Chordates are a diverse group of animals that share certain key features at some stage of their development. These features include a notochord, which is a flexible rod that provides support, a dorsal nerve cord, and pharyngeal slits. Chordates include familiar animals like mammals, birds, reptiles, amphibians, and fish. Most chordates have a backbone, which is part of a more complex skeleton. This group is divided into three main subphyla: Cephalochordata, Urochordata, and Vertebrata. The vertebrates, which include humans, are the most advanced and complex of the chordates, showcasing a wide range of adaptations and behaviors.