Final answer:
Option (a), Jaws first evolved in the extant group of cartilaginous fishes like sharks and rays, belonging to the class Chondrichthyes, which have skeletons made of cartilage.
Step-by-step explanation:
Jaws first occurred in the extant group of cartilaginous fishes, which include species such as sharks, rays, and ratfish. These species belong to the class Chondrichthyes and are distinguished by their skeletons made of cartilage rather than bone. One of the major evolutionary advancements in vertebrates was the development of jaws - a h_inged structure that allows an animal to grasp and tear its food.
The adaptation of jaws allowed for a diverse diet including other organisms and plants, a trait seen in gnathostomes, or "jaw-mouths." The cartilaginous fish descended from jawless fish and possess characteristics such as paired fins, paired nostrils, scales, two-chambered hearts, and cartilaginous skeletons.