''Macrorhizodus'' is an extinct 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 early

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

to early

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

epoch of the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

period. It is often considered ancestral to ''

Isurus ''Isurus'' (meaning "equal tail") is a genus of mackerel sharks in the family Lamnidae, commonly known as the mako sharks. They are largely pelagic, and are fast, predatory fish capable of swimming at speeds of up to . Fossil history and evolu ...

'' and sometimes considered part of it. ''Macrorhizodus'' is also likely ancestral to '' Cosmopolitodus''. It seems to be related to '' Isurolamna''. It is known from isolated teeth and vertebral centra as well as at least two associated dentitions. It is an incredibly widespread shark, known from every continent except Australia. This includes a report from Antarctica.

Species

The genus is composed of the following species: This genus appears to have undergone

anagenesis Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population. This contrasts with cladogenesis, which occurs when branching or splitting occurs, leading to two or more lineages and resulting in separate ...

, making it difficult to draw lines between species. Some authors prefer to lump and others to split. The early Oligocene species ''Macrorhizodus flandricus'' ascribed to this genus now usually considered to be a synonym of ''Isurus desori'', sometimes styled ''Isurus desori flandrica''. However, ''I. desori'' might itself be a junior synonym to '' I. oxyrhincus''. This confusion stems from the proximity of ''Macrorhizodus'' to ''Isurus''.

References

{{Taxonbar, from=Q104853580 Lamnidae Prehistoric shark genera Eocene sharks