Monday, October 17, 2005

Homo floresiensis: More Pieces of the Puzzle

The past week has seen a flurry of activity concerning Homo floresiensis. Starting with an article in the letters section of Nature (kindly sent to me by Aydin at Snail's Tales)and continuing with articles in Nature's News and News and Views Sections. Several bloggers have posted on it as well. Carl Zimmer at Corante has an interesting post on the subject. Orbis Quintus has some interesting thoughts as well. Perhaps, the most interesting though, is Hawks here, here and most importantly here.

My first thought on seeing the pictures of some of the other bones discovered was "Wow, they are really robust" but I'll get to that later. The main article ("Further Evidence for Small-Bodied Hominims from Late Pleistocene of Flores, Indonesia") gives some details on the stratigraphy of the cave where the fossils where found - including spots where samples for thermoluminescence were taken, talks about the tools and faunal remains and provides a table listing the remains that have been recovered so far. There is a new mandible (LB6/1) that is slightly smaller in size than the original. More importantly, there is some post cranial material. Which is were things really get interesting. As I mentioned above, the post cranial material is robust. The pictured bones are compared with similar bones from a human pygmy and the differences are noticable. For example, the humerus has a greater (midshaft circumference wise) as does the recovered tibia. The humerofemoral index (a ratio comparing the lengths of the humerus and femur) is the same as for AL-288-1 (Lucy) and the blades of the pelvis are flared antero-laterally which implies an australopithicine shaped thorax (and hence indicates some climbing behavior). Because of this the authors of the paper have moved away from intepreting H. floresiensis as a dwarf H. erectus. After reading the paper and seeing the pictures I would have to agree. For example, the trochlea and capitulum of the humerus look a lot like Australopithecus robustus - TM 1517 or KNM-ER 739 for example. One other interesting feature was the humeral torsion (rotation of the head of the humerus relative to the plane of the distal end) which is in the range of gibbons and macaques. Humeral torsion occurs mainly when there is a laterally facing shoulder joint and it is necessary for the elbow to flex and extend in an anteroposterior plane. Humans and the great apes have a large degree of humeral torsion (although gorillas, the most ground dwelling, have the least amount of the three). Overall, what the morphology says to me is that this is something new and we need to interpret it in it's own right rather than trying to force it into current species.

Perhaps, the saddest part is that the researchers have been denied permission to return to Liang Bua.