LITMIR.BIZ

Скачать книгу

you something about physiology. If the mother is lying on the nest – birds lie on their nests to keep the eggs at a constant temperature – it may well tell us that these dinosaurs were warm-blooded and in fact were brooding their eggs and keeping their eggs warm.’

      The evidence that supports this theory comes from the layout of the eggs in the nest. The eggs formed a circle around the outside of the nest like a doughnut. The mother was standing in the middle, which allowed her chest to cover the eggs in the front and her tail to cover those in the rear. With her arms outstretched around the eggs to the sides, she could also protect those eggs.

      ‘If you look at the feathered dinosaurs where the feathers are behind the arms, the feathers would cover those eggs on top,’ Currie says. ‘Large dinosaurs couldn’t do that – they didn’t have large enough wingspans. In the case of these dinosaurs that have been found brooding, it has been suggested that there were several reasons that these long feathers developed, including as a mechanism for shading the nest, for protecting the eggs and/or for keeping them warm. Brooding doesn’t work if you are cold-blooded.’

      What have not been found are Tarbosaurus eggs – yet. ‘It’s probably because of the fact that they would have been in an environment with acidic groundwater so the eggs were destroyed,’ Currie says. ‘Of course, there are other possible explanations, one being that they would have nested farther inland in a place where things weren’t getting fossilized. Still, we may eventually find a Tarbosaurus egg in the right place, where it did have a chance to fossilize. If we are lucky, there will be an embryo inside and we’ll be able to put the whole story together.’

      Because of their nesting habits and feathers, it has been established that oviraptorids and dromaesaurids like Velociraptor were probably warm-blooded. That has led Currie and several other palaeontologists to argue that it therefore makes sense that the closely related Tyrannosaurus would have been warm-blooded, though this is still considered somewhat forward thinking.

      Currie lays out the argument. ‘Velociraptor and oviraptorids were warm-blooded in all likelihood,’ he says. ‘They are feathered dinosaurs; it doesn’t make any sense to have feathers on your body as insulation unless you are warm-blooded. The advantage [cold-blooded] lizards have is that when they get cold, they just move into the sun and they warm up pretty quick. But if you put feathers on them, it would be like taking an ice cube and wrapping a blanket around it and sticking it outside; it doesn’t work. So there are a lot of reasons to think that the little guys are warm-blooded; notably these include the fact that they are so close to the ancestry of birds, and that they have bone histology like modern mammals and birds.’

      Tyrannosaurus, like Tarbosaurus and Albertosaurus, was relatively closely related to Velociraptor and oviraptorids, so Currie concludes that because of the fact that they are closely related to these warm-blooded creatures, they were almost certainly warm-blooded, too. ‘It doesn’t make sense that you have guys in your ancestry who are warm blooded, that all your close relatives are warm-blooded and that your descendants are warm-blooded, but you are not,’ he says. ‘So it makes sense that tyrannosaurs were warm-blooded.’

      As radical as it was to accept that dinosaurs were warm-blooded and laid eggs, it was even more revolutionary to see them as big, non-flying birds rather than just scary, oversized lizards. In 1974, John Ostrom, the palaeontologist who found Deinonychus, revised his description after the discovery of a more complete specimen and championed the idea that birds were descended from dinosaurs. Robert Bakker backed it up with additional research, and their work provided the dinosaur renaissance with another major development.

      Ostrom’s scientific paper reiterated the idea that had been presented a hundred years earlier by British scientist Thomas Henry Huxley, a defender of Darwin’s theory of evolution, who had proposed that birds were descended from dinosaurs. Huxley came to this conclusion after studying Archaeopteryx, the oldest known fossilized bird. Archaeopteryx lived during the Late Jurassic period, and its features suggested that it was a transitional fossil between dinosaurs and birds. Since Archaeopteryx was discovered in 1861, only 10 specimens have been found, despite Herculean efforts to find more.

      Additional evidence for this theory came in 1986 when Jacques Gauthier, a scientist who is now based at Yale University, published a list of more than 125 characteristics shared uniquely by birds and dinosaurs. Currie calls this very, very powerful evidence under any kind of modern scientific analysis. ‘We don’t even have such strong evidence for other transitions such as reptiles into mammals,’ he points out. ‘A lot of palaeontologists by the mid-1980s already believed that birds came from dinosaurs. I got into researching it because of the fact that our Late Cretaceous dinosaurs from Alberta were very bird-like in a lot of ways, and it started me thinking about it and publishing on the subject.’

      The theory was slow to make its way into the mainstream. Currie believes this is because most ornithologists don’t work on fossils, and only work on modern birds. ‘Maybe 50 per cent of the scientists working in palaeontology believed birds came from dinosaurs, maybe 5 per cent of ornithologists believed it, and very few people in the public believed it because they had never heard of it.’

      In 1996, Currie himself came face-to-face with the evidence from one of the very first specimens showing the transition in what turned out to be a complicated situation where cultures, science and publishing collided.

      The story began in 1994 when a farmer in north-eastern China found a fossil of what was thought to be a species related to Archaeopteryx and sold it to a local museum. The farmer made some money on the transaction, so he went out and dug some more and found another fossil, which he sold to a different Chinese museum. Scientists were aware of those finds and figured there were more where those had come from. In 1996, at the Tucson Rock and Mineral Show, there were hundreds of specimens resembling this bird, complete with feathers. Excitement began to grow because this was a bird that had never been scientifically described, and suddenly there were already far more specimens of fossil birds than had showed up in more than 100 years. But were they genuine?

      For a long time palaeontologists had talked about the possibility of feathered dinosaurs. This discussion stemmed from the theory that if any dinosaurs were warm-blooded, then the most likely would be small dinosaurs; and if they had any kind of insulation on their bodies, it would probably be feathers. By the late 1970s, many scientists had concluded that dinosaurs gave rise to birds. Though it was mostly speculation and there was scant evidence to prove it at the time, dinosaurs were being illustrated with feathers on their bodies in books everywhere.

      Currie first saw a picture of the Chinese’s farmer’s find in a Beijing newspaper in 1996 after a trip to Mongolia. The article reported that a feathered dinosaur had been found, and the story was accompanied by a picture. ‘It was a little picture that didn’t look like anything,’ Currie recalls. ‘The idea of feathered dinosaurs had been with me for a long time, but still, what are your chances?’

      Through a contact, Currie made arrangements to see the ‘feathered dinosaur’ specimen. He was slightly suspicious because he had been given an exact time for his viewing. When he arrived 10 minutes early, his contact walked him up and down the street so they wouldn’t be early. At the appointed time, the contact ushered Currie into a room full of reporters. ‘I realized that I had walked into a press conference and that they were going to show me this specimen in front of the Chinese press to see what my reactions were.’

      Several different specimens were bought out one at a time. The boxes were then opened in front of Currie. ‘I would see a beautiful insect with spectacular preservation. Then they would bring out another box, and I would open it up and see a spectacular lizard fossil and so on.’

      This dragged on for so long that Currie began thinking it was a diversion and that they weren’t even going to show him the feathered dinosaur. ‘I went to see it not because I thought it was feathered, but because I could see from the photograph that it was a complete specimen of a small dinosaur,’ he says. ‘Small dinosaurs are rare; carnivorous dinosaurs are rare. This was obviously a very, very important specimen’ – provided it actually existed.

      Finally, the box with the feathered dinosaur arrived unannounced. ‘When they opened the lid of the box, my eyes probably

Скачать книгу