Dinosaur ‘belly button’ found on fossil

A parrot-beaked psittacosaurus dinosaur that lived in what’s now China 130 million years in the past had an belly scar that will have been equal to a mammalian stomach button

By Carissa Wong

A herbivorous parrot-beaked dinosaur that lived in what’s now China 130 million years in the past might have had the reptile equal of a mammalian stomach button.

“I’d chalked up a number of oddities throughout a extra routine examination of the specimen… After I noticed this, my thoughts stated umbilical scar!” says Phil Bell on the College of New England, Australia. “I can’t think about many individuals have truly seemed for them, there aren’t many specimens in existence [with fossilised skin].”

Most mammalian embryos achieve vitamins from a placenta by means of an umbilical wire, which ultimately falls off to depart an belly scar, or stomach button.

In birds and reptiles, the embryo is hooked up by way of blood vessels to a yolk sac, which offers vitamins inside the egg. After the animal hatches, the yolk sac is absorbed into its physique, leaving a linear belly scar. Not like in people, this scar normally disappears after a number of days to weeks.

Till now, it was unknown if dinosaurs – which additionally laid eggs – had umbilical scars that lasted for various weeks.

Bell and his colleagues imaged the scar within the dinosaur – a psittacosaurus – utilizing a method referred to as laser-stimulated fluorescence, which revealed the scar was about 10 centimetres lengthy and surrounded by tiny scales, that means it was unlikely to have been attributable to bodily trauma.

“Scars from accidents depart very clear indicators of trauma. The scales could also be disrupted and lose their common look, and actually, they might not regrow in any respect, leaving solely easy pores and skin,” says Bell. “In distinction, what we see on this psittacosaurus is one thing very common, with well-defined scales on either side. It additionally happens in exactly the spot the place you’d anticipate to see it, and it has all of the traits of a reptilian stomach button.”

By evaluating the size of the femur bone within the specimen with different ptsittacosaurus fossils identified to be of animals that had been about 6 years previous, the workforce established that the person was an analogous age and would have been approaching sexual maturity.

“We all know in fashionable animals that if the umbilical scar stays after these first few weeks after hatching, then it stays for the remainder of its life. Provided that this psittacosaurus was round 6 years previous, then undoubtedly it will have had it for the remainder of its life, and sure all people in that species did too,” says Bell.

Nevertheless, additional work might be wanted to verify the findings. “Though this fossil is solely the most effective on the market for learning pores and skin, it’s nonetheless solely a single fossil. New fossils are prone to change our interpretations, however that’s part of science,” says Bell.

It’s also unknown how widespread umbilical scars might have been throughout completely different dinosaur species.

“To hazard a guess, perhaps 5 per cent of grownup dinosaurs may need had them, based mostly on our observations of recent reptiles,” says Bell. The workforce hopes to handle this query by discovering extra dinosaur “stomach buttons”, he says.

Journal reference: BMC Biology, DOI: 10. 1186/s12915-022-01329-9

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