Armoured tank-like dino used camouflage to hide

By Prof Sarah Gabbott
Science writer

  • Published
Borealopelta markmitchelliImage source, Royal Tyrrell Museum of Palaeontology, Drumheller,
Image caption,
An illustration of the 110-million-year-old Borealopelta markmitchelli

A new species of mega-herbivore dinosaur discovered in Alberta, Canada, preserves incredible details of its skin, scales and spines.

The exquisite specimen is a type of armour-plated nodosaurid ankylosaur.

It was camouflaged which suggests that, despite its tank-like appearance, it hid to avoid predation.

That such a large creature needed camouflage indicates the presence of even larger, keen-eyed meat-eating theropod dinosaurs.

A new species of dinosaur named Borealopelta markmitchelli has been discovered from an oil sand mine in Alberta, Canada, and is described this week in Current Biology.

The dinosaur is a nodosaurid ankylosaur and is perhaps the best preserved of its type ever found, as Dr Jakob Vinther, University of Bristol, UK, who co-authored the study describes: "This dinosaur is so complete it looks like it's asleep and we would just need to gently cough to wake it up," he said.

This group of dinosaurs was stout, tank-like and heavily armoured. They walked on short legs and their teeth indicate that they were herbivorous. The new specimen is 5.5m long, and weighed 1,300kg when alive.

Like other ankylosauria, the new specimen's body is covered in osteoderms - robust, bony, scale-like plates arranged in rows.

B. markmitchelli is remarkable because the osteoderms are covered by a keratin sheath, an organic layer that is usually lost in the fossilisation process. The skin of the creature is also preserved and can be seen between the gaps of the osteoderms.

Fossil colour

The colour and the distribution of colour across the body reveal something surprising about the behaviour of the dinosaur and the ecosystem in which it lived.

The keratin sheath and skin on the upper surface of the dinosaur are much darker than on the lower surface, and the scientists suspected that this was the result of skin pigmentation. But chemical confirmation was needed to back up this bold claim.

Using a type of mass spectrometry, called time-of-flight mass spectrometry, and gas pyrolysis, they were able to chemically analyse samples of the dark organic material from the keratin sheaths and the skin. This confirmed their suspicion - the pigment melanin was present.

Melanin occurs in many animals and is the pigment that allows our skin to tan in the sun. The most common type of melanin colours tissues black or brown. Another type - pheomelanin - makes a reddish colour, and the scientists found evidence of this type in the samples of B. markmitchelli.

B. markmitchelli is clearly countershaded - having a reddish-brown back and a pale belly.

Countershading is argued by the researchers to reveal quite a lot about what life was like for B. markmitchelli. As Jakob Vinther explains: "Colour patterns can be used for sexual display, thermoregulation, communication and many other reasons," he said.

"But, today, countershading is used for camouflage and we think that the new species had this type of pigment pattern to help it to hide from predators."

This is surprising given the armour plating and large size of the ankylosaurian.

Image caption,
Impala have countershading camouflage to evade predators. The elephant relies on its large size to avoid predation

In today's ecosystems the largest herbivores, such as elephants and rhino, are usually ignored by predators. It is the smaller, more vulnerable prey, such as antelope, that are selected by predators, and correspondingly, it is these creatures that are frequently countershaded to help them avoid detection by predators.

If antelope are discovered their back-up policy is the ability to run and fast.

Ankylosaurian dinosaurs could not run fast - but they were heavily armoured and this may have served as their second line of defence.

The upshot of this is that there must have been some extremely large, mean and visually acute predators around at this time.

These were likely to be theropod dinosaurs, but they have yet to be discovered in the area where the new specimen was found.

But there is a good candidate as described by Caleb Marshall Brown, lead author on the research: "The most likely predator is a creature called Acrocathosaurus - a 10m-long, 6-tonne, animal that looked superficially like Tyrannosaurus rex, but was not closely related to it."

B. markmitchelli is named in honour of the fossil preparator - Mark Mitchell - who spent over 7,000 hours skilfully revealing the fossil by removing, grain by grain, the iron-carbonate nodule which encased it.