Functional implications of a singular penguin scapula (Aves, Sphenisciformes) from the Eocene of Antarctica

ACOSTA HOSPITALECHE, C.; DI CARLO, U.; REGUERO, M.

Congreso; V Scientific Commeette of Antarctic Research; 2012

Penguins have peculiar modifications in their skeletal anatomy as a consequence of their extreme specialized diving habit. The forelimb is probably one of the structures where morphological changes are more evident. However, the kinematics of the pectoral girdle appears to be a central point in the locomotion of penguins. The scapulae of penguins show an unusual morphology among birds. In all penguins, the scapula is very large, especially concerning its width. The recent finding of a partially complete scapula with a morphologically singular acromion in the Antarctic Peninsula (Antarctica), has motivated the present work. It comes from the Late Eocene Submeseta Allomember of the La Meseta Formation. The main anatomical features and their functional implications are here discussed. Osteological comparisons and muscular dissections of living penguins show that the most striking feature is the curvature of the acromion, and the consequent enlargement of the facies articularis clavicularis. The preserved portion of the scapula allows the reconstruction of a corpus scapula proportionally narrower than those of modern penguins. This would reflect a lack of functional optimization in terms of the resistance to forces transversal to the body axis. Its general morphology suggests that this scapula would belong to a medium- to large-sized penguin species with limited diving skills.