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, 4 (9), e7288

Common Avian Infection Plagued the Tyrant Dinosaurs

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Common Avian Infection Plagued the Tyrant Dinosaurs

Ewan D S Wolff et al. PLoS One.

Abstract

Background: Tyrannosaurus rex and other tyrannosaurid fossils often display multiple, smooth-edged full-thickness erosive lesions on the mandible, either unilaterally or bilaterally. The cause of these lesions in the Tyrannosaurus rex specimen FMNH PR2081 (known informally by the name 'Sue') has previously been attributed to actinomycosis, a bacterial bone infection, or bite wounds from other tyrannosaurids.

Methodology/principal findings: We conducted an extensive survey of tyrannosaurid specimens and identified ten individuals with full-thickness erosive lesions. These lesions were described, measured and photographed for comparison with one another. We also conducted an extensive survey of related archosaurs for similar lesions. We show here that these lesions are consistent with those caused by an avian parasitic infection called trichomonosis, which causes similar abnormalities on the mandible of modern birds, in particular raptors.

Conclusions/significance: This finding represents the first evidence for the ancient evolutionary origin of an avian transmissible disease in non-avian theropod dinosaurs. It also provides a valuable insight into the palaeobiology of these now extinct animals. Based on the frequency with which these lesions occur, we hypothesize that tyrannosaurids were commonly infected by a Trichomonas gallinae-like protozoan. For tyrannosaurid populations, the only non-avian dinosaur group that show trichomonosis-type lesions, it is likely that the disease became endemic and spread as a result of antagonistic intraspecific behavior, consumption of prey infected by a Trichomonas gallinae-like protozoan and possibly even cannibalism. The severity of trichomonosis-related lesions in specimens such as Tyrannosaurus rex FMNH PR2081 and Tyrannosaurus rex MOR 980, strongly suggests that these animals died as a direct result of this disease, mostly likely through starvation.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Tyrannosaurus rex (FMNH PR2081).
Left mandibular ramus exhibiting multiple trichomonosis-type lesions (indicated by arrows); (A and D), lateral view (photo; schematic interpretation). (B and E) medial view (photo; schematic interpretation). (C), schematic interpretation of the reconstructed skull of FMNH PR2081 in left lateral view with the mandibular ramus shown in red. Anatomical abbreviations: ang, angular; art, articular; corn, coronoid; d, dentary; fen mand ext, external mandibular fenestra; for my, mylohyal foramen; for sa caud, caudal surangular foramen; for sa rost, rostral surangular foramen; preart, prearticular; sa, surangular; sd, supradentary; sp, splenial. a and b modified from ©1999 The Field Museum, GEO86260_7c and GEO86262_4c, respectively. Photographer John Weinstein.
Figure 2
Figure 2. Tyrannosaurid mandibular pathology
(arrows indicate trichomonosis-type lesions; the position of each specimen is shown in red on the accompanying schematic interpretation of the reconstructed skull of Tyrannosaurus rex, FMNH PR2081); (A), Tyrannosaurus rex (holotype; CMNH 9380) right caudal mandibular ramus in lateral view, displaying a large circumscribed erosive lesion on the caudal part of the dentary. (B) Daspletosaurus torosus (RTMP 2001.36.01) left caudal mandibular ramus in lateral view, displaying a single erosive lesion. (C), Daspletosaurus torosus (RTMP 2001.36.01) multiple erosive lesions are visible on the right surangular in medial view. (D), Albertosaurus sarcophagus (RTMP 1981.10.01), left caudal mandibular ramus in lateral view, showing a slit-shaped trichomonosis-type lesion in the middle of the angular, (enlarged area, inset). (E) Tyrannosaurus rex (MOR 1125), caudal part of left dentary in lateral view, showing a cylindrical-shaped lesion, with smooth edges and almost no surrounding bony alteration. (F), Daspletosaurus torosus (RTMP 94.143.1), surangular in ventral view, with one slit-shaped lesion and one intermediate lesion. The close-up shows the smooth edges and limited surrounding bony alteration characteristic of a trichomonosis-type lesion. (G), Tyrannosaurus rex (MOR 980), left surangular in lateral view, exhibiting multiple oval- to sub-oval-shaped lesions.
Figure 3
Figure 3. The mandible of a modern falconiform, Pandion haliaetus, the osprey (USNM 561853), exhibiting multiple trichomonosis lesions (indicated by arrows);
the animal most likely acquired the disease by feeding on an infected pigeon . (A) (photo) and (B) (radiograph), mandible in left ventrolateral view, exhibiting multiple oblate to cylindrical erosive lesions. (C), schematic interpretation of the normal skull of Pandion haliaetus (Queensland Museum O31935) in left lateral view with the mandible shown in red. Anatomical abbreviations: d, dentary; ram mand, mandibular ramus; rost mand, mandibular rostrum. (D) (photo) and (E) (X-ray), mandible in right lateral view, exhibiting multiple oblate to cylindrical erosive lesions. The X-rays show that the lesions are largely resolved, except for a slight radiodensity indicative of thickening along the lesion edges.
Figure 4
Figure 4. Hypothesized reconstruction of the Trichomonas-like infection of the oropharynx and mandible of MOR 980, commonly known as ‘Peck's Rex’ (Figure 2G).
Note the yellowing of the oropharyngeal area at the back of the mouth and developed lesions within the mandible that penetrate the full thickness of the bone. This reconstruction is based on photographs of living birds and bird necropsies of individuals with trichomonosis. Illustration by Chris Glen, The University of Queensland.

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