Illustration of a sauropod, with inset showing pigmented structures in the skin as seen with an electron microscope
Tess Gallagher
Microscopic structures seen in the fossilised skin of a sauropod suggest that these giant dinosaurs may have been as brightly coloured as some birds.
Tess Gallagher at the University of Bristol, UK, and her colleagues examined sauropod skin fossils thought to be around 145 million years old, collected in 2019 and 2022 from the Mother’s Day Quarry in Montana.
Although the fossils couldn’t be definitively identified, it is thought they were probably Diplodocus.
The researchers took tiny pieces off the four scales from the fossils using a scalpel, then studied them with a scanning electron microscope, allowing them to see details at a cellular level.
The skin was three-dimensionally preserved, rather than just an impression, says Gallagher. It also showed evidence of diverse melanosomes, the structures inside cells that store melanin, creating colour in skin, hair, eyes and feathers.
“I was expecting to find traces of melanin at the bare minimum,” she says. “What we did find was evidence that sauropods could have diverse melanosome shapes, which ultimately means the potential for diverse colours.”
Every specimen that the team studied had melanosomes and they came in two main types: oblong- and disc-shaped. However, it isn’t yet possible to say exactly which colours the skin of these sauropods would have been – only that the variety in the structures suggests multiple possible shades.
“Diplodocus would have been remarkably textured animals, with potential colour patterning and diverse colours,” says Gallagher.
The closest comparisons that can be made to the disc-shaped structures are the platelet melanosomes found in modern bird feathers. Gallagher says these may be evidence that Diplodocus had the potential to create a variety of colour using their melanosomes. “These animals could have more striking colour patterns, as opposed to being grey like we see in old palaeoart.”
Mike Benton, who is also at University of Bristol but wasn’t involved in the research, says the shape of the structures described and the way they are preserved mean they are plausibly melanosomes.
The researchers are “rightly careful in their presentation, but it seems a possible first record of colour-bearing melanosomes in a sauropod dinosaur”, he says.
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