Quirks & Quarks

A dinosaur's butthole was a Swiss Army knife of orifices

Reconstructing a dino's cloaca gives scientists a new perspective on their mating strategies

Reconstructing a dino's cloaca gives scientists a new perspective on their mating strategies

A reconstruction of Psittacosaurus illustrating how the cloacal vent may have been used for signaling during courtship. (Bob Nicholls / Paleocreations.com 2020)

Using a dinosaur fossil with exceptional skin preservation, a scientist from the University of Bristol in the UK was able to figure out what a dinosaur's rear end orifice would have looked like.

Dinosaurs, along with most other animals, have only a single rear orifice known as a cloaca to defecate, urinate and copulate. 

Jakob Vinther, a paleontologist who had previously worked on uncovering the Psittacosaurus dinosaur's colour patterns, revisited the specimen when he realized how incredibly well preserved its cloaca was and decided to take a closer look.

He discovered that, like baboons, this dinosaur's cloaca was highly pigmented and would have stood out from surrounding areas of skin, which he said likely served as a visual signal to potential mates.

The Psittacosaurus' cloaca most closely resembles that of a modern crocodile, rather than the birds its more closely related to. It's covered in scales with lips on either side of the slit, but instead of converging at the bottom like the crocodile, its lips flare out in the direction of the tail resulting in it being shaped like an inverted "v." 

Close up of the preserved cloacal vent in Psittacosaurus and the authors' reconstruction of it. (Jakob Vinther / Robert Nicholls / Diane Kelly)

On either side of those lips, he said there appear to be glands, again similar to those found in orocodiles that release pheromones with a very particular, strong odour to attract a mate.

But without any other specimen to compare it with, Vinther said he and his colleagues can't tell if it was a male or female, but given what they found, they do suspect it would have had penetrative sex and a penis if it was a male. 

Produced and written by Sonya Buyting

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