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. Mesowear angles, an extension of the traditional mesowear method for reconstructing diet based on the balance between attrition and abrasion, have been previously applied to deinotheres using the inclination of their wear facets. We measured mesowear angles from South American fossil bilophodonts (tapirs, xenungulates, and pyrotheres) from wear facet inclination or dentine valleys and compared those to results from some modern bilophodont taxa. Mesowear angles in modern bilophodonts match the dietary predictions based on observed diet and highlight the potential of these angles for dietary reconstruction in fossil groups. Xenungulates and fossil tapirs all show sharp mesowear angles (< 106˚), indicating a browsing feeding behaviour. In contrast, pyrotheres show significant dietary variation. Some taxa (e.g., Griphodon peruvianus and Pyrotherium romeroi ) show steeply inclined facets indicating browsing. Rounded, shallower facets in Propyrotherium saxeum are interpreted as evidence of frugivory, while Pyrotherium macfaddeni has relatively shallow facets indicating a mixed-feeding ecology. High mesowear angles in Proticia venezuelensis and Colombitherium tolimense support grazing in the colombitheriids, a group with controversial phylogenetic affinities. There is huge potential for the further application of mesowear angles in other bilophodont taxa for dietary reconstruction, and we propose that angles measured in bilophodonts could be compared to those from other dental morphologies for palaeoenvironmental reconstruction.