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

ERCOLI, MARCOS DARÍO; ÁLVAREZ, ALICIA; CANDELA, ADRIANA M.

Communications Biology

Nature Research publishing - Springer Nature

Lugar: New York; Año: 2019

Notoungulates were a diversegroup of South American ungulates that included the rodent-like typotherians.However, they are typically compared with other ungulates and interpreted asgrazers. Here we present the first detailed reconstruction of the masticatorymuscles of the pachyrukhine typotherians Paedotheriumand Tremacyllus. An outstanding feature is the presence of a truesciuromorph condition, defined by an anterior portion of the deep masseter muscleoriginating from a wide zygomatic plate that reaches the rostrum, a trait traceablesince the Oligocene pachyrukhines. Consequently, pachyrukhines are the firstcase of sciuromorph non-rodent mammals. This morphology would have allowed themto explore ecological niches unavailable for the exclusively hystricomorph coexisting rodents. This innovativeacquisition seems to be synchronous in Pachyrukhinae and sciuromorph rodents.and related to hard-food consumption. We postulate the expansion of nut andcone trees during the major environmental changes at Eocene-Oligocenetransition as a potential trigger for this convergence.