Paleobiology | 
Introduction
Sixty-six million years ago a worldwide cataclysmic event marked the end of the Mesozoic Era and changed the whole course of life on earth (Fig. 1). This was the end-Cretaceous mass extinction, and whether it was caused by a bolide strike or triggered by huge volcanic eruptions remains hotly debated. There is geological evidence for both at the time. The outcome, however, is indisputable. The dinosaurs that had dominated the land vertebrate fauna for the previous 125 million years completely and abruptly disappeared, along with the related flying pterosaurs, and the great marine reptiles, the ichthyosaurs, plesiosaurs and others. The vertebrate survivors included birds (which are technically miniature, feathered, flying dinosaurs) and the crocodiles, lizards, snakes and turtles. All of these groups soon proceeded to diversify, although none of them underwent any great evolutionary transformations in body form. A small number of the pre-existing mammals also survived the extinction, but their story was very different. Over the course of the following 66 million year Cenozoic Era, an astonishing array of entirely new kinds of mammals soon evolved. Small, nocturnal ancestors gave rise to numerous large bodied herbivores such as antelopes, camels, hippos, horses, rhinoceroses, kangaroos, and elephants, along with the carnivorous cats, wolves, bears, and hyaenas that preyed upon them. Completely novel forms such as anteaters with long sticky tongues and powerful digging claws, and monkeys, apes and sloths adapted for life in the trees evolved, and within just 25 million years the most specialised mammal groups of all appear in the fossil record: the bats are as accomplished fliers as birds, and the whales and dugongs are superbly adapted physiologically and anatomically for a permanent life in the sea.
