The opening of the Psittacosaurus could have been slit-shaped, like in birds, because they had arranged them in a V-shape.
The University of Bristol and Bob Nicholls/Paleocreations.com are involved.
The cloacal vent may have once looked like this.
Other features were similar to crocodilians. The cloacal lips were covered with scales and colored with melanin. In crocodilians, the musky scent glands that are used during social displays are found in these lobes.
As a paleo artist, it has been amazing to reconstruct one of the last remaining features we didn't know anything about.
Knowing that at least some dinosaurs were signaling to each other gives paleoartists an exciting freedom to speculate on a whole variety of now plausible interactions during dinosaur courting. It is a game-changer.
It is not possible to tell whether the display was sexual or male or female because only one cloaca has been recorded. The researchers noted in their paper that the colorful lobes could hint at the shared ancestry between birds and dinosaurs.
There is a comparison of different cloacae. Vinther et al., Current Biology, 2020.
For lack of samples, this is a very under studied region of dinosaur anatomy, and only by examining a wide range of dinosaur cloacae can we learn more about how they functioned in the social and reproductive lives of these ancient animals.
Other paleontologists are looking for buttholes to fill in the gap in our understanding of dinosaur life.
Current Biology published the research.
An earlier version of this article was published in January.
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