Xenacanthida

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Xenacanthida
Temporal range: Mississippian–Norian
Life restoration of Xenacanthus
Fossil of Orthacanthus senckenbergianus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Order: †Xenacanthida
Glikman, 1964
Families and genera

See text

Xenacanthida (or Xenacanthiforms) is a super-order of extinct shark-like elasmobranchs that appeared during the Lower Carboniferous period. The order includes the families Xenacanthidae, Sphenacanthidae, Diplodoselachidae, and Orthacanthidae. The most notable members of the group are the genera Xenacanthus and Orthacanthus. Some xenacanths 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]

Description

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]

Xenacanths had a long dorsal fin, as well as a large spine projecting from the top of the head, which was a modified dorsal-fin spine. The spine is usually thought to have acted as a defense against attackers.[1]

Ecology

Based on isotope analysis of teeth, some xenacanths are likely to have lived permanently in freshwater environments.[4][5] The diet of freshwater xenacanths is known to have included temnospondyls[6] as well as palaeoniscid fish.[7] In the Early Permian freshwater lakes of the Saar–Nahe Basin in southern Germany, large xenacanths are suggested to have acted as the apex predators of this ecosystem.[6]

Taxonomy

References

  1. ^ a b 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. ^ Pauliv, Victor E.; Martinelli, Agustín G.; Francischini, Heitor; Dentzien-Dias, Paula; Soares, Marina B.; Schultz, Cesar L.; Ribeiro, Ana M. (December 2017). "The first Western Gondwanan species of Triodus Jordan 1849: A new Xenacanthiformes (Chondrichthyes) from the late Paleozoic of Southern Brazil". Journal of South American Earth Sciences. 80: 482–493. doi:10.1016/j.jsames.2017.09.007.
  3. ^ 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
  4. ^ Fischer, Jan; Schneider, Jörg W.; Hodnett, John-Paul M.; Elliott, David K.; Johnson, Gary D.; Voigt, Silke; Joachimski, Michael M.; Tichomirowa, Marion; Götze, Jens (2014-11-02). "Stable and radiogenic isotope analyses on shark teeth from the Early to the Middle Permian (Sakmarian–Roadian) of the southwestern USA". Historical Biology. 26 (6): 710–727. doi:10.1080/08912963.2013.838953. ISSN 0891-2963.
  5. ^ Fischer, Jan; Schneider, Jörg W.; Voigt, Silke; Joachimski, Michael M.; Tichomirowa, Marion; Tütken, Thomas; Götze, Jens; Berner, Ulrich (2013-03-29). "Oxygen and strontium isotopes from fossil shark teeth: Environmental and ecological implications for Late Palaeozoic European basins". Chemical Geology. 342: 44–62. doi:10.1016/j.chemgeo.2013.01.022. ISSN 0009-2541.
  6. ^ a b Kriwet, Jürgen; Witzmann, Florian; Klug, Stefanie; Heidtke, Ulrich H.J (2008-01-22). "First direct evidence of a vertebrate three-level trophic chain in the fossil record". Proceedings of the Royal Society B: Biological Sciences. 275 (1631): 181–186. doi:10.1098/rspb.2007.1170. ISSN 0962-8452. PMC 2596183. PMID 17971323.
  7. ^ Greb, Stephen F.; Storrs, Glenn W.; Garcia, William J.; Eble, Cortland F. (April 2016). "Late M ississippian vertebrate palaeoecology and taphonomy, B uffalo W allow F ormation, western K entucky, USA". Lethaia. 49 (2): 199–218. doi:10.1111/let.12138. ISSN 0024-1164.

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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