A remarkably complete skeleton of a rare dinosaur, the iguanodon, has been unearthed in northeastern China, revealing previously unknown details about the species. The discovery, led by researchers affiliated with the CNRS of France and published in Nature Ecology & Evolution, is providing paleontologists with an unprecedented look at dinosaur skin.
The fossil preserves extensive areas of exquisitely fossilized skin, and among its scales, researchers identified a unique system of hollow cutaneous spikes never before observed in dinosaurs, according to the study. This finding offers fresh insights into the evolution of skin structures in ornithischian dinosaurs.
The new animal has been named Haolong dongi, in honor of Chinese paleontologist Dong Zhiming, and is estimated to be approximately 125 million years old. The discovery highlights the potential for uncovering new information about dinosaur biology through exceptionally preserved fossils.
What sets this find apart is the rare type of evidence it provides: soft tissues preserved at a microscopic level of detail. This level of preservation is crucial for understanding the microanatomy of dinosaur skin and the function of its various structures.
Haolong dongi’s integument combined large, overlapping scales along the tail with tuberculate scales around the neck and thorax. However, the most unexpected discovery was the presence of cellular-level preserved cutaneous spikes interspersed among these scales. To confirm this, the team utilized X-ray scans and high-resolution histological sections.
Analysis revealed that these spikes were cylindrical and hollow structures, formed by a cornified stratum corneum overlying an epidermis with keratinocytes preserved to the level of their nuclei – an extraordinary degree of conservation. This detailed preservation allows scientists to study the internal structure of the spikes with unprecedented clarity.
The authors note that the spikes do not resemble protofeathers found in non-avian dinosaurs or scaly spines in extant squamates, suggesting a distinct evolutionary origin. This indicates that the spikes represent a unique adaptation not previously known in dinosaurs.
The primary hypothesis regarding their function points to defense. As a juvenile individual – more vulnerable due to its size – the spikes likely served as a deterrent, similar to those found on modern porcupines. Researchers do not rule out secondary roles in thermoregulation or environmental sensory perception.
As the specimen is a juvenile, it remains unknown whether adults also maintained these spikes or if they disappeared with growth. This underscores the possibility that other similar innovations may have gone unnoticed, simply because skin is rarely preserved.
Iguanodontes were a group of herbivorous dinosaurs belonging to the ornithopods, or “bird-hipped” dinosaurs. They lived primarily during the Early Cretaceous (approximately 140–110 million years ago, depending on lineage and region) and were highly successful, with species found in Europe, Asia, North America, and Africa.
The name originates from the most famous of them, Iguanodon (“iguana tooth”), because early discoverers noted that some teeth resembled those of a modern iguana. In fact, Iguanodon is one of the first dinosaurs scientifically identified in the 19th century and was key to understanding that extinct giant reptiles once existed.
Generally, iguanodontes had a robust body, a beak for cutting vegetation, and batteries of teeth for grinding plants. Many could move on two legs (bipedally) when running or exploring, but also walk on four when grazing. One of their most recognizable features is a spine-shaped thumb (in several iguanodontids), which may have served for defense or food manipulation.
