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Xenacanthida (or Xenacanthiforms) is an order of prehistoric sharks that appeared during the Lower Carboniferous period. The family includes the families [Xenacanthidae]], Diplodoselachidae and Orthacanthidae and the most notable members of the group are the genera Xenacanthus and Orthacanthus. Some Xenacanthus may have grown to lengths of 4 m. This group of sharks inhabited freshwater environments. Some forms had large serrated spines extending backwards from the neck. Xenacanthus had characteristic teeth. The base or root of each tooth had a pair of hook like cusps. Most Xenacanthus died out at the end of the Permian in the Permian Mass Extinction, with only a few forms surviving into the Triassic period.
[edit] Taxonomy
- Family: Diplodoselachidae Dick, 1981
- Genus: Diplodoselache Dick, 1981
- Genus: Dicentrodus Traquair, 1888
- Genus: Hagenoselache Hampe & Heidkte, 1997
- Family: Orthacanthidae Heyler & Poplin 1989
- Genus: Orthacanthus Agassiz, 1843
- Family: Xenacanthidae Fritsch, 1889
- Genus: Plicatodus Hampe, 1995
- Genus: Triodus Jordan, 1849
- Genus: Xenacanthus Beyrich, 1848
- incertae sedis
- Genus: Anodontacanthus Davis, 1881
