Squalomorphii

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Squalomorphii
Cuban dogfish (Squalus cubensis)

Cuban dogfish ( Squalus cubensis )

Systematics
Superclass : Jaw mouths (Gnathostomata)
Class : Cartilaginous fish (Chondrichthyes)
Subclass : Euselachii
Subclass : Plate gill (Elasmobranchii)
without rank: Sharks (selachii)
Superordinate : Squalomorphii
Scientific name
Squalomorphii
Compagno , 1977
Ray-like sharks such as the Atlantic angel shark ( Squatina dumeril ) led to the assumption that rays are only a subset of the squalomorphic sharks.

The Squalomorphii are a superordinate order of the sharks (Selachii). The taxon was set up in 1977 by the American ichthyologist Leonard Compagno in order to differentiate a group of primeval, partly ray-like sharks from the more developed Galeomorphi , the so-called real sharks. The Squalomorphii combine the dogfish-like (Squaliformes), the nail sharks (Echinorhiniformes), the Hexanchiformes , the saw sharks (Pristiophoriformes) and the angel sharks (Squantiniformes).

As an alternative to the Squalomorphii, the Japanese ichthyologist Shigeru Shirai established the taxon Squalea in 1992 , a systematic group which, in addition to the squalomorphic sharks, also included the rays (Batoidea), which according to various morphological analyzes are only a subgroup of the squalomorphic sharks. The Squalea initially found rapid recognition and largely replaced the Squalomorphii in the scientific debate and in systematic textbooks.

With the increasing spread of DNA sequencing for the analysis of relationships between taxonomic groups, doubts about the monophyly of Squalea are increasing. All molecular biological investigations that have been undertaken in the meantime come to the conclusion that, as previously assumed, there is a basic dichotomy between sharks and rays. The morphological correspondences of the squalomorphic sharks with the rays are only convergent , e.g. B. originated in adaptation to a life near the sea floor.

Since the rays, just like modern sharks, can be traced back to fossil records since the early Jurassic, the origin of the rays at the end of a long evolutionary line of the Squalea is not supported by paleontological data.

features

The Squalomorphii have a unique form of jaw suspension. In them, the palatoquadratum, the upper jaw of primitive jaws, is connected to the skull near the eye sockets by a strong but flexible ligament , a condition called orbitostyly, which is only found in the squalomorphii among all jaws . The squalomorphii can thus as the sharks with orbitostyler pine suspension defined are. In the case of the rays, however, the palatoquadratum is never attached to the neurocranium. In all Squalomorphii, with the exception of the Hexanchiformes, the anal fin has not formed, as in most primitive cartilaginous fish. Compared to their sister group the Galeomorphii , the Squalomorphii are considered to be less developed. Among other things, their brain is much smaller. The Squalomorphii live mainly on or near the sea floor ( benthal ), often also in the deep sea.

Systematics

The following cladogram shows the position of the Squalomorphii within the cartilaginous fish and the probable relationship of the orders belonging to the group to one another.

  Cartilaginous fish  

 Sea cats (Chimaeriformes)


  Neoselachii  

 Stingray (batoidea)


  Sharks  (selachii)  

 Galeomorphi


  Squalomorphii  

 Hexanchiformes


   
  Squantinida  


 Cuticle Sharks (Echinorhiniformes)


   

 Sawshark-like (Pristiophoriformes)



   

 Angel sharks (Squantiniformes)



  Squalida  

 Spiny dogfish (Squaliformes)







The systematic position of the nail sharks ( Echinorhinus ) is highly controversial. They are often classified much closer to the Squaliformes or even as part of the Squaliformes. The American ichthyologist Joseph S. Nelson counts five orders, eleven families, 32 genera and 124 species of shark to the Squalomorphii in his standard work on fish systematics "Fishes of the World". The Fishbase online database lists a total of 172 species (as of April 2018).

Protospinax annectens in the Paleontological Museum in Munich

Fossil record

The fossil record of the Squalomorphii begins in the Jurassic and includes in the Mesozoic Protospinax a relative of the angel and saw sharks, the angel shark Pseudorhina , the six- gill shark Hexanchus gracilis , the dogfish-like Cretascymnus and Protoxynotus , as well as the genera Proetmopterus , Microetmopterus and Eoetmopterus , described only after fossil shark teeth the lantern sharks (Etmopteridae) are assigned.

