About 35 major groups, called phyla, make up the animal kingdom. Each of these has a different basic plan to which the members conform. We, along with various groups of fishes, amphibians, reptiles, birds, and other mammals belong to the major group called the chordates. The ones mentioned are all vertebrates, but some invertebrates, the sea squirts and the lancelets, also belong to our phylum.
Evidence of our relationships is the presence in every one of us of
structures we've inherited from our oh-so-distant common ancestor. At some stage of
development, all chordates have a notochord—a stiffening rod that is later replaced in
ourselves by the backbone. The pharynx forms the part of the throat just behind our
tonsils, and in chordate embryos, a series of pouches form. In fishes, these become
gill slits, but in ourselves are diverted to other functions. Unlike advanced
invertebrates, who have a solid nerve cord near their bellies, ours is hollow and near
the back. Amazing, that after more than half a billion years, we still, down deep,
resemble one another.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.