New Method of Locomotion in Limbless Terrestrial Vertebrates

Abstract

FOUR main types of locomotion have been described in limbless terrestrial vertebrates1,2. Three of these (serpentine, concertina and sidewinding) depend on lateral undulations which are essentially similar to those of aquatic vertebrates, although more complex. The fourth, rectilinear locomotion, is found in some limbless animals which need to move in conditions which prohibit lateral undulations. The skin in these animals is largely free from the underlying muscles for part or all of the body circumference, being attached only by specially developed cutaneous muscles. These move the skin in segmental units and also transmit the locomotor forces to the body, which is driven forwards continuously while the skin is regionally engaged in static friction with the substrate. The spinal column and ribs remain straight. In amphisbaenids, in which rectilinear locomotion is best developed3, the external appearance resembles that of an earthworm. The skin folds between annular regions of attachment to produce thickened regions which pass along the body.