PELVIC LIMB MUSCULATURE IN THE EMU DROMAIUS-NOVAEHOLLANDIAE (AVES, STRUTHIONIFORMES, DROMAIIDAE) - ADAPTATIONS TO HIGH-SPEED RUNNING

Emus provide an excellent opportunity for studying sustained high-spee d running by a bird. Their pelvic limb musculature is described in det ail and morphological features characteristic of a cursorial lifestyle are identified. Several anatomical features of the pelvic limb reflec t the emus' ability for sustained running at high speeds: (1) emus hav e a reduced number of toes and associated muscles, (2) emus are unique among birds in having a M. gastrocnemius, the most powerful muscle in the shank, that has four muscle bellies, not the usual three, and (3) contribution to total body mass of the pelvic limb muscles of emus is similar to that of the flight muscles of flying birds, whereas the pe lvic limb muscles of flying birds constitute a much smaller proportion of total body mass. Generally, the pelvic limb musculature of emus re sembles that of other ratites with the notable exception of M. gastroc nemius. The presence and arrangement of four muscle bellies may increa se the effectiveness of M. gastrocnemius and other muscles during curs orial locomotion by moving the limb in a cranio-caudal rather than a l atero-medial plane. (C) 1998 Wiley-Liss, Inc.