Hobbit news from Stony Brook

3 minute read

In another post I write about the Martin-Falk exchange on the microcephaly issue.

Here, I review the Paleoanthropology Meetings summary by Elizabeth Culotta in Science.

Along with some background, the article basically covers two talks: one by Susan Larson concerning the humerus, and one by Bill Jungers about the pelvis.

Larson concluded that the upper arm and shoulder were oriented slightly differently in H. floresiensis than in living people. The shoulder blade was shrugged slightly forward, changing its articulation with the humerus and allowing the small humans to bend their elbows and work with their hands as we do. This slightly hunched posture would not have hampered the little people, except when it came to making long overhand throws: They would have been bad baseball pitchers, says Larson.
When Larson looked at other human fossils for comparison, she found another surprise: The only H. erectus skeleton known, the 1.55-million-year-old "Nariokotome boy" from Kenya, also has a relatively untwisted humerus, a feature not previously noted. Larson concluded that the evolution of the modern shoulder was a two-stage process and that H. erectus and H. floresiensis preserved the first step.

Humeral torsion was the feature that previously led to the (wrong) idea that the hobbits were quadrupeds, but that wrong idea just shows how odd the feature is in the context of hominids.

In that context, you might wonder how it could be missed in a well-known specimen like KNM-WT 15000. Well, the picture helps explain:

LB1 (top), human (middle), KNM-WT 15000 (bottom) humeri. Sized to approximately equal lengths, not to scale.

Hmm.... I know I wouldn't want to be in that position -- it's a tough assessment to make on that specimen. The head might have been slightly posteriorly oriented there, but the torsion in LB1 is pretty low (low being strange in this comparison) -- so I would be really hesitant to match them up. The problem is that identifying the feature really takes a fairly complete humerus, and there aren't very many either from Australopithecus or early Homo. As reconstructed, AL 288-1 (Lucy) doesn't have low torsion, and I wouldn't have assessed Sts 7 as having it either, although there is some possible distortion there. So it wasn't an ancestral feature in hominids, so far as we can tell. Without an epiphysis, KNM-WT 15000 lacks some of the most relevant anatomy, but there might be enough....

I'll really look forward to seeing more detail about this argument -- it should be interesting to see the anatomical comparisons!

The other talk was Bill Jungers', which focused on the pelvis:

In a separate talk, Jungers reported more unexpected findings. He was able to reconstruct the pelvis, which had been broken when the bones were moved to a competing lab in Indonesia (Science, 25 March 2005, p. 1848). Although previous publications had described the pelvis as similar to those of the much more primitive australopithecines, Jungers found that the orientation of the pelvic blades is modern. The observation adds weight to the notion that hobbits had H. erectus, rather than australopithecine, ancestry.

This should be interesting too -- there has been a lot of disagreement about how flat australopithecine ilia actually were. Many of the most well-known fossils are very flattened, but there is also a lot of distortion. Hopefully any distortion introduced by the breakage (pictures in earlier post) hasn't affected these comparisons.

The spin on these stories is that they make it more likely that the Flores hominids are descendants of early Homo rather than Australopithecus. Personally, I would guess that the extent of dwarfing necessary to explain the size of the specimen pretty much throws its postcranial affinities up for grabs. For example, it's never been clear how many of the Australopithecus-Homo anatomical differences are merely consequences of body size, and how many reflect different adaptations. Since so many of the apparent differences are at least responsive to allometric constraints, it's a problem that always has to be faced.

Let's put it this way: if it weren't a problem distinguishing these genera from postcrania, there would be a lot less confusion assigning the unassociated Koobi Fora postcrania. For LB1, it helps that the bones are complete -- but, hey, we can't even tell yet that it's not a pathological modern human!