Palaeoepidemiology in extinct vertebrate populations: factors influencing skeletal health in Jurassic marine reptiles.

Judith M Pardo-Pérez,Erin E Maxwell,Benjamin Kear

doi:10.1098/rsos.190264

Abstract

Palaeoepidemiological studies related to palaeoecology are rare, but have the potential to provide information regarding ecosystem-level characteristics by measuring individual health. In order to assess factors underlying the prevalence of pathologies in large marine vertebrates, we surveyed ichthyosaurs (Mesozoic marine reptiles) from the Posidonienschiefer Formation (Early Jurassic: Toarcian) of southwestern Germany. This Formation provides a relatively large sample from a geologically and geographically restricted interval, making it ideal for generating baseline data for a palaeoepidemiological survey. We examined the influence of taxon, anatomical region, body size, ontogeny and environmental change, as represented by the early Toarcian Oceanic Anoxic Event, on the prevalence of pathologies, based on a priori ideas of factors influencing population skeletal health. Our results show that the incidence of pathologies is dependent on taxon, with the small-bodied genus Stenopterygius exhibiting fewer skeletal pathologies than other genera. Within Stenopterygius, we detected more pathologies in large adults than in smaller size classes. Stratigraphic horizon, a proxy for palaeoenvironmental change, did not influence the incidence of pathologies in Stenopterygius. The quantification of the occurrence of pathologies within taxa and across guilds is critical to constructing more detailed hypotheses regarding changes in the prevalence of skeletal injury and disease through Earth history.

Highlights

Palaeoepidemiological surveys have the potential to provide novel information on individual health, as well as overarching metrics of ecosystem function such as predation pressure
An example of such is the Posidonienschiefer Formation, a classic konservat lagerstätte yielding a rich assemblage of exceptionally preserved fossil vertebrates and invertebrates, spanning a minor mass extinction associated with ecosystem-level changes in vertebrate and invertebrate faunas (the early Toarcian Oceanic Anoxic Event (T-OAE) [7,8])
We examine the effect of body size, ontogeny and the T-OAE on the prevalence and distribution of pathologies in ichthyosaurs from the Early Jurassic Posidonienschiefer Formation of southwestern Germany in order to statistically assess which factors affect observed prevalence

Summary

Introduction

Palaeoepidemiological surveys have the potential to provide novel information on individual health, as well as overarching metrics of ecosystem function such as predation pressure Such surveys have been attempted in numerous fossil systems (e.g. non-avian dinosaurs [1], and Pleistocene carnivorans [2] and frogs [3]); baseline data are largely lacking for ancient marine systems. The ichthyosaurian fossil record is controlled by lagerstätte-type deposits, in which temporally and geographically restricted formations yield large numbers of associated skeletons [6] An example of such is the Posidonienschiefer Formation, a classic konservat lagerstätte yielding a rich assemblage of exceptionally preserved fossil vertebrates and invertebrates, spanning a minor mass extinction associated with ecosystem-level changes in vertebrate and invertebrate faunas (the early Toarcian Oceanic Anoxic Event (T-OAE) [7,8]). Five ichthyosaur genera are known from these deposits, varying in body size and trophic position: Hauffiopteryx (2.5 m long), Stenopterygius (3.5 m long), Suevoleviathan (4 m long), Eurhinosaurus (7 m long) and the apex predator Temnodontosaurus (greater than 9 m long)

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