Recently, a new paper was published describing an amazing dinosaur fossil, discovered in a mine in Alberta, Canada in 2011. The new species was named Borealopelta markmitchelli, meaning “Mark Mitchell’s northern shield”, after a technician at the Royal Tyrrell Museum in Alberta who prepared the fossil. Hailing from the Early Cretaceous Period, around 110 million years ago, Borealopelta was a 5.5-metre-long nodosaurid, a herbivorous quadrupedal dinosaur with spiky, plated armour along its back.
Image from Brown et al. (2017)
Just from the pictures accompanying the paper, you can see how incredible the fossil is: its three-dimensional preservation reveal just how Borealopelta‘s dermal armour was laid out in life. In the Early Cretaceous Period, the rocks in which Borealopelta was found were a seabed; no dinosaur has been found there before. After being washed out to sea, the animal’s body apparently landed on the seabed on its back and was quickly buried. In fact, it’s so well preserved that palaeontologists can estimate what colour it was!
My old dinosaur books would emphasise repeatedly that colour doesn’t fossilize, even in the rare dinosaur specimens that came with skin impressions – this is true, but in a few fossils (mostly feathered dinosaurs), traces of pigment have been left behind. Chemical analysis of these can reveal what kind of pigments they are, and thus what colour they created. The work on Borealopelta has led to the conclusion that it had a reddish-brown back and a lighter underside.
But knowing what colour Borealopelta was isn’t just cool on its own: it also leads to intriguing questions about its ecosystem. The pattern seen – a dark back and a lighter belly – is known as countershading, which today is used as camouflage by animals such as antelope. (Since the side that receives more light is darker, it creates a counterbalance which helps to hide the animal.) But why would an animal which already possessed impressive armour, and was larger than most herbivores alive today, even need to hide itself?
The conclusion is that Borealopelta must have shared its environment with some very impressive and frightening predators. The fossil record may be incomplete, but we know that around the same time that Borealopelta was plodding peacefully around Alberta, an 11-metre-long carnivorous theropod named Acrocanthosaurus was stalking the United States. It is likely that Borealopelta had to be wary of encounters with a similar predator, which might not be deterred by its size or its armour – hence the need to be as inconspicuous as possible!
Brown, C.M., Henderson, D.M., Vinther, J., Fletcher, I., Sistiaga, A., Herrera, J. & Summons, R.E. (2017), An exceptionally preserved three-dimensional armoured dinosaur reveals insights into colouration and Cretaceous predator-prey dynamics. Current Biology 27, 1-8.