Late Permian-Early Jurassic vertebrate tracks from patagonia: Biochronological inferences and relationships with southern african realms.

Abstract

In recent years, new studies about vertebrate tracks found in the late Permian-Triassic Los Menucos Complex and Early Jurassic Marifil Volcanic Complex (Río Negro province, Patagonia, Argentina) have been published. In those studies, the chronostratigraphic information of each track-bearing unit has been discussed and the relationships between the record from Patagonia and southern Africa have been highlighted. With the aim of deepening both subjects, the biochronological and palaeobiogeographical information of the main ichnotaxa found in the lower Mesozoic units of Patagonia, Dicynodontipus, Pentasauropus and Anomoepus-like tracks, have been analysed. Moreover, the updated chronological data from the Vera Formation, Los Menucos Complex, in the Tscherig and Yancaqueo farm areas, and from the Marifil Volcanic Complex near Perdomo farm, have been studied. The entire biochronological, chronological and tectonic evidence suggests that within the Los Menucos Complex there are two sequences: a lower one, Wuchiapingian-Olenekian in age, near the Tscherig farm and bearing Dicynodontipus tracks, and an upper sequence of Anisian-Rhaetian (?Norian) age, in the Yancaqueo farm and bearing Pentasauropus tracks. This suggests that the rocks historically defined as Vera Formation have different ages in different areas and span a longer time interval than previously thought. In the case of the Anomoepus-like tracks found in the Marifil Volcanic Complex, the biochronological and geological data are consistent with an Early Jurassic age. According to ichnological information and geological background we propose a correlation between Patagonia and southern Africa constrained in three main phases: 1. Lopingian to Early Triassic, Vera Formation (Tscherig farm) and Balfour Formation, respectively; 2. Middle to Late Triassic, Vera Formation (Yancaqueo farm) and lower Elliot Formation, respectively; and 3. Early Jurassic, Marifil Volcanic Complex and upper Elliot Formation, respectively. In addition, this correlation is supported by a similarity in palaeoclimatic settings that allow inferring a homogeneous distribution of trackmakers in both realms of southern Gondwana. Finally, the palaeobiogeographic information of the studied ichnotaxa and their putative trackmakers is consistent and shows an extensive distribution, during a geotectonic moment with most of the continents assembled forming Pangaea.