Australopithecus robustus

eFFING FOSSIL FRIDAYS!

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I’m going to do my best to keep up with the blog during by Big Summer Adventure, and one thing I’d like to do is “F-ing Fossil Friday!” in which I focus on fossils for a bit. We’ll see if I can make this pan out.
Today I got out the rest of the Australopithecus robustus mandibles at the Transvaal Museum (above), save for I think maybe 1. As you can see from the picture, taphonomy (what happens to an animal’s remains between death and our digging them up) creates a serious challenge for the study of variation in this species. I’m focusing on ontogenetic variation – differences associated with growth and development. In spite of its fragmentary nature, so far as I know this is the best ontogenetic series of any fossil hominid (I should probably look more into A. afarensis here, too). In the bottom left you’ll see SK 438, the youngest in the sample, whose baby teeth haven’t quite come in all the way. Poor little guy! At the top right corner is SK 12, probably the oldest individual and also a big bugger.
One thing that I’ve noticed so far, only a preliminary observation that I need to actually run some numbers on, is that as individuals get older, the length of their tooth row (molars and premolars) gets shorter. This is because of the tendency for teeth to move forward during growth – “mesial drift” – and for adjacent teeth to literally wear into one another, their ends becoming flatter and flatter. While I should have realized this, it was surprising at first to find some dimensions of the lower jaw actually decreasing during growth. Now, I still have to run some tests to see if this is a biologically significant phenomenon. But it’s always nice to learn something new, even after just 2 days back with my best extinct buddies.
Stay tuned to future eFfing fossil Fridays!

Where and when the eff am I in time and space?

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I landed in Johannesburg, South Africa yesterday, and after a jet-laggy day and a half or so, I’m now at the Ditsong National Museum of Natural History (nee Transvaal Museum) in Pretoria. It’s winter here in the southern hemisphere, and when I’d landed yesterday, Joburg was in the midst of the kind of mists no one misses (left, Joburg from my hotel). It was seriously super gray and cold, it was like being back in Michigan. The hotel was pretty nice. Here’s a view of sunrise this morning (which I saw since I’m still not adjusted to the time change).



I just finished my first day back with Australopithecus robustus fossils (pic below). It’s nice to be working on fossils again, but I’ve been awake since 2:30 am so as much as I love fossils it was a bit of a struggle some of the time. I’d love to say more but my eyes are about to go on strike and pop out of my head, probably to face something upsetting to punish me for not letting them rest. I’ll do my best to keep the world up to date as to my progress and travels. Good night!

Big trip 2011

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It’s dawning on me now that I leave the country for the rest of the summer in just over 24 hours. First I’ll be in Pretoria for a few weeks studying Australopithecus robustus fossils at the Transvaal Museum. Then I’m off to Nairobi for a few days to check out some fossils at the Natural History Museum there. I’ve never been to Nairobi, and I’ll admit I’m a little nervous; I’ll keep you posted as to how it goes. Then right before my mum’s birthday I head to Tbilisi, Georgia for the 2nd annual Dmanisi Paleoanthropology Field School, until the end of August. Here’s a schematic of what my trip will look sorta like, starting from bottom to top.:
My whole life was up in the air for most of the first half of the year. But everything seems to have come together, so hopefully the second half of 2011 will be better than the first. That said, I don’t think I’m ready to go yet!

SK 63

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Drimolen dental analysis was published yesterday in Journal of Human Evolution, and in the class I’m TAing we’re talking about A. robustus. So I’ve been thinking about A. robustus lately. Here’s a picture of SK 63 I drew this summer. It’s a juvenile, with a nice molarized deciduous first molar, tall ascending ramus with posteriorly-pointing coronoid process.

SK 62 sketch

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Copying John Hawks, here’s a picture I drew a few weeks ago while looking at some of the juvenile Australopithecus robustus material from Swartkrans. This cute little bugger is SK 62. On the left it preserves the deciduous (a.k.a. “baby”) left second incisor through the deciduous second molar; on the right are the deciduous canine and molars. The permanent (“adult”!) central incisors are in the process of erupting, and the left permanent first molar is visible in its crypt behind the dm2. What I like about its deciduous canines (I think most or all A. robustus juvenile canines are like this) is that they are quite asymmetrical, with the bulk of the crown displaced mesially, and a little lingual tubercle/ridge distally. Looks like a mitten. The corpus is tallest anteriorly but gets shorter as it runs posteriorly–this pattern is slightly less marked in adults. It appears to have a weak ‘chin,’ huh?

Summer Research

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I’ve been pretty busy since classes let out, so it’s been a while since I’ve posted anything. Two years of grad school down, n more to go. Hopefully no more than four more….

In a few hours, I leave lovely Ann Arbor, MI for my summer research, to the Transvaal Museum in Pretoria, South Africa. So far as I can tell, this museum has good collections of cultural artifacts, recent mammals, and tons of fossils. Many hominin remains are curated here as well, namely Australopithecus from the region–A. africanus from Sterkfontein and Makapansgat, and A. robustus from Swartkrans, Kromdraai, and I think also maybe Cooper’s Cave(?).

I’ll be focusing on the A. robustus collection. As with many fossil groups, the sample is largely teeth, and most other cranial remains are highly fragmentary–there are only a few relatively complete crania (including a remarkably well preserved skull, DNH 7 from Drimolen, which I don’t think is at the Transvaal and that I doubt I’ll get to examine. Oh well). The main project will examine the relative independence of many of the cranial, facial, and dental features in A. robustus, since these have been important in debates about whether the A. robustus and A. boisei (the latter from E. Africa) are more closely related to one another than to other hominins. Basically I’m going to test a few developmental/functional models that have been proposed, by applying a resampling procedure (that I’m still sort of in the process of developing). Hopefully it will be an interesting (and successful…) way of examining morphological integration in a fossil sample.

There are a few other projects, but this is the one I’m most interested in. I’ll do my best to keep Lawnchair readers (whoever they might be) updated. Here’s to what I hope will be a productive summer!