Feeding the ‘fire beasts’: mesowear angles in bilophodont South American herbivores

Abstract

Bilophodont tooth morphology is found in various groups of extant and fossil herbivores, including tapirs, marsupials,deinotheres, and two groups of Paleogene South American native ungulates: the xenungulates and pyrotheres. Mesowearangles, an extension of the traditional mesowear method for reconstructing diet based on the balance between attrition andabrasion, have been previously applied to deinotheres using the inclination of their wear facets. We measured mesowearangles from South American fossil bilophodonts (tapirs, xenungulates, and pyrotheres) from wear facet inclination or dentinevalleys and compared those to results from some modern bilophodont taxa. Mesowear angles in modern bilophodontsmatch the dietary predictions based on observed diet and highlight the potential of these angles for dietary reconstructionin fossil groups. Xenungulates and fossil tapirs all show sharp mesowear angles (< 106˚), indicating a browsing feedingbehaviour. In contrast, pyrotheres show significant dietary variation. Some taxa (e.g., Griphodon peruvianus and Pyrotheriumromeroi) show steeply inclined facets indicating browsing. Rounded, shallower facets in Propyrotherium saxeumare interpreted as evidence of frugivory, while Pyrotherium macfaddeni has relatively shallow facets indicating a mixedfeedingecology. High mesowear angles in Proticia venezuelensis and Colombitherium tolimense support grazing in thecolombitheriids, a group with controversial phylogenetic affinities. There is huge potential for the further application ofmesowear angles in other bilophodont taxa for dietary reconstruction, and we propose that angles measured in bilophodontscould be compared to those from other dental morphologies for palaeoenvironmental reconstruction.