Extinction is the inevitable concomitant of evolution. As a result of natural selection in changing environments, all existing species must evolve into other chronologically distinct species, or else die out. None remains indefinitely without modification. Extinction is the consequence either of failure to adapt sufficiently rapidly, or else it occurs because the ecological niche of a species has disappeared. It can be caused by a combination of shortage of food, predation and disease, competition, and/or chance events (Hallam and Wignall 1997). There has long been a tendency to attribute the extinction of larger taxa, such as the dinosaurs, to specific catastrophic factors. As a result, incorrect or misleading conclusions have not infrequently been reached (Cloudsley-Thompson 2001).
When the Tertiary era dawned, none of the dinosaurs other than the birds remained (Charig 1989; Benton and Harper 1997; Benton 2004). The mammals were only just beginning to dominate the land and were therefore not serious competitors with them. Any explanation of dinosaur extinction must elucidate not only why many marine taxa, both invertebrate and vertebrate, also disappeared while the crocodilians and chelonians, as well as other reptiles, birds and mammals, survived (Benton 1989). This subject has attracted a tremendous amount of interest in recent years and no attempt will be made to review the voluminous literature. Instead, I shall merely try to indicate the views of many biologists - which have been generally swamped by those of some geologists and their followers among the general public.
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