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

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.

KEYWORDS:

• Bone histology
• body size
• life history
• growth rate
• Pleistocene
• Equus

Acknowledgments

We thank Reinhard Ziegler for access to the collections of the Staatliches Museum für Naturkunde (Stuttgart, Germany) and for permission to cut the metapodia of E. steinheimensis and E. mosbachensis. We are also grateful to Renate Schafberg and Thomas Kaiser for loans and permission to cut bones from the collections of the Museum of Domesticated Animals of the Martin-Luther-University Halle-Wittenberg (Halle, Saale, Germany) and the Zoological Institute of Hamburg University (Hamburg, Germany) respectively. We thank B. Lamglait (currently at Université de Montréal, Canada) and the Réserve Africaine de Sigean (Sigean, France) for a donation of aged equid specimens. Manuel Fernández and Gemma Prats-Muñoz are acknowledged for the preparation of the histological thin-sections of the study. We are also in debt to Meike Köhler for discussion on this paper and the revision of earlier versions of the manuscript. Thanks are extended to Xavier Jordana, Alexandra Houssaye and one anonymous reviewer for their feedback, which resulted in significant improvements of this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Correction Statement

The correct affiliation of Guillem Orlandi-Oliveras is Evolutionary paleobiology department, Institut Català de Paleontologia Miquel Crusafont (ICP), Campus de la Universitat Autònoma de Barcelona, Barcelona, Spain

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by Ministerio de Economía y Competitividad (Spain) under Grant CGL-2015-63777, Grant BES-2013-066335 (to C.N.-M.) and Grant EEBB-I-16-10546 (to C.N.-M.); Generalitat de Catalunya (Spain) under Grant 2014-SGR-1207, Grant CERCA Programme and Grant 2016FI_B00202 AGAUR (to G.O.-O); and the DST-NRF Centre of Excellence in Palaeosciences (South Africa) under Grant COE2019-PD03 (to C.N.-M.). Opinions expressed and conclusions arrived at, are those of the author and are not necessarily attributed to the CoE. Generalitat de Catalunya [2014-SGR-1207,2016FI_B00202,CERCA Programme]; Ministerio de Economía y Competitividad [BES-2013-066335,CGL-2015-63777,EEBB-I-16-10546]; DST-NRF Centre of Excellence in Palaeosciences [COE2019-PD03]