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Monday, July 18, 2011

New beef with boisei - maybe the dingo ate their babies?

ResearchBlogging.orgUnfortunately, the title is not in reference to a study demonstrating that early hominids fell prey to wild dogs. But Elaine Benes would have appreciated it.

As part of my Latitudes Tour, I'm in Nairobi for a couple of days, hoping to spend some quality time with the young Australopithecus boisei kids at the Nairobi National Museum. Recall (that is, if I've mentioned it here?) that my dissertation research is on growth of the lower jaw, in Australopithecus robustus as compared to modern humans. The study of growth obviously requires analyzing individuals across different age groups (an "ontogenetic series" is the fancy term). Admittedly, then, the focus on A. robustus is chiefly because this species has the largest ontogenetic sample of any early hominid (tho at nearly 15 subadults, it's still not as large as one could hope). Also because A. robustus was totally badass.

Australopithecus boisei makes an important comparison for A. robustus, because the two species are allegedly evolutionary 'sisters' - the "robust" australopithecines (though I'm personally not convinced that these two are each other's closest relative). So their growth should be pretty similar. At the same time, though, A. boisei shows much greater adaptations to heavy chewing - they've been referred to as "hyper-robust." So comparing growth in these species should elucidate how their differences arise.

Problem is, there just aren't enough kids! It's like that song by Arcade Fire. Wood and Constantino (2007) published a pretty comprehensive review of A. boisei, including a 1.5-page table of the skulls and teeth attributed to the species. So far as I know, only 4 specimens in this table are subadult mandibles, and so far as I can tell, they're all about the same age (right around the age that the first permanent molar comes in). There are so many jaws of adult A. boisei (although many of these are abraded mandibular bodies lacking teeth) - so how can there be fewer subadults?!?!

A very preliminary observation of infant-child pairs in the two species suggests they both increase in size fairly dramatically between when they only have baby (a.k.a. "deciduous" or "milk") teeth and when the first permanent molar comes in. But this is just a preliminary observation based on 2 specimens of each species! Take with a grain of salt!

On second thought, maybe I'll propose the nearly untestable hypothesis that bone-eating hyenas ate the boisei babes, and that's why we don't have their jaws. What could have been nicely preserved subadult boisei bones are instead coprolites (fossilized poops). A little spectacular, yes, but it's also been hypothesized that many of the A. robustus fossils we know and love came to us as carnivores' scraps.

further reading:
Wood, B., & Constantino, P. (2007). Paranthropus boisei: Fifty years of evidence and analysis American Journal of Physical Anthropology, 134 (S45), 106-132 DOI: 10.1002/ajpa.20732

Saturday, July 16, 2011

eFfing Fossil Friday - Renaissance and Designer Fossils

Sorry I'm a bit late on this one, and that I've fallen behind on keeping the blog updated. I've been scrambling to make all the observations on, and collect all the data from, these Australopithecus robustus mandibles in a short time. As my advisor likes to remind me, everything always takes 3x longer than you initially anticipate, and this is certainly true of my work here. Yesterday (the actual Fossil Friday), in fact, I probably spent only 30 min with these fossils. Instead, I accompanied Lee Berger and John Hawks on a trip to Malapa - the site that recently yielded fossils of the mysterious Australopithecus sediba - and other sites in the area. To get there, I rented a car and drove on the wrong side of the road for the first time - it was a trippy trip, every time I got in the car I reached to my left for a phantom seat belt, and kept searching for the gear-shift my mind thought was in the door. Nuttiness.

Anyway, I have two thoughts for this edition of eFfing Fossil Friday. First point, related to the great tour from Dr. Berger, is that a ton of hominid fossils are lying in wait for us to re-expose them to the light of day. In South Africa, the classic Plio-Pleistocene sites have been Makapansgat (A. africanus), Sterkfontein (A. africanus) and Swartkrans (A. robustus and early Homo). These sites have variously been worked since the early 20th century. Since then, a number of other hominid-bearing sites - largely in the same area as Sterkfontein and Swartkrans - have been discovered: Gladysvale, Gondolin, Drimolen, and most recently Malapa. Yet still a metric-tonne of work is still being done on the more classic sites (except maybe Makapansgat?).
View of the valley, Malapa is somewhere in the background, I think the green patch of trees near the center, just before the big hill-shadow (?).
But these sites are just the tip of a fossiliferous iceberg. A few years ago when I was working here I accompanied some other researchers on a survey for more fossil sites in the area. What I learned then is that if you look across the Sterkfontein valley in the winter, the dessicated grassland is pimpled with the occasional patch of green trees - these small verdant isles are the tells of underlying cave systems (the caves contain water that plants will cut throats for). What was driven home yesterday at Malapa and other sites Dr. Berger showed us, is that these caves are all over the place, many fossil treasure-troves. What's more, the A. sediba discovery (and the massive hominid molars from Gondolin) points to the idea that we are only beginning to understand what hominid life was like in the past. There is a rich prehistory still waiting to be discovered in South Africa, and undoubtedly also the rest of the African continent. Human paleontological work is far from exhausted. Let us usher in a Renaissance of field Paleoanthropology!

My next thought is that the process of fossilization can make the fossil-memories of past life quite beautiful. Now, in life the enamel of teeth is white-ish (yellow/brown is also not uncommon), and bone is this off-white/yellowish color. But during the process of fossilization, the original minerals used to make the bone (and less commonly teeth) are replaced by those in the surrounding soil. Often these minerals gussy up the fossils in neat new ways - manganese for example tends to make bone/tooth black.









Check out SK 61, an infant/child Australopithecus robustus. After fossilization, this thing takes on a designer, tortoise-shell coloration (left, above). SK 12, an older adult A. robustus (right, above), is another good example: some subterranean joker has drawn a smiley face beneath his left premolar (circled). So while we are often left with a meager fossil record, at least the fragments we get are voluptuously variegated.

Friday, July 8, 2011

eFFING FOSSIL FRIDAYS!

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!

Wednesday, July 6, 2011

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


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!




Saturday, July 2, 2011

Big trip 2011

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!