The stream-severed spine

I recently returned from Mangystau, a geologically captivating former seabed in West Kazakhstan. Places like this, or the Tien Shan mountains in the South and Altai mountains in the East, always make me wonder why anyone would decide to build a capital city in the wastes of Aqmola. Astana sprouts up from a sterile steppe, sparingly sprinkled with streams and lakes. Out west, though, are breathtaking landscapes and landforms, such as the giant rocky spheres of Torysh:

Traversing the

Traversing the “Valley of Balls.” It is not yet known what caused these rock formations.

Sherqala (“Lion City”), a rocky uplift that centuries ago hosted a defensive acropolis:

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A flooded salt flat vertiginously reflecting an alternate reality:

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A pile of earth that’s really an octopus waiting in ambush:

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The perfect place to set up camp.

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As I’d pointed out the first time I came out here last year, this rocky terrain is littered with lifeless remnants of the animals that used to call this place home. So many bones reflecting such biodiversity, just lying on the surface. This year, though, I found a subsurface skeleton, teaching an important lesson in taphonomy. Taphonomy (“burial law” from Ancient Greek) is the study of what happens to an animal’s remains from the moment it dies to when it is discovered eons later. This field examines geological and ecological processes that determine whether fossils are found intact or smashed to smithereens.

Walking down into a small gully by our campsite, I noticed some giant lumbar vertebrae eroding out of one side:

Waist-deep in mud. One vertebra is clearly visible, and to its right, beneath a rock, are the spinous processes of two more vertebrae.

Waist-deep in mud. One vertebra is clearly visible, and to its right, beneath a rock, are the spinous processes of two more vertebrae. Notice the differently colored stripes of soil – these are different layers (“strata”), reflecting different periods that soil was laid down on the earth.

I was elated to espy this spinous surprise, but I wasn’t expecting to see what was on the opposite side of the gully:

Died doing a misguided impression of an ostrich.

Died doing a misguided impression of an ostrich. On the left you can see the back of the skull and the first cervical vertebra, then the spine submerges and reemerges to the right.

Sure enough, this once complete carcass was drawn and quartered, pulled apart by the liberal application of time and life-saving water.

Digging out the skull on the west bank, right across from the lumber spine on the east face. The different soil layers (

Digging out the skull on the west bank, right across from the lumber spine on the east face (circled).

Getting our hands a little dirty, we found the face of a camel. It is hard to say how long ago it lived, how long it took to get buried by a few inches of dirt, but I would guess at most only a few decades (but I’m not a geologist, so who knows). It’s also unclear how this animal was bifurcated: Did the camel die and get covered over with soil, and then later a newly forming stream carried away the soil harboring its torso? Or did the carcass lie on the ground unburied for a while, its torso slowly picked apart or trampled, and then the stream formed? I would guess the first scenario is more likely, since the bones seem to run through several strata. But again I’m not an expert in taphonomy so I could be wrong.

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People often wonder why the fossil record isn’t more complete, and why we get so excited about the discovery of even partially complete skeletons. This camel demonstrates one of myriad taphonomic processes, one of the many ways that earth, water and time conspire tear the past asunder.

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Gamarjoba from Dmanisi!

It’s been a bit harder to keep things updated as I journey across latitudes this summer. My last post was from Nairobi, and a few days later I arrived in Tbilisi in the Republic of Georgia (lamazi Sakartvelo). I’ve been involved with the 2nd annual Dmanisi Paleoanthropology Field School, which has been going on for about a week now. Things have been going fast and we’ve been having a lot of fun, so it’s a bit too difficult to recap everything so far. But we’ve had a series of lectures from great people in various fields. Here are some highlights:

Our first lecture was by Dr. Bernard Wood, at the site of Dmanisi itself. He discussed some of the progress and pitfalls in the field of Paleoanthropology. Next was Dr. G. Philip Rightmire, who discussed some aspects of hominid morphology and taxonomy. Then Dr. Reid Ferring discussed the geology of the site. As someone who focuses more on the fossils themselves, Ferring’s lecture was refreshingly fascinating for me. In brief, Argon-Argon dating was used to establish that the Mashavera basalt underlying the hominid (and other!) fossils is around 1.85 million years old. Then there were a series of ash falls that led to the soil formation of the site. A little (stratigraphically) above the fossil deposits is a layer dated by paleomagnetism to correspond to the Olduvai polarity reversal, around 1.76(?) million years ago. So the hominid fossils themselves are pretty well constrained to somewhere between 1.85-1.75 million years ago.

