What feature is common to vertebrates?

Vertebrates are characterized by the presence of a backbone or spine, which is a crucial structural component of their body. This backbone is part of an internal skeleton known as an endoskeleton, which provides support, protects the spinal cord, and allows for greater mobility compared to an external skeleton. The spine consists of vertebrae, which are individual bones that stack together to form the spinal column. This feature distinguishes vertebrates from invertebrates, which do not have a backbone.

The other options do not accurately describe vertebrates. For instance, vertebrates do not have an exoskeleton; that characteristic is found in invertebrates like insects and crustaceans. Additionally, vertebrates are defined by their backbone, contradicting the idea of lacking a spine. While some vertebrates are warm-blooded (endothermic), not all vertebrates share this trait, as many, such as reptiles and fish, are cold-blooded (ectothermic). Thus, possessing a backbone is the definitive and uniform feature among vertebrates.