At 13 metres in length, Tyrannosaurus rex had little to fear from other predators. But it was occasionally attacked by an enemy far smaller than itself. In a wonderful piece of forensic palaeontology, Ewan Wolff from the University of Wisconsin has shown that the tyrant lizard king was often infected by a microscopic parasite, whose relatives still infect the birds of today. Potentially transmitted through bites from other tyrannosaurs, the parasite could have starved the infected animals to death.
Many of the large meat-eating dinosaurs have wounds on their heads that were clearly inflicted during fights with their own kind. Bite marks and long gouges caused by teeth raking bone are both fairly common, but both types of injuries show signs of healing – unlike the marks found on prey, these bites weren’t inflicted to kill. But tyrannosaurs also show a second type of injury – smooth-edged pits and holes, particularly in the jaw, where the bone has been eaten away. Some are small; others are centimetres across. They weren’t made by any tooth and they don’t match the shape of any mouth.
They do, however, bear a striking resemblance to injuries found in the beaks of modern birds, particularly falcons, pigeons and chickens. In birds, these injuries are the result of trichomonosis, a disease spread by a parasite called Trichomonas gallinae. The parasite creates ulcers throughout the bird’s mouth and throat, and erodes its jawbones.
Based on the strikingly similar size, shape and locations of the Tyrannosaurus pits and holes, Wolff thinks that the prehistoric predator was afflicted by a very similar contagion and even mounted a similar immune response. It’s yet further evidence of the close relationships between modern birds and their dinosaur ancestors. They may even have been attacked by the very same parasite, although based solely on the scars left behind, that’s impossible to determine.