Legs evolved only at the end!

Talking about legged locomotion often evokes the idea that animals using such devices are perfectly adapted to this kind of motion and should be copied by robotics. The aim of this contribution is to show that the evolution of legs comes late in phylogeny, be it in arthropods or vertebrates. Neural control of legs in vertebrates has to deal with conservative arrangements 'invented' for axial locomotion of metameric organisms. The structure of this paper is to show the importance of axial driven propulsion in vertebrates without legs, with legs and only at the end how limbs move the body in eutherian mammals.