Lucy (in the sky with diamonds?)

Lucy, also known as Australopithecus afarensis, is the rockstar of paleoanthropology. Ask anyone anything about the field and it seems Lucy is what they come up with. After all, she's super important, and insanely famous. She did something important for us, she showed the world that bipedalism and big brains did not evolve together, nor were big brains a requirement for bipedalism. This is HUGE, since we have for a long time assumed that this was one of those hand in hand sort of things. You can see the tiny braincase below.



So Lucy has a tiny brain and has a locomotor skeleton that is most definitely bipedal as evidenced by the bicondular angle present in the femur, as well as some of the characters present on the pelvis. The presence of the AIIS is another marker that helps support the case for afarensis' bipedal locomotion, since it is a unique attachment point of the illium that allows for muscles that aid in bipedal locomotion to attach.

The big thing to note here is the humongous amount of sexual dimorphism between the Au. afarensis individuals, as shown in the following photos.



Above are the femoral heads of two Au. afarensis individuals, there is a HUGE difference here.



On the left is a human femur, and it's pretty big. But check out the difference in size between the middle and right femur. Both Au. afarensis.



And there's the other end of that set up. Looks pretty much the same as a modern human, just much smaller.

One of the more compelling pieces of evidence for bipedalism in the Australopithecus afarensis species is the presence of the Laetoli Footprints. These are footprints made by this species in volcanic ash, that were then rapidly covered and preserved. This serves as a fossil of the soft tissue, allowing us to see much more than just the bones that we sometimes find.



There are thought to be three individuals represented by this fossil, two distinct tracks, with a third set of tracks right inside of one of the others.