Search

Octodontoidea is the most species-rich clade among hystricomorph rodents, and has a fossil record going back to at least the late Oligocene. Affinities of fossils previous to the late Miocene differentiation of the extant families Abrocomidae, Echimyidae and Octodontidae are controversial, essentially because these fossils may share few apomorphies with modern species. In fact, pre-late Miocene representatives of Abrocomidae had not been recognised until very recently. Here we revise the early Miocene genusAcarechimys, originally assigned to Echimyidae, and alternatively to stem Octodontoidea or to Octodontidae. A systematic and parsimony-based phylogenetic analysis of the species traditionally included inAcarechimysshowed that this genus is part of stem Abrocomidae. These results are primarily supported by morphology of the mandible and lower molars.Acarechimysis here restricted to three species,A. minutus,A. pulchellusandAcarechimys pascualisp. nov., while another species,A. constans, is here transferred to a new abrocomid genus. The remaining species were nested within Octodontidae. According to these results, Abrocomidae might have been as diverse as its sister clade Octodontidae-Echimyidae during the late Oligocene–early Miocene. Extinction of this diversity would have resulted in marked loss of evolutionary history, with extant abrocomids being currently restricted to late-diverged euhypsodont representatives. [ABSTRACT FROM PUBLISHER]

Within South American rodents, the Acaremyidae is an independent fossil lineage of octodontoids represented in the late Oligocene–middle Miocene of Patagonia.Acaremysis represented by six species recorded in the early Miocene, which have not been re-studied since their original description. Morphological and phylogenetic analyses suggest thatAcaremysis paraphyletic. Three species are valid,Acaremysmurinus,Acaremysmajor, andAcaremysmessor.Acaremyskaraikensisis a junior synonym ofAcaremysmurinus. ‘Acaremys’tricarinatusis excluded from the genus being closely related toSciamys. The new species,Pseudoacaremys kramarzi, is closely related to ‘Acaremys’tricarinatusandSciamys. ‘Acaremys’preminutusis excluded from the family being closely related to the early MioceneProtacaremys prior, or living octodontoids. The phylogenetic analysis demonstrated that Acaremyidae includesPlatypittamys,Galileomys,Acaremys,PseudoacaremysandSciamys. The new acaremyid increases the diversity of extinct octodontoids and added a new evolutionary lineage within Acaremyidae. The evolutionary history of the superfamily suggests that the hypsodonty and the consequently occlusal simplification evolved twice within Octodontoidea: in Acaremyidae and in Octodontidae. In addition, the cladistic analysis confirmed that most character ambiguities are due to missing data, and hence, it is essential to find better remains to elucidate the relationships among acaremyids. [ABSTRACT FROM AUTHOR]