Chordates are a group of animals that possess a notochord, which is a flexible rod-shaped structure running down their back. This group includes fishes, amphibians, reptiles, birds, and mammals, who possess various adaptations to their environments. Some synonyms for chordates include vertebrates, as they all have a backbone, and also have spinal cords. Other synonyms include craniates, which means animals that have a skull, and deuterostomes, which refers to animals that are bilaterally symmetrical. Chordates are an important group in the animal kingdom as they are extremely diverse and have evolved numerous adaptations to their respective environments.