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A fleshy fossil find
In a forest in northeastern China, a small dinosaur with a beaked snout, known as Psittacosaurus, died 130 million years ago. A portion of its lower abdomen containing a flesh wound managed to fossilize. The fossilized wound now offers paleontologists an unprecedented peek inside dinosaur skin, showing them just how tough some dinosaurs really were.
“It’s like having a living dinosaur and being able to dissect it,” says paleontologist Theagarten Lingham-Soliar of the University of KwaZulu-Natal in South Africa. Lingham-Soliar noticed the four- to five-centimeter-wide cut near the specimen’s lower ribs while examining a Psittacosaurus fossil from China’s Liaoning Province. The cut penetrated the skin’s surface to reveal a cross-sectional, three-dimensional view of the skin’s inner layers. This was not something Lingham-Soliar or any other paleontologist had ever seen. “We’ve got for the first time an idea of what the deep structure of a dinosaur’s skin was like — all other studies deal with the surface of the animal,” he says.
Although soft tissue usually decomposes rapidly before fossilization can occur, fossils of dinosaur skin have been found before. In fact, paleontologists already knew that Psittacosaurus’ outer skin was scaly and reptilian. But they didn’t know what the inside looked like. With the help of a microscope, Lingham-Soliar investigated the two-centimeter-deep cut to find horizontal layer upon layer of tightly packed collagen fibers arranged in alternating orientations — an arrangement found in modern reptiles and sharks. In total, he counted 25 collagen layers and estimated at least another 15 layers probably had existed in poorly preserved areas of the skin. By today’s standards, that’s remarkably thick skin, he says. “Only one other [known] animal of comparable size has so many layers: nurse sharks,” says Lingham-Soliar, whose results were published online in the Proceedings of the Royal Society B on Jan. 8.
Psittacosaurus’ thick skin was also probably very tough, Lingham-Soliar says. “Collagen gives our skin strength to withstand external forces” and gives it structure, he says. Having strong, thick skin may have afforded the small, gazelle-sized dinosaur some protection against large, toothy predators — although tooth marks in the wound indicate something managed to bite the dinosaur either before or shortly after death.
“Psittacosaurus would have made a tasty hors d’oeuvre for other dinosaurs in its environment,” says Matt Lamanna, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh. The fossilized skin “really gives us a better picture of what Psittacosaurus was like as a living animal,” he says.
David Martill, a paleobiologist at the University of Portsmouth in the United Kingdom, agrees that soft tissue helps scientists reconstruct an animal’s biology in ways that bones alone can’t. “It’s always a special occasion when you find any skeleton with soft parts,” he says. And while he doesn’t doubt Psittacosaurus must have been “a real tough cookie,” Martill suggests researchers now need to study a range of reptiles and relate skin thickness to different ecological conditions to truly flesh out why Psittacosaurus had such thick skin.
