It was found that an iguanodontian dinosaur possessed spines more akin to those on certain mammals than any previously observed on dinosaurs. Since the sole evidence for this defense comes from a juvenile specimen, one cannot rule out the possibility that the species shed these spines upon reaching maturity, though this would be a rather peculiar adaptation. The findings of this new research were published in the journal Nature Ecology & Evolution.
Life for Cretaceous herbivores was precarious, and a defensive mechanism could be the deciding factor between having descendants and perishing. Thus, it is unsurprising that evolution experimented with numerous strategies. The tank-like armor of ankylosaurs and the sharp plates of stegosaurs are well-known, but other defensive methods likely existed of which we remain unaware due to poor preservation in the fossil record.
Under more common fossilization circumstances, a specimen unearthed in Lamagou, Liaoning Province, might have resembled many other members of the widespread iguanodont group, as its bones and teeth showed no apparent anomalies. Fortunately, this is a rare instance where the environment that claimed the animal’s life also preserved its skin, making this discovery quite remarkable.
Some iguanodontian skin impressions have been recovered before, though these primarily belong to Late Cretaceous hadrosaurids. In the earlier periods of dinosaur dominance, the best preserved remains were imprints of small scale patches. Therefore, when the team led by Jiandong Huang from the Anhui Provincial Geological Museum uncovered a surprisingly well-preserved impression in the 125-million-year-old Yixian Formation, they realized they had discovered something extraordinary.
The new species has been christened Haolong dongi, which translates from Chinese as “fierce dragon.” The species name honors Dong Zhimin, a prominent paleontologist who passed away in 2024.
The specimen measured 2.45 meters from snout to tail, but its vertebrae were not fully fused, indicating it was still young and undergoing growth. While we cannot definitively know its full adult size, the authors point to some contemporaneous local species that may have been relatives, reaching 3 meters and 5–5.5 meters in length, respectively. Meanwhile, European iguanodonts from the same time frame attained much larger dimensions.
The skin exhibits two distinct types of scales, reminiscent of those found on many modern reptiles, yet differing from hadrosaurid scales in that those on the tail overlap. The scales covering the body do not overlap, making them more consistent with other dinosaurs.
More significantly, these scales are interspersed with spines that are hollow and nearly cylindrical. While some non-avian dinosaurs developed proto-feathers, and certain lizards use scaly spikes for defense, these features are sufficiently divergent that Huang’s team posits they evolved independently.
Most of the spines are quite small, measuring only 2–3 millimeters, but interspersed among them are longer specimens, with the longest preserved spine reaching 44.2 millimeters in length and 7.8 millimeters in width at its base. Despite this substantial variance in dimension, they all share the same simple morphology. Defenses seen on spiny mammals have a composition similar to hair; in contrast, the material forming the scales here performs a secondary role by structuring the spines.
Unusual body configurations in extinct species are typically attributed to three main factors: predator defense, mate attraction, or thermoregulation (heat retention or dissipation). In this case, the authors lean toward the first explanation, though they acknowledge that the regional climate might have rendered heat retention a secondary benefit. They also speculate that the spines could have served a sensory function, similar to how snake bristles detect vibrations.
Most known predators that H. dongi would have encountered were relatively small, and their mouths would have been vulnerable to such spikes. The authors note, “These defenses would not necessarily provide impenetrable armor against the teeth and claws of theropods, but they would make the prey more cumbersome and difficult to dismember and consume, thereby decreasing the likelihood of a successful predation event.” The larger spines might also have served to deter rivals or draw in mates.
About the Author
