The perception of dinosaurs as uniformly scaly, lizard-like creatures has long dominated popular imagination. This view stemmed from early fossil discoveries that revealed reptilian skin textures. However, the true nature of dinosaur skin was far more varied and complex than initially understood. Exploring the diversity of their integument, from intricate scales to unexpected feather coverings, reshapes our understanding of these ancient animals.
What Did Dinosaur Scales Look Like
Dinosaur scales exhibited a remarkable variety in their shapes, sizes, and arrangements across different species and even on different parts of a single animal. Many had small, polygonal scales, often referred to as “basement scales,” which formed a textured background. These could be round, elongated, or hexagonal, ranging from less than 1 millimeter to about 3 millimeters in diameter.
Beyond these smaller scales, some dinosaurs featured larger, more distinct structures. Hadrosaurs, or duck-billed dinosaurs, for instance, displayed a mosaic of smaller tubercles alongside larger, hexagonal scales, reaching 5-10 millimeters in width. These larger scales could form patterns, occasionally appearing in clusters. Some armored dinosaurs, like ankylosaurs, possessed large, bony plates embedded within their skin called osteoderms, which provided protection.
Even within the same species, scale patterns varied significantly. Tyrannosaurus rex, for example, had small elliptical or polygonal scales over most of its body, but its neck might have featured small, protruding circular scales, while its tail could have displayed larger, hexagonal scales. Triceratops horridus is known for distinctive, large, interlocking tubercles with low bosses and spikes, a skin type not found in other dinosaurs without supporting osteoderms. This demonstrates that dinosaur skin was not uniform and included complex arrangements of different scale types.
Scales Versus Feathers
The traditional image of dinosaurs as entirely scaly reptiles has been challenged by fossil discoveries revealing that many possessed feathers. This paradigm shift began with well-preserved specimens from China in the 1990s, proving that some dinosaurs were ancestors of modern birds. While many dinosaurs, such as hadrosaurs, horned dinosaurs, and armored dinosaurs, clearly had scaly coverings, theropods, the group most closely related to birds, displayed feathers.
Evidence for feathers comes from filamentous structures, often called “proto-feathers,” found on species like Sinosauropteryx. Advanced, fully formed feathers resembling those of modern birds have been observed in non-avian dinosaurs such as Caudipteryx and Protarchaeopteryx. These discoveries show that feathers were a significant part of theropod evolution.
Scales and feathers were not always mutually exclusive. Some dinosaurs, such as Kulindadromeus, a small plant-eating dinosaur, have been found with both scales and feathers, indicating a mix of integument types. Recent research on Psittacosaurus supports this, showing reptile-type skin in non-feathered regions and bird-like skin in feathered areas, suggesting a zoned development of skin. This indicates that while feathers evolved, scaled skin was retained in areas where its protective functions were necessary.
How Do We Know About Dinosaur Scales
Our knowledge of dinosaur scales comes from fossilized skin impressions, which are rare and valuable direct evidence of dinosaur skin. These impressions form when an animal’s skin, often from a foot pressing into soft sediment, leaves a negative space that is later preserved as rock. Paleontologists meticulously analyze these impressions to discern the texture, pattern, and size of the scales.
A notable example is the “Trachodon mummy,” an Edmontosaurus fossil discovered in 1908, which preserved skin impressions over almost its entire body, including the neck, shoulders, chest, belly, and forelimbs. This specimen provided insights into hadrosaur skin, revealing a mosaic of larger and smaller tubercles. Other well-preserved skin impressions exist for species like Carnotaurus, showing bumpy, gecko-like skin, and patches of scaly skin have been found for Diplodocus, Triceratops, and Tyrannosaurus.
Beyond direct skin impressions, osteoderms, which are bony plates embedded within the skin, provide indirect evidence of a dinosaur’s armored integument. These structures, found in many armored dinosaurs like ankylosaurs and some stegosaurs such as Borealopelta, indicate the presence of hardened, protective coverings. The study of these fossilized remains allows scientists to reconstruct the appearance and arrangement of dinosaur scales, even revealing cellular structures and pigment-carrying cells, hinting at coloration.
The Function of Dinosaur Scales
Dinosaur scales served multiple purposes, with protection as a primary role. These tough, keratin-based coverings would have shielded dinosaurs from physical injuries, abrasions, or predator attacks. Similar to modern reptiles, scales provided a durable outer layer against environmental factors such as rough terrain or vegetation.
Scales also played a part in thermoregulation, managing body temperature. While large scaly dinosaurs, like sauropods and hadrosaurs, generated enough internal heat to stay warm due to their massive size, scales could have aided in reducing water loss, which is a common function of reptilian skin. Conversely, some scale arrangements could help in heat dissipation in warmer environments.
Beyond protection and thermoregulation, scales could also be involved in display or camouflage. The varied patterns, shapes, and coloration, suggested by pigment-storing cells (melanosomes) found in fossilized skin, suggest roles in visual communication or blending into their surroundings. This parallels the diverse uses of skin patterns and colors seen in many modern reptiles, where skin serves functions beyond physical defense.