UNE Researchers Discover World’s Oldest Bellybutton!

By Dr Kieran Meaney, UNE Discovery

Science continues to answer the big questions, like “Did dinosaurs have bellybuttons?”

A bellybutton seems like a pretty normal thing for us humans. Before we are born we grow in our mother’s womb, and we are given all our vital nutrients to let us develop through our umbilical cord. All placental mammals share this trait, and our bellybutton is essentially the scar from where the umbilical cord was once attached.

Dinosaurs, however, were not placental mammals but rather hatched from eggs. Since they were not growing inside their mother being fed by an umbilical cord, they should not have a bellybutton, right? This is partly what made UNE palaeontologist Dr. Phil Bell’s most recent discovery so amazing!

125 million years ago, during the Cretaceous in what we now call China, lived a distant relative of the triceratopscalled Psittacosaurus (Say sit-tah-coh-saw-us). When one particular individual of this species died, it was lucky enough to be preserved with the skin intact. The team led by Dr. Bell studied this fossilised skin and found a strange and distinctive pattern of scales on the stomach of the creature. As it turned out, this is now the world record holder for the oldest bellybutton!

An artist impression of Psittacosaurus with a close up view of its umbilical scar, or ‘bellybutton’. Image Credit: Jagged Fang Designs

The bellybutton in question is probably not what you’re imagining; rather than the little round indent in your stomach that you’re familiar with, this dinosaur bellybutton is a long thin scar with enlarged scales on either side of it. Rather than being where an umbilical cord attached to the growing dinosaur, this was where the yolk sac from the egg (think the yellow bit in a bird egg) attached to provide all the nutrients the dino bub needed.

Similar umbilical scars can be found on birds and reptiles such as crocodiles, but what is even more unusual is that the scar in these modern animals fades before reaching adulthood. This specimen of Psittacosaurus held on to its umbilical scar well into adulthood. Whether or not all dinosaurs had an umbilical scar, or bellybutton, like this is a question to be answered another day.

This is not the first media attention for this particular fossil of Psittacosaurus. The preservation of its soft tissue led this fossil to make the news in 2021 when researchers identified its cloaca – the all in one multitool for passing waste and laying eggs, similar to that seen in birds and reptiles today.

The team mapped out the texture of the fossilised skin using laser-stimulated fluorescence to identify the “bellybutton” scales.

Image credit: Bell, P.R., Hendrickx, C., Pittman, M. et al. Oldest preserved umbilical scar reveals dinosaurs had ‘belly buttons’. BMC Biol 20, 132 (2022).