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{{Short description|Extinct genus of mammals}}
{{Taxobox
{{Automatic taxobox
| color = pink
| fossil_range = {{Fossil range|Oligocene|Miocene}}
| name = Squalodon
| image = Squalodon bariensis.jpg
| fossil_range = Middle [[Oligocene]] - Middle [[Miocene]]
| image_caption = Skull of ''S. bariensis'' in Brussels
| image = Squalodon.gif
| display_parents = 2
| image_width = 245px
| parent_authority = [[Johann Friedrich von Brandt|Brandt]], 1873
| image_caption= Reconstruction of ''Squalodon''
| regnum = [[Animal]]ia
| taxon = Squalodon
| authority = [[Jean-Pierre Sylvestre de Grateloup|Grateloup]], 1840
| phylum = [[Chordate|Chordata]]
| subdivision_ranks = Species
| classis = [[Mammal]]ia
| subdivision =
| ordo = [[Cetacea]]
†''S. grateloupii'' von Meyer, 1843<br /> ([[Type (biology)|Type]])<br />
| subordo = [[Odontoceti]]
†''S. antverpiensis'' van Beneden, 1861<br />
| superfamilia = [[Squalodontoidea]]
†''S. bariensis'' Jourdan 1861<br />
| familia = '''Squalodontidae'''
†''S. barbarus'' Mchedlidze and Aslanova 1968<br />
| genus = '''Squalodon'''
†''S. calvertensis'' Kellogg 1923<br />
†''S. whitmorei'' Dooley 2005<br />
†''S. catulli'' Molin 1859
| synonyms =
}}
}}


'''''Squalodon''''' is an [[extinct]] [[genus]] of [[whale]]s, belonging to the superfamily [[Squalodontoidea]] and family [[Squalodontidae]]. Named by Grateloup in [[1840]], it was originally believed to be an [[iguanodont]]id [[dinosaur]] but has since been reclassified. The name ''Squalodon'' comes from ''[[Squallus]]'', a genus of shark. As a result its name means "Squallus tooth."
'''''Squalodon''''' is an [[extinct]] [[genus]] of [[whale]]s of the [[Oligocene]] and [[Miocene]] epochs, belonging to the family [[Squalodontidae]]. Named by [[Jean-Pierre Sylvestre de Grateloup]] in 1840,<ref>Grateloup, ''Description d'un fragment de mâchoire fossile, d'un genre nouveau de reptile (Saurien), de taille gigantesque, voisin de l'Iguanodon...'', Bordeaux 1840.</ref> it was originally believed to be an [[iguanodont]]id [[dinosaur]] but has since been reclassified. The name ''Squalodon'' comes from ''[[Squalus]]'', a genus of shark. As a result, its name means "shark tooth". Its closest modern relative is the [[South Asian river dolphin]] (with its two subspecies the Ganges river dolphin and Indus river dolphin).<ref>{{cite web |title=Shark-toothed dolphins (Family Squalodontidae) |url=https://www.otago.ac.nz/geology/research/paleontology/squalodontidae.html |website=University of Otago}}</ref>


== Description ==
== Description ==
[[File:Squalodon BW.jpg|thumb|left|Reconstruction of ''S. calvertensis'']]
Species of ''Squalodon'' are [[odontocete]]s that lived during the late Oligocene into the middle Miocene, about 28 to 15 million years ago.<ref name="Fordyce">{{Cite web
| last = Fordyce | first = R Ewan | title = Shark-toothed dolphins (Family Squalodontidae) | publisher = University of Otago, Department of Geology
| url = http://www.otago.ac.nz/geology/research/paleontology/squalodontidae.html | access-date = 28 September 2020}}</ref> The genus ''Squalodon'' belongs to the order Odontoceti, the toothed whales. They are named after the shark ''Squalus'' because their cheek teeth look like the teeth of a squalus shark. The largest species, ''Squalodon whitmorei'', reached up to 5.5 meters in length.<ref>{{Cite journal|last1=Nobile |first1=F. |last2=Collareta |first2=A. |last3=Perenzin |first3=V. |last4=Fornaciari |first4=E. |last5=Giusberti |first5=L. |last6=Bianucci |first6=G. |year=2024 |title=Dawn of the Delphinidans: New Remains of ''Kentriodon'' from the Lower Miocene of Italy Shed Light on the Early Radiation of the Most Diverse Extant Cetacean Clade |journal=Biology |volume=13 |issue=2 |at=114 |doi=10.3390/biology13020114 |doi-access=free |pmc=10887126 }}</ref> 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 ==
Squalodontids lived from the early-middle Oligocene into the middle Miocene. The genus ''Squalodon'' belongs to the order Odontocete, the toothed whales. The superfamily Squalodontidae is named after the shark ''Squallus'' because its cheek teeth apparently resemble the teeth of a ''Squallus'' shark. Squalodontidae consists of four different groups of medium-sized shark toothed whales. They are short snouted shark toothed whales, the ''Prosqualodon'', the medium-snouted shark toothed whales, the ''Phoberodon'', and the long-snouted shark toothed whales, the ''Squalodon'', belonging to the family Squalodontidae.
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.<ref name=mmb2002>Marine Mammal Biology: An Evolutionary Approach By A. Rus Hoelzel. Published 2002 Blackwell Publishing. {{ISBN|0-632-05232-5}}</ref> 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.
These unique creatures can be found throughout the world in warm waters during the Oligocene and Miocene. An explanation for the extinction of this family isn't well known. Hypotheses for why this family went extinct involve other competing dolphins and climate change (Fordyce, R.E.)
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.<ref name=mmb2002/>
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.<ref>Whitmore, Jr., F.C., and Sanders, A.E. 1977. Review of the Oligocene Cetacea. Systematic Zoology, 25(4):304–320.</ref>


