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

KRAPOVICKAS, VERÓNICA; CANALE, JUAN IGNACIO; HALUZA, ALEJANDRO; GARRIDO, ALBERTO

Trelew, Chubut

Jornada; XXIII Jornadas Argentinas de Paleontología de Vertebrados; 2007

New tridactyl tracks have been found from 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 had not been reported. The tracks occur in fine-grained sandstones, characterized by the inclusion of reworked gypsum. The lithofacial analysis suggests a saline-slough environment, developed in a distal alluvial-fan system. They 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, has small “heel” impression and no hallux. These tracks differ from Aquatilavipes Currie (1981), Barrosopus Coria et al. (2002) and Yacoraitichnus Alonso y Marquillas (1986) in its larger size and its smaller digits divarication angle.  Saurexallopus Harris (1997) has a distinctly hallux and larger size. Differ from Magnoavipes Lee (1997) in its smaller size and its 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 theropod, however a large bird track-maker can’t be discarded. Footprints at level 1 are true tracks and have a subtle collapsed appearance because of the softness of the substrate. Level’s 2 footprints are undertracks, shows increase horizontal dimensions and were therefore wider and longer than the true tracks, while vertical sculpture is reduced.