This statement highlights the relationship between chordates and vertebrates.

• Chordates – All animals with a notochord, dorsal nerve cord, and gill slits at some stage (e.g., Amphioxus, tunicates, fishes, reptiles, birds, mammals).
• Vertebrates – A subgroup of chordates where the notochord is replaced by a vertebral column (backbone).

So, all vertebrates (fish, birds, mammals) are chordates, but not all chordates (like Amphioxus or tunicates) are vertebrates.