The gradualist hypotheses favoured by many biologists and palaeontologists are even more numerous than the cataclysmic ones. Although many of those listed earlier (Sect. 12.2) are clearly nonsense, some unusual claims do merit consideration. For instance, Croft (1982) argued very convincingly that the dinosaur eye might well have lacked the protein p-crystalline which is present in all modern endothermal animals but not in reptiles. This protein is both photostable and thermally stable. Its absence would have rendered the dinosaurs particularly susceptible to the development of premature cataract blindness and this, over a long period, could have contributed to their extinction. Indeed, the body projections from the skulls of both ceratopsians and theropod carnosaurs might, in addition to their other functions, have served to shade the eyes from sunlight. Milne (1991) and others have, however, criticised this idea on the grounds that is unlikely that every dinosaur would have been selectively affected in this way. (The same objection also applies to hypotheses in which parasites, disease, mutations and so on are considered in isolation.) Furthermore, if the dinosaurs had evolved homeothermy, they might also have evolved P-crystalline.
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