MICRO-CT ANALYSIS OF AN IDIOPATHIC EROSIVE LESION ON THE SURANGULAR OF ALLOSAURUS FRAGILIS WITH COMPARISONS TO COMMON TYRANNOSAURID PATHOLOGIES

Pathologies and feeding traces have been thoroughly described in theropod dinosaurs.In tyrannosauridae, unusual pathologies in the form of circular, smooth-edged erosive lesions are commonly present on the surangular and posterior dentary. These lesions - commonly described in the mandibles of tyrannosauridae - have a debated etiology; they may be infectious having resulted from Trichomonas gallinae-like protozoans, or traumatic-infectious caused by intraspecific combat and subsequent infection. In either origin, both ecological and behavioral interactions play key roles. Infections due to protozoa and other pathogenic microbes may indicate transmissions in highly dense populations, such as those for Allosaurus fragilis in the Cleveland-Lloyd Quarry. While these lesions are common in tyrannosauridae, they have not been observed or described in other theropod clades. Here we describe a right surangular of A. fragilis from the Cleveland-Lloyd Dinosaur Quarry at Jurassic National Monument possessing pathologies with similar features to those found in tyrannosauridae. The surangular (CLDQ-S-17-040) has a maximum length of 365 mm and width of 80 mm, suggesting a juvenile or subadult individual. The bone tissue surrounding the lesions is mildly coarse texture and has an undulating surface, suggesting active osteological reaction at the time of death. To further investigate the bone tissue surrounding the lesion and test the competing diagnoses of these lesions, we conducted micro-CT scans using a dual tube GE Phoenix CT scanner. Using both external morphology and internal histological features, we provide deeper insight into the cause of these common tyrannosaurid pathologies. While the exact nature of these pathologies is currently unresolved, further comparison with other theropod specimens may assist in identifying their origin.