Long bones are commonly recovered in the fossil record and often used as operational taxonomic units but are shaped by functional and developmental constraints that may decouple morphological differentiation from species diagnosability. Here, morphological variation in the humerus and femur is examined across extant great apes to assess their utility for species delimitation, with implications for extinct hominins. At the genus level, differences between groups are expressed through significant differences in morphology and commonly in disparity. Among species-level taxa, mean shape differences were consistently detected, although without corresponding differences in disparity, indicating morphological differentiation within a constrained envelope.