Recently, paleontologist Ewan Wolff, out of the University of Wisconsin, and several others from universities across the country, coauthored a study on what had long appeared to be bite marks on many of the discovered Tyrannosaurus rex fossilized jawbones. Their findings, however, dispute this claim; instead, these bone lesions are, quite possibly, the mark of trichomonosis, a parasitic infection that sickens modern birds.
Tyrannosaurus rex Bone Lesions
A significant number of the Tyrannosaurus rex fossils that have been collected, mandibles in particular, display a unique type of bone lesion. These lesions are smooth-edged, on either one or both sides of the jawbone, and they often occur in multiple groupings.
Until recently, these lesions in Tyrannosaurus rex mandibles have been attributed to a number of different possible causes: actinomycosis (an inflammatory bone disease that occurs in modern humans, cows, and sometimes pigs), bacterial infections, and even bite marks from similarly sized theropods.
Wolff and his fellow researchers, however, take due note of the many similarities between the mandibular lesions of the Tyrannosaurus rex and those occurring commonly in modern pigeons, chickens, and even birds of prey. The modern avian lesions are a result of a parasitic infection called trichomonosis, which led scientists to believe that this avian infection, or a very similar infection, contributed to the downfall of the Tyrannosaurus rex.
What is Trichomonosis?
In short, and as mentioned above, trichomonosis as it is known today is an erosive parasitic infection that is caused by a protozoan called Trichomonas gallinae. There are many different strains of avian trichomonosis, and some strains are believed to help immunize hosts against other trichomonas strains.
Avian trichomonosis occurs in many types of birds, from pigeons (in fact, most pigeons harbor the infection) to, less commonly, raptors. There are a number of ways birds encounter this parasite; most often, the protozoa that causes the infection is picked up through tainted prey. Beak-to-beak contact, especially with parent-to-chick, is another mode of transmission, as is feeding chicks tainted food. Trichomonosis is particularly deadly to young birds, causing them to lose weight and often die.
Trichomonosis and Tyrannosaurus rex
Many Tyrannosauarus rex jawbones were looked at during this project, but the focal point of the study was the famous “Sue,” the most logical starting point because of all the hypothesized causes for the dinosaur’s mandibular lesions. Wolff et al, however, realized that these lesions weren’t particularly characteristic of any of the proposed explanations.
Looking first to a number of bacterial infections that plague the modern archosaurs helped give the researchers insight as to why these were not a good explanation for the Tyrannosaurus rex lesions. A number of infectious agents were examined in crocodiles and other reptiles, such as Parapoxvirus or “crocodile pox,” gingivitis, and a number of others. None of the bacterial or viral infections observed matched the resulting bone lesions in Tyrannosauarus rex.
Researchers also ruled out bite wounds as an explanation for the lesions. Bite wounds are fairly well-documented, and upon further examination, they determined that the bone lesions were not consistent with deep bite wounds (the ones that reach bone) in shape and construction.
How Trichomonosis Affected Tyrannosauarus rex
Wolff and his team feel very confident in their findings, and judging by how trichomonosis affects modern birds, they find it likely that Tyrannosauarus rex may have been subjected to starvation because of the disease. Through a number of modes of transmission – fighting amongst each other, dissemination through watering holes, eating infected prey, and even cannibalism - Tyrannosauarus rex may have been severely afflicted by the parasitic infection.
If this is the case, trichomonosis may have played a significant role in the deaths of these large theropods. As easily as trichomonosis is spread amongst modern birds, this doesn’t seem like too far a stretch. In any case, Wolff and his fellow researchers will continue to study the mark of trichomonosis and other similar infections on the now-extinct creatures.
Resource: Wolff EDS, Salisbury SW, Horner JR, Varricchio DJ (2009) Common Avian Infection Plagued the Tyrant Dinosaurs. PLoS ONE 4(9): e7288.
Kristina Bjoran - Kristina Bjoran is an English major from Atlanta, Georgia, recently graduated Summa Cum Laude with a Bachelor's degree. She has worked as ...
