The origin and early evolution of chordates: The ‘Hydroskelett-Theorie’ and new insights towards a metameric ancestor

The ‘Hydroskelett-Theory’ (Gutmann 1972) was the first coherent model for chordate evolution, based on the principles of engineering and constructional morphology. As a result of further investigations, the ‘Hydroskelett-Theory’ is revived, broadened, and stated more precisely.