In an extraordinary paleontological breakthrough, researchers in China have unearthed a largely intact fossilized skeleton belonging to a hitherto unidentified iguanodontian dinosaur species. This specimen is distinguished by exceptionally detailed fossilized skin impressions, revealing structures that are unprecedented in other non-avian dinosaur fossils.
Life reconstruction of a juvenile Haolong dongi. Image credit: Fabio Manucci.
The newly identified species, christened Haolong dongi, inhabited the region now recognized as northeastern China during the Early Cretaceous geological epoch, approximately 125 million years ago.
This novel species belongs to the iguanodontian group, a significant lineage within the ornithopod dinosaurs, which can be found via the provided link: iguanodontian.
From an evolutionary perspective, iguanodontians occupy an intermediate position between diminutive, early bipedal ornithopods and the more recently evolved, highly specialized duck-billed dinosaurs, known as hadrosaurs.
“Iguanodontia constituted the predominant herbivorous dinosaur clade across most terrestrial ecosystems throughout the Cretaceous period,” stated Dr. Pascal Godefroit of the Institute of Natural Sciences in Brussels, alongside his research associates.
“This evolutionary branch achieved its peak development during the concluding phase of this era, as hadrosaurids — commonly referred to as duck-billed dinosaurs — achieved widespread distribution across numerous continents.”
“The discovery of remarkable fossilized ‘mummies’ in North America and Mongolia yielded invaluable insights into hadrosaurid integument, which comprised a complex and often varied arrangement of tubercle-like scales that did not overlap, along with larger, tabular scales positioned along their dorsal midline.”
“Conversely, less comprehensive information exists regarding the integument of more primitive iguanodontians. Only isolated impressions of scales have been documented in Tenontosaurus, Iguanodon, and Mantellisaurus, offering hints of a scale pattern analogous to that of hadrosaurids.”
Preserved integumentary structures in the holotype of Haolong dongi. Image credit: Huang et al., doi: 10.1038/s41559-025-02960-9.
The fossilized remains of a juvenile Haolong dongi, measuring 2.45 meters in length, were excavated from the Yixian Formation.
This particular specimen is noteworthy not only for the superior preservation of its skeletal structure but also for the exceptionally detailed retention of its integument, or external skin.
The fossil exhibits overlapping scales on the tail and distinct tuberculate scales on the neck and thorax — patterns that diverge significantly from those previously documented in other iguanodontians.
However, the most arresting feature is the presence of cutaneous spikes interspersed among the scales.
Through the application of advanced imaging techniques and microscopic examination, the paleontologists ascertained that these spikes possess a hollow, cylindrical form. They are constructed from a highly cornified external layer overlying a multi-layered epidermis, with keratinocytes preserved down to their nuclei. At the center of each spike, a porous dermal pulp is discernible.
This distinct anatomical composition differentiates these spikes from both the protofeathers found in certain other dinosaur species and the scaled spines observed in contemporary lizards, strongly suggesting an independent evolutionary trajectory.
The morphology and positioning of these spikes imply that their primary function was defensive, serving as a deterrent against predators. Nevertheless, they may also have played secondary roles in thermoregulation or sensory perception.
“This remarkable discovery offers unparalleled insights into the microscopic anatomy of non-avian dinosaur skin and underscores the intricate evolution of integumentary structures within ornithischian dinosaurs,” the researchers concluded.
The disclosure of this new dinosaur species is detailed in a published manuscript accessible via the following address: paper in the esteemed journal Nature Ecology & Evolution.
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J. Huang et al. Cellular-level preservation of cutaneous spikes in an Early Cretaceous iguanodontian dinosaur. Nat Ecol Evol, published online February 6, 2026; doi: 10.1038/s41559-025-02960-9
