Of the 14 orders that compose Euselachii, 8 belong to the sharks, 6 to the rays, without an intermediate taxon separating sharks of rays. For this reason, some authors have separated Euselachii in two:
super-order Selachimorpha corresponding to orders of sharks; super-order Rajomorphii corresponding to the orders of rays, torpedoes, sawfish and guitar fish. For those who do not recognize these two super-orders, Euselachii therefore has for synonyms Pleurotremata, Selachimorpha and Rajomorphii.
Both oviparity and viviparity are found in Euselachii. Around 70% of sharks are viviparous, including some members of Carcharhiniformes such as requiem sharks and hammerhead sharks, while the remaining 30% of sharks as well as all rays are either oviparous or ovoviviparous.
There was a recent discovery that a Palaeozoic chondrichthyan (carcharopsis) was found to no longer resemble the "triple-layer" tooth structure that the modern day chondrichthyan sharks model.
List of ordersEdit
- Superorder Selachimorpha (sharks):
- Superorder Rajomorphii or Batoidea (rays, torpedoes, sawfish and guitar fish):
- Euselachii incertae sedis
- †Ctenacanthiformes Cappetta 1988
- "Infraclass Euselachii Hay 1902". Fossilworks.org.
- Nelson, J. S. (2006). Fishes of the World (4 ed.). Hoboken, NJ: John Wiley & Sons. p. 49. ISBN 978-0-471-25031-9.
- "Euselachii". Integrated Taxonomic Information System. Retrieved 21 May 2018.
- "Fish glossary". FishBase.
- "Mating and Reproduction of Sharks", Shark Foundation
- J. A. Long. 2011. The Rise of Fishes: 500 Million Years of Evolution (Second Edition) 1-287 [G. Lloyd/G. Lloyd/M. Uhen]