Snout shape and masticatory apparatus of the rodent-like mesotheriidungulates (Typotheria, Notoungulata): exploring evolutionary trends in dietary strategies through ancestralreconstructions

ERCOLI, MARCOS D.; ARMELLA, MATÍAS A.

PALAEONTOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021

0031-0239

Mesotheriidae were small to medium-sized native South American ungulates. Mesotheriids radiated from the early Oligocene to the early?middle Pleistocene, grouped into two subfamilies: Trachytheriinae and Mesotheriinae. Beyond the conspicuous fossil record, little is known about mesotheriid palaeobiology and, particularly, the dietary habits. To date, different studies suggest grazing habits, similar to some extant ungulates, but recent contributions are challenging this vision. In this contribution, we explore dietary preferences in mesotheriids, focusing on the food intake and oral processing strategies. We performed a shape analysis of the snout and reconstructed ancestral shapes to assess evolutionary trends within the clade. Also, we considered other morphological variables of the masticatory apparatus to perform a functional characterization. We recognized three snout configurations: Trachytherus, "Intermediate", and Mesotherium morphotypes that can be associated with different food intake capabilities and, considering other morphological proxies, to the consumption of different food items. Taking into account palaeoenvironmental conditions, the evolution of the masticatory apparatus were interpreted in the context of a consumption gradient from coarse and tough foods (roots, tubers, tough leaves) to grasses. We propose that during the ecomorphological evolution of mesotheriids, an initial phase took place during the late Oligocene-Miocene, in which there was diversification and a specialization to the consumption of hard-to-break food items. A second phase incipiently started during the late Miocene, and became well-defined during Pliocene-Pleistocene, characterized by an ecomorphological displacement towards grazing habits. Inferred dietary habits in Mesotheriidae could provide light on palaeoecological evolution and niche partitioning within South American herbivorous mammalian communities.