Homo floresiensis and the evolution of the hominin shoulder

J Hum Evol. 2007 Dec;53(6):718-31. doi: 10.1016/j.jhevol.2007.06.003. Epub 2007 Aug 13.

Abstract

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.

MeSH terms

  • Animals
  • Biological Evolution*
  • Biomechanical Phenomena
  • Fossils
  • Hominidae / anatomy & histology*
  • Hominidae / physiology
  • Humans
  • Male
  • Shoulder Joint / anatomy & histology*
  • Shoulder Joint / physiology