A quadrupedal ornithopod trackway from the Lower Cretaceous of La Rioja (Spain): inferences on gait and hand structure

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Abstract
A quadrupedal ornithopod trackway has been discovered at Cabezón de Cameros (La Rioja, Spain). The strata at the Valdemayor site is Early Cretaceous in age (probably Hauterivian). The trackway is formed by five footprints and four manus impressions. Size and footprint structure suggest that it has been produced by an iguanodontid dinosaur using a quadrupedal gait. The estimated speed is 4 km/h. The lesser depth of manus prints suggests that the center of gravity is located near the hindlimbs. Ornithopod dinosaurs used a similar type of locomotion in both bipedal and quadrupedal gaits, showing inward rotation of pes prints. This fact suggests that the use of such an optional locomotion does not modify significantly the role of the tail during progression. The structure of the manus prints indicates that there is probably not an unique soft-tissue structure enclosing the digits II, III, and IV.