The skull and mandible of the Miocene hegetotheriine notoungulate Hegetotherium mirabile are described. Although conventional models of hegetothere biology propose that these animals filled a lagomorph-like ecological niche, study of the cranial and dental anatomy of Hegetotherium suggests that this extinct South American ungulate may have fed by breaking through wood in order to eat xylophagous grubs and other organisms. This mode of life is seen in two extant mammals, the monotypic Malagasy primate Daubentonia madagascariensis and diprotodont marsupials of the genus Dactylopsila. It has also been proposed as a feeding mechanism for two extinct groups of mammals: the “proteutherian” apatemyids from the Paleogene of Europe and North America, and the enigmatic marsupial Yalkaparidon from the early Miocene of Australia. Collectively, these living and extinct taxa have been proposed as mammalian woodpeckers. They are defined by a suite of morphological characteristics, including unusually developed and continually growing incisors, molars adapted to have a constantly sharp edge, exaggerated klinorhynchy, deep zygomatic arches and a shortened snout. Hegetotherium mirabile shares almost all characteristics common to the mammalian woodpeckers, although it lacks several features that are likely to be adaptations for an arboreal, nocturnal lifestyle. This suggests that although the feeding techniques of this species were similar to those of the mammalian woodpeckers, H. mirabile occupied a diurnal, cursorial niche, feeding on grubs and insects within fallen trees and logs.