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Feb 21, 2010 7:50 am


Prehistory




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Andrew D. Todd - 2/24/2010

You should understand that there are very few bones from that age, period. Any self-respecting hyena who finds a bone a few months old is going to do with it more or less what your dog does. When bones are found together, there is often a question of whether or not they were brought home by a leopard. In particular, as related to skull size and shape, there is enormous room for someone reassembling fragments to make the skull highbrow or lowbrow, according to his preconceptions. Teeth survive fairly well, and conclusions based on teeth are comparatively reliable. You can get a fairly good idea of what an animal might have eaten.

Any elaborate conclusions, based on a few bones, should be treated with considerable skepticism, not uninformed by a knowledge of the extent to which human paleontologists are self-promoters.

Australopithecines are found in East and South Africa because there were certain geological events, that is volcanism producing widespread areas of volcanic tuff rock, followed by prolonged erosion, producing deep canyons. This means that a paleontologist can walk for miles along a cliffside, looking for mineralized bones which have been exposed by erosion over, say, the last hundred years. He doesn't have the resources of a diamond or gold mine behind him, and he cannot move very much rock. In effect, you are looking for a geological accident: something which was buried thoroughly enough to survive for a million years, and yet, not so thoroughly buried that a person whom a real miner would consider an amateur prospector cannot find it.

Sedimentary rock is not going to produce good ape fossils. It tends to come from ancient seas or lakes, or swamps-- places where vast thicknesses of mud accumulate. Areas which are above water tend to erode, and the dirt goes downhill. Coal, for example, is full of pressed plant leaves, and it is sometimes possible to recover images of plant leaves from the boundary between coal and limestone in a coal mine. Similarly, rocks containing fossil shellfish are very common. However, all of this is based on an essentially aquatic environment.

If you look at the distribution of the great apes, you find Gorillas and Chimps in Africa, Gibbons in Southeast Asia, and Orangutans in Indonesia, effectively in a belt across the tropical portions of Africa and Asia. The ancestral great apes, the Ramapithicines, as the name suggests, have been found in South Asia. It would not be particularly surprising to find that Australopithicines had a range over a more or less continuous region of broadly similar climate. What we know about apes and monkeys in general is that they are not hole-dwellers. They climb trees and make nests, by bending and interlacing branches. If an ape dies in his nest, small animals, starting with insects, come and eat him, a little at a time. His tree is likely to live for an additional five hundred years or so, so it will be a long time before his mortal remains wind up in the ground. In that kind of environment, primitive men often copy the apes by building tree-houses or stilt-houses, in order to live dry and out of the mud. Cats, on the other hand, are big on living in holes.

The most economical explanation for early Australopithicines is the so-called Jolly-T hypothesis, formulated by the physical anthropologist Clifford Jolly. T stands for Thereopithicus, otherwise the Gelada, a kind of baboon living in the Ethiopian highlands. The Gelada makes its living by foraging stands of wild grain, moving hunkered down and using both hands to pick with, more or less one grain at a time. Joly argued that Australopithicines might have been doing something similar.


Jane S. Shaw - 2/22/2010

I was fascinated -- thanks for sharing this well-written article. It did make me wonder at how quickly conventional wisdom in the field of paleontology can be overturned -- with a few skeletal remains. How fragile is all the other evidence?


Amy H. Sturgis - 2/21/2010

This is fascinating.