Dolphins are classified in the phylum Chordata because they possess the key characteristics that define this group of animals. Members of Chordata are characterized by having a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some point in their development.
In dolphins, the notochord is present during their early embryonic development, serving as a flexible rod that supports the body. Although it is replaced by the vertebral column as the dolphin matures, its presence during development is a hallmark of chordates. The dorsal nerve cord, which differentiates into the spinal cord and brain in dolphins, is also a key feature of this phylum.
Furthermore, dolphins, like all chordates, have pharyngeal slits at some stage of their life cycle, even if they do not develop into gills as they do in fish. Lastly, they possess a post-anal tail, which aids in their swimming capabilities. All these characteristics affirm the dolphin’s classification within the phylum Chordata, emphasizing their evolutionary connection to other vertebrates.