THE PALEOPATHOLOGICAL RECORD OF NON-AVIAN DINOSAURS: IMPLICATIONS OF THE DISTRIBUTION OF DISEASE AND INCIDENCE OF INJURY THROUGHOUT THE MESOZOIC

As the fossil record of injuries and/or diseases, paleopathologies are one of the most direct insights into dinosaur paleobiology. In spite of the vagaries of vertebrate fossil taphonomy and the restriction that diseases must be recorded on hard parts, there are more than 400 reports of paleopathological dinosaur body fossils in the peer-reviewed literature. Many more are known from anecdotal evidence, abstracts, and unpublished datasets. We have synthesized the peer-reviewed literature of the dinosaurian paleopathological record (DPR) paleogeographically (by continent), chronologically (Late Triassic, Early, Middle, and Late Jurassic; Early and Late Cretaceous), across five major clades (Theropoda, Sauropodomorpha, Thyreophora, Marginocephalia, and Ornithopoda), and over five orders of magnitude of body mass (1–10 kg, 10s kg, 100s kg, 1000s kg, 10,000+ kg). We broadly divided paleopathologies into injuries (e.g., broken bones) or diseases (e.g., arthritis) with the caveat that many infectious diseases (e.g., osteomyelitis) may be caused by injuries that may not be preserved. Our null hypothesis was that pathologies should be evenly distributed across Dinosauria chronologically, geographically, and taxonomically.

The DPR is strongly biased toward North America (>80% of occurrences; almost all others are Eurasian), so it essentially mirrors the North American dinosaur record, with extensive evidence of pathology in the Late Cretaceous and, to a lesser extent, the Late Jurassic, with rare other occurrences. Essentially all (95%+) pathologies occurred in individuals with body masses ≥ 1000 kg. It is difficult to normalize the DPR for the “monograph effect,” due to large, focused studies on paleopathologies in hadrosaurs, ceratopsians, and large theropods. The DPR supports hypotheses regarding dinosaur behavior, namely that taxa that engaged in predatory (theropod) or other antagonistic (ceratopsian) activities are more likely to bear presacral injuries (or a combination of injuries and diseases) than are more docile animals, such as ornithopods, thyreophorans and sauropodomorphs. One challenge to interpreting the DPR is the lack of similarly broad analyses of pathologies in extant wild populations, which hampers our ability to develop hypotheses for expected rates of incidence in fossil taxa.