Xenacanthida (or Xenacanthiforms) is an order of prehistoric sharks that appeared during the Lower Carboniferous period. The order includes the families Xenacanthidae, Diplodoselachidae, and Orthacanthidae. The most notable members of the group are the genera Xenacanthus and Orthacanthus. Some, like Xenacanthus itself, may have grown to lengths of 4 m (13 ft). This group of sharks inhabited freshwater environments, unlike most modern sharks, save those of the genus Glyphis. 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 Xenacanthids died out at the end of the Permian in the Permian Mass Extinction, with only a few forms surviving into the Triassic period as the age of dinosaurs began. Why these sharks died out is a mystery, but may be linked to the rise of other types of freshwater sharks.
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