Squalodon: Difference between revisions
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== Fossil Record & Classification== |
== Fossil Record & Classification== |
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One of the first fossils described in scientific Literature is that of a specimen of Squalodon (Fordyce, R.E.). Fossils of this species are identified mainly by the teeth but also somewhat by their quite complete skull. These odontocete fossils have been discovered in Europe, eastern North America, and Argentina. 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 (Fordyce, R.E.) The classification of this species is not clear. A book by Charles Darwin states that "....Squalodon, which have been placed by some naturalists in an order by themselves, are considered......to be undoubtedly cetaceans..." (Darwin, C.) Many of the fresh water dolphins are differentiated phylogenitically very well, while the argument of some of the river dolphins has been going on for more than a century. The taxon is characterized during the Oligocene and Miocene in which heterodont teeth is standard amongst the family. But some modern features of the scapula contradict with current phylogenetic relationships. |
One of the first fossils described in scientific Literature is that of a specimen of Squalodon (Fordyce, R.E.). Fossils of this species are identified mainly by the teeth but also somewhat by their quite complete skull. Most of the fossil record consists of teeth. Some fossils are of fragments of the skull. Currently a complete fossil skull has yet to be discovered. These odontocete fossils have been discovered in Europe, eastern North America, and Argentina. Because teeth fossils are insufficient for species identification the fossil record only indicates the family (Dooley,A.). 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 (Fordyce, R.E.) The classification of this species is not clear. A book by Charles Darwin states that "....Squalodon, which have been placed by some naturalists in an order by themselves, are considered......to be undoubtedly cetaceans..." (Darwin, C.) Many of the fresh water dolphins are differentiated phylogenitically very well, while the argument of some of the river dolphins has been going on for more than a century. The taxon is characterized during the Oligocene and Miocene in which heterodont teeth is standard amongst the family. But some modern features of the scapula contradict with current phylogenetic relationships. |
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==References== |
==References== |
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[http://www.] |
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[http://www.tolweb.org/Odontoceti/16025] |
[http://www.tolweb.org/Odontoceti/16025] |
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[http://www.otago.ac.nz/geology/features/paleontology/squalodontidae.html] |
[http://www.otago.ac.nz/geology/features/paleontology/squalodontidae.html] |
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Revision as of 18:56, 24 October 2007
| Squalodon | |
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| Reconstruction of Squalodon | |
| Scientific classification | |
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| Family: | Squalodontidae
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| Genus: | Squalodon
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Squalodon is an extinct genus of whales, belonging to the superfamily Squalodontoidea and family Squalodontidae. Named by Grateloup in 1840, it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squallus, a genus of shark. As a result its name means "Squallus tooth."
Description
Squalodontids lived from the early-middle Oligocene into the middle Miocene, about 33 to 14 million years ago. The genus Squalodon belongs to the order Odontocete, the toothed whales. The superfamily Squalodontidae is named after the shark Squallus because its cheek teeth superficially 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.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 as well as climate change. (See reference)
Ancestral features
This superfamily is interesting in that it is characterized by both ancestral and modern 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. 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.
Modern features
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. (Kowinsky, J.)
Fossil Record & Classification
One of the first fossils described in scientific Literature is that of a specimen of Squalodon (Fordyce, R.E.). Fossils of this species are identified mainly by the teeth but also somewhat by their quite complete skull. Most of the fossil record consists of teeth. Some fossils are of fragments of the skull. Currently a complete fossil skull has yet to be discovered. These odontocete fossils have been discovered in Europe, eastern North America, and Argentina. Because teeth fossils are insufficient for species identification the fossil record only indicates the family (Dooley,A.). 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 (Fordyce, R.E.) The classification of this species is not clear. A book by Charles Darwin states that "....Squalodon, which have been placed by some naturalists in an order by themselves, are considered......to be undoubtedly cetaceans..." (Darwin, C.) Many of the fresh water dolphins are differentiated phylogenitically very well, while the argument of some of the river dolphins has been going on for more than a century. The taxon is characterized during the Oligocene and Miocene in which heterodont teeth is standard amongst the family. But some modern features of the scapula contradict with current phylogenetic relationships.
See also
References
- The Free Dictionary
- Shark-toothed dolphins (Family Squalodontidae)
- DinoRuss
- Family †Squalodontidae - Hierarchy - The Taxonomicon
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