Even large armored dinosaurs—like the tank-sized ankylosaur—lived in fear of predators. That’s the conclusion of a new study, which suggests the 1300-kilogram Borealopelta markmitchelli, which roamed North America more than a hundred million years ago, may have used camouflage to hide from its enemies. If true, the find would be the first example of camouflage in such large animals. But other experts say the evidence is too weak to support that conclusion.
“[This] could have been a really cool case, but I would like to see more data,” says Johan Lindgren, a paleobiologist at Lund University in Sweden who was not involved in the work.
The Borealopelta fossil was found by accident in a mine in the Alberta province of Canada, which millions of years ago was part of a large inland sea that cut North America into eastern and western halves. The remains of the dinosaur, which may have fallen to the sea floor after it drowned, were so well preserved that researchers were able to recover fossilized skin retaining the creature’s pigmentation. The intensity of that pigmentation decreased from the dino’s back to its sides, suggesting that the underside of the animal was lighter in color than the top side, researchers report today in Current Biology.
The variation in color would have been effective camouflage, says lead author Caleb Brown, a paleontologist at the Royal Tyrrell Museum of Paleontology in Drumheller, Canada. That’s because such a pattern keeps the animal’s top half darker, even in direct sunlight, allowing it to blend in with the ground. Such countershading is seen in modern animals like antelopes and foxes, he notes.
But there are other explanations for the pattern, Lindgren says. If the dinosaur settled to the sea floor on its back, the skin on the upper side of the animal would have been better preserved than that of the rest of the body, he says, possibly explaining the decreased intensity in pigmentation.
Study co-author Donald Henderson, a dinosaur curator at the Royal Tyrrell Museum, disagrees. His team’s analysis of the sediments around the fossil suggests that Borealopelta was entirely buried soon after the animal reached the seabed, preventing the skin on its belly from degrading. In addition, the dark pigments are most abundant on the back and decrease gradually toward the sides, as in most living animals. If the coloration were an effect of being only partially buried, says Henderson, there would be a sharp cutoff.
Also up for debate is what color the dinosaur was. Typically, researchers determine this by looking at preserved melanosomes, structures inside cells whose shape correlates with the hue of the pigment melanin they contain. The team couldn’t find any melanosomes in the new fossil, however, weakening the case for both camouflage and coloration, says Sandra Siljeström, an organic biochemist at the RISE institute in Boras, Sweden. But Sarah Gabbott, a paleobiologist at the University of Leicester in the United Kingdom, counters that melanosomes tend to disappear after being underground for long periods of extreme heat and pressure, so their absence doesn’t necessarily mean anything.
As an alternative, the researchers turned to a kind of chemical analysis that heated and broke apart molecules in the dinosaur’s skin to determine its components. The team found a lot of the compound benzothiazole, the building block of red melanin, says study co-author Jakob Vinther, a paleobiologist at the University of Bristol in the United Kingdom. The results indicate that Borealopelta was a ginger, he says.
But experts are skeptical here, too, saying that heating such samples can lead to unreliable results. And Maria McNamara, an expert on fossil preservation at University College Cork in Ireland, warns that the compounds found in the sample could have come from different sources, including bacteria living on the corpse.
If Borealopelta was indeed camouflaged, it would significantly change thinking about prey-predator dynamics in the time of the dinosaurs, Henderson says. Today large “attack-proof” animals like elephants and rhinos do not use camouflaging, he says. Scientists have always assumed that massive dinosaurs would be equally shielded from predators. But the newly discovered fossil suggests that millions of years ago bulky dinosaurs like Borealopelta might have been preyed on by even larger dinosaurs, Henderson says. Those could have included the sharp-toothed, long-clawed Acrocanthosaurus, which grew as long as 10 meters. “These predators were making life miserable for both the big and the small.”
Despite the lack of consensus, everyone agrees that the new specimen is remarkably well-preserved. It’s a “truly wonderfully complete fossil,” says Thomas Holtz, a paleontologist at the University of Maryland in College Park, who was not involved in the research. For the curious—or the skeptical—the fossil is currently displayed at the Royal Tyrrell Museum.
*Correction, 4 August, 11:06 a.m.: This story originally misstated the location of University College Cork. It has been updated to the correct location.