How did birds evolve from dinosaurs?

Louise:: Hello and this month, I'm talking to Dr. David Norman from the Department of Earth Sciences at the University of Cambridge. Benoit in Bristol wanted to know how exactly did birds evolve from dinosaurs? Is there thought to have been a breakthrough mutation or did various kinds of birds evolve and intermixed bird-like characteristics in a more parallel process? Dr. Norman.

David:: That's a very complicated sort of question, but birds evolved from dinosaurs and if you look back at the history of the fossils that seem to go through the transition from being genuinely dinosaur and to genuinely bird-like you see a very, very gradual transition, changes in the anatomy of these creatures. In essence, what you find is that there's a trend within carnivorous dinosaurs, things known as theropods, which become progressively smaller, at least one branch of them. And that smaller branch changed its anatomy. One of the most important changes is the reduction of the tail. The tail becomes thin and very whippy, and that completely changes the balance of the animal and the way its legs work. As a result, they become very nimble, very delicate creatures that are capable of moving very rapidly. And if you link that with how they must've worked as biological organisms then if you build a little nippy creature then it has to be fuelled by a very powerful little engine, and that's the beginning of a change in the way in which the metabolism or the speed at which these animals work changes.

So the smaller you are, the more active you are, the more in a sense, dynamic, your general makeup. And once you get to that point, not only do you become more nimble and more agile, but you also need to be to some extent more intelligent. And you also suffer a problem which is that when you're very small, your surface area becomes very large. As a result, you can lose body heat to the environment very quickly, you need insulation. So, you end up with small, very nimble, very intelligent insulated - that is to say, feathered or filament-covered creatures that look awfully like birds. And honestly, the transition from those small, nimble carnivorous dinosaurs that probably ate small animals, maybe insects through to genuine birds which have an insulated covering and are capable of flapping flight is almost imperceptible. So, you go from one conventional dinosaur, through to a feathered avian or bird-like creature in a very, very smooth transition. It's actually quite a marvellous example of evolution.

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