Many dinosaurs had cancer, researchers have discovered. Their tumours were like those of human patients, showing that cancer has been around for a very long time. "Diseases look the same independent of what critter is affected," says radiologist Bruce Rothschild of the Northeastern Ohio Universities College of Medicine in Rootstown.

Rothschild's team travelled North America with a portable x-ray machine, scanning 10,000 dinosaur vertebrae from more than 700 museum specimens. They looked at dinosaurs such as the Stegosaurus, Triceratops and Tyrannosaurus.

Only one group - the Hadrosaurs, or "duck-billed dinosaurs" - suffered from cancer. The team found 29 tumours in bones from 97 individuals of this herbivorous group from the Cretaceous period, about 70m years ago. Dinosaur tumours have been mooted before, but this is the first large-scale survey of them.

It is not known for certain what gave the Hadrosaurs cancer, although Rothschild points out that they ate conifers, which are high in carcinogenic chemicals. The structure of their bones also suggests they were warm blooded, which might have increased their cancer risk.

"We know very little about dinosaur diseases," says palaeontologist David Norman of the University of Cambridge. "Quite why Hadrosaurs should be prone to [cancer] is a fascinating, if ultimately unanswerable, question." The animals might have lived unusually long lives, allowing more time for tumours to develop, he suggests.

The most common growths were hemangiomas - benign tumours of the blood vessels that are present in about 10% of humans. The 3.5 metre species Edmontosaurus was the most prone to cancer, and was the only one with a malignant tumour. About 3% of its bones contained a lump of some sort, reports the team in this month's Naturwissenschaften.

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