(ORDO NEWS) — When the dog-sized Psittacosaurus lived out its days on Earth, it was probably preoccupied with mating, eating, and not being killed by other dinosaurs. It never occurred to him that after 120 million years, scientists would be staring at his ass.
However, this is exactly what scientists did when they published in 2021 an elegantly detailed description of the cloaca of a non-African dinosaur: a versatile opening used to urinate, poop, mate and lay eggs.
This “Swiss army knife” is common today throughout the animal world – all birds, amphibians, reptiles and even some mammals have a cloaca. But we know little about dinosaur cesspools, including their anatomy, what they looked like, and how the animals used them.
“I noticed the cloaca several years ago after we reconstructed the color pattern of this dinosaur from a remarkable fossil exhibited at the Senckenberg Museum in Germany, which clearly preserved its skin and color pattern,” paleobiologist Jakob Winter of Bristol explained last year. university in the UK.
“It took a long time before we could get it right because no one had ever compared the appearance of living animal cloacal openings, so it was pretty much uncharted territory.”
This is exactly what the team was doing, comparing the fossilized cesspool with modern cesspools.
Their specimen was the only non-African dinosaur fossil to have a cloaca preserved, but due to the way it was located, the internal anatomy of this opening was not preserved; only the outer hole is visible. This means that the researchers could not evaluate much information.
“We found that the hole looks different in different groups of tetrapods, but in most cases it does not reveal much about the sex of the animal,” says anatomist and animal reproductive expert Diana Kelly of the University of Massachusetts Amherst.
“These distinguishing features are found inside the cloaca, and unfortunately they are not preserved in this fossil.”
However, the external anatomy can provide some pretty interesting insights into what the cloacae of some dinosaurs looked like and how they were used.
Although the dinosaur’s cloaca does not resemble any known modern animal, the team was able to identify several similarities with crocodile reptiles such as alligators and crocodiles and birds.
The dorsal lobe seemed similar to the cloacal prominence seen in birds – a rounded bulge near the cloaca during the breeding season where the male accumulates sperm – though, again, without internal anatomy, it’s impossible to say for sure.
Secondly, the cloaca had lateral lips on either side of the opening, like those of crocodiles. However, unlike crocodiles, in Psittacosaurus they were located in a V-shape, so the hole could be slit-like, or it could be round, like in birds.
Other features, however, were also similar to those of crocodiles. The cloacal lips were covered with small, overlapping scales and heavily pigmented with melanin.
In crocodilians, these lips function as musky scent glands that are used during social displays, a function the researchers say is supported by strong pigmentation.
“As a paleoartist, it was absolutely amazing for me to be able to reconstruct one of the last remaining dinosaur features that we knew nothing about,” said paleoartist Robert Nicholls.
“Knowing that at least some dinosaurs signaled each other gives paleoartists an exciting freedom to speculate about a range of now plausible interactions during dinosaur courtship. It changes the game!”
Since only one fossilized cloaca has been found, it is impossible to say whether this display act was sexual, and whether the fossilized dinosaur is male or female. But the multicolored lobes may hint at a common origin for birds and non-African dinosaurs, the researchers note in their paper.
Due to the lack of specimens, this is a very little-studied area of dinosaur anatomy, and only by examining a wide range of dinosaur cloacas can we learn more about how they functioned in the social and reproductive life of these ancient animals.
No doubt other paleontologists are on the lookout for fossilized asses to try and fill this gap in our understanding of dinosaur life.
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