Forelimb performance in turtle locomotion: a comparative approach in aquatic and terrestrial media.

PONSSA, M.L., TULLI, M.J., VERA CANDIOTI, M.F. & MORGAN, C.

Punta del este

Congreso; IX International Congress of Vertebrate Morphology,; 2010

International Society of Vertebrate Morphologists

Variations in locomotor mode are correlated with anatomical differences and muscular coordination during movement. Also, locomotion in media with differing properties likely imposes demands on the structure and control of the musculoskeletal system. Turtles are an interesting group to investigate these ideas, because their forelimbs are used for different purposes: body support and propulsion on land vs. mainly propulsion in water. We studied some parameters of locomotion in two turtles: Phrynops, an aquatic turtle whose forelimb musculature follows a generalized reptilian pattern, and Geochelone, a terrestrial turtle with derived forelimb muscular pattern. Our goal was to determine if differences in anatomy and locomotor habits are correlated with variation in movements of the forelimb in different media. We obtained film sequences for both species and we recorded forelimb and hand excursion, along with limb segment proportions, displacement velocity, and potential excursion of hand and limb. Forelimb excursion in Phrynops is maximum in water because limb movements are mostly horizontal (optimal direction of forces required for swimming). In contrast, in terrestrial locomotion of both species, limb excursion is similar and lesser, because forward extension is limited by the angle required for the limb to generate propulsive force. Wrist mobility is maximum in Phrynops on land, but it is lower in water where the entire limb works as a paddle. In Geochelone, the wrist is not mobile. Variations in performance are related to differences in limb segment proportions and physical characteristics of terrestrial and aquatic media.