Scientists Found Proof of Dinosaur Belly Buttons

Advancing technology is shedding light on dinosaurs like never before. Dinosaur belly buttons are the latest discovery to come out of these closer looks at old fossils. Baby animals, like birds and reptiles, that develop inside of eggs get their nutrients from a yolk sac connected to their abdomens. Some living species have an umbilical scar for life while others heal within a few days. A well-preserved Psittacosaurus fossil showing skin, scales, and other fine details includes the oldest known belly button.

Fossil Psittacosaurus dinosaur showing scales on its stomach
Bell et al 2022/BMC Biology

Scientists can’t rely on perfectly intact fossils to determine what dinosaurs really looked like. They often have to work with small fragments. This group of researchers used a newer technique called laser-stimulated fluorescence to see even more details without damaging the fossil. Then they compared the scale patterns to modern examples. They found similarities to some, like alligators, that have umbilical scars for life. The peer-reviewed journal BMC Biology published the results, which we saw in Smithsonian magazine. 

This discovery comes from the same fossil that another team of scientists used to identify the dinosaur’s cloaca—the all-purpose hole used for mating, laying eggs, and expelling waste. The specimen, found in China in 2002, continues to yield groundbreaking insights thanks to its exceptional state of preservation. The skin coloration also indicates counter-shading, meaning it was lighter on its belly than on its back. This is used as camouflage in many environments.  

The scientists also shared an artist’s illustration (above) of the Psittacosaurus, umbilical scar and all. No word on whether it allows tummy rubs.

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth. 

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