Xenacanthida

Xenacanthida Temporal range: Mississippian–Norian PreꞒ Ꞓ O S D C P T J K Pg N
Orthacanthus senckenbergianus
Orthacanthus senckenbergianus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Superorder:	Selachimorpha
Order:	†Xenacanthida Glikman, 1964
Families and genera
See text

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 Xenacanthida may have grown to lengths of 5 m (16 ft).^[1] Most forms had large serrated spines extending backwards from the neck. Xenacanthus had characteristic teeth. Most xenacanths died out at the end of the Permian in the Permian Mass Extinction, with only a few forms surviving into the Triassic period. They were native to freshwater, marginal marine and shallow marine habitats.^[2]

The foundation of the tooth is prolonged lingually with a circlet button and a basal tubercle on the oral and aboral surfaces individually. Xenacanthida's teeth are famed by articulated bones, cephalic vertebrae and isolated teeth and found global in each aquatic and clean environment. The family Xenacanthidae consist of five genera that are Xenacanthus, Triodus, Plicatodus, Mooreodontus and Wurdigneria; all of these are distinguished by cross sections of the points, crown center, length of the median edge, type of vertical cristae, and microscopic anatomy. These kinds of fishes are largely marked from Paleozoic remains and their diversity cut drastically throughout the period of their extinction.

Xenacanths are divided into two groups based on dental characteristics. Group one has tricuspid crown containing two stout, slightly diverging lateral cusps pointing in the same direction, a high median cusp, with a crown-base angle almost at 90 degrees, a large, rounded, apical button with several foramina and multiple, 8-9 coarse vertical cristae on all the cusps. Group two has bicuspid crowns with two upright, asymmetric cusps, where the medial cusp is thicker than the distal one, and consistently lacks a median cusp.^[3]

Taxonomy[]

• Family: Diplodoselachidae Dick, 1981
  • Genus: Dick, 1981
  • Genus: Traquair, 1888
  • Genus: Hampe & Heidkte, 1997
  • Genus: Lebachacanthus Soler-Gijon, 1997
• Family: Heyler & Poplin 1989
  • Genus: Orthacanthus Agassiz, 1843
• Family: Xenacanthidae Fritsch, 1889
  • Genus: Ginter et al., 2010 North America, Europe, South America, Australia, India, Triassic
  • Genus: Plicatodus Hampe, 1995
  • Genus: Triodus Jordan, 1849
  • Genus: Xenacanthus Beyrich, 1848
• incertae sedis
  • Genus: Davis, 1881
  • Bhat, Ray & Datta, 2018. Tiki Formation, India, Late Triassic

References[]

Further reading[]

• Bhat, Mohd Shafi; Ray, Sanghamitra; Datta, P.M. (September 2018). "A new assemblage of freshwater sharks (Chondrichthyes: Elasmobranchii) from the Upper Triassic of India". Geobios. 51 (4): 269–283. doi:10.1016/j.geobios.2018.06.004.
• Huttenlocker, Adam K.; Henrici, Amy; John Nelson, W.; Elrick, Scott; Berman, David S; Schlotterbeck, Tyler; Sumida, Stuart S. (June 2018). "A multitaxic bonebed near the Carboniferous–Permian boundary (Halgaito Formation, Cutler Group) in Valley of the Gods, Utah, USA: Vertebrate paleontology and taphonomy". Palaeogeography, Palaeoclimatology, Palaeoecology. 499: 72–92. Bibcode:2018PPP...499...72H. doi:10.1016/j.palaeo.2018.03.017.

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