Australopithecus africanus

Australopithecus africanus (found in South Africa, where dating fossils is a wretched thing to behold,) has an interesting feature that I've become quite enamored with. They're called "anterior pillars." They appear to be some sort of reinforcement for some hard core chewing. They are unique to this species, and are just really cool. You can see them clearly on this specimen that we refer to as Mrs. Ples.



Look closely at the area right above the canines, there is a thickening that runs up the face. These are the anterior pillars.

So for some god-awful reason, our type specimen for Au. africanus, is a child, called Taung due to its discovery in a locality named Taung. That's pretty nasty, until you realize that the Taung child has a brain endocast, which allows us to see an imprint of the brain itself. Soft tissue preservation is rare due to the bias in the fossil record, and so this endocast is sort of special.



When you compare the Au. africanus pelvis to that of Au. afarensis, you'll notice that Au. afarensis has a noticeably longer pelvis. Au. africanus seems to be headed more toward the short and broad side of things here, which seems to show that the pelvis is becoming even more suited toward long term bipedal locomotion.



And if you take a look at the acetabulum, you'll notice that Au. africanus has a more complete and closed in acetabulum. It's still quite shallow, but is markedly more closed in than in Lucy's kind.



Another interesting feature on these guys is the fact that they begin to show some pretty large teeth. Large teeth become the focal point later on with the robust australopithecines and it seems like we're just getting closer and closer to crazy teeth. As the resources changed with the environment becoming cooler, drier, and more seasonal, obviously they needed to deal with the way they processed foods that were no longer squishy. Enter.... big teeth!

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.

Ardi

Have you met her?



Ardi (more formally known as Ardipithecus ramidus) is a pretty cool gal. She's got some weird stuff going on with her feet (more on that in a moment) and her pelvis looks like one of those 3D puzzles that take FOREVER to complete. She's also got some stuff going on with her teeth that isn't so common to find in the fossil record.

Ardi has this super cool foot. It's not totally like a human foot yet, but is totally capable of supporting bipedal walking, though in this weird tri-pod sort of way. The foot doesn't have a bony arch built into it, instead Ardi used her muscles to pull her foot up into an arch in order to be able to go for a stroll bipedally. There are a couple of bits of bone evidence showing this, where you can clearly see the grooves where the muscles ran through and would pull on to make an arch.



The cuboid bone here shows the groove beautifully.



This is the talus, which is the bone that sits in between those knobs on your leg that you tend to call your ankle. It looks a lot like a human talus, and yet, it belongs to Ardi.



This one is the cream of the crop. From left to right we see chimp, Ardi, and human feet. Ardi definitely has the ability to wrap the feet around as a chimp would and obviously has no bony arch like a human foot.

There is another important comparative feature that Ardipithecus ramidus has that I took photos of, and that is the form of the sciatic notch. In a chimp, we don't see this notch, but in a human and other hominin forms it's one of the things that we know causes our hips to be short and broad and accommodating to bipedalism. Ardi most definitely possesses this notch, and as Dr. Kramer pointed out, it may be the one single bit of really GOOD evidence for bipedalism on that insane puzzle of an illium that we have for Ardi because it hasn't been pieced together from tiny fragments and it is absolutely in the correct place.



This is Ardi's sciatic notch.



Here we have a human. If you compare the two you can actually see that though Ardi's is on a smaller scale, they actually follow about the same curvature.



And here's the chimp. Notice the lack of any real distinguishable sciatic notch, which allows for a much taller illium.

So there we have Ardi, a really interesting specimen that is still really new to those of us studying human evolution. It's a really cool stop along the path to life as we know it.