ZOOLOGICAL PALEOPATHOLOGY AND THE CASE OF THE TYRANNOSAURUS JAW: INTEGRATING PHYLOGENY AND THE STUDY OF ANCIENT DISEASES

The analysis of diseases by pathologists relies on gross observation, serology, bacteriology, histopathology and clinical history. Paleopathologists are left with a fraction of that information from which to draw conclusions. Paleopathology has historically disregarded microbial evolution, and falls within the Victorian mindset that views the human model of disease as the arbiter of diagnosis. Although human pathology research is extensive, disease comparisons taken outside of phylogenetic context must be questioned. Therefore, the author proposes a new approach, here termed zoological paleopathology, that allies this field with zoological medicine. Zoological paleopathology accepts that pathogens evolve, and that susceptibility to non-transmissible conditions may also evolve, such that patterns can only be distinguished by inter-clade investigation. This method draws upon a history of zoological pathology research on numerous taxa, deferring to human pathology only in those mammalian cases that justify direct comparison. It is also pattern-based, preferring differential diagnosis of well-defined broad-scale trends to peremptory diagnosis of individuals.

As a test case for zoological paleopathology, the author studied oral pathology in tyrannosaurids. Of fifty-six individuals examined, one fourth of the mandibles displayed some form of anomaly, typically of the surangular or dentary. The dentaries had abnormalities classified as tooth traces from scavenging, an isolated bite wound, and idiopathic periosteal reactive ridges, which are observed on some specimens to display cranial curvature and overlap between the lingual and labial aspects. The surangulars often display resorptive fenestrae that are random in distribution. The fenestrae are ovate, ringed by normal periosteum, and generally lie proximal to other abnormal fenestrae. The tentative differentials for this condition are developmental abnormality, bite trauma, osteomyelitis, fibriscess, idiopathic neoplasia and metastatic carcinoma. Preliminary results indicate that these abnormalities more closely resemble those found in crocodilians than ratites.