17th April, 2012
Using a computer model, researchers in Switzerland have suggested that huge size changes the large dinosaurs underwent throughout life was a major reason why they did not survive the mass extinction at the end of the Cretaceous.
There were few small or medium-sized dinosaur species as they would have to compete with the numerous young of the larger dinosaur species. Dinosaur eggs and correspondingly their young had to be small to allow an egg thickness able to allow oxygen diffusion, even for very large species.
After the mass extinction there were no survivors larger than a spaniel, meaning there were many more smaller mammal species than reptiles. This made it impossible for dinosaurs to repopulate after the extinction, allowing mammals to diversify and become the dominant land animals.