Gnathostomata is the group of vertebrates with jaws. The group is traditionally a superclass, including the familiar classes of fish, birds, mammals, reptiles, and amphibians, and a sister group of the jawless vertebrates Agnatha. However, recent genetic studies are causing a reassessment of Gnathostomata as a grouping. New fossil founds suggests thelodonts as the closest relatives of the Gnathostomata. It is believed that the jaws evolved from anterior gill support arches that had acquired a n… (More on Gnathostomata)