Oral pathology of the Archosauria : bony abnormalities and phylogenetic inference

Abstract

As a reaction to comparative paleopathology, which homologizes human and dinosaur disease, this project proposed that a broad-scale survey of oral pathology in archosaurs would reveal unique relationships in disease. The approach that was created to pursue this study was termed zoological paleopathology. The justification of this approach lies in the differences between the immune and inflammatory response in mammals and archosaurs. This response governs disease progression within the body and the morphology of many lesions. 2,443 skulls and heads were examined for abnormalities from specimens representing four major groups of archosaurs; the crocodiles, pterosaurs, dinosaurs and birds,. Skulls of iguanids, monotremes and marsupials provided outgroup comparisons for the study. Lesions were analyzed, photographed and interpreted for 123 total cases. The majority of cases related to either traumatic or inflammatory diseases. The disease patterns within the study were compared using cladograms and addition reports from the veterinary literature.

When the patterns in disease were compared between archosaurs and the outgroups, the influence of anatomy, behavior and immunology, or phylogenetic constraint, was evident in the disease categories of trauma, inflammatory diseases, congenital/developmental diseases, neoplasia and certain unknown diseases. In fact, 77.7% of the diseases could only be explained adequately with reference to archosaur pathology. The comparative paleopathology approach was able to explain fracture and metabolic bone diseases through cross-vertebrate comparison, but was only relevant for a fraction of the cases. The results demonstrate a clear division of work between the phylogenetic comparisons of zoological paleopathology and the general comparisons of comparative paleopathology. In addition to establishing the domain of a new discipline, this project also delved into the nature of dinosaur immunity and contributed methods for the naming of unknown diseases in the fossil record. The dinosaur immune system was inferred to be homologous with that of crocodiles and birds on the basis of similar inflammatory diseases resulting from immune response. The construction of phylogenetic comparisons in ancient disease research, the elucidation of disease development and progression, and the exploration of undiscovered diseases in the fossil record will provide new fronts in the expanding field of paleopathology.