Squalodontidae or the shark-toothed dolphins is an extinct family of large

toothed whales The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of t ...

who had long narrow jaws. Squalodontids are known from all continents except Antarctica, from the Oligocene to the Neogene, but they had a maximal diversity and global distribution during the Late Oligocene and Early to Middle

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

(). With their cosmopolitan Miocene distribution and heterodont dentition, squalodontids are the most common and basal platanistoids. They are relatively large odontocetes, comparable in size to extant

mesoplodont whale Mesoplodont whales are 16 species of toothed whale in the genus ''Mesoplodon'', making it the largest genus in the cetacean order (biology), order. Two species were described as recently as 1991 (pygmy beaked whale) and 2002 (Perrin's beaked wha ...

s. The

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

e on their elongated

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

have large and slightly convex fossae for the air sacs associated with the presence of a

melon A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a " pepo". Th ...

, indicating the ability for echolocation. ''

Squalodon ''Squalodon'' is an extinct genus of whales of the Oligocene and Miocene epochs, belonging to the family Squalodontidae. Named by Jean-Pierre Sylvestre de Grateloup in 1840, it was originally believed to be an iguanodontid dinosaur but has sinc ...

'' and '' Eosqualodon'' are based on partial or complete skulls. The synapomorphic traits of the family are, however, based mostly on one of the bones of the inner ear, the

periotic bone The periotic bone is the single bone that surrounds the inner ear of mammals. It is formed from the fusion of the prootic, epiotic, and opisthotic bones. References External links * http://www.encyclopedia.com/doc/1O8-perioticbone.html ...

, which is unknown in these genera except in ''Squalodon''. The

monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

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 dolphin Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...

s but, according to French palaeontologist Christian de Muizon, more closely related to the

South Asian river dolphin South Asian river dolphins are toothed whales in the genus ''Platanista'', which inhabit fresh water habitats in the northern Indian subcontinent. They were historically considered to be one species (''P. gangetica'') with the Ganges river dol ...

(''Platanista gangetica''). The genus ''Squalodon'' was named by French naturalist

Jean-Pierre Sylvestre de Grateloup Jean-Pierre Sylvestre de Grateloup (31 December 1782 – 25 August 1862) was a French physician and naturalist. He completed his medical studies at Montpellier and remained attached to the countryside of the southwest of France. In company with h ...

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 with all teeth reduced to simple, undifferentiated conical shapes. In squalodonts the teeth resemble those of the archaic whales,

Archaeoceti Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initial ...

, with conical incisors anteriorly and low-crowned, serrated teeth posteriorly.

References

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