What defines vertebrates in the animal kingdom?

Vertebrates are defined by the presence of a backbone or vertebral column, which is a key characteristic that distinguishes them from invertebrates, the animals that lack a backbone. This backbone is an integral part of their skeletal system, providing both structural support and protection for the spinal cord, which is essential for the central nervous system. Vertebrates encompass a wide range of animals, including mammals, birds, reptiles, amphibians, and fish, each sharing the common trait of having a backbone, enabling them to have more complex movements and adaptations compared to those that do not possess this feature.