The first fishes with jaws, the acanthodians, or spiny sharks, appeared in the late Silurian, about 410 million years ago, and became extinct before the end of the Permian. Acanthodians were generally small shark-like fishes varying from toothless filter-feeders to toothed predators.
The Placoderms, another group of jawed fishes, appeared at the beginning of the Devonian, about 395 million years ago, and became extinct at the end of the Devonian or the beginning of the Mississippian. Placoderms were typically small, flattenedbottom-dwellers. The upper jaw was firmly fused to the skull, but there was a hinge point between the skull and the bony platingof the trunk region.
The cartilaginous-skeleton skarks and rays, which appeared about 370 million years ago are generally believed to be the descended from the bony-skeleton placoderms. The cartilaginous skeletons are considered to be a later development.
The modern bony fishes appeared in the late Silurian or early Devonian, about 395 million years ago. The early forms were freshwater fishes, for no fossil remains of modern bony fishes have been found in marine deposits older that Triassic.
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