From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so they can be classed in groups under groups.

Charles Darwin, Origin of Species, Chapter 13

Phylum Chordata comprises those animals most often occupying the top of the food chain, including the fishes, reptiles (and thus the extinct dinosaurs), reptiles, birds and mammals (including humans). The Chordates primary common feature is a notochord, a rod extending most of the length of the organism. Lying dorsal to the gut but ventral to the central nervous system, it stiffens the body and acts as support during locomotion. More specifically, the notochordat should be present at least during some part of the organisms development. Other common morphologies include bilateral symmetry, segmented body, a well-developed coelom, a single, dorsal, hollow nerve cord, usually with an enlarged anterior end (i.e., brain), a tail projecting beyond (posterior to) the anus at some stage of development, ventral heart, with dorsal and ventral blood vessels and a closed blood system, a complete digestive system, and usually, a bony or cartilaginous endoskeleton.

Note: Classification for vertebrates is in a state of change. As genomes are sequenced and the phylogeny of genes studied for homology across species, changes are sure to result, and in turn the implied evolutionary decendency in the table below.

This table ends at Tetrapoda, with its obvious importance in the tree-of-life and evolution. Please link to the next table when it is available.