New ‘Spiny Dragon’ Fossil Preserves Dinosaur Skin Cells, Redrawing a Familiar Herbivore

The small dinosaur lies spread across a slab of gray rock in an Anhui museum, its bones still nearly where they fell 125 million years ago. Around the skeleton, a faint halo of tissue forms a ragged outline. Under laser light and through high-powered microscopes, that ghostly fringe sharpens into a coat of hollow spikes and skin cells so crisp that scientists say they can pick out the ghosts of nuclei.

The animal, a newly named species called Haolong dongi — “spiny dragon” — is forcing paleontologists to rethink what some of the most familiar plant-eating dinosaurs actually looked like, and how much of their biology can still be read in stone.

A fossil with skin preserved in unusual detail

In a study published Feb. 6 in Nature Ecology & Evolution, an international team reports that the fossil preserves skin in extraordinary detail, including a previously unknown type of epidermal spike that is neither feather nor bony armor. Histological slices and micro-CT scans show layers of skin cells inside the spikes and dark, rounded structures the authors interpret as fossilized nuclei or their mineral replicas.

“Finding dinosaur skin preserved at the cellular level is extraordinary,” said Pascal Godefroit of the Royal Belgian Institute of Natural Sciences in Brussels, a senior author on the paper. “It opens a window onto dinosaur biology we never thought possible.”

The specimen, cataloged as AGM 16793, was discovered in rocks of the Yixian Formation in western Liaoning Province in northeastern China. The formation, part of the Jehol Biota, is a volcanic-lacustrine deposit often compared to a “Dinosaur Pompeii” for its finely preserved birds, feathered theropods, mammals and plants.

The fossil was excavated and is housed at the Anhui Geological Museum in Hefei. The skeleton is that of a juvenile iguanodontian ornithopod, about 2.4 meters (roughly 8 feet) from snout to tail. Unfused bones at the shoulder, hip and skull indicate it had not yet reached adult size, which the authors estimate at around 5 meters based on close relatives.

Lead author Jiandong Huang, who heads research at the Anhui Geological Museum, said the team initially recognized the specimen as a small plant-eating dinosaur but only later realized the extent of the soft tissue.

“We knew we had a beautifully articulated skeleton,” Huang said in a statement released by the museum. “But under special light, we suddenly saw that the entire animal was surrounded by skin and these unusual spikes. Even animals we think we know well, like iguanodontians, can still surprise us.”

Scales—and a new kind of spike

The skin itself is not a uniform sheath. Along the tail, large, overlapping scaly plates known as scutate scales form a kind of flexible armor above and below the vertebrae. On the neck and torso, the surface is broken into smaller, pebbly tuberculate scales.

Threaded between these scales are the structures that give Haolong its name: hollow, spike-like appendages the researchers call cutaneous spikes. The smallest are only a few millimeters long; the largest reach about 4 centimeters, projecting backward like stiff, blunt quills.

Darren Naish, a British vertebrate paleontologist who was not involved in the study but reviewed the findings for a popular science outlet, compared their appearance to short, backward-pointing bristles rather than long porcupine quills. The Haolong team stresses that while the spikes likely played a defensive role similar to quills, they are anatomically distinct and entirely made of skin tissue, with no supporting bone.

Thin sections taken through several spikes reveal a layered architecture. An outer horny layer, or stratum corneum, encases a multi-layered epidermis made of keratin-producing cells, or keratinocytes. Inside, a more porous, pulp-like tissue fills the hollow core. Within many epidermal cells, the researchers report seeing dense, rounded bodies they interpret as nuclei or mineralized casts where nuclei once sat.

In accompanying press materials, the Royal Belgian Institute of Natural Sciences said that “even keratinocyte nuclei are still visible” under the microscope, and the French National Centre for Scientific Research described the spikes as exhibiting “unprecedented properties” for a dinosaur skin fossil.

A finding likely to draw scrutiny

Those claims place Haolong squarely in the middle of a long-running debate over how much of a dinosaur can truly be preserved. Over the past decade, several teams have reported microscopic soft-tissue structures — from melanin-carrying organelles in feathers to vessel-like tubes in bone — and even fragments of ancient proteins. Others have cautioned that some of those features may be mineral look-alikes or traces of ancient microbes.

