Foot posture in a primitive pterosaur

The nature of the hindlimb posture and gait of pterosaurs has been controversial1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16, partly because most of the pterosaur skeletons that have been found were flattened in thin-bedded rocks, therefore obscuring three-dimensional anatomy. A major controversy concerns the extent to which pterosaurs move on the ground; they have been variously interpreted as ranging from sprawling, quadrupedal walkers to erect, bird-like bipedal cursors1. Study of pelvis and femur material from the derived group Pterodactyloidea11,12,13 has resolved which movements are possible at the hip, but the lack of three-dimensional, articulated pterosaur feet has prevented examination of all of the movements that are possible within the foot. We have found a large, uncrushed, partial skeleton of a new species of the basal pterosaur Dimorphodon in thick-bedded deposits of Tamaulipas, Mexico; this material includes such a three-dimensional foot. The nature of this skeleton contradicts an important part of the cursorial interpretation, that is, that only the toes contacted the ground during terrestrial locomotion2,3,4,5,6,7. The flattened metatarsal–phalangeal joint at the base of the first four toes of this specimen would not allow such a digitigrade posture without separating most of the joints. A flat-footed stance is consistent with presumed footprints of pterosaurs8,9,10 that show impressions of the entire sole of the foot.