I’m currently in Kent, United Kingdom, examining African ape jaws to follow up on my dissertation research comparing jaw growth in humans and Australopithecus robustus (having a tough time writing this stuff up for journal publication, but hopefully things’ll start coming out soon). One thing I’d assumed (with evidence, of course), was that aspects of mandibular size could serve as a proxy for body size, to make inferences about body growth. Now that I’m in Kent, I’m hoping to get good evidence of this in the non-human African apes.
The Powell Cotton Museum in Kent has an awesome collection of chimpanzees and gorillas (see the Human Origins Database by Adam Gordon and Bernard Wood for more information on these samples). This collection was accumulated during a time last century when explorers would go out and collect specimens from the wild, usually by finding and killing them. Now, when Major Percy Powell-Cotton was out doing this, he or some of his assistants actually collected measurements on some of the corpses – arm span, height, head+body length, and chest girth. This means we can see which aspects of the mandible correlate with body size, which is important since the fossil record usually affords us mandibles more than any other part of the skeleton.
There aren’t body size measurements for all individuals, and I’ve been biasing my own sampling toward subadults. So I only have body size data for up to 15 of the 70+ gorillas I’ve been able to look at. From this meager sample, though, it looks like many aspects of mandible size may well end up correlating with aspects of body size. For instance, the distance from the back of the mandibular ramus to the front of the P4 is highly correlated with all 4 of Powell-Cotton’s bodily measures (right).
Will an expanded sample size uphold these high correlations? Will we see major differences between the sexes, or between different age groups? Will chimpanzees follow the same rules as gorillas? Hopefully I’ll be able to let you know by the time I’m done working in the museum!