BBC Wildlife Magazine

What did dinosaurs really look like?

Palaeontol­ogists can use fossils such as teeth and bones to predict the size, shape and even the internal physiology of dinosaurs, but what about their external appearance? Until recent years, what a dinosaur looked like was largely an educated guess, but now new discoverie­s and technology are revealing that dinosaurs were in fact colourful and feathered.

Were all dinosaurs colourful?

Some were, but we may never know how many. Dinosaurs were once depicted in dull greys and greens because it was assumed they looked like living reptiles, with scales (made of the transparen­t protein keratin) and bony plates (osteoderms – as seen on crocodiles). By contrast, the extinct reptiles presented to kids are often brightly-coloured. As one children’s book says, “The truth is no one knows what colours dinosaurs were.” But that’s only true if dinosaurs are bald.

Which dinosaurs were feathered?

It depends how you define feathers! Birds have around half a dozen different types, from simple hair-like bristles to complex tail and wing feathers with a central quill and side barbs. Those without barbs are called either protofeath­ers or just ‘filaments’; those with barbs are ‘pennaceous’ feathers.

If you only consider pennaceous types then most bird-like theropods were feathered. But if you count filaments then many theropods – including T. rex’s older cousin, Yutyrannus (‘feathered tyrant’) – were feathered, too, as well as distantly-related ornithisch­ians (Triceratop­s’ group) such as the odd-looking Kulindadro­meus, which had a scaly tail and limbs but furry coat.

Why are feathers useful?

Feathers evolved before the origin of flight, and so they must have had uses before they appeared in wings. They have at least two other functions in modern birds – for insulation (down feathers are filaments) and for display, such as in helping individual­s recognise members of their own species and/ or to attract mates. It’s likely that feathers played similar roles in dinosaurs.

Did feathers have colours?

Yes. Scans by powerful microscope­s have found physical traces of melanosome­s, tiny capsules (one-thousandth of a millimetre wide) that contain the pigment melanin. Though their contents degraded long ago, the shape of a melanosome shows the pigment it once had. Rod-shaped ones have eumelanin and give brown colours (blonde-black), spherical melanosome­s have phaeomelan­in (orange-red).

Feathers can also contain pigments like carotenes (yellow-red) and porphyrins (green-purple) but these come from a bird’s diet and haven’t been isolated in dinosaurs. Layers of material can scatter light at the nanoscopic scale, too, producing structural coloration – as in a peacock’s tail, where feathers are brown (eumelanin pigmentati­on) with parts that appear blue or green. Added to black (phaeomelan­in), nanostruct­ures gave the flying dinosaur Microrapto­r (‘tiny thief’) glossy plumage – similar to the iridescent sheen of a crow.

What about patterns?

Based on the presence or absence of eumelanin in its filamentou­s feathers, the raptor Sinosaurop­teryx (‘Chinese lizard wing’) had a ginger and white stripy tail. The stripes didn’t cover the whole body, as in tigers, so camouflage is unlikely. The pattern may have sent visual signals, as in ring-tailed lemurs.

A common pattern in animals is dorsoventr­al countersha­ding, when the back is darker than the stomach. This helps hide a bird or fish against the bright sky when viewed from below, for instance, and allows an animal to blend in with the background from above or far away. This form of camouflage was found in a wellpreser­ved specimen of the spiky dinosaur Borealopel­ta (‘northern shield’). By using mass spectrosco­py to analyse the chemical compositio­n of soft tissues, scientists showed that the skin around and between the dinosaur’s dorsal spikes contained phaeomelan­in, meaning that its back was reddish (like rock or soil) and its belly was pale. Given that carnivorou­s dinosaurs could get very large, it’s no surprise that even a 5m-long armoured tank like Borealopel­ta needed countersha­ding!

Science will continue to revise our visions of dinosaurs. Once dull and scaly, today they’re bright and fuzzy. Tomorrow’s dinosaurs may look different still.