Some characteristics that all chordates have in common are: a dorsal hollow nerve cord, pharyngeal slits, notochord and post-anal tail. However, some of these features, such as the post-anal tail, are only found in some chordates during the embryonic stages. This is true for chordates belonging to the class Mammalia, such as humans and apes.
The notochord is the flexible and rod-shaped structure that is present in all chordate embryos. In vertebrates, the vertebral column replaces this structure in later stages of development. The dorsal hollow nerve cord is situated above the notochord. In some chordate animals, this structure becomes the spinal cord and brain. The function of pharyngeal slits is to filter water and food. Although chordates have this structure in the embryonic stage, they develop into different structures in later stages, such as gills in fish. The phylum Chordata is subdivided into different classes, including fish, reptiles, birds and mammals.