New characterisation of the Late Miocene insular bear Indarctos anthracitis

The genus Indarctos is recorded from Eurasia, Northern Africa and North America since the Late Miocene. However, its record is utterly scarce, often represented by isolated remains. This has led to taxonomic confusion and hindered phylogenetic reconstruction of the genus. Here we reappraise Indarctos anthracitis, based on original and new material, providing key insights into its morphological adaptations and ecology. Our analysis of the mandibular and dental features confirms its distinction from Indarctos atticus, Indarctos arctoides, and Indarctos vireti. Despite dental similarities to I. atticus, I. anthracitis is significantly smaller, consistent with insular size reduction driven by limited food resources. Study of the dental microwear, despite the small sample size, suggests that I. anthracitis had a more specialised diet compared to the one of I. atticus, composed mostly of invertebrates as a response to environmental constraints. Scavenging cannot be ruled out, as it could have been key for survival in an insular setting. The study of fossil Indarctos species contributes to understanding dietary evolution within the Ailuropodinae. Unlike other fossil and extant island bears, which are remnants of mainland populations, I. anthracitis represents a rare example of insular adaptation of a large-sized carnivoran.