Occurrence of Dicolpomys (Echimyidae) in the late Holocene of Argentina: The most recently extinct South American caviomorph genus

Echimyidae is an ancient, widely diversified hystricomorph clade whose evolutionary history is linked to the Neotropical forested areas. Its fossil record, mostly from southern South America, shows temporal stages concurrent with Cenozoic climatic trends. Fossils from the late Oligocene to middle Miocene are related to living arboreal species, whereas those known since the late Miocene are restricted to lineages currently inhabiting the Chacoan diagonal of open vegetation in eastern South America. Since the late Quaternary, echimyid faunas were already composed of currently living genera, with the only exception of Dicolpomys. Here we report the discovery of a mandibular fragment of Dicolpomys in the late Holocene of Argentina. In accordance with phylogenetic affinities, geographic distribution, and fossorial adaptations, the new record, like those of the late Miocene-Pleistocene echimyids of Argentina, can be interpreted as a southward expansion of open-adapted Brazilian lineages through the Chacoan corridor. This supports a previously proposed pattern of changes of the southern boundary of these Chacoan faunas linked to Cenozoic paleoclimatic fluctuations. The occurrence of Dicolpomys in the late Holocene represents the most recent record of an extinct South American caviomorph genus. Since the phylogenetic pattern of echimyids among Octodontoidea supports the hypothesis of the survival of lineages at lower latitudes after their extinction at higher latitudes, the absence of Dicolpomys in Brazilian sites contemporaneous with, or younger than the new Argentinian site, is here interpreted as a case of taphonomic or sampling bias.