We can scratch a couple of suspects from the list of possible dinosaur killers. Too few dinosaur fossils show evidence of bone cancer to conclude that a lethal dose of ionising radiation did them in – or that they took up smoking, as Gary Larson once whimsically suggested in a Far Side cartoon.
Adrian Melott, an astrobiologist at the University of Kansas in Lawrence, has suggested that periodic overdoses of cosmic rays or bursts of gamma rays might have caused mass extinctions. Past periods of heavy radiation leave little direct trace, but cancers induced by cosmic rays could have spread to bones.
So Melott turned to data collected by his colleague Bruce Rothschild on signs of cancer in the fossilised bones of 708 dinosaurs. When they compared the incidence of bone cancer with that in today’s birds and reptiles, they found ().
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However, Melott is going to keep looking. He says the results for hadrosaurs, which lived during the final 5 million years of the dinosaurs’ reign, are intriguing. Hadrosaurs had the only case of bone cancer and the only cases of benign abnormalities called haemangiomas.
