Robyn Williams: Many, many years ago on this program we broadcast a palaeontological engineer called Cherry Bramwell who announced that constipation, not asteroids may have killed off the dinosaurs.

I took it as the kind of fun engineers like to have, if you know what I mean, but now the story has come up again and this time through Paul Barrett at the Natural History Museum in London who's studying the origins of flowering plants on earth.

Paul Barrett: Well it's been suggested that actually dinosaurs invented flowering plants, that changes in dinosaur feeding behaviour drove the evolution of plants in such a way that it was advantageous for the characters of flowering plants to appear. So did these animals actually push the evolution of that big group of plants? - which is a fascinating question, or was it something else? Other people have suggested that for instance atmospheric carbon dioxide might have driven the evolution of flowing plants or that insects may have done it through pollination and things like that. But the idea that maybe dinosaurs did it is one that obviously really grabs the imagination.

Robyn Williams: It certainly does grab the imagination but does it grab the evidence as well, what is there?

Paul Barrett: Well that's a really good question. I mean what you have to do is try and find direct evidence that dinosaurs were actually eating these flowering plants and that they were adapted to eat those and maybe not very much else and also that the flowering plants were responding to being eaten by the dinosaurs by producing defences like spines and thorns, or maybe just ways in which the distributions of the two groups changed. Did certain types of flowering plants only with certain types of dinosaur and vice versa. So those are the kinds of questions we have to try and look at and try and test to see if there's anything in this idea.

Robyn Williams: When did flowering plants actually turn up for the first time?

Paul Barrett: Well the very first fossil flowering plants or angiosperms as they're technically called appear in the fossil record about 125 million years ago which is during a period we call the early Cretaceous. Some people have suggested they may have appeared quite a lot earlier, maybe way back in the Triassic period over 225 million years ago but the first definite fossils we have are these ones actually from China that are about 125 million years old. And then after that we see them in the fossil record but they're very, very rare and it's only about 70 to 75 million years ago when we start seeing them taking over and more like the floras we see today that are dominated by flowering plants rather than the things we saw before that which were mainly conifers and cycads and ferns.

Robyn Williams: One can imagine a relationship obviously with zillions of insects which go way, way back but what would flowers have done for dinos?

Paul Barrett: Well flowers themselves probably not very much, I mean you think today actually quite a lot of things live by eating flowers, various birds, lizards, insects and so on. But we're not talking so much about the flowers per se it's actually the type of reproduction the plant has. The thing that's special about flowering plants is they actually reproduce very quickly and also you can disturb them and awful lot when they grow and they actually like to be disturbed. If you think of mowing your lawn, grass is a type of flowering plant and it actually grows much better if you're cutting it than if you leave it alone. The reason for that is because it has a very compressed life cycle, it can actually reproduce very quickly and respond to these changes. And also they're used to this kind of disturbance so they do very well where lots of animals are trampling them or eating them. Whereas in fact conifers and cycads do very badly, they tend to die off or stop growing.

Robyn Williams: Yes indeed with grass of course being grazed on, if you don't respond to that and recover from it you're dead.

Paul Barrett: Oh absolutely and grasses have various defences to stop too much grazing as well. They have little pieces of silica embedded in their leaves to try and prevent it. But they also manage just to grow in such a way that they can cope with that response from the animals trying to eat it all the time. And so perhaps what we have with dinosaurs was them actually making an evolutionary pressure to actually force some types of plants to go in for this type of growth and that's the kind of question we want to address.

Robyn Williams: Yes, I suppose they lived together for about what 50 million years, that's quite some time. I had heard a rumour, in fact I think we broadcast it a long time ago, that the oils may have been not terribly good for dinosaurs, that some of them may have got some sort of mighty constipation.

Paul Barrett: Yeah, that has actually been suggested. It's actually several people have suggested that flowering plants led to dinosaur extinction, simply because they weren't adapted to deal with the different types of chemicals that you find in them that you don't find in conifers and in ferns and so on. However I don't really believe that idea, as you've already said they lived alongside each other for a very long time so they must have had some time to get used to it or find some kind of dinosaur equivalent of a laxative to get around it. And actually when you look at things like conifers and ferns they are packed full of noxious chemicals so they must have had quite good mechanisms for dealing with that kind of thing.

Robyn Williams: So on your quest, where are you looking and what have you found?

Paul Barrett: Well what we're actually doing at the moment is building a huge data base of all dinosaur and plant occurrences through a period called the Cretaceous which is when the flowering plants first appear. And we're using a fairly sophisticated computer-based technique called a geographical information system to actually analyse the distributions of all these dinosaurs and plants through time in order to find out if there are any changes in the two sets of organisms that occur at the same time. And if we can show there are changes going on at the same time, in the same places in a coordinated fashion, we have quite good evidence that actually the evolution of one group is driving the evolution of the other.

Robyn Williams: Any luck so far?

Paul Barrett: Well so far no, we're still in the phases of building the data base, it's already got something like 5,000 entries in it and we think that by the time we're finished building it, it'll have about 15,000 to 20,000 entries. But once we have that in place the software should actually allow us to do the analyses relatively quickly.

Robyn Williams: Of course we're lucky if they did have some affect that we depend so much on flowering plants as human beings that we would have inherited so much as a result of this dinosaur pressure. So if the world were nothing but Christmas trees and things like that, cones, we probably wouldn't be here would we?

Paul Barrett: No, that's absolutely true. I mean the most obvious ones are grasses, we depend on grasses for almost all our food. Wheat is a grass, rice is a grass and if you didn't have these types of plants evolving we wouldn't have had most of our staple foodstuffs.

Robyn Williams: Intriguing idea, dinosaurs inventing flowering plants and so making human agriculture possible. Leaps of the imagination from Paul Barrett at the Natural History Museum in London.