The badlands from Mendoza and the huayquerian age: insights into the late miocene

Abstract

The badlands exposed in central-northern Mendoza, Argentina, have been the subject of paleontological studies in the first half of the 20th century. The area is a large faulted anticline with the Huayquerías Formation cropping out in the east. This formation is estimated to date from less than 10.5/9.5 Ma (dating from the lower Tobas Angostura Formation) to 5.8 Ma (dating from the upper levels of the Huayquerías Formation). The Huayquerian Age (late Miocene) was defined on the basis of a small mammalian association from the Huayquerías Formation and currently includes: Megatheriops rectidens (Megatheriidae), Proscelidodon gracillimus (Mylodontidae), Hemihegetotherium achataleptum (Hegetotheriinae), ?Proterotherium? sp. (Proterotheriidae), Huayqueriana cristata (Macraucheniidae), Cyonasua pascuali (Procyonidae), and Lagostomus pretrichodactyla (Chinchillidae). Consequently, the Huayquerian Age is currently characterized by other associations from South America that are considered to be equivalent in time. This grouping, along with inclusion of taxa with controversial geographical and stratigraphical location renders the definition of the Huayquerian Age imprecise. New field work has been conducted in the Huayquerías Formation with the aim of characterizing this age with the faunal content from the type locality. The new findings (housed in IANIGLA-PV) include Macrochorobates? sp., Chasicotatus cf. Ch. ameghinoi, and Chorobates sp. (Dasypodidae), Paedotherium sp. and Tremacyllus sp. (Pachyrukhinae), a probable new Macraucheniidae (Litopterna), cf. Cyonasua larger than C. pascuali (Procyonidae), Pseudoplataeomys aff. P. formosus, Pithanotomys? and Palaeoctodon sp. (Octodontidae), aff. Palaeocavia (Caviidae) and Lagostomus pretrichodactyla (Chinchillidae). Also recovered were vertebrae of Boidae indet. (Serpentes), a maxilla referred to cf. Ceratophrys sp. (Anura), large tridactyl footprints referred to Macrauchenichnus rector, an ichnogenus that could be used to represent litopterns, and small tridactyl footprints produced by rodent-like mammals, possibly small notoungulates. These include the first footprints found in the Huayquerías Formation and 13 new taxa, elevating the taxonomic list from seven to 20 taxa. This association is currently accepted to be largely congruent with other late Miocene faunas referred to the Huayquerian Age. Uncertainties exist with the rodent Pseudoplataeomys aff. P. formosus. Previously, only the holotype of P. formosus was known, collected from Monte Hermoso (Buenos Aires, type locality of the Montehermosan Age, lower Pliocene), lacking precise stratigraphic data. Although this recent work has expanded the taxonomic list, the association remains small compared to other assemblages. Further work may append many more taxa to the list with the potential to improve the definition of the Huayquerian Age and its calibration in the biostratigraphic chart of the late Neogene.