Many biologists have argued that most species become extinct when new 'fitter' competitors arrive on the scene. For example, some scientists believe the dinosaurs became extinct after a large meteorite hit the Earth 65 million years ago because warm-blooded mammals were better able to survive the long cold spells that followed. However, palaeontologists now argue that the collapse of the dinosaurs' food sources had a bigger impact on the species than competition from mammals. The new computer model proves that mass extinctions are more dependent on an amplification effect between predators and their prey than any other factor.