''Squalodon'' 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 ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

whale 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 ...

s of the

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 ...

and

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 ...

epochs, belonging to the family

Squalodontidae 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 to the Neogene, but they had a maximal diversity ...

. Named by

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 hi ...

in 1840, it was originally believed to be an

iguanodont Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (). They represent one of the most successful groups of herbivore, herbivorous dinosaurs during the Cretaceous. The most primitive members of the group were bipedal and rel ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

but has since been reclassified. The name ''Squalodon'' comes from ''

Squalus ''Squalus'' is a genus of dogfish sharks in the family (biology), family Squalidae. Commonly known as spurdogs, these sharks are characterized by smooth dorsal fin spines, teeth in upper and lower fish jaw, jaws similar in size, caudal peduncle ...

'', a genus of shark. As a result, its name means "shark tooth". Its closest modern relatives are the 2 species of the genus

Platanista South Asian river dolphins are toothed whales in the genus ''Platanista'', which inhabit the waterways of the Indian subcontinent. They were historically considered to be one species (''P. gangetica'') with the Ganges river dolphin and the Ind ...

( the

Ganges river dolphin The Ganges river dolphin (''Platanista gangetica'') is a species of freshwater dolphin classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It ...

and

Indus river dolphin The Indus river dolphin (''Platanista minor'') is a species of freshwater dolphin in the family Platanistidae. It is endemic to the Indus River basin in Pakistan and Beas River in northwestern India. This dolphin was the first discovered side- ...

Description

Species of ''Squalodon'' are

odontocete The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales with teeth, such as beaked whales and the sperm whales. 73 species of toothed whales are ...

s that lived during the late Oligocene into the middle Miocene, about 28 to 15 million years ago. The genus ''Squalodon'' belongs to the order Odontoceti, the toothed whales. Their name is derived from the term ''

'' because their cheek teeth were thought to resemble the teeth of a ''Squalus'' shark. The largest species, ''Squalodon whitmorei'', reached up to 5.5 meters in length. The unique-looking squalodontids were likely distributed throughout the world in warm waters during the Oligocene and Miocene. Squalodontidae became extinct in the middle of the Miocene, leaving no descendants. Hypotheses of why this family lead to extinction have to deal with competition of other groups of dolphins as well as climate change.

Ancestral and modern features

These whales are characterized by both ancestral and modern features. Their teeth are the most evident ancestral feature. At this time in history other toothed whales were evolving simple conical teeth while Squalodontidae retained their primitive dentition that their ancestors (the archaeocetes) had developed.Marine Mammal Biology: An Evolutionary Approach By A. Rus Hoelzel. Published 2002 Blackwell Publishing. Today living odontocetes have little variation in their teeth. Squalodontids' teeth are much more complex: they are widely spaced apart; their cheek teeth are triangular and serrated for grasping and cutting. Due to the efficiency of their primitive dentition squalodontids could have a diverse variety of prey. Another ancestral quality of the Squalodontidae is their necks. Squalodontid necks are more compressed than their ancestors, the Archaeoceti. Compared to toothed whales at that time, the squalodontids were likely more mobile. Paleontologists also believe that the dorsal fins were reduced but larger than that of the ancestors. Shark toothed whales also possess many modern features. Their crania were well compressed, their rostrums were telescoped outward, and their skulls show proof of the origin of echolocation.

Fossil record and classification

Fossils of this genus are identified mainly by the teeth but several different species have been named based on skull characteristics and size (the biggest being S. whitmorei). Most of the fossil record consists of teeth. These odontocete fossils have been discovered in Europe, eastern North America, New Zealand, and Argentina. Because isolated teeth are insufficient for species identification, most specimens lacking the skull can only be identified to genus. The fossils of squalodontids indicate that this species is more closely related to endangered species of dolphins and not to most of the living dolphins today.C. Muizon. 1984. Les vertebres fossiles de la Formation Pisco (Perou) II: Les Odontocetes (Cetacea, Mammalia) du Pliocene inferieur de Sud-Sacaco. Institut Francais d'Etudes Andines Editions Recherche sur les Civilizations Memoire 50:1–188 Squalodon bariensis skull

The systematic placement of ''Squalodon'' within Odontoceti was long unclear. For a long time, it was thought to be close of the ancestry of modern dolphins and porpoise. Many of the fresh-water dolphins are differentiated phylogenetically very well, while the argument of some of the species has been going on for more than a century. The taxon is characterized during the Oligocene and Miocene in which heterodont teeth are standard amongst the family. Some modern features of the scapula, however, contradict with current phylogenetic relationships. Squalodontids were believed to be the last common ancestor of the odontocetes until 1984. Muizon came to the conclusion that rather than to any of the living species this family is closer related to the endangered species. Therefore, the ancestry of today's dolphins has little to do with the squalodontids.

Species

As the type genus of Squalodontidae, ''Squalodon'' has become a repository for various squalodontids or even taxa that were once thought to belong to Squalodontidae. However, there has been no revision of ''Squalodon''.

Species currently recognized as valid

* ''Squalodon grateloupii'' Meyer, 1843 (type species) * ''Squalodon antverpiensis'' van Beneden, 1861 * ''Squalodon bariensis'' (Jourdan 1861) * ''Squalodon barbarus'' Mchedlidze and Aslanova 1968 * ''Squalodon calvertensis'' Kellogg 1923 * ''Squalodon whitmorei'' Dooley 2005 * ''Squalodon catulli'' Molin 1859

Questionably or originally assigned to ''Squalodon''

* ''Arionus servatus'' Meyer, 1841 = ''Squalodon meyeri'' Brandt, 1873 * ''Pachyodon mirabilis'' Meyer, 1838 * ''Rhytisodon tuberculatus'' Costa, 1852 * ''Smilocamptus burgueti'' Gervais, 1859 * ''Phocodon melitensis'' (Blainville, 1840) = ''Phoca melitensis'' Blainville, 1840 = ''Phocodon scillae'' Agassiz, 1841 * ''"Squalodon" kelloggi'' Rothausen, 1968 * ''Squalodon bellunensis'' Dal Piaz, 1901 * ''Squalodon peregrinus'' Dal Piaz, 1971 * ''Squalodon imperator'' Cigala-Fulgosi & Pilleri, 1985 * ''Squalodon gambierensis''Glaessner 1955

References

External links

Squalodon Facts and Information: Fossilguy.com

Tree of Life

The Free DictionaryFamily †Squalodontidae – Hierarchy – The Taxonomicon
{{Taxonbar, from=Q774918 Miocene mammals of South America Miocene mammals of North America Miocene mammals of Europe Miocene mammals of Oceania Oligocene mammals of South America Oligocene mammals of North America Oligocene mammals of Europe Oligocene mammals of Oceania Squalodontidae Oligocene cetaceans Miocene cetaceans Miocene genus extinctions Prehistoric cetacean genera Fossil taxa described in 1840 Rupelian genus first appearances Fossil cetaceans misidentified as reptiles