Ewan D. S. Wolff; Steven W. Salisbury; John R. Horner; David J. Varricchio

“ The distribution, size, shape and nature of trichomonosis-type lesions in tyrannosaurid specimens are similar in nature to those manifested in modern falconiforms infected with the protozoan Trichomonas gallinae. Our differential diagnosis of possible diseases within the phylogenetic bracket of tyrannosaurids and modern falconiforms supports the diagnosis of a trichomonosis-type disease in these non-avian theropod dinosaurs. Thus, there is a good possibility that the disease we have identified in tyrannosaurids is homologous with modern avian trichomonosis. ”

“ Disease development of a triomononosis-type disease in tyrannosaurids likely followed the same trajectory as in modern birds. Regardless of the scenario of initial infection with a T. gallinae-type protozoan, an infection within the oropharynx would then have seeded protozoa into surrounding tissues by invading through the mucosal surface, as is seen in modern birds [15] , [16] . Lesions represent focal sites of chronic infection within the mandible that can be reconstructed to give a general sense of the appearance of the lesions in life (Figure 4) . ”

“ Face-biting in devils transmits a type of malignant debilitating oral cancer, and infected individuals find themselves ultimately unable to eat [32] . Through the vehicle of disease, this head-biting behavior is bringing about a population bottleneck. In the late Maastrichtian, a disease like modern-day avian trichomonosis may have been the scourge of tyrannosaurids, thanks in part to their antagonistic behavior. ”

“ Consumption of infected prey is an important mode of Trichomonas transmission among modern birds of prey [18] – [20] . From traces left on bones, tyrannosaurids can be shown to have consumed a wide variety of dinosaur prey as is evidenced by bite marks on hadrosaurs, ceratopsians, other ornithischians and tyrannosaurids [28] , [29] . Despite extensive records, no ornithischians of the Late Cretaceous have been reported to bear trichomonosis-like lesions. ”

“ Vertical transmission from parents to offspring has also been demonstrated among falconiforms, either through nestlings being fed meat with adherent flagellates in it or by direct bill-to-bill contact with infected parents [18] , [19] , [22] , [20] . The disease can have the most serious effects in young birds, often causing rapid weight loss and eventually death [18] , [20] .
In severe cases, trichomonosis in falconiforms leads to the formation of large oropharyngeal lesions [18] , including erosive deformations of the craniomandibular apparatus [20] (Figure 3) . ”

“ Many tyrannosaurids display a second category of cranial abnormalities distinct from the traumas associated with head-biting. These abnormalities are smooth-edged fully erosive lesions that are most commonly present in the mandible. ”

“ In osteological specimens that we have observed, these erosive deformations are typically cylindrical or oblate in shape, and may occur on one or both of the mandibular rami, either fully penetrating the bone, or just the lateral surface. ”