Dinosaur Extinction Improbable Hypotheses

Numerous different hypotheses have been evoked to explain dinosaur extinction. Over 50 were listed by Glenn L. Jepson in 1964, and several more have been added since by M.J. Benton (1990a) and others (Fastovsky and Weishampel 1996). They include climatic deterioration; nutritional problems; disease; parasites; internecine fighting; anatomical or metabolic disorders such as slipped vertebral discs, malfunction or imbalance of hormone and endocrine systems etc.; racial senility; evolutionary drift into overspecialisation; changes in the composition and pressure of the atmosphere; widespread anoxia; too much or too little atmospheric carbon dioxide; poisonous gases including methane that destroyed the ozone layer and created an excessive rise in temperature; volcanic dust; excessive oxygen from plants; comets; meteorites; mammals preying on dinosaur eggs; extermination of herbivorous forms by carnivores, which then starved; temperature-induced changes in the sex ratios of embryos; fatal mutations caused by increased cosmic radiation - perhaps resulting from the explosion of a supernova; mountain building; fluctuation of gravitational constants; shifts of the poles; changes in the rotation of the earth; extraction of the moon from the Pacific basin; drainage of swamps and lake environments; the small size of dinosaur brains and the consequent stupidity of the animals; gigantism; suicidal psychoses and others even more far-fetched. Many of these are obviously untenable (Norman 1991), and only the most plausible suggestions will be considered here.

Although they blend into one another, hypotheses which might account for the K-T extinction tend to fall into two groups - those which attribute extinction to a sudden catastrophic event, and those which propose a gradual change over a much longer time. Extinction over a period of 100,000 years would appear to be very sudden in the palaeontological record! The idea of an extraterrestrial cause, such as fall out from a comet or impact with a bolide (a meteoric fireball) has a dramatic appeal to the popular imagination. The media are continually exploiting it, while Luis Alvarez (Alvarez et al. 1980,1984) and James Lovelock, among many others, have been won over by it (Frankel 1999). Expertise in one subject does not, however, necessarily bestow insight into a completely different one. Palaeontologists such as David Archibald, Michael Benton, Alan Charig, Peter Dodson and Beverly Halstead, as well as most ecol-ogists, tend to favour or have favoured more synthetic gradualist hypotheses based on careful consideration of all the evidence that can be accumulated from geology, meteorology, palaeontology and biology. These hypotheses may be less dramatic than those that evoke cosmic cataclysms alone but, because they are able to encompass several lines of evidence, they are more likely to approximate to the truth. As N. MacLeod has recently pointed out, Alvarez and his coworkers (1980, 1984) did at least move the question of extraterrestrial causes for mass extinction into the mainstream of science from which it had been excluded for some 150 years.

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