Age-constrained therapsid tracks from a mid-latitude upland (Permian–Triassic transition, Los Menucos Complex, Argentina)

Abstract

The Los Menucos Complex (North Patagonian Massif, Río Negro province, Argentina) has been long regarded as Late Triassic in age. A Dicynodontipus-dominated record is historically known from this complex and particularly from the Puesto Tscherig locality. Here we report the Puesto Vera site, where a new track-bearing horizon was discovered within a 73-m-thick volcano-sedimentary succession. Footprints from this site are morphologically similar to those from Puesto Tscherig and resemble footprints classically referred to the ichnogenus Dicynodontipus, thus we assigned the new material to Dicynodontipus isp. The new ichnological material is age constrained to a time interval between the Changhsingian (Lopingian, Permian) and the Olenekian (Early Triassic), on the basis of recently obtained U–Pb radiometric datings from two ignimbrites, respectively at the base and top of the Puesto Vera stratigraphic section. Interestingly, the Dicynodontipus record from the Los Menucos Complex is older than previously supposed. The inherent chronostratigraphy is consistent with the temporal occurrence of the ichnotaxon, which to date has a global distribution spanning from the Wuchiapingian (Lopingian, Permian) of northern Italy to the early Middle Triassic of Germany. Taking into account the most recent datings as well as previous literature about the geology and paleontology of Los Menucos, the new age-constrained finding turns out to encompass the Permian–Triassic transition and mirror a tetrapod fauna dwelling in a mid-latitude, highland paleoenvironment of southwestern Gondwana.