125-million-year-old fossil reveals a previously unknown 'hedgehog' dinosaur species

BEIJING — Scientists have identified a new species of plant-eating dinosaur featuring hollow skin spikes never before seen in the fossil record.

The discovery of Haolong dongi, a member of the Iguanodontia group, was based on an extraordinarily well-preserved fossil found in China. The specimen dates back approximately 125 million years.

According to a study published in the journal Nature Ecology & Evolution, researchers from the CNRS and collaborating institutes used advanced imaging techniques to analyze the fossil’s skin at a cellular level. They found that the unique spikes originated from the skin itself rather than the animal's skeletal structure.

The research team suggests the spikes may have served as a defensive mechanism similar to the quills of a porcupine. Other potential functions include sensory perception or thermoregulation.

Because the fossilized specimen is a juvenile, scientists are not yet certain if adult members of the species retained these specialized features.

Experts say the discovery opens new avenues for understanding the anatomical diversity and complex biological structures of dinosaurs.

The identification of Haolong dongi represents a paradigm shift in paleontology rather than a mere taxonomic addition. The discovery’s true significance lies in the exceptional preservation of soft tissue—an exceedingly rare phenomenon that has allowed researchers to conduct cellular-level analysis on skin structures dating back 125 million years.

This breakthrough underscores the degree to which high-resolution X-ray imaging and advanced histological analysis are currently disrupting the field. By moving beyond traditional skeletal reconstruction, these technologies allow for a more nuanced mapping of ancient biological systems. The presence of hollow dermal spines, in particular, challenges established evolutionary models concerning defense mechanisms. It remains to be determined whether these structures functioned as passive deterrents—analogous to modern porcupines—specialized thermoregulatory tools, or sophisticated environmental sensors.

The fact that the specimen is a juvenile further complicates the biological narrative, opening a new front in the study of dinosaur ontogeny and the developmental transitions from neonate to adult. Ultimately, Haolong dongi serves as a critical reminder that the prehistoric record remains full of untapped data, capable of forcing a wholesale re-evaluation of Earth’s evolutionary history.