Surrounded by hungry predators, a little plant-eating dinosaur from the early Cretaceous did the only sensible thing. It donned camouflage.
Analysis of the exquisitely preserved fossil remains has revealed one of the most elaborate dinosaur paint jobs ever seen, including a brown back and a lighter belly. Modern-day antelope, fish and other animals have similar dark-and-light zones, which confuse predators, but this is the first discovery of such markings on a dinosaur.
“This one is unique,” says paleontologist Jakob Vinther of Britain’s University of Bristol, co-author of a study describing the fossil published in the journal Current Biology. “We can very clearly see that there are colour patterns … stripes, spots.”
The fossil is also memorable for a more embarrassing reason: It appears to be pooping. Protruding from its bottom is a rounded object much like a dog dropping. The researchers say the object could be a bone, but its composition suggests faecal material.
Even so, the animal “probably didn’t die while defecating,” Vinther says via email. Gases from the animal’s decay may have pushed out the waste, he says, or perhaps the dinosaur’s guts continued to churn after death.
The fancy-pants reptile is a type known as a Psittacosaurus, or “parrot-lizard.” It was about the size of a golden retriever, with stubby spikes on its cheeks and a beaked jaw. Luxuriant quills sprouted along its tail like bristles from a toothbrush.
This particular Psittacosaurus lived some 120 million years ago in what is now China. It was not a safe neighborhood. Local predators includedYutyrannus, a T.-rex-like giant weighing a ton or more, and a smaller T. rex relative named Dilong.
Psittacosaurus’s dark back and lighter belly, visible on the specimen’s remaining scales, could have helped it stay out of a hungry carnivore’s claws. Modern-day predators rely on an object’s shading to assess its shape, Vinther explains, and when prey is darker on top than on the bottom, a colour scheme known as countershading, shadows are minimized and the animals look flatter.
The dinosaur Psittacosaurus, illustrated, is the first dinosaur to show evidence of countershading, a type of camouflage in which animals have darker-coloured backs and lighter bellies [Image: Bob Nicholls]
To learn more about the dinosaur’s environs, the researchers built a life-size model of the Psittacosaurus and painted it grey. At a nearby botanic garden, the model was photographed on both clear and cloudy days, out in the open and under cover of vegetation.
The images show that the Psittacosaurus’s colouring provided the best camouflage in diffuse light, not full sun. So the reptile probably lived in the forest rather than on the savanna, the researchers conclude.
The dinosaur’s dark pigments probably served other purposes as well. Dark stripes on the inside of its legs may have warded off insects, like the slashes adorning the legs of modern-day zebras. And spots on the outside of the front legs could have hardened the skin, thanks to the toughening qualities of pigment molecules.
Other scientists say that given the difficulty of reconstructing extinct animals and their environments, the new study makes a good case that this animal turned to camouflage.
“It’s no surprise” that a dinosaur should do so, paleontologist David Hone of Britain’s Queen Mary University of London says via email. But “it is very important as it shows that these patterns really were present. … That gives confidence we will find more, and then can start to see how things change over time.”
The new results are “very cool,” says paleontologist Gareth Dyke of Hungary’s University of Debrecen, who has found that the extinct reptiles known as mosasaurs had dark backs and may have had light bellies. What’s interesting, Dyke says, is “the variety of different colours seen on this single fossil. We don’t see that, as far as I know, in many, if any other, fossil dinosaurs.”
Feathered dinosaurs are known to have boasted beautifully coloured plumage, but Vinther argues that this specimen had scales, not feathers. And that makes this Psittacosaurus the clear winner in its division of the dinosaur beauty contest.
“This is definitely the best specimen,” says Vinther, “the Holy Grail for naked dinosaurs.”