Feather-like structures in fossils of the dinosaur Sinosauropteryx (above) suggest it had reddish-brown and white tail stripes. Image: Chuang Zhao and Lida Xing
Scientists have recreated the colourful plumage of some of the earliest dinosaurs to grow feathers in research that shines fresh light on the evolution of the beasts.
The flesh-eating Sinosauropteryx, which lived 125m years ago, sported a mohican-style crest on its head and a racoon-like tail marked with alternating russet and white stripes, researchers say.
Paleontologists reconstructed the hues of the dinosaur’s coat after discovering pigments preserved in fossilised remains of the creatures. It is the first time fossil hunters have known the true colours of a dinosaur.
Scientists at Bristol University and the Chinese Academy of Sciences in Beijing analysed fossils of Sinosauropteryx unearthed in the Jehol rock beds in northeast China. The rocks have been dated to between 131m and 120m years old.
The knee-high Sinosauropteryx, a less fearsome cousin of Tyrannosaurus rex, stood on two legs and had an early version of feathers, made of bristles as long as a fingernail. The metre-long creature used its tail for balance when running.
The colourful tail stripes led researchers to believe that feathers evolved primarily for ornamental reasons and only later became adapted for insulation and flight.
Sinosauropteryx had short, muscular forearms and powerful claws to grasp prey. The creature fed on early lizards and cockroach-like insects that were plentiful in the Florida-like environment of the region. Its jaws were lined with tiny, sharp teeth used to pierce flesh.
Professor Michael Benton, who led the study, examined the remains of bristles under an electron microscope and found tiny structures called melanosomes that contain melanin, a common pigment found in human skin.
In modern birds and mammals, different kinds of melanosomes produce black, grey, orange and brown tones. Black colouration comes from sausage-shaped melanosomes, while spherical ones produce an orangey brown.
Samples from Sinosauropteryx show its tail had bands of melanosomes which produced white and orange rings. The technique gives paleontologists a way of mapping the colours of feathers across the whole body of a dinosaur.
"Two things we thought we would never know about dinosaurs were the noises they make and their colours. We’ve discovered evidence that can tell us for sure some aspects of colour in dinosaurs," Benton said. The research is published in the journal, Nature.
In birds, bright colours are always associated with display, with the tail of the peacock being an extreme example. The colours are used to attract mates or to frighten off rivals or predators. “From the fact that Sinosauropteryx has a stripey tail, we would say that it’s a display function,” Benton said. “It’s clearly not for flight because these are just short bristles.
"What we don’t know is how substantially the body was covered in feathers. The whole body may have been covered in feathers or maybe not. If it was not, then display is the primary purpose."
The team also found melanosomes in the feathers of a primitive bird, Confuciusornis, recovered from the same rocks. Pigments in the feathers suggest it was covered in patches of black, white and brown. The pigments survived for millions of years because melanosomes are made from tough proteins that are hard to break down.
The multicoloured plumages of modern birds are produced by a variety of pigments that are not as hardy as melanosomes. These pigments, which are responsible for flashes of red, purple and green in many birds, may have evolved in early dinosaurs but are too fragile to be preserved in fossils.
"We’re giving a minimum palette. There could be more colours, including flashes of purple and green, that we haven’t been able to see," said Benton.
The team plans next to look for arrangements of melanosomes that produce striking iridescent blues and greens in modern birds such as the kingfisher.
Last year, scientists at Yale University in Connecticut studied iridescent colours in a 40m-year-old bird fossil. The wings changed from a metallic green to blue or copper depending on the viewing angle.
Chances of determining the colour of scaly dinosaurs, like those depicted in the BBC series Walking With Dinosaurs, are slim, since skin and fur is not preserved in their fossils.