A Dinosur for Dinner?

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A DINOSAUR FOR DINNER?

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47th Annual Meeting of the Palaeontological Association December 14-17

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What's the difference between a turkey and a crocodile?

This could be a line straight out of a Christmas cracker, but you might be surprised to discover that there is a real evolutionary problem behind the question - a problem that was the subject of lively discussion at the University of Leicester just before Christmas.

Academics gathered at the University for the Annual Meeting of the Palaeontological Association to discuss how the fossil record can reveal that missing-links are not really missing. In fact, they are there to find in the fossil record - but experts have just been looking for them in the wrong way.

Dr Mark Purnell of the University of Leicester's Department of Geology said: "Living animals are generally easy to classify: we can all put an animal into a group with its near relatives because of the distinctive features they share. In the case of turkeys, the toothless beak, feathers, and - of seasonal importance - the wishbone all say 'bird'.

"A crocodile has none of these and is obviously not a bird. But that is where the problem arises - creationists are keen to point out that if different kinds of organisms evolved, we should see links between them, but where is the animal that is half bird and half crocodile?

"Put in this way, the problem is one of simple misunderstanding. Turkeys and crocodiles may be related (as indeed they are) but one did not evolve from the other so we should not expect to see a missing-link that combines the features of both. A link does exist, but it is the last ancestor that the two kinds of animal shared millions of years ago, not something that exists today.

"Its a bit like distant cousins -their family relationship only makes sense if you trace their family trees back to their shared ancestor ...who is unlikely to be alive." But palaeontologists are now able to go further than this. Recent years have seen the development of new ways of looking at evolution, and rather than seek out missing-links palaeontologists now focus on understanding the branching patterns of evolution, the family trees of groups of organisms.

"When fossils are included in these trees an interesting thing happens: if we try and do the simple classification job of putting things into place based on the distinctive characters they possess (beak, feathers, wishbone, for example) we find many fossils are neither one thing nor another, but lie on branches between living groups. Crocodiles and turkeys provide a great example of this because the large group of animals that lies between them are well known to us as dinosaurs," says Purnell.

"There is no missing link as such, but by looking at the family tree of crocodiles, dinosaurs and birds we can see how something that started out as neither bird nor crocodile, gradually, over millions of years, gained the features that are now unique to the living groups. Certain dinosaurs, for example, had feathers, wishbones and other features that are today found only in birds, but only later in evolution did they lose their teeth and learn how to fly."

And, as Purnell notes "when you look at the family tree of dinosaurs and birds there is no doubt about it: your Christmas turkey is a dinosaur!"

"This is what they discussed in Leicester. Not just turkeys, crocodiles and dinosaurs, but how all kinds of animals and plants were put together through sequences of links over millions of years. Links that now exist only as fossils and can be revealed only by looking at their family trees."

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