New tridactyl footprints from Villa El Chocón, Patagonia, Argentina (Candeleros Formation, Cenomanian, Upper Cretaceous)

KRAPOVICKAS, V.; CANALE, J.I.; HALUZA, A.; GARRIDO, C.A.

Museo Paleontológico Egidio Feruglio. Trelew, Argentina

Jornada; XXIII Jornadas Argentinas de Paleontología de Vertebrados; 2007

New tridactyl tracks have been found in a small outcrop of the Candeleros Formation (Cenomanian, Upper Cretaceous) at Villa El Chocón, Patagonia, Argentina. This area is well known as a rich Cretaceous dinosaur tracksite, but this type of footprints is reported here for the first time. The tracks occur in fine-grained sandstone, characterized by the inclusion of reworked gypsum. The lithofacies analysis suggests a saline water body developed in a distal alluvial-fan system. The structures are narrow-toed tridactyl footprints, slightly longer than wide (average 14.2 cm long and 12.0 cm wide), has claw marks, divarication between digits II and IV range from 73º - 100º, small “heel” impression and no hallux. These tracks differ from Aquatilavipes Currie 1981, Barrosopus Coria et al. 2002 and Yacoraitichnus Alonso and Marquillas 1986 in their larger size and smaller digit divarication angle. Saurexallopus Harris 1997 has a distinct hallux and larger size. In addition, they differ from Magnoavipes Lee 1997 in their smaller size and slightly greater length to width ratio. Irenichnites Sternberg 1932 has similar size and length to width ratio, but smaller digits divarication. These bird-like footprints can be interpreted as produced by a small gracile theropods. However, a large bird trackmaker can not be discarded. Footprints at level 1 are true tracks and have a subtle collapsed appearance because of the softness of the substrate. Level 2 footprints are undertracks that are wider and longer than the true tracks, while vertical sculpture is reduced.