Investigation of finger motion in two quadrupedal dinosaurs: the sauropod <i>Camarasaurus</i> and stegosaur <i>Stegosaurus</i>

The metacarpals of sauropod dinosaurs were arranged to form a tube or semi-tube, and those of stegosaurs were arranged to form a semi-tube. This orientation aimed the fingers toward each other during flexion and would have caused the fingers to crowd each other and obstruct each other’s movements during flexion if the fingers were as mobile as they were in other dinosaurs. I therefore sought to determine whether finger movement in members of these two lineages involved any special modifications to prevent such obstruction. I posed the bones of the hand skeletons of the sauropod Camarasaurus sp. and the stegosaur Stegosaurus sulcatus in sandboxes to measure their range of motion (ROM). The results indicate that limitations upon finger mobility in both Camarasaurus and Stegosaurus prevented the fingers from crowding each other or obstructing each other’s movement. In Camarasaurus, ROM in fingers I–IV was limited to the field of hyperextension. In Stegosaurus, ROM in finger II was limited to the field of hyperextension, and the other fingers were immobile. These two dinosaur lineages thus provide a remarkable example of convergent evolution, not only in metacarpal configuration but also in the special modification (limited finger mobility) to prevent the potential predicament (fingers obstructing each other’s movements) that said configuration would otherwise have caused.Philip J. Senter [[email protected]], Department of Biological and Forensic Sciences, Fayetteville State University, 1200 Murchison Road, Fayetteville, North Carolina 28301, USA.