Figure 1

Phylogenetic tree of the major extant vertebrate groups. The relationships of the most common chondrichthyan (cartilaginous fish) model species (Elephant shark, Callorhinchus milii; Little skate, Leucoraja erinacea; Lesser spotted catshark, Scyliorhinus canicula; Spiny dogfish, Squalus acanthias) are shown, as are representative lineages from the ray-finned (actinopterygian) and lobe-finned (sarcopterygian) fish. The origin of the combined endocrine and exocrine pancreatic gland at the base of the jawed vertebrates is indicated.