Positional strategy of trunk muscles among aquatic, semi-aquatic and terrestrial species in Urodela

Abstract

Clarification of the trunk structure in Urodela is important in understanding the locomotive evolution of basal tetrapods. The components of the muscular trunk wall among Urodela using different modes of locomotion were compared. Since the whole trunk may be used for swimming and the effect of limbs may be small in the more aquatic species, they showed smaller differences in the trunk muscles among anterior, middle and posterior sections of the trunk. By contrast, in the more terrestrial species, the dorsal and abdominal muscles are larger in the middle section than those in the anterior and posterior sections. High compressive stresses occur in the supporting limbs and their insertion at the trunk on the ventral side, and spread from the forelimbs along the back to the supporting hindlimbs on the dorsal side. Tensile stresses occur in the middle ventral part. The components of the trunk muscles among the three sections may reflect differences in stresses occurring in the trunk of the more terrestrial species. The findings also suggest that in the middle section, larger dorsal muscles for stiffening the back to maintain posture and larger abdominal muscles are responsible for balancing the body weight while it is supported by the limbs in the more terrestrial species.

Morphological Correlates of Locomotion in the Aquatic and the Terrestrial Phases of Pleurodeles waltl Newts from Southwestern Iberia

“…In both phases, longer individuals were proportionally faster, which supports findings on other urodeles [81]. This fact might be representative of the role of epaxial undulations on both terrestrial and aquatic locomotion in this [82,83] and other urodeles [84]. However, the negative relationship between SMI and locomotion in the terrestrial stage involves that proportionally more massive individuals had hindered terrestrial locomotion, likely due to the burden of extra body mass.…”