Eight years ago, as a bitter cold gripped the forests north of Alberta, Canada, a worker in a bitumen mine noticed a clang as his excavator hit something unexpected. Rocks of an unusual colour tumbled into view. Quite by chance, he had stumbled upon the most exquisitely preserved fossil of an armoured dinosaur ever discovered – a species of ankylosaur that in 2017 would be named Borealopelta.
After being unearthed, the 110-million-year-old fossil ended up at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta, where technicians spent 7,000 hours over the next six years chiselling away the rock entombing it. What they revealed looks more like a statue than a fossil – the preserved specimen includes much of the nearly six-metre-long animal, from its head to its hips, including remains of skin, armour plates and spikes.
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But it was dark smears that caught the attention of University of Bristol palaeobiologist and fossil colour expert, Dr Jakob Vinther. Analysis of the smears revealed traces of a reddish pigment, indicating the dinosaur’s skin colour. Borealopelta had entered the select group of dinosaurs to have their true colours revealed.
Skin and feather colours and patterns might seem like superficial details, but they could help rewrite our understanding of how dinosaurs lived and behaved. Today, animals use colour for camouflage, communication, attracting mates and warding off predators. Dinosaurs almost certainly did, too.
We now know the colours of a handful of dinosaurs, including Borealopelta, the Caihong and the Sinosauropteryx. Improved technology promises to reveal many more. In the meantime, dinosaur experts are poring over these latest finds to reveal some surprising new insights into these creatures’ lives.
Shady science
When Vinther was invited to Drumheller to see the Borealopelta fossil in December 2016, he dropped everything. “It’s a spectacular specimen,” he says. “It was very emotional, because it’s just so lifelike – it really feels alive when you see it.”
Even more exciting were the traces of reddish pigment that Vinther found when he analysed samples of the fossil. This pigment, called phaeomelanin, belongs to a group of natural pigments known as melanin, which are responsible for the colours of the skin, feathers, scales, hair and fur of animals (and red-headed humans) today.
More intriguing, however, was evidence of a pattern of colouration called countershading, which is common in the natural world today. Many modern animals have countershading – a form of camouflage where the animal’s back or upper surface is darker than the underside. In the case of Borealopelta (see Technicolourdinosaurs below), far more phaeomelanin was present in the skin tested on the back than the fossil’s lower surface. Generally, sunlight will make the upper surface of an animal lighter than the underside. By having shading that reverses this gradient, the animal appears flatter to predators, helping it to blend into the shadows.
“If you take any wild mammal that is less than a couple of kilos, 100 per cent of them will have countershading,” says Vinther. “Basically, all animals have it unless they are too big to worry about predators.”
This is what makes the discovery of countershading in a 1.3-tonne, armoured dinosaur so surprising. “Having an ankylosaur that needed countershading means the predator-prey landscape in the Cretaceous was very, very different,” says Vinther. “There were some scary predators around. Even if you were armoured to your teeth, you were not safe.”
Borealopelta is far larger than any animal that requires countershading today, probably because it had to evade predators such as the 11-metre-long, six-tonne Acrocanthosaurus that terrorised what is now Canada during the mid-Cretaceous.
Vinther and his colleagues have found similar countershading in two other dinosaurs: Sinosauropteryx and Psittacosaurus. Sinosauropteryx was a long-tailed, turkey-sized meat-eater that lived 124 million years ago in northeastern China and sported a gingery-brown coat of downy feathers, with a dark back and lighter underbelly. It also had white tail stripes like a ring-tailed lemur and a bandit mask across its eyes, similar to a raccoon.
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Psittacosaurus, also from China, was a primitive herbivore and an early relative of Triceratops. It was about the size of a golden retriever and had red-brown scaly skin and bristle-like feathers emerging from its tail. It seems that Psittacosaurus was countershaded in a slightly different pattern to Sinosauropteryx, with the dark colouration reaching lower down on its body. Palaeontologists think that Psittacosaurus’s patterning was best suited to a dense, forested environment with more diffuse light, while Sinosauropteryx may have lived in more open, lake-side environments that had direct light and strong shadows.
Flights of fancy
The first dinosaur colour discoveries were made in 2010 by two competing groups, one led by Vinther, then at Yale University in the US, and the other by palaeontologist Prof Mike Benton at the University of Bristol. Benton’s team found evidence of the gingery hue in Sinosauropteryx, while Vinther’s team mapped out black, white and grey feathers and a russet head-crest on the crow-sized, four-winged, flying dinosaur Anchiornis.
These discoveries relied on a method developed in part by Vinther for determining the colour of dinosaur and prehistoric bird feathers, not based on chemical traces of the melanin pigment (as with Borealopelta), but on the shape of fossilised microstructures in the feathers called melanosomes.
These tiny, durable structures are packages of melanin that are also found in the feathers of modern birds, and the hair and fur of mammals. Conveniently for palaeontologists, the shape of the melanosomes in modern animals tends to correlate to their colourings.
Reddish phaeomelanin, for example, is typically found in melanosomes that are round and 400-500 nanometres wide. Black or brown ‘eumelanin’ is packaged in 300nm sausage-shaped melanosomes. This means that, even though little actual melanin remains in many of these fossils, researchers are still able to study the melanosomes and make reasonable guesses about the colour of these dinosaurs.
Using these techniques, we now know that early bird Archaeopteryx was black and white. Microraptor, the four-winged dinosaur from China, has melanosomes that suggest not only a blue-black colouration, but also a beautiful sheen, similar to a Eurasian magpie or a crow. The duck-sized Caihong was potentially even more stunning, with the colourful iridescence seen in modern hummingbirds.
