Disease and the Demise of the Dinosaurs

There are more than 100 hypotheses for the extinction of the dinosaurs. Asteroid impact is the most famous, and the effects of volcanic eruptions, sea level change and climate fluctuations remain debated, but other fantastic and weird ideas have been tossed around. Many of the discarded notions, proposed before we knew an extraterrestrial bolide struck the Yucatán Peninsula, cited pathologies as the deciding factor. Cataracts, slipped discs, epidemics, glandular problems and even a loss of sex drive have all been proposed as the reason non-avian dinosaurs perished about 66 million years ago. In fact, pioneering paleopathologist Roy Moodie suggested that a startling number of accidents and injuries could have killed Triceratops and kin.

Moodie wrote an initial report, Studies in Paleopathology, in 1917 and followed with a full book called Paleopathology in 1923. The books are surveys of fractures, infections, arthritis and other pathologies visible in fossils. And after examining these cases, he created a graph of injury and ailment incidence over time. Dinosaurs and their reptilian neighbors seemed to have a rough time. Bone breaks, infections and other pathologies “reached a maximum of development among the dinosaurs, mosasaurs, crocodiles, plesiosaurs and turtles,” and the curve dropped off only when the Mesozoic “Age of Reptiles” ended. The increasing occurrence of pathologies may have driven dinosaurs into extinction. “It seems quite probable,” Moodie wrote, “that many of the diseases which afflicted the dinosaurs and their associates became extinct with them.”

Dinosaurs really did suffer from a variety of ailments. Dinosaurs scratched at parasites, endured bone infections, and even developed cancer. But we now know that there wasn’t a dramatic uptick in dinosaur sickness between the Triassic and Cretaceous. There is no sign that pathologies did in the dinosaurs, and this hypothesis doesn’t explain why so many other creatures—from the seagoing lizards known as mosasaurs to coil-shelled ammonites—disappeared at the same time. Focusing on dinosaurs too narrowly hides the true pattern of extinction. Exactly what happened at the close of the Cretaceous will remain hotly debated for decades to come, but dinosaur disease no longer figures into the discussion.

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.