The oldest dinosaur tracks record in the Neuquén Basin from a fluvio-aeolian Hauterivian forced regressive wedge (Avilé Member), Agrio Formation, Patagonia, Argentina.

PABLO J. PAZOS; ARTURO M. HEREDIA

Idanha-a-Nova

Congreso; Fourth International Congress on Ichnology; 2016

UNESCO Geopark Naturtejo/International Ichnological Association

The Agrio Formation (Hauterivian-Barremian) contains a forced regressivefluvio-aeolian wedge (30-50m thick) known as Avilé Member (early LateHauterivian). In the aeolian interval, at the Cerro Rayoso anticline, several vertebrate tracks were documented. Three track morphotypes (I-III) are distinguishable: I) one isolated sub-circular shallow track with lateral rims-like, remnant stratification and a mark preserved inside (fig. 1); II) incomplete footprints wider than length, composed of three parts very flats (tridactilar) with rounded endings (fig. 2); III) a group of three tracks, crescent in shape and wider than length showing four-five short digits mostly rounded and blunt; the basal section is deepest incised frontally (fig. 3). Morphotype I resembles a sauropod pes track, but such producer is debatable; Morphotype II, even incomplete, is a tridactilar ornithopod-theropod track. Morphothype III was produced by a thyreophoran dinosaur, considering morphology, L/W ratio and short I-IV/V digits. In South America, dinosaur tracks in fluvio-aeolian deposits during the Upper Jurassic-Lower Cretaceous (see Francischini et al., 2015 table 1) were absent from Patagonia. Thyreophoran remains (stegosaurs) were documented in the Aptian-Albian La Amarga Formation in the basin (Pereda-Suberbiola et al. 2012). Apesteguía and Gallina (2011) recorded thyreophoran tetradactilar tracks from the Jurassic-Cretaceous of Bolivia, finding morphological differences with classical ichnogenera documented in Jurassic successions. The stegosaur tracks in the Parana Basin from fluvioaeolian deposits are considered now sauropod tracks (cf. Pererda-Suberbiola et al. 2012). It is the first record of thyreophoran tracks in Argentina and the older record of dinosaur tracks in the basin.