Godefroit acknowledged that the team’s interpretation, particularly of the nucleus-like bodies, will attract scrutiny. “We are very cautious,” he said. “We are not claiming intact DNA or anything like that. What we see are structures in the right place, the right shape and the right context within the skin layers. Further work will test these interpretations.”

Rethinking dinosaur coverings

Beyond the microscopic details, the spikes themselves represent a bigger-picture surprise. For decades, paleontologists divided dinosaur outer coverings into a few broad categories: scales like those of modern reptiles; filamentous or feather-like structures in many theropods and some ornithischians; and bony armor plates, or osteoderms, in stegosaurs and ankylosaurs, often sheathed in keratin.

The Haolong spikes have no bony core and are not filaments branching from follicles, as feathers do. Their layered structure also differs from the spiny scales of modern lizards. The authors argue that they represent an independently evolved class of skin organ in dinosaurs — essentially a third way of building bristling defenses.

Why grow such spikes in the first place? The team sees predator deterrence as the most likely function. As a small, juvenile herbivore in an ecosystem full of predatory theropods, Haolong would have been vulnerable to attack. A coat of rigid spikes interspersed with scales may have made it more difficult and painful for a predator to bite or swallow.

Other roles are possible. The hollow, surface-increasing structures might have helped dissipate heat, and a dense field of stiff bristles could have transmitted subtle vibrations, giving the animal tactile information about its surroundings. Direct evidence for blood vessels or nerve endings is lacking, however, and the authors present these ideas as hypotheses.

One key uncertainty is whether adult Haolong individuals kept their spikes. Because the only known specimen is a juvenile, paleontologists cannot yet say whether the bristling coat expanded, shrank or vanished as the animal grew. In some modern vertebrates, defensive spines or crests are more pronounced in young animals and change with age.

Where Haolong fits on the dinosaur family tree

Phylogenetically, Haolong dongi slots into the base of the hadrosauroid branch of the iguanodontian family tree, just outside the “duck-billed” hadrosaurids that dominated many Late Cretaceous ecosystems. It sits between a cluster of early European iguanodontians and other Chinese forms from the same region, suggesting that these plant-eaters were diversifying into distinct regional lineages in the Early Cretaceous.

For curators in Brussels, the discovery has a particular resonance. The Royal Belgian Institute of Natural Sciences is home to the famous Bernissart Iguanodon skeletons, unearthed in a Belgian coal mine in the 19th century and long displayed as large, almost featureless herbivores with smooth, reptilian skin.

“This fossil shows that the relatives of our Bernissart Iguanodon were probably much more ornamented than we thought,” Godefroit said. “We might have to imagine them with patches of spikes and complex skin patterns, not just as big gray lizards.”

Jehol Biota’s continuing scientific draw

The Haolong study also underscores the continuing importance of China’s Jehol Biota for understanding dinosaur life in fine detail. The Yixian Formation has already yielded feathered tyrannosaurs, primitive birds with flight feathers, pterosaurs with hair-like pycnofibers and mammals with preserved fur and soft tissue outlines.

China’s laws generally prohibit the export of scientifically significant fossils, keeping specimens like Haolong in regional museums. To conduct their work, researchers from Belgium, France and Hong Kong traveled to Chinese institutions and shared imaging and analytical techniques on site, rather than shipping the fossil abroad.

Huang said that model of collaboration is essential if scientists are to keep extracting new kinds of information from familiar rocks.

“Our study shows that we have not exhausted what these fossils can tell us,” he said. “With the right technology and international cooperation, we can now study dinosaur skin, organ by organ, and even cell by cell.”

For a juvenile that died on the floor of an Early Cretaceous lake, encased in ash-laden mud, the posthumous spotlight is intense. Yet the rock encasing Haolong dongi still holds questions: whether adults bristled like their young, how far soft-tissue preservation can be pushed, and how many other dinosaurs hid similarly inventive armor just beneath the skin.

What is clear, the authors say, is that the long-held image of big, bland, scaly plant-eaters is giving way to something stranger — and that even under a microscope, dinosaur skin has new stories to tell.