The Ruditayoj-Tunasniyoj fossil area (Chuquisaca, Bolivia): a Triassic chirotheriid megatracksite and reinterpretation of purported thyreophoran tracks

Abstract

The South American tetrapod track record is highly diverse and well known mainly from Argentina, Brazil, Bolivia, Chile and Peru. To date, many tracksites are known from Bolivia, most studied during the past century. From the Jurassic-Cretaceous La Puerta Formation of the Tunasniyoj locality (Incapampa-Icla syncline) thyreophoran trackways have previously been described. New geological studies related with the Central Atlantic Magmatic Province in Bolivia recognised the track-bearing unit as the Ipaguazú Formation, dated as Late Triassic in age. In this significantly new context, we present here a new track-bearing locality: Ruditayoj, neighbour to Tunasniyoj, near Icla, Chuquisaca, Bolivia. A detailed study of the trackways from this new site allowed new interpretations consistent with the geological context. Hundreds of Brachychirotherium trackways are present at the site with a wide diversity of preservational types. Behavioural issues such as gregariousness and grouping around ponds are suggested. Trackway parameters, track size and shape support large ‘rauisuchid’ or aetosaur pseudosuchian producers. Previous assignations to thyreophoran producers are discussed. This is the first record of Brachychirotherium from Bolivia, filling the lack of information about suchian fossils, well known in other South American sites.