Speeds of dinosaurs from the Albian-Cenomanian of Patagonia and sauropod stance and gait

Estimates of locomotory speeds of small to large-sized Patagonian dinosaurs are presented for the first time. These estimates are inferred from trackw ays found on fine to coarse-grained brown sandstones located in the lower s ection of the Candeleros Member of the Rio Limay Formation (Albian-Cenomani an), Neuquen Province, Argentina. The method used is based on the measureme nt of the stride length (distance between two successive prints of the same foot) and of the length of the hindfoot print, which in turn, allows us to estimate the height at the hip joint and, therefore, the approximate size of the animal. The hypothesis of dynamic similarity implies that the moveme nts of geometrically similar animals, although of different sizes, are dyna mically similar only when they move with the same Froude number. The dynami cally similar movements (i.e., those with equal Froude number) require equa l values of relative stride length (ratio between the stride length and the hip joint height). The relationship between the relative stride length and the Froude number allows us to estimate the speeds of dinosaurs. The dinos aurian ichnofauna studied reveals low speeds that range from 0.5 to 2.6 m s (-1). Our analyses show that the sauropods responsible for these trackways were either walking very slowly in a bipedal stance or alternatively they w ere progressing quadrupedally on a slippery surface.