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March 05, 2005
More on the Hobbit's Femur
My post the other day entitled The Hobbits Brain Revealed but Don't Forget the Hobbit's Femur didn't say much about the Hobbit's femur. It did allude to it in the discussion of LB1's (the Hobbits) body mass and that was just the point. When all that remains is parts of a skeleton, body mass must be estimated and there are really two ways of doing this. One way is to calculate stature based on long bone (i.e. the femur) comparisons with reference populations. The other is based the girth of the load bearing bones (i.e. the femur) again comparing it with reference populations of modern humans and apes. And that is why the femur is so important.
The most complete specimen of H. floresiensis (LB1) has a very think femur for such a short individual. I calculate a length-girth index of 23.6 for LB1's femur. This is at the very top of measurements of modern female H. sapiens - 18.5-24.7 (Aiello, 1990, p. 256). As I said in the previous post, this give a body weight of 36 kg, based on modern human and ape populations. Its even higher if one uses human reference populations only.
The problem is two fold. First, anthropologists tend to think that body mass based on femur girth is more accurate than body mass based on stature estimates. The reason is that this bone must bear the body weight and therefore is related to the weight it bears (Aiello, 1990, p. 257). In addition, body mass estimates on stature are often thought to be low (Aiello, 1990, p. 255).
Second, if one uses femur girth based body mass for LB1 and applies this to all her ancestors and contemporaries one gets a very chucky population: really roly-poly.
There are three possible conclusions: (1) Femur girth must be discounted in the case of H. floresiensis. Or (2) H. floresiensis was a roly-poly species with a very low EQ (encephalization quotients) for a Homo of any species. Or (3) LB1 is not representative of the population as a whole (i.e., her femur is abnormal, sort of a sub class of conclusion 1). This problem remains even if we use human pygmy reference populations as Dean Falk suggests. An additional problem has to do with statistics. While we know the empirical distribution of these various parameters for fossil populations, there are not enough samples to know the statistical distribution with certainty. For example, I calculated the length-girth index of Trinil 3, Femur 1 to be 19.6 and of KNM-WT 15000 to be 17.7. Are these typical of H. erectus/egaster or is one of them out at the two sigma point? In addition, Trinil 3, Femur 1 is clearly from a seriously deceased individual. Should we discount it for that reason alone? And KNM-WT 15000 was not an adult. How much of a difference does that make?
A new post that I have been working on for sometime will be an attempt to address this issue. I still need to dig through a lot of literature but I'm getting closer.
Reference:
Aiello, Leslie and Christopher Dean, An Introduction to Human Evolutionary Anatomy. (Academic Press, San Diego, CA, 1990)
Posted by DuaneSmith at March 5, 2005 11:38 AM | Read more on Paleoanthropology |
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Comments
This fossil discovery is a fascinating one and may reveal more insight as to the origin of man, both physical and social roots.
[I've moved this comment, originally posted 2005-03-08 07:07:35, to this post because I think it more relevant here. DS]
Posted by: Mary at March 9, 2005 11:39 AM
Sorry, comments are closed for this post.
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