1Department of Anatomy, Midwestern University, 2Department of Human Evolution, Max Planck Institute
Thursday Morning, 301D
Recent discoveries of early hominin scapulae from Ethiopia (Dikika, Woranso-Mille) and South Africa (Malapa) have motivated new examinations of the relationship between scapular morphology and locomotor function. In particular, infraspinous fossa shape has been shown to significantly differ among hominoids, but this region presents relatively few homologous landmarks, such that traditional distance and angle-based methods may oversimplify this complex, three-dimensional structure. To more thoroughly assess infraspinous fossa shape variation as it relates to function among adult representatives of Homo, Pan, Pongo, Gorilla, and Hylobates, we considered two Procrustes superimposition methods – one employing five homologous landmarks and another with sliding semilandmarks along the entire border of the infraspinous fossa.
The landmark-based method identified general differences in the sample that largely agree with more traditional assessments: Homo infraspinous fossae are superoinferiorly broad with transversely oriented scapular spines, which distinguish them from Hylobates and Pan. However, Pongo approaches Homo in relative infraspinous breadth. In comparison, the semilandmark method offers a more complete assessment of three-dimensional fossa shape: all nonhuman hominoids possess obliquely oriented scapular spines, and the Pongo spine is relatively shorter than the axillary border, effectively elongating the medial portion of the infraspinous fossa. This, in part, explains the aforementioned convergence with Homo, while also highlighting the fact that, like other suspensory hominoids, Pongo infraspinous fossae are relatively longer and narrower throughout, and obliquely oriented with respect to the vertebral border. We hypothesize that this configuration allows the infraspinatus muscle to better stabilize the glenohumeral joint during suspensory activities and postures.
We wish to acknowledge the National Science Foundation IGERT grant (9987590), NSF Doctoral Dissertation Improvement Grant (BCS-0824552), the Wenner-Gren Foundation, and Midwestern University's Dr. Kenneth A. Suarez Fellowship for funding support.