Abstract
Traditional palaeontological techniques of disease characterisation are limited to the analysis of osseous fossils, requiring several lines of evidence to support diagnoses. This study presents a novel stepwise concept for comprehensive diagnosis of pathologies in fossils by computed tomography imaging for morphological assessment combined with likelihood estimation based on systematic phylogenetic disease bracketing. This approach was applied to characterise pathologies of the left fibula and fused caudal vertebrae of the non-avian dinosaur Tyrannosaurus rex. Initial morphological assessment narrowed the differential diagnosis to neoplasia or infection. Subsequent data review from phylogenetically closely related species at the clade level revealed neoplasia rates as low as 3.1% and 1.8%, while infectious-disease rates were 32.0% and 53.9% in extant dinosaurs (birds) and non-avian reptiles, respectively. Furthermore, the survey of literature revealed that within the phylogenetic disease bracket the oldest case of bone infection (osteomyelitis) was identified in the mandible of a 275-million-year-old captorhinid eureptile Labidosaurus. These findings demonstrate low probability of a neoplastic aetiology of the examined pathologies in the Tyrannosaurus rex and in turn, suggest that they correspond to multiple foci of osteomyelitis.
Highlights
In the early twentieth century, Roy Lee Moodie, a geologist and palaeontologist, established the field of palaeopathology, the study of diseases and traumatic injuries that caused visible abnormalities of the skeleton in fossil vertebrates[1]
Radiological imaging is a substantial asset in palaeopathology as it aids in visualising internal structures and reveals many additional diagnostic features, bringing to
This study describes a comprehensive palaeopathological approach for diagnosing disease using morphological analysis and radiological imaging combined with phylogenetic disease bracketing[6,12,28]
Summary
In the early twentieth century, Roy Lee Moodie, a geologist and palaeontologist, established the field of palaeopathology, the study of diseases and traumatic injuries that caused visible abnormalities of the skeleton in fossil vertebrates[1]. The morphological features presented by a particular disease can vary among species, which calls for a multistep approach in diagnosing pathological lesions in the fossil r ecord[6,9] In this test case, the Extant Phylogenetic Bracket (EPB)[10,11] was applied to derive further information from previous pathology reports and epidemiological analyses comparing different species. Consideration of the prevalence of a disease in the species of interest and its close extant relatives (narrow phylogenetic disease bracket, NPDB) limits the number of possible differential d iagnoses[12,13,14,15] Such data can contribute substantially to more robust and reliable findings. Phylogenetic evidence and disease prevalence were not systematically taken into account[26,29,30,31,32,33]
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