Quadrupedal locomotion in all non-human hominids relies on using the long arms to support the bulk of the animal's preacetabular weight (the part of the body above the hip socket). All human-like hominids (australopithecines and species of
Homo) have shorter arms than quadrupedal, faculative bipedal apes, and have modified the pelvic girdle to the point where quadrupedal locomotion is all but impossible on the ground (unless the knees are used). The shorter, wider preacetabular blade of the ilium (the main blade of the hip bone) means that rearing up from a quadrupedal stance is also more difficult for a human than an ape since the shorther moment arm of the muscles means that more exertion needs to be applied. From the available sample of fossils and living hominids, it seems that there never really was a part-time biped. Australopithecines were already well adated to bipedal terrestrial locomotion (possibly as a carry-over from bipedal
arboreal locomotion).
Looking at Patty, her arms are well within the australo.-human range of length, and nothing at all like what would be expected from a partially-quadrupedal hominid like a gorilla or chimp. Her torso is long, and the pelvis is quite wide (compared to the very narrow pelvic region of Great Apes), with a huge buttocks, suggesting that it is not at all designed for rearing up from a quadrupedal stance. Bears, apes, and even some dinosaurs had very similar pelvic adaptations for this behavior, despite being not at all related. So, Patty from all apparances has the arms, pelvis, butt, and legs of a fully-committed biped.
Is her gait truly different from a modern
Homo sapiens?
Welllllll...maybe, maybe not...the flex-kneed gait is common to all people in a fast walk-about to run. Watch someone trying to catch a train or cab. Her pelvis appears to be the same as a human, and her feet are obscured by braches (though her tracks reveal a
lot of flexibility in midfoot). Is any (or all) of this biomechanically significant? Can't tell for sure. Recent speculation that
Australopithecus afarensis walked with a flex-kneed walk has been thrown around in the literature, and even there, the case is far from settled. And we
have specimens of the thing!
Now, if only we could check Patty's knuckles for callusses and enlarged pads...