英語音頻雜志:恐龍是什么樣子的?
By Linda Baxter
Can we believe what we see?
Dinosaur art has a long history. Life-size models in natural history museums, paintings and drawings, children's toys, and of course, the recent spate of computer generated films. It captures the imagination, popularises the science and raises money for museums to support more research. We love looking at dinosaurs. But what are we seeing? The real thing? Or a little fact and a lot of imagination? Did the velociraptor look like a giant lizard? Or like a snake with long legs? Or did it look more like a bird with feathers but no wings?
Bones
All dinosaur reconstruction begins with bones. The good news is that more and more fossils of different types are being discovered all over the world. The bad news is that we don't have complete skeletons for all the species that are being discovered. And it can be surprisingly difficult to work out where all the bones are supposed to go. One of the first reconstructions of the Iguanadon, over a hundred years ago, had a small horn on its nose. It was actually the creature's thumb. Nowadays, we have multiple examples of complete sets of bones for some species, but that doesn't mean that everyone agrees about their skeletal structure. Scientists are still arguing about whether the triceratops family had straight legs like a rhinoceros or bent legs like a lizard. And you'll see both versions in dinosaur art. There are things that bones don't tell us.
Muscles
The next step is to put muscles onto the skeleton. Muscles make marks on the bones that they are connected to, so we can study these marks in existing animals and draw conclusions about dinosaurs. But there are large parts of bodies without any bones - the whole abdominal area for example. How much muscle is there? A lot, like a horse? Or a little like a bird? Computer modelling can help with this problem, but not everyone reaches the same conclusions. A computer model has been produced that shows that Tyrannosaurus Rex didn't have big enough leg muscles to run very fast. And scientists are still arguing about it. There's other evidence to show that he could run very fast indeed.
Soft tissue
Who could guess from its skeleton that an elephant has enormous ears and a long trunk? Soft tissue doesn't fossilise. Some imprints of dinosaurs' soft tissue have been found in rock possibly showing humps, or frills on the back of the creature or on the top of its head, but not in much detail. There really isn't enough evidence for a lot of the additional features that we see in our favourite images of some dinosaur species. Scientists are studying soft tissue to try to find out what organs dinosaurs had and what they used them for. If you examine an elephant's skull, you'll find evidence that it has a long trunk - spaces for passages for blood and nerves and tiny muscle connections for example. This research will be able to give us a lot of information about dinosaurs' outward appearance.
Skin
Some preserved imprints of dinosaur skin show reptile-like scales, but it isn't clear if they covered the whole body. Dinosaur fossils with feathers have been found in China and more and more scientists are now accepting that many dinosaurs, including T Rex, probably had primitive feathers as a way of keeping warm. And maybe primitive fur. That's certainly a revolution in the traditional depiction of dinosaurs. The colour of the skin, or scales, or feathers or fur, is another problem. There is no evidence at all from the fossils. The colours that are traditionally used are based on what we know of the animal's natural habitat and whether it needed to hide for protection. But we could be completely wrong. We don't even know how well dinosaurs could see colour. Most of the assumptions are based on what we know about birds and reptiles today.
Faces
We don't know the shape of dinosaur eyes. Were they thin and slit-like, like reptiles? Or round, like birds? In traditional dinosaur art, the dangerous, predatory dinosaurs often have slit-like eyes because it makes them look nastier. The gentle vegetarians are given soft, round eyes. And what about nostrils? Traditionally, dinosaur nostrils have been placed quite high on their heads. But it's now believed that they were much lower down, closer to the mouth. This discovery has a lot of implications for how the animals lived and breathed. It's a big change for the artists to consider too.
So what's the conclusion?
A 77 million-year-old mummified dinosaur (Brachylophosaurus) was found recently, and scientists are hoping that he (or she) will answer a lot of questions, particularly about skin, scales, muscles and soft tissue in general. Only a handful have ever been found before and this is the first one that can be studied in detail with modern technology.
Until then, the fact remains that a lot of very different looking dinosaurs can be drawn from the same basic scientific evidence. And I think that the dinosaur-loving public should get to see all of them.
