Locomot behaviour in Early Permian reptiles: insights from an unusual Erpetopus trackway

An Erpetopus trackway recorded in the Lower Permian Collio Formation (Orobic Alps, northern Italy) is investigated as a source of data to reconstruct ancestral patterns of locomotion in eureptiles. The inferred small- sized captorhinid-‘‘protorothyridid’’ producer cut an inclined muddy surface dragging its front limb digits, tail, and belly on the ground. Integrating ichnological and anatomical data we suggest that small captorhinids (‘‘protorothyridids’’) locomotion was performed with an obligatory, rigid sprawling posture with the trunk only slightly lifted from the substrate in a low, sprawled ‘belly walk’.