Final answer:
The jaws of vertebrates are hypothesized to have evolved from the skeletal rods that supported pharyngeal (gill) slits. This adaptation allowed jawed fishes to handle a wider variety of food, facilitating a major evolutionary step towards the diversification of vertebrates.
Step-by-step explanation:
According to one hypothesis, the jaws of vertebrates were derived by the modification of skeletal rods that had supported pharyngeal (gill) slits. This evolutionary change marked a significant development in the history of vertebrates, offering advantages such as the ability to grasp and tear food. The first pair of gill arches, which originally supported the gills in jawless fishes, are believed to have modified over evolutionary timescales to become the jaws in gnathostomes, or jawed fishes.
The existence of pharyngeal slits in the pharynx of aquatic organisms and their initial role in the exit of water during feeding support this hypothesis. As vertebrates evolved, the structures supporting the pharyngeal slits adapted, and in jawed fishes, they became modified into jaw supports—therefore allowing for a greater exploitation of food sources and contributing to the diversification of vertebrate species.