The intriguing thing about all of these more brightly coloured dinosaurs is that they lived in the trees. “If you live in more shaded environments then you’re less exposed, both as predator and prey, and can become more colourful,” says Vinther. So, in these animals, bright colours may have been used in sexual displays to attract mates and intimidate rivals.
On the ground, however, it was a different story. Dinosaurs such as Sinosauropteryx, Borealopelta and Psittacosaurus would have been more exposed and vulnerable, so their colouring was more camouflaged and drab, Vinther argues. It’s likely that their dinosaur predators would have had excellent vision. Modern birds (the descendants of the dinosaurs) have some of the best eyesight in the animal kingdom, and can see ultraviolet light on top of all the colours that we see.
“You really had to be well camouflaged to stay alive, and camouflage strategies had to be more precise,” says Vinther, explaining why countershading may prove to be the norm for all but the largest and scariest ground-dwelling dinosaurs. This countershading was probably patterned – rather than the uniform greys, greens and browns that dinosaurs historically sported in illustrations. It’s unlikely that any of these beasts were truly vibrant, however.
“I don’t think there was ever a purple or pink dinosaur that walked on the ground,” Vinther says. A psychedelic dinosaur wouldn’t last long in a world filled with predators.
Missing pieces
The field of dinosaur colour is not without its controversies. Some experts have cautioned that the research might be reading the melanosome evidence too literally, missing out on other details that could affect a dinosaur’s colouration.
Dr Maria McNamara is a palaeobiologist and expert on fossil colour at University College Cork in Ireland who, in 2018, was part of a team that found definitive evidence of downy feathers and melanosomes in pterosaurs, the flying reptilian contemporaries of the dinosaurs. She cautions that many kinds of bright colours in birds today are actually created by organic ‘carotenoid’ pigments, which rarely get preserved in fossils.
The colours of feathered dinosaurs elucidated so far “are a fair reconstruction of the melanin-based pigmentation,” she says, “but that may have no relationship to the actual colour of those animals. It does nothing for the science if we produce beautiful coloured fluffy dinosaur reconstructions and then have to retract them.”
Vinther agrees that carotenoid pigments are a gap in our knowledge, but points out that while carotenoids colour the feathers of about 40 per cent of songbirds (the dominant group of birds today), they only colour the feathers of 13 per cent of other birds. As such carotenoids were likely less important during the time of the dinosaurs, before songbirds evolved.
Vinther and others are trying to find fossil hints or traces of new kinds of colour-creating structures and pigments, including carotenoids. Whatever they find, though, all the experts agree that there are exciting times ahead.
“It goes much further than ‘what colour is this dinosaur?’,” says McNamara. “It can actually tell us the evolutionary driving forces there were at stake… Were the visual signalling strategies we see today already in place, or did dinosaurs communicate in novel ways?”
Prof Mike Benton, who led the work to reveal the colour of Sinosauropteryx, concurs: “The best thing about the whole 10 years of colour research in dinosaurs is that it has pushed back the field of speculation several notches – we can determine colours and patterns now, and we can begin to think about behaviour.”
Every dinosaur fossil that palaeontologists unearth over the coming years will be a new story waiting to be told. Now it seems that we’re finally beginning to read these stories in all their technicolour glory.
Technicolour dinosaurs
So far, seven dinosaurs have had their colours or patterns revealed by scientists
Anchiornis huxleyi
Length: 40cm, with a 50cm wingspan
Weight: 250g
Lived: Northeastern China, late-Jurassic (160 million years ago)
Crow-sized, four-winged flying dinosaur.
Similar to four-winged Microraptor, Anchiornis is known from hundreds of fossil specimens, meaning that it’s well understood as a species.
Microraptor gui
Length: Up to 80cm, with a 1m wingspan
Weight: 1kg
Lived: Northeastern China, early-Cretaceous (120 million years ago)
Four-winged relative of Velociraptor that glided and flapped between the trees.
Most dinosaurs are only known from a single fossil, but more than 300 skeletons of Microraptor have been found, suggesting it was abundant in its ecosystem.
Borealopelta markmitchelli
Length: 5.5m
Weight: 1.3 tonnes
Lived: Western Canada, mid-Cretaceous (110 million years ago)
A type of heavily armoured ankylosaur, known as a nodosaur.
Ankylosaurs are typically thought to have had spikes and armour plates for defence, but Borealopelta may also have used its exaggerated spines to impress possible mates.
Caihong juji
Length: 40cm
Weight: 500g
Lived: Northeastern China, late-Jurassic (160 million years ago)
Duck-sized, gliding carnivore covered in feathers.
This dinosaur’s name means ‘rainbow with the big crest’ in Mandarin. It’s since been suggested that what appeared to be a head crest may have been a small ridge above its eyes to avoid glare from the sunshine, as some eagles have today.
Archaeopteryx lithographica
Length: Up to 50cm, with a 50cm wingspan
Weight: 1kg
Lived: Southern Germany, late-Jurassic (150 million years ago)
Small flying carnivore, often regarded as the earliest known bird.
Unlike modern birds, Archaeopteryx didn’t have a bony breastbone for large flight muscles to attach to, so was likely a much weaker flier.
Psittacosaurus sp.
Length: 1-2m
Weight: 20kg or more
Lived: Asia, mid-Cretaceous (110 million years ago)
Golden retriever-sized herbivore with long tail bristles. Walked on its two hind legs.
Most dinosaur genera have only one species, but up to 11 different kinds of Psittacosaurus are known from China, Mongolia, Siberia and Thailand.
Sinosauropteryx prima
Length: Just over 1m
Weight: 550g
Lived: Northeastern China, early-Cretaceous (124 million years ago)
Slender, turkey-sized carnivore with a long tail.
Revealed to the world in 1996, Sinosauropteryx was the first dinosaur ever confirmed to have feathers.
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