A REVIEW OF TRIASSIC TETRAPOD TRACK ASSEMBLAGES FROM ARGENTINA

Abstract:  This paper contains the first comprehensive ichnotaxonomic review of the Triassic tetrapod track record in Argentina, including previous accounts and new material recently discovered, and an analysis of its composition and stratigraphic distribution. Triassic footprints have been recorded from three basins: the Ischigualasto-Villa Unión and Cuyo basins in north-west Argentina, and the Los Menucos depocentre in northern Patagonia. Most are in successions of Middle Triassic age; a lower number are from the Late Triassic, and there are two records from Early Triassic rocks. The known track types include: Brachychirotherium isp., cf. Brachychirotherium isp., Chirotherium barthii, Dicynodontipus ispp., Grallator isp., Rhynchosauroides isp., Rigalites ischigualastianus, Rigalites isp., Tetrasauropus isp., and bird-like, chirotheriid and unidentified tridactyl footprints. The ichnogenera GallegosichnusCasamiquela, 1964, CalibarichnusCasamiquela, 1964, PalaciosichnusCasamiquela, 1964 and StipanicichnusCasamiquela, 1975 are considered to be synonyms of Dicynodontipus (Hornstein, 1876). In addition, the abandonment of the following ichnogenera (and single ichnospecies) that are based on poorly preserved material is suggested: Ingenierichnus sierraiCasamiquela, 1964, Rogerbaletichnus aguileraiCasamiquela, 1964 and Shimmelia chirotheroidesCasamiquela, 1964. At least eight Triassic ichnofaunas can be recognized. The most peculiar is that of the Late Triassic Los Menucos depocentre, which is characterized by the dominance of therapsid footprints (Dicynodontipus ispp.). The track assemblages from the Cuyo Basin display the highest ichnodiversity, with five footprint types.