Reptiles are classified as part of the phylum Chordata due to several key characteristics that define this group. The main features that reptiles share with other chordates include:
- Presence of a Notochord: During some stage of their development, reptiles possess a notochord, a flexible rod that provides structural support.
- Dorsal Nerve Cord: Reptiles have a dorsal hollow nerve cord, which develops into the central nervous system, including the brain and spinal cord.
- Pharyngeal Slits: They exhibit pharyngeal slits at some point in their life cycle, which can develop into structures such as gills in aquatic species.
- Post-anal Tail: Reptiles have a post-anal tail, which is an extension of the body past the anus, contributing to mobility.
These characteristics are found in varying degrees across the Chordata phylum, including fish, amphibians, birds, and mammals. Reptiles are specifically placed within this group because they share these fundamental traits during at least one stage of their development, distinguishing them from non-chordate animals.