In the spring of 1985, researchers from the Zigong Dinosaur Museum in Sichuan Province collected a relatively complete Stegosaurus fossil skeleton in Pengtang, Zhongquan Township, on the outskirts of Zigong City, and numbered it "ZY-1".
Zigong Dinosaur Skin
In the winter of 1989, scientists began to repair the "ZY-1" Stegosaurus skeleton. A pair of large, comma-shaped bony spines, known as "shoulder spines," had been discovered on the shoulder of the skeleton. It was while repairing the left shoulder spine that curator Ouyang Hui unexpectedly discovered dinosaur skin fossils.
At the time, the technicians were intently repairing the fossils, while Ouyang Hui carefully examined the surface of the stone that had been chipped open by the chisel and the rock fragments that had been knocked off, hoping to find small fossils such as plesiosaur teeth or shark-like scales. Suddenly, the technicians struck a spot on the stone, revealing an unusual flat surface with scaly patterns. Ouyang Hui picked up a fragment of rock and discovered a reversed image on it. "Isn't this dinosaur skin fossil!" he exclaimed in delight.
Ouyang Hui's excitement is understandable, as the fact that skin can fossilize is indeed quite incredible. Generally, the primary condition for an organism's remains to fossilize is the preservation of its hard parts; therefore, only the internal and external skeletons of animals are most likely to fossilize. However, sometimes, a series of coincidences in natural factors can lead to miracles.
The "ZY-1" Stegosaurus fossil skeleton is a perfect example. It is not only complete but also remarkably continuous; almost all the fossilized bones are intertwined and preserved within the rock, vividly reflecting its final moments—lying helplessly in the mud. This state of burial suggests that the Stegosaurus likely fell into a river or lake and died, quickly being buried by sediment. When Ouyang Hui calmed down from his initial surprise and continued observation, he discovered that the rock burying the fossil skeleton was primarily grayish-green sandstone, but the small section preserving the skin fossil was a purplish-red mudstone. A plausible hypothesis immediately came to Ouyang Hui's mind: when the Stegosaurus's body was buried by the sand in the river or lake, it carried a small piece of mud, which, like a sculptor shaping a clay figure, perfectly imprinted the pattern of a piece of skin near the shoulder spines. Coincidentally, the hadrosaur skin discovered in Alberta, Canada, was also preserved in mudstone.
It's important to understand that the chance of ancient life forms surviving as fossils is only one in ten million, and the chance of finding skin imprints within fossilized bones is even smaller—this is truly a natural miracle. It is through studying these rare wonders of nature that scientists have unraveled one age-old mystery after another.
We know that dinosaurs are ancient members of the reptile family. Therefore, scientists' inferences about their living morphology, especially their understanding of skin surface morphology, are often derived from modern reptiles. The outermost layer of skin on modern reptiles such as snakes, lizards, and crocodiles is a keratinous layer, sometimes consisting of keratinous scales, sometimes keratinous plates. This is an effective structure to prevent the loss of body moisture, thus adapting to the dry terrestrial environment. Did dinosaurs also possess this scaly skin? What did it look like?
The dinosaur skin fossil discovered in Zigong shows that stegosaurs did indeed have scaly skin with hexagonal horny scales on its surface. However, these scales are much smaller than those depicted in previous ecological reconstructions of stegosaurs or carved on stegosaur statues, which referenced extant reptiles.
The dinosaur skin fossils in Zigong are another major discovery following those found in Canada, Mongolia, the United States, and the United Kingdom, including skin fossils of hadrosaurs, ceratopsians, ornithopods, and carnivores. All these dinosaur skin fossils provide important clues for scientists to explore the mysteries of the Mesozoic dinosaur world.
In the UK, fossilized skin traces of a species of ornithopod dinosaur, Celidosaurus, were discovered, showing small, rounded horny scales embedded in the skin surface, forming an exquisite mosaic pattern.
In North America, scientists have discovered a hadrosaur mummy, a dried-up carcass of the hadrosaur. This discovery revealed that hadrosaurs possessed very thick skin. Correspondingly, the surface of this 400-square-centimeter skin fossil from Zigong is almost parallel to the surface of the scapular spine, filled with several centimeters of sandstone. While it's generally assumed that the thickness of this sandstone layer represents the thickness of the skin and subcutaneous muscle tissue, since the scapular spine, like the stegosaur's blade, is a bony derivative of the skin, it's unlikely that it would have had very thick muscles growing on it. Therefore, it's inferred that the stegosaur's skin must also have been very thick. This phenomenon is not difficult to understand, because for herbivorous dinosaurs, thick skin would undoubtedly serve as a barrier against predatory dinosaurs.
