Penguins may look charmingly awkward on land, but new research shows their bodies are finely tuned for powerful, efficient movement both on land and underwater.
A team of anatomists from Midwestern University, in collaboration with SeaWorld San Diego and Scarlet Imaging, has published a detailed study of the limb musculature of the macaroni penguin (Eudyptes chrysolophus), uncovering previously unknown features that help explain how these birds swim, dive, and even stand upright.
Unlike most birds, penguins don't fly through the air—they "fly" through water. To do this, their bodies have evolved dramatically.
The researchers found that key wing muscles are significantly modified compared to flying birds. In particular, a muscle called the supracoracoideus—responsible for lifting the wing—is much larger in penguins. This allows them to generate power during both the upstroke and downstroke of their flipper motion, a crucial adaptation for moving through dense water. A unique configuration of shoulder muscles also gives penguins an "underwater flying" wing stroke with a stronger backwards component, improving propulsion in the water.
Solving a 100-Year-Old Anatomical Mystery
One of the study's most significant discoveries is the identification of a distinct muscle in the penguin's hindlimb that has puzzled scientists for over a century.
Previously debated and inconsistently described, this muscle appears to play a key role in keeping the penguin's legs tucked close together. This streamlined posture allows for efficient swimming, while also helping penguins maintain balance while standing bipedally on land.
The team proposes a new name for this muscle: the adductor tibialis.
Insights for Science, Conservation, and Animal Care
Beyond solving anatomical puzzles, the findings have practical implications. Penguins are common in zoos and wildlife rehabilitation centers, yet detailed anatomical references have been limited.
By providing a modern, comprehensive map of penguin musculature, this research can improve veterinary care, injury treatment, and rehabilitation strategies.
It also sheds light on how penguins evolved from flying ancestors into expert swimmers by offering clues about the broader evolution of birds.
The study helps explain the penguin's signature waddle. Their leg positioning, combined with specialized muscles that keep their limbs close to the body, results in the distinctive side-to-side gait seen on land. What looks clumsy in these bird bipeds to us human bipeds is actually an energy-efficient locomotory strategy both on land and at sea.
About the Study
The research involved detailed dissections of two macaroni penguins and comparisons with the anatomy of flying birds. The study appears in The Anatomical Record (2026).
