Paleontologists often reconstruct organismal function by estimating joint range of motion (ROM) and excluding behaviors that require impossible joint poses. This “ROM-based exclusion” has been considered conservative because it is thought that manipulations of bones overpredict true ROM. However, some analyses have concluded that they might actually underpredict true ROM, meaning that viable joint poses might erroneously be excluded from functional reconstructions. Our goal was to test the validity of ROM-based exclusion with data from the main hindlimb joints of the Helmeted Guineafowl (Numida meleagris) and the American alligator (Alligator mississippiensis). We first estimated the rotational mobility of each joint using CT-derived bone models. We then compared these estimated mobilities to each joint’s true ROM, as measured from an ex vivo marker-based X-Ray Reconstruction of Moving Morphology study. We found that even when we allowed interactions among all three rotational degrees of freedom (DOF), we still failed to capture all possible cadaveric poses. Therefore, we developed an automated method for incorporating interactions among all six DOF at each joint. Only when we implemented this new method did our “paleontological” ROM estimates succeed in capturing the full cadaveric ROM of all joints studied. We thus conclude that all six DOF are essential to reconstructions of articular function – and as a result, that existing functional interpretations founded on ROM-based exclusion must be re-evaluated to determine if their inferences still hold when joint translations are incorporated. More broadly, this work counters the assumption that joint translations are minimal and therefore negligible. Moving forward, we must measure and explore interactions among all six DOF to advance our understanding of how joints work.