Pentadactyl ankylosaurian manus tracks from the Lower Cretaceous of Galve (Teruel, Spain): first occurrence of Tetrapodosaurus in the Iberian Peninsula

Abstract

This work is a detailed description of ankylosaurian natural casts found in Galve (Teruel, Spain), with the identification and classification of the major dynamic and static structures that depend on the phase of autopodial (hand) movement. Specimens come from the Lower Cretaceous (Barremian) of the eastern sector of the Iberian Range. The depositional environment is of continental coastal influence with both fluvial and tidal current structures. We studied the morphology and main features of approximately 50 manus casts of Tetrapodosaurus. The structures were correlated with the different stages of the movement during the formation of the print (footprint formation phases of Thulborn and Wade 1989). We describe the prints, lithological composition and the features observed at the top, the base and the walls of the casts (striae, lineations, grooves and polygonal scales) for understand the autopodial shape, the response of the pads and the hand movement. Manus prints of sauropods, stegosaurs and ankylosaurs may show a similar morphology. However, the presence of five perfectly-distinct, protruding and separate digits in the Galve specimens make these ichnites incompatible with those of stegosaurs or with those of sauropods. We examine the original definition and the diagnosis of Tetrapodosaurus, including other similar pentadactyl tracks; also the global distribution and palaeoenvironments of these ankylosaurian ichnites, and the possible affinities of the trackmaker. The first citation of Tetrapodosaurus in Galve (Spain) confirms the palaeontological importance of this area, due to the variety of sites and dinosaur fossil types found. Careful examination of the casts has allowed reconstruction of the kinds of joint and forelimb movements that are independent of, but consistent with, interpretations based on functional aspects of the forelimb skeleton. The structures observed in the walls and in the base of the casts indicate that the digital pads of the ankylosaur hands were flexible calluses.