The Vertebrates are part of larger group known as the Chordates.

Chordates
All chordates exhibit the following features at some point during their life cycle:

There are three groups of Chordates, the Urochordates, Cephalochordates, and Craniates. Urochordates lose the notochord and nerve chord as adults and become sessile filter-feeders. The only living members are the tunicates.

Cephalochordates retain the notochord and nerve chord but do not develop a brain. This group includes the lancelets.

Craniates have skulls, and in all but one case a bony or cartilaginous backbone. The Craniates consist of hagfishes and vertebrates.

Vertebrates
As the name suggests, the vertebrates have vertebrae, or back bones, which line up to form a backbone. Other shared features include cephalization, a closed circulatory system, an internal skeleton, and paired muscles and appendages.

Vertebral column - gradually replaces the notochord during embryonic development. The vertebral column is composed of individual vertebrae that are made of either cartilage or bone.

Cephalization – possession of a distinct head region that contains a concentration of nervous tissue and sense organs. A head on the end of the body that moves forward provides animals with the ability to make sophisticated assessments and responses to their surroundings. In vertebrates, the head includes a distinct brain, enclosed inside a skull.

Endoskeleton – an internal skeleton composed of bone or cartilage. This protective yet flexible structure serves as a point of attachment for nerves and muscles and for rapid movements. The pairing of skeletal appendages set the stage for vertebrate evolution out of water and on to land.

Closed circulatory system – blood is contained entirely within vessels, and never flushes through the body cavity. This arrangement, which is not unique to vertebrates, allows for more rapid and controlled blood flow than open circulatory systems.

Taxonomy and Phylogeny
Humans have long been fascinated with the vertebrates as food, companions, and fellow travelers. But familiarity has bred taxonomic confusion.

The seemingly obvious subdivision into fish, reptiles, amphibians, birds, and mammals doesn’t reflect the diversity or evolutionary relationships of these groups particularly well. Still, they are useful groups whose names instantly convey a great deal about the appearance and lifestyle of their members.