Xenacanthida

Taxobox
name = Xenacanthida

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image_width = 250px
image_caption = "Orthacanthus senckenbergianus"
fossil_range = Lower Carboniferous - Middle Triassic
regnum = Animalia
phylum = Chordata
classis = Chondrichthyes
subclassis = Elasmobranchii
superordo = Euselachii
ordo = Xenacanthida
ordo_authority = Glikman, 1964
subdivision_ranks = families and genera
subdivision = See text.

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.

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

References