== Fossil record and classification==
== Ancestral Features ==
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.<ref>A. C. Dooley. 2003. A review of the eastern North American Squalodontidae (Mammalia: Cetacea). Jeffersoniana 11:1–26</ref> 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.<ref name=muizon84>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</ref>
[[File:Squalodon bariensis skull.jpg|thumb|''S. bariensis'' skull]]
This superfamily is intriguing in that it is characterized by both ancestral and derived features. The most evident ancestral feature is that of their teeth. At this time other toothed whales were evolving simple conical teeth while Squalodontidae retained their primitive dentition that their ancestors (the archaeocetis) had developed. Squalodontid teeth 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.
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.<ref>K. Rothausen. 1968. Die systematische Stellung der europäischen Squalodontidae (Odontoceti, Mamm.). Paläontologische Zeitschrift 42(1–2):83–104</ref> 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.<ref name=muizon84/>
Another ancestral quality of the Squalodontidae is that they possess mobility in their necks. Squalodontid necks are more compressed than their ancestors, the Archaeoceti. Compared to living toothed whales, the squalodontids were probably much more mobile. Paleontologists also believe that the dorsal fins were larger than that of the ancestors but still reduced.


==Species==
[[File:Squalodon 1.JPG|thumb|Partial skull]]
[[File:Squalodon atlanticus (fossil shark-toothed porpoise tooth) (Miocene; Randle Cliff, Maryland, USA).jpg|thumb|Tooth]]
[[File:Squalodon.jpg|thumb|1840 illustration]]
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===
== Modern features ==
* ''Squalodon grateloupii'' Meyer, 1843 (type species)

* ''Squalodon antverpiensis'' van Beneden, 1861
Shark toothed whales also possess many modern features. Their crania were well compressed, their rostrums were telescoped outward, and their skulls show proof of ability of echolocation.
* ''Squalodon bariensis'' (Jourdan 1861)
The unique-looking squalodontids can be found throughout the world in warm waters during the Oligocene and Miocene. Squalodontidae went 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.
* ''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<ref>{{cite web |title=†family Kekenodontidae Mitchell 1989 |url=https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=63494 |website=PBDB}}</ref>




== See also ==
== See also ==
{{Portal|Paleontology}}
*[[Evolution of cetaceans]]
*[[Evolution of cetaceans]]
*[[Phocodontia]]
*[[Toothed whale]]


==References==
==References==
{{Reflist}}

==External links==
* [http://www.fossilguy.com/gallery/vert/mammal/marine/squalodon/index.htm Squalodon Facts and Information: Fossilguy.com]
* [http://www.tolweb.org/Odontoceti/16025 Tree of Life]
* [https://web.archive.org/web/20060709160448/http://www.otago.ac.nz/Geology/features/paleontology/squalodontidae.html Otago University]
* [https://web.archive.org/web/20070810224016/http://www.calvertmarinemuseum.com/cmmfc/index.html Calvert Marine Museum]
*[http://www.thefreedictionary.com/Squalodon The Free Dictionary]
*[http://www.thefreedictionary.com/Squalodon The Free Dictionary]
*[http://www.otago.ac.nz/geology/features/paleontology/squalodontidae.html]
*[https://web.archive.org/web/20060709160448/http://www.otago.ac.nz/Geology/features/paleontology/squalodontidae.html Shark-toothed dolphins (Family Squalodontidae)]
*[http://sn2000.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=68654 Family †Squalodontidae – Hierarchy – The Taxonomicon]
*[http://www.dinoruss.com/de_4/5a93559.htm DinoRuss]
*[http://sn2000.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=68654 Family †Squalodontidae - Hierarchy - The Taxonomicon]

