THE PALEOPATHOLOGICAL RECORD OF DINOSAURS: 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 to the paleobiology of dinosaurs. Given the vagaries of vertebrate fossil taphonomy and the restriction that diseases must be recorded on hard parts, preserving paleopathologies might appear unlikely. However, there are more than 135 reports of dinosaurian paleopathologies from at least 123 specimens in the peer-reviewed literature, with many more known from anecdotal evidence, abstracts, and databases. Working from the null hypothesis that pathologies would be evenly distributed chronologically and taxonomically across Dinosauria, we have synthesized the existing literature to compile paleopathological occurrences stratigraphically, by clade, body mass, and type (disease, injury, or both). Thus we index pathologies across six stages (Late Triassic, Early, Middle, and Late Jurassic; Early and Late Cretaceous), five major clades (Theropoda, Sauropodomorpha, Thyreophora, Marginocephalia, and Ornithopoda), and body masses across five orders of magnitude (1–10, 10–100, 100–1000, 1000–10000, 10,000+ kg).

The paleopathological record is strongly biased toward North America (75% of occurrences; almost all others are Eurasian), so it mirrors the North American record of dinosaurs, with “spikes” of pathology during the Late Jurassic and Late Cretaceous but few occurrences otherwise. Essentially all pathologies (>80%) occur in specimens that weighed 1000s to 10,000+ kg—only theropods have multiple pathological occurrences at smaller body size.

This record also supports hypotheses regarding dinosaur behavior, namely that taxa that engage in predatory (theropods) or other antagonistic (ceratopsian) behavior are more likely to bear injuries (or a combination of injuries and diseases) than are more docile clades. Theropods and marginocephalians (principally ceratopsids) each represent ~30% of paleopathologies and more than a third of all injuries. Ornithopods, sauropods, and thyreophorans (stegosaurs and ankylosaurs) each account for less than ~20% of pathological occurrences and experience diseases at a higher rate than injuries (<15% for each clade). Normalizing these data to the fossil record will be challenging, but provides a further test of the null hypothesis.