Then Dr. Martha Tappan gave a lecture about the taphonomy (site formation and burial processes) of the site; the neighbors invited me in for some delicious ch’ach’a shortly before the lecture, so I’m afraid my memory of this one is a bit foggy. 😦

Last night Dr. Jordi Agusti lectured about the micromammals at Dmanisi, and at some Spanish Pleistocene sites. Micromammals have large litters and short generation times, so they are good indicators for relative dating. Tonight Dr. Adam Van Arsdale will be lecturing about early Homo from Dmanisi and other sites. It’s been a great lecture series so far, and there are sure to be many great more lectures in the next few fast-paced, fun-filled weeks.

We’ve also been excavating the site, working mostly so far on taking down some of the layers stratigraphically above the hominids to hopefully more fossiliferous layers. I injured my hand on some monkeybars at the park yesterday (they seriously ripped off a big layer of skin, so I’m partially mummified), so I was down for the count today, doing lab work in lieu of excavating. I should be ready to go by tomorrow though.

I know I owe the world a few Effing Fossil Friday posts, so I’ll hopefully have those up soon, too. Nakhvamdis!

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

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!

Bloodsport in Australopithecus africanus?

ResearchBlogging.orgA few months ago in a post about the ilium and cannibals, I relayed a quote by Dr. Raymond Dart who was the first to recognize (and name) the hominid genus Australopithecus, back in 1925. I’d also mentioned that he was described [in a reference that escapes me] as “blood-thirsty.” This macabre descriptor came to mind again, as I’m reading his (1948) description of the MLD 2 mandible, of a juvenile A. africanus from Makapansgat cave in South Africa (figure is from the paper):

“[Individuals represented by MLD2 and another skull fragment] met their death by manually applied violence. The fractures exhibited by the mandible show that the violence, which probably occurred in fatal combat, was a localized crushing impact received by the face slightly to the left of the midline in the incisor region, and administered presumably by a bludgeon… this youth probably met his fate at the hands of a kinsman more expert than himself in the accurate application of directed implements” (p. 393-394)

This rather fanciful hypothesis may reflect Dart’s alleged bloodlust, and the condition of the fossil likely reflects damage that occurred after death during the sometimes abusive process of fossilization.


Reference
Dart, R. (1948). The adolescent mandible of Australopithecus prometheus American Journal of Physical Anthropology, 6 (4), 391-412 DOI: 10.1002/ajpa.1330060410

Field Update 1: Things Fall Apart

So, I’ve been here for a week now, pretty much left to my own devices. What have I learned from my first real trip to the field (that’s right, the field in a building)?

Well, the project I was so psyched about before I came will not work out. The sample is just too small, that is, not enough specimens preserve all the traits I need. I contacted Dr. Miriam Zelditch at UM who is a pretty amazing scientist working on integration, among other things. She confirmed my suspicion that even with resampling, such a small empirical sample size will not work out. I still think it’s a neat idea, so I’m contemplating heading over to the Mammals collection to test it out on larger samples of extant primates. So Life Lesson #1 (which I’ve learned elsewhere): often, things don’t work out they way you’d intended.

Everyone at the museum has been lovely so far. Very friendly and very helpful. And the fossils! I’ve only examined things Swartkrans and Kromdraai (I found out that some of the Kromdraai teeth I looked at today might be early Homo instead of Australopithecus robustus). But the real fossil are amazing! I never realized the extent to which the fossils were reconstructed–I don’t think I’ve ever seen so much glue before. In fact, one specimen had a note from the late Dr. Charles Lockwood pointing out that it appears to have been reconstructed (glued together) slightly incorrectly. So it’s not all taphonomy after all…

But then the taphonomy is incredible, too. Taphonomy literally means “burial laws” in Greek, and it’s the study of how fossils come to look the way they do–that is, what happened after the organism died, how long did it take to be buried, what geological processes affected it, etc? The South African cave systems have interesting taphonomy: Many, or most, Swartkrans specimens may have been victims of carnivores like leopards, that subsequently fell into the caves. Once in the caves, they were buried by other debris and bones that fell in the caves. Many of the specimens have been distorted–squished flat or contorted in other weird ways. COB 101, for example, is part of a cranium that has been flattened on itself, such that the forehead is right next to the hard palate (I’m told they call the specimen “Pancake” around here).

So even where there are fairly complete specimens, many have been ‘morphed’ from having spent over 1 million years under the moving earth, further preventing quantitative analyses. Milford likes to note that with fossils, the data don’t speak for themselves. Earlier in the week he asked me if the fossils had talked to me yet. I replied that they seem to be whispering, “try harder.” Really, though, they were yelling at me, “You suck! You’ll never figure us out, you hack.” Milford replied that the fossils, in their condition, are telling me (and other paleontologists) to be innovative. Which I believe is true. So, here’s Life Lesson #2 (I haven’t tasted the fruits of the lesson, but I sincerely believe it): Most research questions are answerable; however, some require more creativity than others.