Homo floresiensis and the evolution of the hominin shoulder.
The holotype of Homo floresiensis, diminutive hominins with tiny brains living until 12,000 years ago on the island of Flores, is a partial skeleton (LB1) that includes a partial clavicle (LB1/5) and a nearly complete right humerus (LB1/50). Although the humerus appears fairly modern in most regards, it is remarkable in displaying only 110 degrees of humeral torsion, well below modern human average values. Assuming a modern human shoulder configuration, such a low degree of humeral torsion would result in a lateral set to the elbow. Such an elbow joint would function more nearly in a frontal than in a sagittal plane, and this is certainly not what anyone would have predicted for a tool-making Pleistocene hominin. We argue that Homo floresiensis probably did not have a modern human shoulder configuration: the clavicle was relatively short, and we suggest that the scapula was more protracted, resulting in a glenoid fossa that faced anteriorly rather than laterally. A posteriorly directed humeral head was therefore appropriate for maintaining a normally functioning elbow joint. Similar morphology in the Homo erectus Nariokotome boy (KNM-WT 15000) suggests that this shoulder configuration may represent a transitional stage in pectoral girdle evolution in the human lineage.
Larson
Susan G
SG
Anatomical Sciences, Stony Brook University School of Medicine, Stony Brook, NY, USA. susan.larson@stonybrook.edu
Jungers
William L
WL
Morwood
Michael J
MJ
Sutikna
Thomas
T
Jatmiko
Saptomo
E Wahyu
EW
Due
Rokus Awe
RA
Djubiantono
Tony
T
D000818:Animals; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D005580:Fossils; D015186:Hominidae / Q000033:anatomy & histology* / Q000502:physiology; D006801:Humans; D008297:Male; D012785:Shoulder Joint / Q000033:anatomy & histology* / Q000502:physiology