Craniates, or animals with skulls that protect their brain, have synonyms in the scientific world. One of the more common synonyms is "vertebrates," which refers to animals that have a backbone or spinal column. Another synonym for craniates is "gnathostomes," which are animals with jaws that are hinged to the skull. Both of these synonyms include a wide array of animals, from fish to mammals, that have evolved to have a cranium or skull to protect their brain. While there are slight differences between these terms, all refer to animals with a recognizable head structure that sets them apart from other groups of animals.