Lost giants, lost functions: palaeodietary insights into the ecological niches of Pleistocene ground sloths.

Ground sloths were terrestrial megafauna that inhabited the Western Hemisphere. While they are inferred to have been browsers and grazers based on craniodental morphology, it is plausible that they performed a wide range of ecological functions, including seed dispersal, bioturbation and nutrient cycling. Understanding ground sloth ecology is challenging due to their enamel-free dentition, which poses limitations to palaeodietary methods, like stable isotope analysis, due to the increased probability of diagenesis in more porous tissues. Here, we conduct dental microwear texture analysis on Paramylodon harlani and Nothrotheriops shastensis specimens from the La Brea Tar Pits in southern California to compare these species to each other, to co-occurring megafauna and to modern analogues to clarify ground sloth dietary ecology. DMTA of P. harlani (i.e. low anisotropy and high complexity) and N. shastensis (i.e. low anisotropy and low complexity) suggests that P. harlani consumed significantly harder foods (e.g. tubers, roots, seeds, fruit pits) than N. shastensis. Findings underscore that these species were not functional replicates of each other or of co-occurring browsers and grazers (e.g. camels and bison). Considering the high degree of dietary overlap in extant folivorous sloths, the extinction of giant ground sloths represents a true loss of ecological function.