Diplodocus might have sported speckles or even a shimmer, thanks to pigment structures hidden in its scaly skin.
Juvenile sauropod dinosaurs like Diplodocus had diverse pigment-producing organelles in their epidermis, hinting at unexpected color patterns, researchers report in Royal Society Open Science. The discovery marks the first peek at sauropod coloration and challenges the view of these giants as drab, uniform gray or brown behemoths.
The fossil skin comes from baby Diplodocus specimens unearthed at the Mother’s Day Quarry in Montana’s Morrison Formation, a Late Jurassic site packed with young sauropods that likely died together during a dry spell before a debris flow buried them.
To probe the skin, the team chipped off small pieces from several scale patches and examined them under scanning electron microscopy, revealing layered structures and tiny impressions.
The scales, mostly polygonal and about 10 millimeters across, preserved as carbonaceous films atop sediment, with two distinct layers: a flaky upper one rich in aluminum and silica, and a smoother lower one packed with carbon.
Within these layers, especially the upper one, clustered groups of microbodies stood out. “The first are oblong-shaped and interpreted as melanosomes,” the study authors note. These averaged around 200 to 400 nanometers long, similar in size to those producing brown hues in modern birds, though they might have created darker shades like in some reptiles.
A second type caught the eye: flat, disk-shaped microbodies about 350 nanometers wide, often mingled with the oblong ones. “The nature of the second disk-shaped microbody is unclear, but their flat shape is reminiscent of platelet melanosomes, though they are smaller in size,” the researchers write.
These disks resemble structures in bird feathers that create iridescent effects, boosting brightness and saturation. If confirmed as melanosomes, they would be the first sign of shape diversity in dinosaur scales, potentially allowing for speckled or shiny patterns.The groupings — spaced 10 to over 100 micrometers apart and varying from 5 to 50 micrometers wide — suggest sparse, dotted pigmentation rather than solid color blocks.
The upper layer likely represents the fossilized stratum corneum, the dead outer skin, replaced by clay minerals during fossilization as keratin degraded away. “We hypothesize that the original keratin layer was diagenetically replaced with aluminosilicates during the fossilization process,” the authors explain.
This setup preserved the melanosomes in place, unlike flattened fossils elsewhere. The lower carbon-rich layer may trace where pigment cells once sat.While full-body patterns remain unknown, the mix of microbody types opens doors to vibrant sauropods. “The presence of two distinct microbody morphotypes suggests the potential for complex colour patterning in the epidermis of juvenile Diplodocus,” the paper states.It also ties into sauropod biology: their fast growth and possible high metabolism might have driven diverse melanosome shapes, like in birds and mammals.
“This study paves the way for future work to determine the colour pattern over the entire sauropod body and provides the first constraints on the colour of juvenile Diplodocus, which are also the first constraints on the colour of sauropods in general,” the researchers conclude.
Citations: Royal Society Open Science. DOI: 10.1098/rsos.251232
