Compared to humans, the chimpanzee has limited wrist extension, presumably to facilitate knuckle walking. The greater range of extension in the human wrist is thought to be an adaptation for dextrous and powerful manipulation of tools and throwing. The purpose of this study was to determine whether features of the scaphoid – considered a bridge between the carpal rows – influence maximum extension in both humans and chimpanzees. Using surface models acquired from CT, we performed separate shape analyses on humans (n = 9) and chimps (n=5), and regressed max extension as a function of shape. We also examined max extension as a function of the neutral wrist position of the trapezoid-scaphoid contact centre, scaled to centroid size. Scaphoid shape predicted max extension strongly in humans (PC2) and weakly in chimps (PC1), but the modes captured different features in both groups, suggesting no specific feature of the scaphoid influences extension mobility across species. We also found the trapezoid contact location was strongly related to max extension. In humans, extension increased in subjects with a distally located trapezoid. Chimpanzee trapezoids were much more proximal compared to humans, which may help explain their comparatively limited extension mobility; however, we did not detect a relationship between trapezoid location and max extension within chimps. These results highlight that while scaphoid morphology influences within species ROM, an approach that integrates the neighboring bones may be required to infer important differences in function across species. Mapping wrist form to function may provide insight into how selective pressures altered the musculoskeletal system as these groups diverged from our last common ancestor.