The shoulder blade of Australopithecus afarensis toddler (approx. 3 years old) from Ethiopia shows that bipedalism was not a sudden, catastrophic change in skeletal anatomy. This tiny little scapula has the same shape and orientation as shoulder blades of arboreal primates, while A. afarensis knees and pelvis show evidence of upright bipedalism. It looks like A. afarensis were doing both — sometimes walking, sometimes taking to the trees. This shows that change in locomotion was gradual, with long transitions.
“What we’re showing is that bipedalism wasn’t this sudden change that took shape in an early common ancestor,” said study co-author David Green, an anatomy professor at Midwestern University in Downers Grove, Illinois.
“As bipedalism was developing, there were other forms of locomotion that were still important.”
National Geographic has video and a story on this find (they call it “Lucy’s baby,” or Selam). Oh, and there are some really cute (afarensis) baby pictures.
(One of the less cute photos of Selam)