Friday, 17 February 2017

The science behind the movie: what we really know about dinosaurs and how

This is an article that I wrote to accompany a lecture I gave at the Royal Albert Hall, back in November 2016, in conjunction with some screenings of Jurassic Park that were accompanied by a live orchestra. For various reasons, this didn't get published and I just found it again and thought I might as well pop it on here ...

The premise underlying the Jurassic Park franchise is an elegant one: that dinosaur DNA, preserved in the guts of ancient mosquitoes trapped in amber, could be used to clone these animals, bringing them back to life using the latest genetic technology. A terrific idea, but, sadly, one that remains deeply within the realms of science fiction as - to date - no-one has discovered even a fragment of dinosaur DNA, nor do we currently have the means to clone a dinosaur even if we were lucky enough it’s original genetic material. More hopefully, some scientists are attempting to bring back other famous animals from extinction, including the iconic woolly mammoth. Mammoths are lot younger than dinosaurs, having gone extinct only a few thousand, rather than millions, of years ago, and this means that many of their remains, frozen in Siberian permafrost, can yield large amounts of viable DNA for scientists to work with. However, even in this case a cloned mammoth is still a long way off. In addition to the numerous ethical problems that would surround the resurrection of an extinct species (the world has changed significantly since the last mammoth drew breath), there are still numerous scientific obstacles to mammoth cloning, not the least of which is that we have yet to learn enough about the reproduction of those animals that would be the best hosts for implanted mammoth embryos – elephants. So, given that we’re unlikely to see dinosaurs roaming our zoos and safari parks anytime soon, how do scientists determine how these amazing animals fed, ran, bred and died?

Palaeontologists, the scientists that study extinct life, have a surprising array of tools with which they can examine the fossilized remains of animals and plants to determine how they might have appeared and behaved when alive. In the case of dinosaurs we have their skeletons, but we also have other evidence that can give deep insights into their daily lives, including preserved gut contents, eggs, nests, footprints, skin impressions and even dinosaur poo. Detailed examination of skeletons provides information on the shapes of the bones and how they fit together. Comparisons with living animals are also key, as if we can identify similar features in these living animals, whose biology we can study in real time, we can then infer similar functions for those same features in extinct animals. Rough patches and flanges on bone can be used to reconstruct the positions of muscles, cartilage and ligaments, and studying the scratches and wear patterns on teeth reveals vital information on diet and feeding. This type of work has been carried out since dinosaurs were first discovered, in the early eighteenth century, and continues to provide new results today. However, this classical approach has been expanded thanks to the advent of an array of modern technologies, pioneered in fields as disparate as medicine and engineering, which are now being applied to fossils on an almost routine basis.

Perhaps the most significant of these advances has been the application of computed tomographic (CT) scanning. CT scanning uses rotating X-rays to build up a three-dimensional model of both the internal and external anatomy of an object and has diverse applications ranging from diagnostic use in medicine to checking car or airplane parts for flaws before they leave the factory floor. CT can be used to peer inside dinosaur bones and reveal features of the skeleton that were previously difficult to access, including the shapes of the brain and the air-filled sacs that ran through many dinosaur bones. The CT scans produce perfect virtual models of the bones that can then be subjected to testing in ways that would be impossible with a fragile or cumbersome fossil. By importing these virtual models into different computer programmes, dinosaur skeletons can be clothed in muscle, subjected to forces generated by walking, running and feeding, and tested to destruction in ways that no worthy museum curator would permit on the original bones themselves.

By carefully cutting thin sections through dinosaur bones and putting them under the microscope, we can age dinosaurs and work out how fast they grew to adulthood. This is done by counting the growth lines in the bone walls, which were laid down each year in a tree-ring like fashion. Dinosaurs grew really fast, with even the largest species reaching full size in no more than 30 years – and like humans dinosaurs had a teenage growth spurt. Some dinosaur fossils are so spectacularly preserved they include evidence of soft tissues like skin, muscle and internal organs, which give vital clues on dinosaur biology and appearance. For example, some spectacular fossils from China show that many meat-eating dinosaurs were covered in thick coats of feathers, helping to cement the idea that birds are nothing more than small, meat-eating dinosaurs that gained feathers and learnt how to fly. The recognition that birds are dinosaurs is an idea that has been proven beyond reasonable doubt in the last 20 years and also gives us new clues on what extinct dinosaurs might have been like. As living dinosaurs they can be used to test some of the ideas that palaeontologists have proposed based on bones alone. Moreover, they carry a direct genetic legacy of their dinosaurian ancestry, which means that bird genes are dinosaur genes, even though birds represent only one specialized branch of the dinosaur family tree. Some scientists are currently attempting to switch on long dormant genes in living birds that might have been responsible for producing the teeth, characteristic skull shapes and long tails of their dinosaur ancestors. These efforts are already producing impressive results, with genes being found that can transform bird beaks back into more dinosaur-like snouts and those that can stimulate hens to form teeth. Surprisingly, this work is not only interesting in its own right, but it has implications for human health as some of the key genes are also important in regulating various strains of human cancer, so this pure science project on dinosaur genes is providing insights that could improve human health too. Moreover, this type of genetic manipulation, based on the DNA of living dinosaurs, is probably the closest we will ever get in reality to a Jurassic Park scenario.

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