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Dryad

Data from: Evolutionary pattern of Metacaremys gen. nov. (Rodentia, Octodontidae) and its biochronological implications for the late Miocene–early Pliocene of southern South America

Abstract

Octodontoidea rodents (Hystricognathi) are particularly useful for analysing evolution of diversity and derived biochronological patterns. Despite its significance, our knowledge of the systematics of octodontoids from the late Miocene–early Pliocene, a key time interval in the evolution of this group in South America, is still partial. Here, we analyse the taxonomic status and diversity of the late Miocene octodontoid Cercomys primitiva and related samples, a taxon known hitherto only by the holotype specimen. New findings associated with an extensive review of late Miocene rodents, has allowed us to recognise the occurrence of this and other related species in several localities of central and western Argentina, and in southcentral Bolivia. We discuss the invalidity of Cercomys, and propose the new genus Metacaremys, which includes the type species Metacaremys primitiva comb. nov and two new species, Metacaremys calfucalel sp. nov. and Metacaremys dimi sp. nov. Osteological, brain, and dental morphology shows that the new genus is not related to Brasilian Echimyidae, as previously considered, but to the southern family Octodontidae. Although the molar morphology within this genus is quite conservative, the comparison among samples shows variation in size. We discuss the plausible evolutionary pattern explaining this variation and the implied biochronological and biostratigraphical information. It is recognised as an anagenetic lineage in which an increase in size occurs from the oldest M. primitiva comb. nov. (lower late Miocene, c. 9.23 Ma) to the youngest M. dimi sp. nov. (Miocene–Pliocene boundary, c. 5.28 Ma). Metacaremys calfucalel is intermediate in size and age between the two latter. The polarity of this pattern of change is consistent with that shown by other partially synchronous independent lineages of octodontoids, thus providing new evidence for the biochronological-biostratigraphic scheme of the late Miocene–early Pliocene of southern South America.