The earliest fossil vertebrates are 550 million years old. These were jawless fish and for over 100 million years they were the only vertebrates on earth. There were many groups, but today only the lamprey and hagfish remain. These earliest vertebrates were filter feeders. Water entered their mouths and passed out through a number of paired gill openings. Suspended food was strained out of the water. Filter feeders are limited to eating small items of food. In all fish, successive gill openings are separated and supported by skeletal structures called gill arches. These arches are in a series like a row of V’s on their sides with their openings toward the animal’s mouth. Each arch has a hinge at the angle of the V. Jaws are thought to have evolved from an anterior gill arch. The first jawed fish appeared 430 million years ago. The two earliest classes are extinct, but they were succeeded by the cartilaginous and bony fish which survive to the present. There are no fossils intermediate between jawless and jawed fish, but evidence from comparative anatomy and embryology supports the theory of jaw evolution from gill arches. Jaws offered the enormous advantage of new feeding modes as fish could open and close mouths with teeth on their edges. These descendants of early jawed vertebrates illustrate some of the variety of feeding modes.