Squalodontidae or the shark-toothed dolphins is an extinct family of large toothed whales who had long narrow jaws. Squalodontids are known from all continents except Antarctica, from the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

to the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

, but they had a maximal diversity and global distribution during the Late Oligocene and Early to Middle Miocene (). With their cosmopolitan Miocene distribution and

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...

dentition, squalodontids are the most common and basal platanistoids. They are relatively large odontocetes, comparable in size to extant mesoplodont whales. The premaxillae on their elongated rostrum have large and slightly convex fossae for the air sacs associated with the presence of a melon, indicating the ability for echolocation. '' Squalodon'' and ''

Eosqualodon ''Eosqualodon'' is a genus of squalodontid odontocete from the Late Oligocene to Early Miocene (Chattian-Aquitanian) of northwestern Germany and northeastern Italy. Taxonomy and description Two species are recognized, ''E. langewieschei'' and ...

'' are based on partial or complete skulls. The

synapomorphic In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

traits of the family are, however, based mostly on one of the bones of the inner ear, the periotic bone, which is unknown in these genera except in ''Squalodon''. The monophyly of the family is, therefore, uncertain. '' Patriocetus'' has also been included. Some squalodontids are known from rather complete fossils, but most were described based on a few isolated teeth. Squalodontids are most likely very distantly related to extant oceanic dolphins but, according to French palaeontologist Christian de Muizon, more closely related to the South Asian river dolphin (''Platanista gangetica''). The genus ''Squalodon'' was named by French naturalist Jean-Pierre Sylvestre de Grateloup in 1840 based on a jaw fragment he thought belonged to a reptile. Fossils discovered later, nevertheless, showed that this was a toothed whale. In extant odontocetes, however, the dentition is

atavistic In biology, an atavism is a modification of a biological structure whereby an ancestral genetic trait reappears after having been lost through evolutionary change in previous generations. Atavisms can occur in several ways; one of which is when ...

with all teeth reduced to simple, undifferentiated conical shapes. In squalodonts the teeth resemble those of the archaic whales, Archaeoceti, with conical incisors anteriorly and low-crowned, serrated teeth posteriorly.

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* ** * ** * Prehistoric toothed whales Chattian first appearances Miocene extinctions Prehistoric mammal families {{Paleo-whale-stub