Floresiensis presentations03 Apr 2007
There were several interesting papers given today, but I wanted to pass along the abstracts of the two pertaining to the Flores hominids:
"Allometric Scaling of Craniofacial Shape: Implications for the Liang Bua Hominins"
K. Baab, K. McNulty, and P. Brown
There has been considerable controversy concerning the taxonomy and evolutionary history of the hominin fossils recovered from the Indonesian island of Flores. One hypothesis is that these individuals were the result of insular dwarfing of H. erectus or a small bodied and as yet unknown hominin from the Asian mainland (e.g., Brown et al., 2004). Alternatively, some have claimed that LB 1 is a microcephalic modern human. This study will take a new approach to investigating the affinities of the Flores hominins by focusing on the three dimensional shape of the LB 1 craniofacial skeleton. To address the possibility of dwarfing in the evolutionary history of the Flores hominins, we also examined allometric scaling of craniofacial shape within the African apes and humans. As a first step, generalized Procrustes analysis was performed and principal components analysis (PCA) was used to explore the shape of the LB 1 neurocranium within a broad range of specimens representing both fossil and extant Homo species using geometric morphometric techniques. PCA indicated that the shape of the neurocranium was aligned most closely with H. erectus. A landmark set which also incorporated facial landmarks again showed similarities with H. erectus, particularly Asian H. erectus, but also with modern humans. The second set of analyses occurred in size-shape space, which, in addition to the Procrustes shape coordinates, also includes the logarithm of centroid size as an additional variable (Mitteroecker, 2004). By performing a PCA in size-shape space, we were also able to explore allometric patterns within and between Gorilla, Pan and Homo. While the apes, modern humans and archaic Homo all have separate trajectories, their slopes are quite similar. The position of LB 1 in size-shape space is compatible with its interpretation as a scaled down version of an archaic Homo species.
The second paper was much more interesting:
Morphological affinities of the wrist of Homo floresiensis
M. Tocheri, W. Jungers, S. Larson, C. Orr, T. Sutikna, Jatmiko, E. Saptomo, R. Due, T. Djubiantono, M. Morwood
The shape of the trapezoid in Homo sapiens is derived in comparison to the shape in other primates. Whereas the trapezoid of nonhuman primates is shaped like a pyramidal wedge (the narrow tip is palmar while the wide base is dorsal), that of H. sapiens is boot-shaped, resulting from a radio-ulnar and proximo-distal widening of the palmar half of the bone. The human trapezium, scaphoid, capitate, and second metacarpal base exhibit a derived complex of features that correlates with the distinctive shape of the trapezoid. Current paleontological evidence indicates that this derived complex of features evolved as early as 800,000 years ago and is a synapomorphy of H. sapiens and Homo neanderthalensis. The Homo floresiensis type specimen (LB1) includes a trapezoid, scaphoid, and capitate, all well-preserved and non-pathological. These small carpals display none of the aforementioned shared, derived features of H. sapiens and H. neanderthalensis. Rather, these bones are morphologically identical to the conditions seen in all African apes and in Australopithecus afarensis. The trapezoid is wedge-shaped with a small, dorsally-placed facet for the capitate and a large, triangular-shaped facet for the scaphoid, while the capitate and scaphoid exhibit the morphology that is typically correlated with the primitive trapezoid condition. As might be expected, the scaphoid and os centrale of H. floresiensis are completely fused, which is a synapomorphy of Gorilla, Pan, and Homo. The primitive carpal morphology of H. floresiensis is not consistent with hypotheses of a congenital or developmental abnormality afflicting a modern H. sapiens. Rather, the evidence is more consistent with hypotheses that H. floresiensis is descended from a hominin ancestor that migrated out of Africa prior to the evolution of the shared, derived carpal morphology characteristic of H. sapiens and H. neanderthalensis.
OK, after pasting that and fixing all the markup, I have to say that abstract drops entirely too many taxonomic names. But the basic point of the paper was that the wrist bones associated with the LB 1 skeleton don't look like modern humans. They look like the wrist bones of OH 7, which for these particular bones (trapezoid, scaphoid, and capitate) are similar to chimpanzees and other apes. Tocheri was fairly compelling in the description of the initial shape formation of the wrist bones prior to week 10 of fetal development; any genetic change that affected these shapes would have to be expressed very early. That would tend to make it unlikely that a single developmental change could have caused a modern human to have both the cranial form and the wrist morphology of LB 1.
There were some missing parts that should be fleshed out -- for instance, how much interpopulational variation is there in these bones in recent humans? The Neandertals overlapped with the modern human distribution, but there was no comparison of means.
Still, this may be a compelling argument for LB 1 not being modern, assuming the association of the wrist is good.
In the morning, I'm moderating a session with some more papers about the Flores hominids. I'll report anything interesting (including fights!).
UPDATE (4/2/2007): Sharp-eyed reader Brian Witte found an html error that spread a case of the italics across the site; many thanks for pointing it out!
In the last couple of days, I have had correspondence with a number of people about the wrist. Again, I should note that this is an area where a publication will really be required to evaluate the claims; particularly concerning developmental stability as a function of early differentiation.