What does the term vertebrate mean?

The term "vertebrate" refers specifically to animals that possess a jointed backbone, which is an essential characteristic of this group. Vertebrates belong to the phylum Chordata and are distinguished by having a vertebral column (or spine) that encloses the spinal cord. This structure supports the body, allows for greater movement and flexibility, and plays a crucial role in the overall anatomy of the organism. Vertebrates include groups such as mammals, birds, reptiles, amphibians, and fish, all of which share this common structural feature.

The other definitions do not accurately represent what defines vertebrates. Laying eggs pertains to a reproductive method that can apply to various species, not exclusive to those with backbones. Animals without a backbone would be classified as invertebrates, which are a separate category entirely. The term warm-blooded specifically relates to metabolic regulation in some vertebrates, but does not apply to all vertebrates, as cold-blooded vertebrates (like certain fish and reptiles) exist as well. Therefore, having a jointed backbone is the defining trait of vertebrates, making the correct definition clear.