The dinosaurs remaining. — Found in China's Liaoning Province, the *Psittacosaurus* fossil now sits on display in Frankfurt, Germany’s Senckenberg Natural History Museum, where it has yielded one discovery after another.
Photograph by MICHAEL RICKS

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A dinosaur ‘belly button’? This 130 million-year-old fossil reveals that—and more

This dog-size dinosaur called Psittacosaurus is stunningly well-preserved and has revolutionized paleontologists’ understanding of dinosaur skin.

ByMichael Greshko

July 11, 2023

5 min read

In the entryway of Frankfurt, Germany’s Senckenberg Natural History Museum, a remarkable ambassador from the distant past holds court: a dog-size dinosaur called Psittacosaurus that died some 130 million years ago. The creature is so well preserved, scientists can see the finest details of its skin with astounding fidelity.

Soft tissue along of dino's body. — QUILL THRILLDescribed in 2002, these filaments along the dinosaur’s tail were the first non-scale skin structures ever found on an ornithischian, the large and diverse group of dinosaurs that includes *Psittacosaurus, Triceratops, and Stegosaurus.*
PHOTOGRAPH BY MICHAEL RICKS (WHOLE SPECIMEN); THOMAS G. KAYE, FOUNDATION FOR SCIENTIFIC ADVANCEMENT, AND MICHAEL PITTMAN, CHINESE U. OF HONG KONG (SOFT-TISSUE DETAILS, USING LASER-STIMULATED FLUORESCENCE)

The specimen—officially known as SMF R 4970—left China in the 1990s under legally dubious circumstances, amid a rash of fossil smuggling out of the country’s Liaoning Province. After the fossil traveled through the U.S. and Europe in the hands of a German dealer, the museum bought it in 2001 to keep it available to science (repatriation efforts at the time fell apart). Ever since, the dinosaur has yielded one stunning discovery after another.

Dinosaur-skin fossils aren’t unheard of: North American hadrosaur “mummies,” for instance, preserve areas of scales. But this Psittacosaurus has possibly the most skin preserved from a single non-avian dinosaur—and even contains vestiges of its melanin pigmentation. “It’s been such a treasure trove,” says Jakob Vinther, a paleontologist at the U.K.’s University of Bristol who has closely studied the dinosaur.

Picture of dino's body part. — STEALTH MODEA 2016 study led by paleontologist Jakob Vinther found that the dinosaur had a dark back and light stomach—a kind of camouflage called countershading—and most likely lived in diffusely lit habitats such as forests.
BOB NICHOLLS ART 2020 (DETAILS, MADE UNDER CROSS POLARIZED LIGHT); ILLUSTRATION BY GABRIEL UGUETO

It also keeps yielding surprises. In 2021, a team led by Vinther found that this Psittacosaurus is the only known non-avian dinosaur with a preserved cloaca, an all-purpose orifice for defecation, urination, and sex. Last year, researchers doing a deep-dive study of the dinosaur’s scales announced that they had spotted its “belly button”: a wondrous snapshot of the ancient creature’s time in ovo.