New large ornithopod tracks from the Yacoraite Formation (Maastrichtian-Danian), Northwestern Argentina.

IGNACIO DÍAZ MARTÍNEZ; SILVINA DE VALAIS; CARLOS CÓNSOLE GONELLA

Colonia

Simposio; Tercer Simposio Lationoamericano de Icnología; 2015

The term ?largeornithopod tracks? is normally used to name tracks with the following features: tridactyl, mesaxonic, clover-like tracks with wide digits and roundedends, digits converging proximally into a broad metatarsophalangeal impressionor ?heel pad?, and similar in anteroposterior and mediolateral dimensions. Latest Cretaceous large ornithopod tracks are veryabundant in North America and Asia, but their record is very scarce in Europeand Gondwana. There are only four Campanian-Maastrichtian Gondwanan largeornithopod track records, all of them from South America (Argentina, Peru andBolivia). Two of these sites are from the Valle del Tonco, Salta province,Argentina, in the Yacoraite Formation; where the ichnotaxa Hadrosaurichnus australis Alonso 1980, Taponichnus donottoi Alonso and Marquillas 1986, and Telosichnus saltensis Alonso andMarquillas 1986, originally related to ornithopod dinosaurs, were defined.Recently, three new large ornithopod track-bearing surfaces have been discoveredin the Yacoraite Formation, two of them are in the Valle del Tonco, and thethird is in Maimará, Jujuy province, Argentina. This formation is consideredMaastrichtian-Danian in age on the basis of palaeontological and isotopic data.It is composed of carbonates and siliciclastic sediments that represent anepicontinental sea that covered the most part of northwestern Argentina. The palaeontologicalrecord is abundant but scarce in diversity as is typical of a stressedenvironment, with fluctuations in salinity and oxygenation. Both the Valle delTonco and Maimará localities belong to two different shoreline positions at thebasin: the northwestern Tres Cruces Subbasin sub-basin and the southwesternAlemanía sub-basin, respectively. This aspect is remarkable, because thesedepocenters are located almost 300 km apart, with a palaeogeographic barrier in between,the Salta-Jujuy dorsal. The new Valle del Tonco large ornithopod tracks are mesaxonic, tridactyl, subsymmetrical, and have one padimpression in each digit and in the heel. The tracks are not well preserved andare classified as Iguanodontipodidae indet. There is a partial trackway from the Maimará locality, composed of atleast four large ornithopod tracks and probably two associated hand prints. Theclearest footprint is characterized by having a large and bilobed heelimpression and wide and short digit impressions with blunt claw traces. Thesefeatures allow assigned it to HadrosauropodusLockley et al. 2003. Previous records of Hadrosauropodusare from Laurasia and this is the first record of this ichnotaxon fromGondwana, expanding the geographic range of this ichnogenus. A member ofHadrosauridae is emphasized as possible trackmaker of the uppermost Cretaceous largeornithopod tracks. Hadrosaurid dinosaurs are scarce in Gondwana, being the bonerecord limited to Patagonia, La Pampa province and Antarctica. The tracks from the YacoraiteFormation represent the majority of large ornithopod tracks of Gondwana andincrease the knowledge on Gondwana Hadrosauridae dinosaurs.