fossilization

The stream-severed spine

/ zcofran / 3 Comments

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.

eFfing Fossil Friday – Renaissance and Designer Fossils

/ zcofran / 2 Comments

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.