"The question of what diseases affected dinosaurs is an intriguing one. Actually, dinosaurs may have been healthier than people are today. As far as we can tell from the fossil record, disease was relatively rare among most dinosaurs. For this discussion, I will consider injuries as well and divide my response into the following categories: developmental abnormalities, trauma and injury, infection, osteoarthritis, tumors and structural modifications.
"One of the most prominent kinds of such abnormalities is an overgrowth of bone, called exostosis. The shoulder blade of the Allosaurus skeleton on exhibit at the Smithsonian Institution in Washington, D.C., has such an overgrowth, which transforms the bone's appearance from a long, thin rectangle (its normal shape) to a mimic of the shape of the human scapula. Exostosis has also been noted on a Triceratops jaw, possibly the result of injury.
Trauma and injury
"Fractured dinosaur bones are actually rare. Isolated injuries have been reported in Camptosaurus, Iguanodon, Deinonychus and Syntarsus. Carnosaurs (large carnivorous dinosaurs, including Tyrannosaurus rex, Albertosaurus and Allosaurus) often show evidence of the hazards of their profession. One eighth of their injuries were to the head, and roughly one quarter each were to the vertebral column and ribs, proximal (upper) forelimbs and distal (lower) hind limbs. An Albertosaurus skeleton on exhibit at the Royal Ontario Museum shows impressive evidence of surviving a broken bone, as denoted by healing of the fracture.
"An epidemiologic study conducted by Darren Tanke of the Royal Tyrrell Museum of Paleontology in Alberta, Canada examined more than 30,000 bones from horned dinosaurs (notably Centrosaurus and Pachyrhinosaurus). Tanke found a frequency of fracture of less than one in 1,000. The distribution of those fractures was intriguing. In a report that Tanke and I published together, we related mid-rib and posterior rib fractures to territorial defense and courtship behavior. Similarly, we suggested that fractures to the neural spine (the structure coming off the back of the vertebrae) of duckbill dinosaurs were damage resulting from the injuries sustained during the mating process itself.
"Whereas acute trauma and injury can produce fractures, bone can also be altered by repeated subthreshold stresses. Each individual trauma may be insufficient to produce a fracture, but repetitive exposure to such trauma can bring it about, similar to 'march' fractures that occur among military recruits. Such injuries are called stress fractures. They could perhaps be considered partial fractures and are relatively common in some horned dinosaurs. Bumps on the foot bones of horned dinosaurs were caused by stress fractures. But why did they get such fractures? One could postulate foot stamping and pawing, as is done by bulls, or long migration efforts, similar to the strains encountered by military recruits.
"Infections were quite rare; there are only isolated known examples, which have been observed in Dilophosaurus, Troodon, Camptosaurus, Allosaurus, as well as duckbill and horned dinosaurs. The most famous instance of infection might be the skull of a duckbill dinosaur (a Lambeosaurus) which shows a dental abscess. Given the size of a duckbill dinosaur's tooth row, that must have hurt! Such infections must have been either rare events or else incompatible with survival.
"The most famous claim of disease in dinosaurs relates to osteoarthritis, previously referred to as degenerative joint disease. This claim was the precipitating factor for my entry to the fascinating field of paleopathology. Researchers routinely asserted that osteoarthritis was common in dinosaurs, and I simply wanted to illustrate a lecture. My search and x-ray studies failed to identify a single example, until I saw the famous fossils of an Iguanodon herd in Brussels. Two herd members had osteoarthritis of the ankle. To date, they are the only identified dinosaurs that show signs of osteoarthritis.
"The mistaken perspective that osteoarthritis was common in dinosaurs derived from semantic confusion. Diagnosis of osteoarthritis is based on recognition of a certain type of bony overgrowth at joint margins. Dinosaurs more commonly have overgrowths adjacent to vertebral disks. Such overgrowths have been falsely cited in the past as evidence of osteoarthritis. They were thought responsible for human back pain--something that is now known to be untrue. If the overgrowths do not cause pain and do not affect joints, they are not osteoarthritis. The fact that osteoarthritis has been observed only among two somewhat diminutive dinosaurs (though diminutive is relative--they did weigh two to three tons) but not among the 30-ton heavyweights carries a message for humans. Dinosaurs had well designed, but constrained joints, that supported body stresses. Those joints bent and straightened, whereas human joints also often wobble. Weight is not the cause of osteoarthritis. It is the impact on the unstable or 'wobbly' joint that causes the damage.
"It is unclear if dinosaurs developed tumors. The only claim of a malignant tumor in a dinosaur has now apparently been retracted, although researchers are currently studying a variety of possible benign (noncancerous) tumors.
"The last category for this discussion is structural alterations. There is a phenomenon in humans referred to as DISH, an acronym for diffuse idiopathic skeletal hyperostosis. DISH is a ligament-calcifying process, predominantly affecting spinal (vertebral) ligaments. It was present in most dinosaurs, including ceratopsians (horned), hadrosaurs (duckbill), iguanodonts and pachycephalosaurs (head-butting dinosaurs). The ligamentous calcification was not a pathology but rather a useful mechanism that helped to keep the tail straight. Whereas dinosaurs were once considered tail-dragging animals, fossil dinosaur tracks prove that they must have walked with their tails above the ground. Spinal ligamentous fusion apparently assisted in keeping their tails elevated, perhaps for use as a weapon. Analogous tendon ossification was found in half of the sauropods (such as Apatosaurus, previously called Brontosaurus). In this case, the ossification was thought to be a sexual dimorphism, allowing the female to keep her tail out of the way during mating.
"Paleopathology is a fascinating subject. The field calls for collaborative approaches among anatomists, dentists, paleontologists, physicians, veterinarians and other basic and applied scientists and engineers. This kind of cross-disciplinary work reminds me of a cartoon I have in my office. It shows a physician cutting his patient's hair. The nurse walks in saying, 'Don't you think you should draw the limits to your expertise somewhere?'
"Our studies represent a window on the diseases and behaviors of animals from the Mesozoic. There is much research yet to be done in this area. The future of paleopathology is yours to develop."
Rothschild recommends the following further readings:
Dino Fest: Proceedings of a Conference for the General Public. Edited by G. D. Rosenberg and D. L. Wolberg. Geology Department, Indiana University-Purdue University; Paleontological Society Special Publication #7, 1994.
Paleopathology: Disease in the Fossil Record. B. M. Rothschild and L. D. Martin. London/ Boca Raton, Fla., CRC Press, 1993.
Paleopathology of Vertebrates: Insights to Lifestyle and Health in the Geological Record. B. M. Rothschild and D. Tanke in Geoscience Canada, Vol. 19, No. 2, pages 73-82; June 1992.