Phylogeny of Chordata & Vertebrata

Chordates evolved from deuterostomic coelomates. Contemporary Urochordata (Tunicata) provide models of their development. Contemporary Cephalochordata (Amphioxus) provide a model for the basic body plan of early chordates and vertebrates.

The Vertebrata are characterized by the deposition of CaPO₄ as bone and development of a backbone. The seven groups identified above correspond roughly to the seven traditional classes of Vertebrata, some of which are poly / paraphyletic. For example, the jawless Agnatha include hagfish (Myxiniformes) and lampreys (Petromyzontiformes), which though superficially similar are very distantly related. Jawed vertebrates (Gnathostomata) form a monophyletic group.