The life history of European Middle Pleistocene equids: first insights from bone histology

Abstract

ABSTRACT Evolutionary trends in body size are a central issue of study in Palaeontology. However, and despite body size being one of the most important life history traits of an animal, iconic size-decrease trends such as the one experienced by Equus during the European Pleistocene have never been analysed under a life history framework. Here, we studied the metapodial bone histology of two large Middle Pleistocene species (Equus mosbachensis and Equus steinheimensis) to reconstruct key life history traits that correlate with body size (e.g. size at birth, growth rate), and compare them with that of smaller extant Equus (Equus grevyi, Equus quagga, Equus zebra and Equus hemionus). Our results show that neonatal size of these Middle Pleistocene equids fits predictions from body mass scaling. We estimate a similar age of epiphyseal fusion for the metapodia of E. mosbachensis and E. steinheimensis and that of extant equids. Our findings also reveal that extinct equids grew at higher rates than extant Equus. This result conforms to the predictions of life history theory on environments with different levels of resource availability and provides a new framework of study for body size shifts on European Pleistocene equids.