Otodus

Otodus obliquus jaws

Otodus is an extinct genus that contains several species of mackerel shark that lived from the Paleocene to Pliocene epochs, having a cosmopolitan distribution around the world.

The genus includes many species and subspecies, such as the type species Otodus obliquus. Perhaps the most famous species of Otodus is O. megalodon (colloquially known as the megalodon shark), the largest carnivorous fish of all time.

Otodus was the undisputed apex predator of the oceans throughout the Cenozoic era, with each species growing larger over time to help it take on larger prey such as baleen whales.

Description

As Otodus is a cartilaginous fish, its skeleton cannot preserve well with fossilization and thus the genus is only known from fossilized teeth and several isolated vertebal centra from four large species. The teeth of Otodus are large with a triangular crown, smooth cutting edges, and visible cusps on the roots. Some Otodus teeth also show signs of evolving serrations.

The size of Otodus varies between species. Megalodon has been estimated at sizes of up to 20.3 meters (67 feet) long and 58 metric tons (65 short tons), while the type species O. obliquus measured at around 8-9 meters (26-30 feet long). Larger species included O. augustidens, which was estimated at a length of 11-12 meters (36-39 feet). Most Otodus species were very large macro-predatory sharks, patrolling the coastlines and open ocean during most of the Cenozoic.

Distribution

Otodus had a cosmopolitan distribution, with fossils being found on every continent on the planet. O. megalodon teeth have been excavated from Europe, Africa, the Americas, and Australia, most commonly in subtropical to temperate latitudes. An earlier species, O. auriculatus is known from the La Meseta Formation on Seymour Island off the coast of the Antarctic Peninsula, where it would've dominated the oceans alongside the basilosaurid whales. During the Eocene epoch, Antarctica enjoyed a temperate ice-free climate that allowed fish such as the tropical-living Otodus to thrive in the most southern environments. A possible O. obliquus reproduction area has been discovered in the Ganntour basin of Morocco.

The genus as a whole lived in a variety of environments, including coastal and open ocean habitats. Like modern-day sharks, adults would have primarily lived in deep water environments while their offspring grew up in shallower locations near lagoons and areas of coastal upwelling with large amounts of food and protection from the predators of offshore waters. O. megalodon, O. augustidens, and O. obliquus are known to have made use of nursery habitats to birth their young in.

Diet

Otodus was exclusively carnivorous, as with all other sharks. As an apex predator, it commonly preyed upon large fishes, sea turtles, sea cows, pinnipeds, and even large whales in the case of O. megalodon. The larger species may have even hunted macroraptorial sperm whales, their main environmental competitors. A fossilized tooth of a small sperm whale resembling Acrophyseter was discovered in North Carolina with bite marks on its roots, suggesting that either a megalodon or O. chubutensis aimed for its head to inflict a fatal bite. Due to the immense bite force of the shark, the whale's jaw was presumably broken during the struggle, the first known instance of direct aggression upon a macroraptorial sperm whale by an otodontid shark.

Evolution

It is widely considered that Otodus evolved from the genus Cretalamna, since the two shark genera share strong similarities in tooth morphology. Throughout its evolution, Otodus had been growing in size, with its teeth changing to become much more robust, serrated, and triangular. The shark's diet was evidently changing from small fish to marine mammals by the time the first cetaceans started entering the oceans during the Eocene epoch. Otodus's growth also coincides with the evolutionary growth of whales. Its evolution line is debated, but one such model is the evolution of O. obliquus into O. aksuaticus, then to O. auriculatus, O. augustidens, O. chubutensis, and finally culminating in O. megalodon, the largest species.