Biostratigraphy and biochronology of the Late Miocene of central Argentina: Evidence from rodents and taphonomy

Abstract: Biostratigraphy and biochronology of the Late Miocene of central Argentina is analyzed through evolutionary patterns of octodontoid rodents. The studied faunas were found in continental sediments assigned to the Cerro Azul and Saldungaray formations (La Pampa and Buenos Aires provinces, respectively). Taphonomic attributes of recovered mammals, linked mostly to the development of paleosols or to predators’ activities, constraint the deposition lapse to short intervals. A biostratigraphic scheme based mainly on the anagenetic pattern of change in the octodontoid rodent lineage Chasichimys-Xenodontomys is proposed. Since there is no stratigraphic superposition among the studied levels, relationships among deposits are established through the polarity evidenced by the stage of evolution of chronomorphs of this lineage. Five new biozones for the Late Miocene of central Argentina are recognized. Evidence of other anagenetic sequences, and general trends of increasing hypsodonty in octodontoids, support this proposal. The results enhance the value of the “stage of evolution” concept as a correlation tool in biostratigraphic and biochronologic studies, mainly when applied through phyletic sequences. [Copyright &y& Elsevier]