The question of which group of spineless relatives the ancestry of the vertebrates is to be found within has been a popular scientific parlour game since the formalization of evolutionary theory. Scope for controversy has narrowed dramatically with the availability of molecular data for phylogenetic analysis in genomic depth and taxonomic breadth, as well as the discovery and reinterpretation of key fossils that evidence the origin of the fundamental bodyplans of vertebates. It now appears impossible to recover anything other than tunicates as the sibling lineage of the vertebrates and cyclostome monophyly. However, despite widespread perception to the contrary, the interrelationships of fossil invertebrate chordates, early vertebrates and their living relatives, remain poorly resolved or supported. This is of consequence since understanding of the relationship between phenotypic, developmental and genome evolution depends critically upon how knowledge of the timing and sequence of assembly of bodyplan characteristics preserved in the fossil record. Recent work, stimulated by annotation of a hagfish genome, has allowed us to constrain not only the timing and tempo of early vertebrate evolution, but also that of the whole genome duplication events that characterize this formative episode in our own evolutionary history. Integrating evidence from living and fossil vertebrates it is clear that not all such genomic events are imbued with the same evolutionary potential and we explore why the evolution of jawed vertebrates has been so different from their jawless and spineless kin.
Origin and early evolution of vertebrates