Individual evidence

  1. ↑ a b c d Joseph S. Nelson : Fishes of the World , John Wiley & Sons, 2006, ISBN 0-471-25031-7
  2. ^ A b c Alfred Goldschmid: Chondrichthyes. Page 220 in: W. Westheide and R. Rieger: Special Zoology. Part 2. Vertebrate or skull animals. Spectrum, Munich 2004. ISBN 3-8274-0307-3
  3. ↑ Christophe J. Douady, Miné Dosay, Mahmood S. Shivji & Michael J. Stanhop: Molecular phylogenetic evidence refuting the hypothesis of Batoidea (rays and skates) as derived sharks. Molecular Phylogenetics and Evolution, Volume 26, Issue 2, February 2003, Pages 215-221 doi : 10.1016 / S1055-7903 (02) 00333-0
  4. ↑ MP Heinicke, GJP Naylor, SB Hedges: Cartaginous fishes. in SB Hedges, S. Kumar: The Timetree of Life. Oxford University Press, USA, 2009, ISBN 9780199535033
  5. ↑ BA Humana, EP Owena, LJV Compagnob & EH Harleya: Testing morphologically based phylogenetic theories within the cartilaginous fishes with molecular data, with special reference to the catshark family (Chondrichthyes; Scyliorhinidae) and the interrelationships within them. Molecular Phylogenetics and Evolution, Volume 39, Issue 2, May 2006, pages 384-391, doi : 10.1016 / j.ympev.2005.09.009
  6. ↑ a b Jon. Mallatt, CJ Winchell: Ribosomal RNA genes and deuterostome phylogeny revisited: more cyclostomes, elasmobranchs, reptiles, and a brittle star. Molecular Phylogenetics and Evolution (2007), Volume: 43, Issue: 3, Pages 1005-1022, doi : 10.1016 / j.ympev.2006.11.023
  7. ^ John A. Musick & Julia K. Ellis: Reproductive Evolution of Chondrichthyans. in William C. Hamlett: Reproductive Biology and Phylogeny of Chondrichthyes Sharks, Batoids and Chimaeras. Science Publishers, US ISBN 1-57808-314-1 PDF
  8. ↑ GJP Naylor, YES Ryburn, O. & A. Lopez Fedrigo: Phylogenetic Relationships among the major lineages of. Modern Elasmobranchs. PDF  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / www.duke.edu  
  9. ^ A b C. J. Underwood: Diversification of the Neoselachii (Chondrichthyes) during the Jurassic and Cretaceous. Paleobiology, 32 (2) (2006). pp. 215-235. PDF
  10. ↑ a b Ximena Vélez-Zuazoa & Ingi Agnarsson: Shark tales: A molecular species-level phylogeny of sharks (Selachimorpha, Chondrichthyes). Molecular Phylogenetics and Evolution, Volume 58, Issue 2, February 2011, pages 207-217 doi : 10.1016 / j.ympev.2010.11.018
  11. ↑ CJ Winchell, AP Martin, J. Mallatt: Phylogeny of elasmobranchs based on LSU and SSU ribosomal RNA genes. Molecular Phylogenetics and Evolution, Volume 31, Issue 1, April 2004, Pages 214-224 doi : 10.1016 / j.ympev.2003.07.010
  12. ↑ Elasmo-research.org Galea and Squalea: Two Great Branches of Elasmobranch Evolution
  13. ^ Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton Field Guides, Princeton University Press, Princeton and Oxford 2005, ISBN 978-0-691-12072-0 . Page 103.
  14. ^ Karl Albert Frickhinger: Fossil Atlas of Fishes , page 188-194, Mergus-Verlag, Melle, 1999, ISBN 3-88244-018-X
  15. ↑ Adnet, S. & Cappetta, H. 2001 09 14: A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes: Squaliformes) based on dental characters. Lethaia, Vol. 34, pp. 234-248. Oslo. ISSN  0024-1164