''Otodus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

, cosmopolitan genus of

mackerel shark The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the g ...

which lived from the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

to the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

(, meaning "ear") and (, meaning "tooth") – thus, "ear-shaped tooth".

Description

All species are known from their

fossilized A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

, and four of them (''O. obliquus'', ''O. auriculatus'', ''O. angustidens'' and ''O. megalodon'') are also known from their fossilized

vertebral centra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

. Like other

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

s, the

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

of ''Otodus'' was composed of

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

and not

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

, 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. Otodus obliquus multiple 021313

Size estimation

The

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of ''Otodus'' sharks indicate that they were very large macro-predatory sharks. The largest known teeth of ''O. obliquus'' measure about in height. The vertebral centrum of this species are over 12.7 cm (5 inch) wide. Scientists suggest that ''O. obliquus'' would have measured about long. Other species were much larger, with ''O. auriculatus'', ''O. angustidens'' and ''O. chubutensis'' being estimated to have reached maximum body lengths of , and , respectively. The largest species, ''O. megalodon'', was estimated to have reached a maximum body length of approximately .

Growth and reproduction

Comparative studies of the centrum radii and growth rings on the vertebrae of ''O. obliquus'' and the extant great white shark through X-rays have concluded that the sizes of the vertebrae at birth are similar, meaning that the offspring of both species would have the same size (between in length); they also revealed that they grew at the same rate until reaching 10 years of age, during which ''O. obliquus'' would have become sexually mature and attained a growth rate faster than that of the extant great white shark. A sexually mature individual of ''O. obliquus'' would have measured about long. Like the extant great white shark, it is likely that males could have reached sexual maturity earlier than females. ''O. angustidens'' also had a faster growth rate than the extant great white shark, while ''O. auriculatus'' and the extant

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...

had a similar growth rate. ''O. megalodon'' had a much faster growth rate (nearly two times that of the extant great white), but likely had an extremely delayed sexual maturity based on the result of the study that the slowing or cessation of somatic growth in megalodon occurred around 25 years of age. Like contemporaneous sharks, at least two species of ''Otodus'' (''O. angustidens'' and ''O. megalodon'') made use of nursery areas to birth their young in, specifically warm-water coastal environments with large amounts of food and protection from predators. A possible reproduction area of ''O. obliquus'' has been discovered in the Ganntour basin, Morocco.

Distribution

''Otodus'' had a worldwide distribution, as fossils have been excavated from

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Diet

''Otodus'' was likely the

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

of its time and commonly preyed upon

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

sea turtles Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerh ...

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

(e.g.

whales Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...

), and sirenids. There is also potential evidence that ''Otodus'' hunted raptorial sperm whales; a tooth belonging to an undetermined long physeteroid closely resembling those of '' Acrophyseter'' discovered in the Nutrien Aurora Phosphate Mine in North Carolina suggests that a

megalodon ''Otodus megalodon'' ( ; meaning "big tooth"), Common name, commonly known as megalodon, is an extinction, extinct species of giant mackerel shark that lived approximately 23 to 3.6 million years ago (Mya), from the Early Miocene to the Earl ...

or ''O. chubutensis'' may have aimed for the head of the sperm whale in order to inflict a fatal bite, the resulting attack leaving distinctive bite marks on the tooth. While scavenging behavior cannot be ruled out as a possibility, the placement of the bite marks is more consistent with predatory attacks than feeding by scavenging, as the jaw is not a particularly nutritious area for a shark to feed or focus on. The fact that the bite marks were found on the tooth's roots further suggest that the shark broke the whale's jaw during the bite, suggesting the bite was extremely powerful. The fossil is also notable as it stands as the first known instance of an antagonistic interaction between a sperm whale and an otodontid shark recorded in the fossil record.

Evolution

It is widely believed that the genus originates from a lineage of sharks belonging to the genus ''

Cretalamna ''Cretalamna'' is a genus of extinction, extinct Otodontidae, otodontid shark that lived from the latest Early Cretaceous to Eocene epoch (about 103 to 46 million years ago). It is considered by many to be the ancestor of the largest sharks to ha ...

,'' 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 The Nanjemoy Formation is a Formation (geology), geologic formation pertaining to both the Wilcox Group and the Pamunkey Group of the eastern United States, stretching across the states of Virginia, Maryland, and the District of Columbia. The f ...

in Maryland, USA, Ypres clay in Belgium, and western

Kazakhstan Kazakhstan, officially the Republic of Kazakhstan, is a landlocked country primarily in Central Asia, with a European Kazakhstan, small portion in Eastern Europe. It borders Russia to the Kazakhstan–Russia border, north and west, China to th ...

, 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

) in order to be

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

Undescribed species

''Otodus'' includes species that have not yet been formally described. One of these is ''Otodus debrayi'', which is known to have lived in the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

and

Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...

epochs. This species has been found in

Central Asia Central Asia is a region of Asia consisting of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. The countries as a group are also colloquially referred to as the "-stans" as all have names ending with the Persian language, Pers ...

, and

, dating from 47.8 to 38 milion years ago. Also undescribed is ''Otodus poseidoni'', which measured 12 meters in length. Its

measure up to 10 cm in length (4 inches). Some scientists consider these possible species to be a variation of '' Otodus sokolovi'', '' Otodus aksuaticus'' or '' Otodus auriculatus'', but this is not confirmed.

References

{{Taxonbar, from=Q3293316 Otodontidae Paleocene sharks Eocene sharks Prehistoric fish of Africa Fossil taxa described in 1843 Prehistoric shark genera