[[Category:Prehistoric cetaceans]]
[[Category:Oligocene mammals]]
[[Category:Miocene mammals]]



{{Odontoceti|O.}}
{{paleo-mammal-stub}}
{{Taxonbar|from=Q774918}}


[[Category:Miocene mammals of South America]]
[[zh:原鮫鯨]]
[[Category:Miocene mammals of North America]]
[[Category:Miocene mammals of Europe]]
[[Category:Miocene mammals of Oceania]]
[[Category:Oligocene mammals of South America]]
[[Category:Oligocene mammals of North America]]
[[Category:Oligocene mammals of Europe]]
[[Category:Oligocene mammals of Oceania]]
[[Category:Squalodontidae]]
[[Category:Oligocene cetaceans]]
[[Category:Miocene cetaceans]]
[[Category:Miocene genus extinctions]]
[[Category:Prehistoric cetacean genera]]
[[Category:Fossil taxa described in 1840]]
[[Category:Rupelian genus first appearances]]
[[Category:Fossil cetaceans misidentified as reptiles]]

Latest revision as of 10:12, 5 August 2024

Squalodon
Temporal range: Oligocene–Miocene
Skull of S. bariensis in Brussels
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Superfamily: Platanistoidea
Family: †Squalodontidae
Brandt, 1873
Genus: †Squalodon
Grateloup, 1840
Species

†S. grateloupii von Meyer, 1843
(Type)
†S. antverpiensis van Beneden, 1861
†S. bariensis Jourdan 1861
†S. barbarus Mchedlidze and Aslanova 1968
†S. calvertensis Kellogg 1923
†S. whitmorei Dooley 2005
†S. catulli Molin 1859

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,[1] it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squalus, a genus of shark. As a result, its name means "shark tooth". Its closest modern relative is the South Asian river dolphin (with its two subspecies the Ganges river dolphin and Indus river dolphin).[2]

Description

[edit]
Reconstruction of S. calvertensis

Species of Squalodon are odontocetes that lived during the late Oligocene into the middle Miocene, about 28 to 15 million years ago.[3] The genus Squalodon belongs to the order Odontoceti, the toothed whales. They are named after the shark Squalus because their cheek teeth look like the teeth of a squalus shark. The largest species, Squalodon whitmorei, reached up to 5.5 meters in length.[4] 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

[edit]

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.[5] 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.[5] 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.[6]

Fossil record and classification

[edit]

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.[7] 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.[8]

S. 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.[9] 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.[8]

Species

[edit]
Partial skull
Tooth
1840 illustration

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

[edit]
  • 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

[edit]
  • 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 gambierensisGlaessner 1955[10]


See also

[edit]

References

[edit]
  1. ^ Grateloup, Description d'un fragment de mâchoire fossile, d'un genre nouveau de reptile (Saurien), de taille gigantesque, voisin de l'Iguanodon..., Bordeaux 1840.
  2. ^ "Shark-toothed dolphins (Family Squalodontidae)". University of Otago.
  3. ^ Fordyce, R Ewan. "Shark-toothed dolphins (Family Squalodontidae)". University of Otago, Department of Geology. Retrieved 28 September 2020.
  4. ^ Nobile, F.; Collareta, A.; Perenzin, V.; Fornaciari, E.; Giusberti, L.; Bianucci, G. (2024). "Dawn of the Delphinidans: New Remains of Kentriodon from the Lower Miocene of Italy Shed Light on the Early Radiation of the Most Diverse Extant Cetacean Clade". Biology. 13 (2). 114. doi:10.3390/biology13020114. PMC 10887126.
  5. ^ a b Marine Mammal Biology: An Evolutionary Approach By A. Rus Hoelzel. Published 2002 Blackwell Publishing. ISBN 0-632-05232-5
  6. ^ Whitmore, Jr., F.C., and Sanders, A.E. 1977. Review of the Oligocene Cetacea. Systematic Zoology, 25(4):304–320.
  7. ^ A. C. Dooley. 2003. A review of the eastern North American Squalodontidae (Mammalia: Cetacea). Jeffersoniana 11:1–26
  8. ^ a b 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
  9. ^ K. Rothausen. 1968. Die systematische Stellung der europäischen Squalodontidae (Odontoceti, Mamm.). Paläontologische Zeitschrift 42(1–2):83–104
  10. ^ "†family Kekenodontidae Mitchell 1989". PBDB.
[edit]
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