Lost cities of the Khmer Empire, ancient Roman aqueducts and roads, Aztec and Mayan ruins — these are just a few of the archaeological finds that laser imaging has enabled. Many of these discoveries have reshaped our understanding of human civilization and history. Recently, paleontologists used the technology to peer even deeper into the past to uncover a secret that predates human history. Their discovery will not rewrite history books, but it might surprise even those who are well versed in dinosaur anatomy.

Researchers from The Chinese University of Hong Kong employed laser imaging to reveal what may be the world’s oldest belly button on record. The navel belongs to a 125-million-year-old fossilized specimen of Psittacosaurus, a 2-meter-long, two-legged plant eater that lived in China during the Cretaceous period. The dinosaur is a distant relative of the more commonly known Triceratops.

Conventional wisdom holds that reptiles and birds don’t have belly buttons; however, this is something of a misconception. Reptiles are born from eggs, meaning that they’re nonplacental. But they do have yolk sacs that adhere to their bellies via a slit-like opening during development. After the creatures hatch, the yolk sac detaches from their bodies, leaving behind a long umbilical scar where the opening sealed up.

The egg-laying nature of dinosaurs predicted a scar similar to those carried by contemporary egg-laying land animals, such as lizards, crocodiles, and other reptiles. But over the past 65 million years, paleontologists have found it increasingly difficult to turn up dinosaurs that they can examine in search of confirmatory evidence of this theory.

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Though science has confirmed that navels emerged as early as the age of dinosaurs, the practice of navel gazing would not arise until millions of years afterward. Courtesy of Bell et al. Courtesy of Bell et al.

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Now, photonics has allowed scientists to use lasers to probe fossil evidence. By applying the laser-stimulated fluorescence imaging technique, the university researchers identified distinctive scales that surrounded a long umbilical scar in the Psittacosaurus specimen, similar to that found in certain living lizards and crocodiles, said Michael Pittman, assistant professor at the university’s School of Life Sciences. The discovery marks the first dinosaur fossil on record to display a well-preserved belly button, he said.