A new narrow-gauge sauropod trackway from the Candeleros Formation (Upper Cretaceous, Patagonia, Argentina): a singular case for the Cenomanian sauropod track record

HEREDIA, ARTURO MIGUEL; PAZOS, PABLO JOSÉ; DÍAZ MARTÍNEZ, IGNACIO ; FERNÁNDEZ, DIANA ELIZABETH; COMERIO, MARCOS

Paris

Congreso; 5th International Palaeontological Congress; 2018

Whereas theropod and ornithisquian dinosaur tracks are abundant in the Cenomanian rocks worldwide, sauropod tracks are relatively scarce. Hitherto, Cenomanian sauropod tracks are only known from Croatia, Morocco and Argentina. The Candeleros Formation (Neuquen Basin, Patagonia, Argentina) comprises a multiplicity of continental paleoenvironments. Its fluvial deposits exhibit the richest Cenomanian sauropod track record in the world, including the medium-gauge ichnotaxon Sauropodichnus giganteus and a new sauropod trackway reported herein. This new finding is preserved in an alluvial plain paleoenvironment and is composed of five manus-pes track sets of a narrow-gauge trackway. Both manus and pes tracks are large in size and include conspicuous rims with very well-preserved symmetrical ripples on the top that are unprecedented in the track record. Such ripples suggest shallow waters previous to the track record and desiccation cracks all around in the surface indicate subaerial exposure after the tracks were produced. In the islet of Fenoliga (southern Istria, Croatia), wide-gauge and medium-gauge sauropod trackways have been related to the ichnotaxon Brontopodus. In the Kem Kem Beds (Morocco), two isolated and undetermined sauropod tracks have been reported. In the three occurrences, the tracks are preserved as concave epirelief, but it is not usually clarified if they are true tracks or undertracks, an important distinction for the gauge analysis. While wide-gauge trackways are dominant throughout the Cretaceous record and have been mainly attributed to titanosauriforms, narrow-gauge trackways, practically absent in Late Cretaceous deposits, have been referred to diplodocoids. The gauge in the Croatian trackways and in previous Argentinian records point to titanosauriforms as trackmakers. This new Argentinian record presented here is a narrow-gauge trackway. The trackmaker is attributed to diplodocoids, which in the Cenomanian are only represented by rebbachisaurids. This record represents the first sauropod narrow-gauge trackway for the Cenomanian (and possibly for all the Upper Cretaceous) worldwide.