Barros, AP; (2014) Ontogeny, phylogeny and functional morphology of the hominoid shoulder girdle. Doctoral thesis , UCL (University College London).

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Abstract

The shoulder is of particular relevance for resolving issues of locomotor ancestry since, as a group, living hominoids can be defined by the set of functional similarities that they share at this anatomical area (such as a scapula located on the back of the ribcage, and a shoulder joint adapted to allow extensive abduction). However, there is ongoing debate over which selective pressures are responsible for these shared morphologies. The current study addresses the question of whether the similarities in this anatomical structure in hominoids are a product of common ancestry (homology) or rather the product of parallelism (homoplasy) from an ontogenetic and phylogenetic perspectives. To this end, 30 measurements were collected on the clavicle, scapula and humerus of six hominoid species (Homo sapiens, Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus and Hylobates lar) and one macaque species (Macaca fascicularis); information on the dental development of each individual specimen was collected for the purpose of creating an ontogenetic sample for each species; all measurements were collected on surface scans of individual bones and analysed in a 3D environment (Geomagic Suite 12.1 and Amira 3.1), and all statistical analyses (ontogenetic, phylogenetic as well as within- and between-species differences) were conducted using R version 2.12.2 (R Core Team 2011). Overall my results provide a more detailed understanding of ontogenetic change in shoulder morphology across hominoid species, and demonstrate (1) a relative lack of phenotypic plasticity in other key traits (such as the proximal curvature of the clavicle and glenoid-axillary angle of the scapula), and (2) high levels of plasticity in key diagnostic traits of hominoid shoulder morphology in humeral torsion, the distal curvature of the clavicle, and the orientation of the scapular spine and glenoid fossa (all correlated with each other). However these seem to operate within phylogenetic constraints and to be modulated by the underlying anatomy of the thorax and shoulder girdle. Overall my results support the notion of an arboreal origin to the ape lineages and parallel evolution of quadrupedalism in the great apes.

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