The male and female of the oviraptosaur Avimimus, which may have used its feathered forelimbs for display.
Credit: Peter Schouten: Zhao Chang and Xing Lida
IF YOU COULD step back to the late Jurassic, 160 million years ago, and conceal yourself in the prehistoric foliage of Mongolia, you would see something remarkable. Between the tree ferns and cycads, an unusual looking bird would appear. It tidies up a clearing – removing leaves, sticks and other debris.
Then, with a dramatic flourish, the pigeon-sized creature stands on tip toes, puffs-up its strikingly coloured plumage, and starts to jerkily dance from side to side, all the while producing clicks and shrill little calls. Most conspicuous are its four long tail feathers, which flick and waft as it shimmies to an internal beat.
This is actually a courtship ritual, very much like the kind played out by birds of paradise today in New Guinea. But the performer isn’t a bird at all.
It doesn’t have wings, but lightly feathered forelimbs with sharp little claws; and instead of a beak, it has a full set of pointy teeth. What you are spying on is actually a small dinosaur named Epidexipteryx, Greek for ‘display feather’.
A delicately preserved fossil of Epidexipteryx hui, featuring impressions of four 20-centimetre-long, ribbon-like feathers, was unearthed in Inner Mongolia in 2007, and described in the British journal Nature the following year.
It was the first clue that feathers found a use in display long before they ever helped a creature become airborne. The scenario above is fanciful, but the paper’s authors, at the Chinese Academy of Sciences, are convinced the feathers were used for seduction.
“Ornamental plumage is used to send signals essential to a wide range of avian behaviour patterns, particularly relating to courtship,” they write. “It is highly probable that the [tail feathers] of Epidexipteryx similarly had display as their primary function.”
This fossil is one small pebble of proof in an avalanche of evidence that has emerged over the last 15 years, confirming that birds are the descendants of theropod dinosaurs (the majority of the bipedal carnivorous species) and that, in some ways, they were very bird-like. There is now good evidence that even fearsome and well-known species – such as Velociraptor and Tyrannosaurus – had feathers.
“The most startling revelation about Velociraptor and its kin is that many are now known to have possessed feathers. This fact has made us think again not only about the transition to birds, but also about how they might have used their feathers,” says Australian palaeontologist John Long in his book Feathered Dinosaurs (CSIRO Publishing, 2008).
“Did they use feathers in complex mating rituals? Did they use them to brood their young? Or did feathers act primarily as a stepping-stone in the evolution of flight? We know from fossil evidence that some of these scenarios, and possibly all of them, were true.”
Mark Norell is the curator of palaeontology at the American Museum of Natural History (AMNH) in New York, USA. He was the co-author of a 2007 study that reappraised Velociraptor arm bones to show they have ‘quill knobs’ – pits where the feathers of living birds are attached with ligaments.
