Sciuromorphy outside rodents reveals an ecomorphological convergence between squirrels and 2 extinct South American ungulates

M. ERCOLI, A. ALVAREZ AND A. CANDELA

Communications Biology

springer Nature

Año: 2019

2045-2322

Notoungulates were a diverse group of South American ungulates that included the rodent-liketypotherians. However, they are typically compared with other ungulates and interpreted as grazers. Here we present the first detailed reconstruction of the masticatory muscles of the pachyrukhine typotheriansPaedotherium and Tremacyllus. An outstanding feature is the presence of a true sciuromorph condition,defined by an anterior portion of the deep masseter muscle originating from a wide zygomatic plate thatreaches the rostrum, a trait traceable since the Oligocene pachyrukhines. Consequently, pachyrukhines arethe first case of sciuromorph non-rodent mammals. This morphology would have allowed them to exploreecological niches unavailable for the exclusively hystricomorph coexisting rodents. This innovativeacquisition seems to be synchronous in Pachyrukhinae and sciuromorph rodents. and related to hard-foodconsumption. We postulate the expansion of nut and cone trees during the major environmental changesat Eocene-Oligocene transition as a potential trigger for this convergence.