Stunning fossil suggests dinosaurs lured mates with smell and vision
A reconstruction of the only fossilised dinosaur cloaca in existence may help illuminate how the prehistoric animals mated.
The cloaca is an all-purpose opening on the body of many animals – including lizards, turtles and birds – that is used for mating, laying eggs, urinating and defecating.
In 2016, Jakob Vinther at the University of Bristol, UK, and his colleagues were assessing evidence of camouflage in the well-preserved skin of a metre-long horn-billed dinosaur called Psittacosaurus. They noticed that the animal also seemed to have a surprisingly intact cloaca.
Vinther and his colleagues took the fossil, flattened by years of compacting, and turned it from a 2D pancake into a 3D digital model. The team then tried to compare the Psittacosaurus’s cloaca against those of other animals.
Most birds, which evolved from dinosaurs, don’t have a penis and reproduce using “cloacal kissing”, im which cloacas touch. Vinther believes that Psittacosaurus didn’t do this. Its cloaca had two flaps of skin covering most of the cloacal vent, which gives it an appearance more like that of a crocodile’s cloaca rather than a bird’s. Male crocodiles have a penis that emerges from the cloaca and Vinther’s team suspects that Psittacosaurus did too. Vinther reckons the Psittacosaurus’s skin flaps could have hidden musk glands producing sexually attractive scents.
The conclusions mirror those reached by another team that analysed the same Psittacosaurus fossil and posted their findings to a preprint server last year.
The new analysis also shows that the cloaca contains large amounts of the pigment melanin. Vinther initially thought that the melanin was to protect against microbial infection. But the melanin is in the outer skin, rather than inside the body, “so it’s probably to make the cloaca stand out”, he says.
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