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I’ve done so much flip flopping on whether or not Homo floresiensis is in fact a new species of human over the last 3 years that I sometimes forget what opinion I currently hold. The only consistency in my debate has been the call for analysis of the other remains. It seems like I got my wish after catching last week’s Science publication of the The Primitive Wrist of Homo floresiensis and Its Implications for Hominin Evolution. The title is pretty self-explanatory.

H. floresiensis is a hominin found in 2003 from the Ling Bau cave on the island of Flores in Indonesia. The bones found are about 18,000 years old. There’s been a lot of back and forth discussion whether or not H. floresiensis deserves a new species. At first people thought it was a representative of H. erectus, then it was suggested that H. floresiensis is a primitive microcephalic modern human. I like many others held this opinion.

Earlier this year, Dean Falk did a comparison of the endocranial volume of the H. floresiensis skull, LB1, to a number of microcephalic humans, and primates. She found H. floresiensis to be uniquely different in size and morphology. For many that wasn’t enough because, we don’t have many microcephalic human skulls to measure and compare too.

The other bones found at the site are just as diagnostic, especially the bones of the wrist and hand. So what Tocheri et al. did was to use fancy 3-D methods to calculate all the different dimensions, areas, and angles of the trapezoid, scaphoid, and capitate bones and multivariate statistics were used to compare the Flores carpal bones to set of archaic and modern humans, Neandertals, australopithecines, gorillas, chimpanzees, and also OH 7 a.k.a. Olduvai Hominid № 7 or the type specimen for H. habilis. Here’s a quick run down on what they found.

The trapezoid is the main bone where the index finger’s metacarpal articulates with the rest of the wrist. It’s a small bone in modern humans. The Flores trapezoid is wedge shaped like humans but has a different orientation on the ulnar side. Here’s the figure they showed which illustrates LB1, Flores trapezoids, compared to the others.

Figure 1 - Tocheri et al., 2007 Trapezoid Comparison

The Flores scaphoid shape and articular surfaces are more triangular in shape and lacks the larger articular surface on the palmar side which is seen in modern humans and Neandertals. Curiously, the scaphoid also has a fused centrale; a condition seen in H. habilis.

The authors say this fusion is a primitive condition for all hominins, because in modern humans it is separate. But that is not entirely true. The centrale sometimes fuses onto the scaphoid as the tubercle of the scaphoid; but occasionally it stays separate. It is not as definitive as they authors are making it out to be.

Anyways, here’s the line up of the scaphoid comparison.

Figure 2 - Tocheri et al., 2007 Scaphoid Comparison

Last but not least, is the sweet capitate. The capitate is the largest bone in the wrist and it falls smack dab in the center. Aside from the size, I remember the capitate because it has a rounded head which reminds me of Captain Picard’s bald head. And no, I’m not a Star Trek fan… it just that this bone has a remarkable resemblance to his unforgettable head.

Parts of the capitate, like the head, look like a chimpanzee’s capitate. Check out the light blue part below. But others, such as the proximal surface (green part) resemble modern humans. All in all the authors say the articular facets and shapes are more primitive than not because of a “waisted neck” characteristic that I don’t know about.

Can you see it?

Figure 3 - Tocheri et al., 2007 Capitate Comparison

I must admit they have a pretty complete line up of capitates, and the images let us all see for ourselves how these three bones compare…

…But I wonder why they didn’t include microcephalic or even dwarf humans into the mix?

That’s my biggest complaint with this study. You’d think that they’d include them, considering the biggest competing hypothesis is the whether or not H. floresiensis was a bunch of small humans. I’ve never seen bones from a microcephalic’s or dwarf’s hand to say that their bones would be more primitive than not… but I would assume since dwarf skeletons are much more distorted they would have different morphological features.

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