The origin of sharks is even more obscure than that of most other groups of animals, for they have left very little evidence of their existence. Since their skeletons consist of cartilage rather than bone, the only early shark fossils we have are those of dermal denticles, teeth, spines and the occasional skeleton, preserved under exceptional circumstances.
The oldest shark-like creatures appeared in the fossil record towards the beginning of the Silurian period, about 450 million years ago, but the earliest known fossil teeth of true sharks do not appear until the Early Devonian, about 400 million years ago. Their teeth are small, no more than 4 mm (0.16 in) across, so their owner may have been no more than 30 cm (12 in) long. The skeleton of such a creature, a common ancestor for all the sharks and their relatives, has yet to be found. A candidate for close relative, however, is Antarctilamna, whose fossils have been found in rocks on the Antarctic continent. This fish was just 40 cm (16 in) long, and distinctly shark-like. It had a spine in front of a long dorsal fin, and teeth that had two large splayed cusps, with smaller cusps between them.
The oldest shark-like creatures appeared in the fossil record towards the beginning of the Silurian period, about 450 million years ago, but the earliest known fossil teeth of true sharks do not appear until the Early Devonian, about 400 million years ago. Their teeth are small, no more than 4 mm (0.16 in) across, so their owner may have been no more than 30 cm (12 in) long. The skeleton of such a creature, a common ancestor for all the sharks and their relatives, has yet to be found. A candidate for close relative, however, is Antarctilamna, whose fossils have been found in rocks on the Antarctic continent. This fish was just 40 cm (16 in) long, and distinctly shark-like. It had a spine in front of a long dorsal fin, and teeth that had two large splayed cusps, with smaller cusps between them.