What is the first example of an animal in subphylum Vertebrata?

• A. Jawless fish
• B. Mammal
• C. Bird
• D. Reptile

Answer: (A)

Vertebrates are animals with a backbone. The earliest vertebrates were jawless fishes, often called agnathans, like lampreys and hagfish. They show the basic backbone-supporting structure before jaws evolved, making them the first recognizable members of the subphylum Vertebrata. The other groups listed—mammals, birds, and reptiles—are all later, more derived vertebrates that developed after jaws appeared. So the jawless fish are the best example of the earliest vertebrate.