A species capable of significant foreleg rotation would likely possess which anatomical feature in the foreleg bones?

The ability to achieve significant foreleg rotation is heavily influenced by the anatomical structure of the forelimb bones, particularly the ulna and the radius. In species that exhibit remarkable rotational capability, it is essential for the radius to be able to move freely over the ulna.

When the ulna is completely unfused to the radius, it allows for a greater range of motion between these two bones. This is because the radius can pivot around the ulna, facilitating pronation and supination movements—essential for actions like digging, climbing, or swimming. In contrast, a fused ulna and radius would restrict this rotational movement, limiting the animal's ability to maneuver its forelegs effectively.

Furthermore, while alterations in the lengths of the radius and ulna might also affect mobility, having a complete ulna that is unfused to the radius specifically enhances the potential for rotation, making it a key anatomical feature for species that require significant foreleg rotation for their behaviors.