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Issue 498, 5 May 2004
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Was male domination deadly for dinosaurs?

velociraptorsDinosaurs suddenly died out because they gave birth to too many males as a result of climate change. This is the theory put forward by David Miller of medicine and Jonathen Summers of mechanical engineering.

They believe that dinosaur populations died out because the sex of their offspring was determined by temperature.

Dr Miller said: “The theory does not contradict ideas that extinction was caused by a giant meteorite striking the earth or that there was a long-term change which dinosaurs could not cope with – it elaborates on these ideas.”

In many creatures, such as humans and other mammals, sex determination is genetically controlled to ensure an approximate 50/50 male to female ratio.

But some reptiles and fish use temperature-based methods to determine sex of offspring. They produce roughly 50/50 ratios under ideal conditions but a variation of temperature brings a skew towards males or females, with a skew towards males leading to population decline.

In particular, all crocodiles, which are essentially similar to dinosaurs, use temperature sex determination, and Dr Miller argues that this could mean the extinct giant reptiles used the same mechanism.

Dr Miller hit upon the idea during research into the evolution of the Y chromosome in humans, which he is carrying out in collaboration with Dr Sherman Silber of St Louis Infertility Center in the US. Dr Summers brought in mathematical techniques to model the effects of variations in male/female ratio on populations.

Professor Neill Alexander of the school of biology, who is an authority on dinosaurs and has advised the BBC, said: “Here we have an old suggestion about dinosaur extinction being examined in very new ways. Dr Miller and his colleagues cannot prove that the suggestion is correct, but they have gone a long way towards showing that it is feasible.”

More complex modelling is planned to explore the effect of temperature change on different sized dinosaurs and eggs.

Dr Miller said, “We think that there was an abrupt and prolonged change in the environment and that the dinosaurs could not adapt to it in time to save themselves. A temperature change made them produce too many males and they died out as a result."

Dr Miller said that temperature control of sex determination may have been the original mechanism for animals.

He said: "Birds, which probably descended from dinosaurs over 170 million years ago, may have been early adopters of genetically determined sex and hence immune from the environmental vicissitudes that affected their dinosaur cousins. Nevertheless, temperature based sex determination continues to exist because it may offer an effective means of rapid niche exploitation favouring one sex over the other. But it works best in reasonably stable conditions and that was one luxury that the dinosaurs didn’t have 65 million years ago when they vanished from the fossil record."

For more information see: Miller, Summers and Silber, 2004. 'Environmental versus genetic sex determination: a possible factor in dinosaur extinction?' Fertility and Sterility, 81, pp 954-964.

 

Page owner: pressoffice@leeds.ac.uk | Updated: 10/5/04

 

 
 
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