|Reconstructed jaws of a Paleogene Otodus (O. obliquus)|
|Reconstructed jaws of a Neogene Otodus (O. megalodon)|
Otodus is an extinct genus of mackerel shark which lived from the Paleocene to the Pliocene epoch. The name Otodus comes from Ancient Greek (?t, meaning "ear") and (odoús, meaning "tooth") - thus, "ear-shaped tooth".
This shark is known from its fossilized teeth and vertebral centra. Like other elasmobranchs, the skeleton of Otodus was composed of cartilage and not bone, resulting in relatively few preserved skeletal structures appearing within the fossil record. The teeth of this shark are large with triangular crown, smooth cutting edges, and visible cusps on the roots. Some Otodus teeth also show signs of evolving serrations.
The fossils of Otodus indicate that it was a very large macro-predatory shark. The largest known teeth measure about 104 millimetres (4.1 in) in height. The vertebral centrum of this shark are over 12.7 cm (5 inch) wide. Scientists suggest that this shark at least reached 9.1 metres (30 ft) in total length (TL), with a maximum length of 12.2 metres (40 ft).
Otodus had a worldwide distribution, as fossils have been excavated from Africa, Asia, Europe, and North America.
It is widely believed that the genus originates from a lineage of sharks belonging to the genus Cretalamna, due to strong similarities in tooth morphology. Scientists determined that Otodus evolved into the genus Carcharocles, given substantial fossil evidence in the form of transitional teeth. Some teeth have been excavated from the sediments of the Nanjemoy Formation in Maryland, USA, Ypres clay in Belgium, and western Kazakhstan, which are morphologically very similar to Otodus teeth but with lightly serrated cusplets and a serrated cutting edge. These transitional fossils suggest a worldwide evolutionary event, and support the theory that Otodus eventually evolved into Otodus aksuaticus and thus initiated the Carcharocles lineage. A more recent study of Megalolamna's taxonomic relationships demonstrates the possibility that Otodus needs to include the species sometimes assigned to Carcharocles (i.e., the megatoothed lineage, including megalodon) in order to be monophyletic.