THE GORGOSAURUS was a giant among dinosaurs, a meat-eating cousin of tyrannosaurus rex that terrorised Cretaceous swamps in search of smaller plant-eating prey. Weighing more than two tonnes, measuring up to nine metres (30ft) long and yet fleet of foot, not much escaped its powerful jaws and cone-shaped teeth.

But the specimen that resides in the Black Hills Institute of Geological Research in Indianapolis appears to have been felled by a pint-sized predator. Researchers studying the fossil believe that they have found the first brain tumour in a dinosaur, and say that the thumb-sized mass is barely distinguishable from human tumours. Their findings, along with a recent paper in Nature showing that another family of dinosaurs suffered from tumours in their tailbones, suggest that cancer is an ancient foe dating back at least 70 million years, when the gigantic lizards roamed the planet.

Peter Larson, from the institute, says that the brain tumour was more likely than not to have been cancerous, but there is no way of proving it: “We do know that it was life-threatening, but if it did not directly cause death, it led up to it.” At the very least, suggests Dr Rachel Reams, a veterinary pathologist from the pharmaceutical company Eli Lilly, who studied the fossils, the dinosaur would have been unsteady on its feet.

“We have not conclusively identified the type of brain tumour found in this specimen, but we are sure that it impaired the mobility of the dinosaur,” says Reams, who was brought in to examine several fossils before they were exhibited. “It almost certainly affected its balance and locomotor ability.”

The tumour, about 5cm (2in) in diameter, was found when Larson saw a dark lump “like crumpled paper” inside the brain case of the exhibit. He chipped off a small piece and bombarded it with X-rays. The dense lump, found near the brain stem, showed a similar absorption profile to a human brain tumour. The growth occupied almost the whole of the cerebrum, the double-hemisphere structure that forms the most recognisable chunk of the brain. The cerebrum is the hub of high-level skills, such as language and reasoning. The find was announced last month at a meeting of the Society of Vertebrate Palaeontology in Minneapolis.

In a separate piece of research published last month, Dr Bruce Rothschild, a radiologist at the Northeastern Ohio Universities College of Medicine, led the largest scale study of cancer in dinosaurs. Rothschild and colleagues from Kansas, Pittsburgh and Alberta in Canada roamed the natural history museums of North America with a portable X-ray machine, and examined more than 700 dinosaur fossils. They scanned around 10,300 vertebrae, including those of the stegosaurus, triceratops and the feared tyrannosaurus rex.

They found evidence of cancer in only one group — the hadrosaurs, or duck-billed dinosaurs. These common herbivores, which had toothless beaks but harboured almost 1,000 teeth in their cheeks, could grow to 12m. Much of that was accounted for by their stiff tails, probably used for balance while running, and this is where the cancers were found. Of 97 hadrosaur skeletons, 29 tailbones appeared to contain tumours. Four tumour types were identified, of which hemangiomas — benign tumours of the blood vessels that are borne harmlessly by one in ten people — were the most common. Metastatic cancers (those that have spread) were also found.

Why the hadrosaurs were so plagued is unknown. The secret could lie in their genetic profile or in their environment. In his paper for the online journal Naturwissenschaften, Rothschild suggests a possible environmental cause. Hadrosaurs are known to have dined on conifers, and conifers are rich sources of carcinogens.

Professor Mike Archer, director of the Australian Museum, suggests that cycads are a more likely culprit, however. Cycads are large ancient plants with beautiful fans of palm-like fronds (but not closely related to palms). Their nutritional value would have made them a sought-after nibble. The drawback, Archer says, is that “cycads contain some of the most powerful carcinogens known to mankind”. The plants also contain toxins that have been linked to brain diseases such as Alzheimer’s and motor neurone disease.

Dr David Norman, a palaeontologist at Cambridge University, suggests in Nature that hadrosaurs may have had a longer lifespan than other dinosaurs. Cancer is primarily a disease of ageing — which is why the disease is more common today than in the past — so pensionable hadrosaurs would have been more likely to develop tumours.

The problem with assessing diseases of old age in the fossil record is that evidence is scant, partly because hallmarks of the disease may have vanished. Animals weakened by disease were also particularly vulnerable to predators, and therefore were more likely to be consumed and so erased from the fossil record. So, while researchers find evidence that cancer predates the existence of modern humans, we are unlikely ever to know just why it afflicted those who walked the Earth before us.

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