Xenacanthida

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 Xenacanthus died out at the end of the Permian in the Permian Mass Extinction, with only a few forms surviving into the Triassic period (Mooreodontus).

Xenacanthida
Temporal range: Lower Carboniferous–Upper Triassic
Orthacanthus senckenbergianus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Superorder: Selachimorpha
Order: †Xenacanthida
Glikman, 1964
Families and genera

See text

The foundation of the tooth is prolonged linguistically 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 generals 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.

Xenacanthida's preserved tooth anatomy is used to classify new species into taxons. Group one is classified by tricuspid crown containing two stout, slightly diverging lateral cusps pointing in the same direction, a high median cusp, crown-base angle almost at 90 degrees, large, rounded, apical button with several foramina and multiple, 8-9 coarse vertical cristae on all the cusps. Group 2 is determined by bicuspid crowns with two upright, asymmetric cusps, where the medial cusp is thicker than the distal one, and consistently lack a median cusp.[2]

Taxonomy
  • Family: Diplodoselachidae Dick, 1981
    • Genus: Diplodoselache Dick, 1981
    • Genus: Dicentrodus Traquair, 1888
    • Genus: Hagenoselache Hampe & Heidkte, 1997
  • Family: Orthacanthidae Heyler & Poplin 1989
  • Family: Xenacanthidae Fritsch, 1889
  • incertae sedis
    • Genus: Anodontacanthus Davis, 1881

References
  1. Beck, Kimberley G.; oler-Gijón, Rodrigo; Carlucci, Jesse R.; Willis, Ray E. (December 2014). "Morphology and Histology of Dorsal Spines of the Xenacanthid Shark Orthacanthus platypternus from the Lower Permian of Texas, USA: Palaeobiological and Palaeoenvironmental Implications". Acta Palaeontologica Polonica. 61 (1): 97–117. doi:10.4202/app.00126.2014
  2. Bhat, M. S., Ray, S., & Datta, P. (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

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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