‘My eyes probably expanded 20 times like a cartoon character.’
Fossilized tarbosaur skin.
Dr Philip J Currie
Whether or not it was a legally collected, genuine specimen would take years to resolve. A week after Currie returned to Canada, he began fielding calls first from Japanese reporters and then from British reporters. Days later, on 19 October 1996, the story hit the front page of the New York Times under the headline ‘FEATHERY FOSSIL HINTS DINOSAUR– BIRD LINK‘. The story was accompanied by a drawing done by Michael Skrepnick, the artist who was travelling with Currie in China, and it reported Currie’s assessment that this was, in fact, a feathered dinosaur. ‘The whole world went a little crazy for a while,’ Currie says.
For years, dinosaur feathers continued to provide something of a mystery for scientists. Currie believes there is a possibility all the meat-eating dinosaurs known as coelurosaurs (‘hollow-tailed lizards’) had feathers as babies to provide insulation. The big species then shed those feathers as they grew into adulthood and no longer needed the feathers. The larger a dinosaur became the less its surface area was in relation to its mass or volume. Big animals have a problem ridding themselves of excess body heat. However, a small animal would lose heat really fast. So if small animals are warm-blooded, they have to be insulated in some way, such as with feathers or fur. However, a whale or an elephant is so large that it doesn’t need the insulation. Could it have been the same for Tarbosaurus?
‘It may well be that Tarbosaurus is free of feathers only because it’s big,’ Currie says. ‘When Tarbosaurus were born, they were probably only a half metre or 18 inches long. At that stage, they may have needed feathers. So there was a prediction, which is kind of cool, that if we ever find a small Tyrannosaurus then it should have feathers because it is closely related to these feathered dinosaurs.’
The cool part, Currie says, is that in 2004 a small Tyrannosaurus was found in north-eastern China that was about the size of a German shepherd and it had feathers. Currie explains that the big problem is that there are very few places in the world where conditions are such that feathers would be preserved, though skin impressions are often found in Mongolia and Alberta. Feathers rot away pretty quickly, so typically they decompose before they have a chance to fossilize.
The environment controls what is preserved. In most dinosaur-fossil sites there are no eggs or feathers found. However, in an environment like north-eastern China, where there was a lot of volcanic action, things preserve far better. Volcanic ash would rain down on the lakes. Sometimes the ash would kill a bird or a dinosaur running along the shore, and they would fall into the lake. Because the ash is very fine grained, mixed with the mud in the lake it preserves details very well. More importantly, it alters the chemical environment and kills the bacteria that would otherwise decompose the keratin – the horny material that forms fingernails, beaks and feathers – and leaves these structures preserved for science. ‘Suddenly, you have this amazing situation where you not only get fingernails and beaks but also feathers preserved,’ Currie says. That kind of preservation is critical for scientists to formulate theories about dinosaur feathers that connect them to birds.
Fossilized feathers have also provided scientists of the first evidence of dinosaur colours. Melanosomes, the biological structures that give feathers colour, were recently found to have been preserved in the small feathered theropod dinosaur seen by Currie in 1996 and subsequently named Sinosauropteryx, which lived 125 million years ago. The melanosomes allowed scientists to determine that the dinosaur had a red Mohican with a red and white striped tail. However, scientists have not been able to determine the colour for most other dinosaurs, even those whose skin has been preserved. Early artistic renderings of dinosaurs were in browns and greys and were based on the colour of the larger modern animals such as elephants and Komodo dragons, but scientists still have little to no evidence that dinosaurs were similar in colour to these.
‘We are absolutely nowhere with the colour of Tarbosaurus,’ Currie admits. ‘So far all we have is tarbosaur skin, but we don’t have any evidence of colour banding to show us that there might be melanosomes preserved. Of course, that doesn’t mean that they are not, because what might happen eventually is that somebody might take a look at the skin impression and find out that, yes, there are melanosomes there and we can actually figure out the colour on these guys.’
A close up of Komodo dragon skin – one of the largest reptiles alive on Earth at present – shows what dinosaur skin may have looked like.
Steve Gschmeissner/Science Photo Library
The fact that birds are the direct descendants of dinosaurs means that dinosaurs are not extinct. There are some 10,000 species still around. In fact, dinosaurs are actually divided into two groups, avian (those that fly, which we call birds) and non-avian (the land-dwellers that we normally think of as dinosaurs). For the sake of simplicity, when everyone from the layperson to the veteran palaeontologist uses the generic term ‘dinosaurs’ in conversation, they are generally referring to non-avian dinosaurs.
Dinosaurs were divided into two orders by the British palaeontologist Harry Seeley in 1888: the saurischians and the ornithischians. Seeley characterized these orders (or lineages) by the arrangement of the bones in the hip. The saurischians, which have a pubic bone that slopes down and forward, were named ‘lizard-hipped’ because their hip structure resembled that of a lizard. The ornithischians, which have a pubic bone that slopes down and backwards, were named ‘bird-hipped’. Despite the fact that ornithischians were named bird-hipped because their hip structure was similar to birds, Seeley did not identify any similarity to birds. In fact, further study determined that modern birds actually evolved from the lizard-hipped saurischian dinosaurs, not the bird-hipped ornithischians.
The saurischians include two major dinosaur groups, the sauropods (large herbivores such as Apatosaurus and Diplodocus) and the theropods (meat-eaters such as Velociraptor and Tyrannosaurus). The ornithischians include armoured dinosaurs (such as Ankylosaurus), horned dinosaurs (ceratopsia), and duckbilled dinosaurs (hadrosaurs). Though scientists have concluded that the oldest dinosaurs were 225 million years old, they do not know how much earlier in time the common ancestor of the lizard-hipped and bird-hipped dinosaurs lived.
As with most areas of the study of dinosaur science, there is also a major controversy about the extinction of what we commonly call dinosaurs. Did dinosaurs die out catastrophically as a result the Cretaceous–Tertiary extinction event that occurred 65 million years ago, or did they die out gradually over a long period of time due to climate changes or environmental forces? There is quite a bit of evidence to suggest that an asteroid hit the earth 65 million years ago and that not only wiped out dinosaurs but a great numbers of other animals and plants as well. Except for a few explainable aberrations, there are no non-avian dinosaur fossils above the Cretaceous–Tertiary boundary in rocks younger than 65 million years old.
Like many palaeontologists, Currie believes that when the asteroid hit natural selection was already at work. By the end of the Late Cretaceous period, temperature shifts on the planet were becoming extreme. He points to the rocks along Alberta’s Red Deer River that stretch into Dinosaur Provincial Park as evidence that factors such as climate change were already at work phasing out certain species.
‘If you look at 10 to 15 million years before the asteroid hit, you have more than 40 species of dinosaurs in this region,’ he explains. ‘By 5 million years before dinosaurs became extinct, you have about 25 species of dinosaurs. The rocks that were laid down a million or so years before the end of the Cretaceous along the Red Deer River have fewer