Astragalus ecomorphology in Quaternary elephantids

Abstract

The astragalus plays a fundamental role in the graviportal locomotion of proboscideans, reflecting the biomechanical constraints imposed by large body masses. This study analyses the morphological variability of the astragalus in Quaternary elephantids using linear biometry and 3D geometric morphometrics, incorporating an unpublished astragalus of Mammuthus meridionalis from the Calabrian (ca. 0.9 Ma) of Barranc de la Boella (eastern Iberian Peninsula) within a broad comparative framework of fossil and extant forms. The results reveal a marked allometric relationship, whereby larger individuals have relatively flatter astragali, regardless of their taxonomic affinity. The Barranc de la Boella specimen fits this pattern perfectly, showing dimensions comparable to those of the largest elephantids of the Gelasian, Calabrian and Chibanian. No clear phylogenetic signal is detected in the morphology of the astragalus, suggesting that body size dominates the observed variation and limits its usefulness in discriminating specific taxonomic affinities or ecological adaptations.