A new Pliocene true toad (Anura: Bufonidae): first record of an extinct species from South America

Abstract

Bufonids, known as true toads, constitute a very specious clade of hyloid neobatrachian frogs with an almost cosmopolitan distribution. Despite they are currently a major component of the extant anurofauna of South America, their fossil record there is still scarce and consists mostly of isolated bones assigned to extant species or regarded as indeterminate species, shedding little light on the evolution of the group. Herein we describe a new species of Rhinella, R. loba, from the Chapadmalalan (late Pliocene) of the Pampean Region of Argentina based on a partial skull. Rhinella loba is closely related to the species of the R. marina group but differs from all extant species of this group, constituting the first indisputable extinct bufonid species from South America. Its morphology suggests a close relationship with R. arenarum, the only extant species of the R. marina group currently inhabiting the South American Pampas. According to this hypothesis, R. loba is part of the stem lineage of R. arenarum is nested within the crown group of the R. marina group. Noteworthy, the late and early Pliocene ages of the new species and the earliest certain records of R. arenarum, respectively, are consistent with the previous estimated divergence of R. arenarum from its closest extant relatives during the earliest Pliocene around 5 Ma. In this regard, R. loba bridges the gap in the lineage towards R. arenarum, providing evidence of greater bufonid diversity in Buenos Aires province in Late Cenozoic times.