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Gnathostomata

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Gnathostomata /ˌnθstˈmɑːtə/ are the jawed vertebrates. The term derives from Greek: γνάθος (gnathos) "jaw" + στόμα (stoma) "mouth". Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates. In addition to opposing jaws, living gnathostomes have teeth, paired appendages,[1] and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons. Another is an adaptive immune system that uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene.[2]

It is now assumed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins.[3] Until recently these ancestors, known as antiarchs, were thought to have lacked pectoral or pelvic fins.[3] In addition to this, some placoderms were shown to have a third pair of paired appendages, that had been modified to claspers in males and basal plates in females—a pattern not seen in any other vertebrate group.[4]

The Osteostraci are generally considered the sister taxon of Gnathostomata.[1][5][6]

It is believed that the jaws evolved from anterior gill support arches that had acquired a new role, being modified to pump water over the gills by opening and closing the mouth more effectively – the buccal pump mechanism. The mouth could then grow bigger and wider, making it possible to capture larger prey. This close and open mechanism would, with time, become stronger and tougher, being transformed into real jaws.

Newer research suggests that a branch of Placoderms was most likely the ancestor of present-day gnathostomes. A 419-million-year-old fossil of a placoderm named Entelognathus had a bony skeleton and anatomical details associated with cartilaginous and bony fish, demonstrating that the absence of a bony skeleton in Chondrichthyes is a derived trait.[7] The fossil findings of primitive bony fishes such as Guiyu oneiros and Psarolepis, which lived contemporaneously with Entelognathus and had pelvic girdles more in common with placoderms than with other bony fish, show that it was a relative rather than a direct ancestor of the extant gnathostomes.[8] It also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes.[9] Fossils findings of juvenile placoderms, which had true teeth that grew on the surface of the jawbone and had no roots, making them impossible to replace or regrow as they broke or wore down as they grew older, proves the common ancestor of all gnathostomes had teeth and place the origin of teeth along with, or soon after, the evolution of jaws.[10][11]

Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians[12] or "shark-like fishes",[13] may mark Gnathostomata's first appearance in the fossil record. Undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian, and become abundant by the start of the Devonian.

Classification

The group is traditionally a superclass, broken into three top-level groupings: Chondrichthyes, or the cartilaginous fish; Placodermi, an extinct clade of armored fish; and Teleostomi, which includes the familiar classes of bony fish, birds, mammals, reptiles, and amphibians. Some classification systems have used the term Amphirhina. It is a sister group of the jawless craniates Agnatha.

Vertebrata Gnathostomata

Placodermi Dunkleosteus intermedius.jpg

Eugnathostomata

Acanthodians, incl. Chondrichthyes (cartilaginous fishes)Carcharodon carcharias drawing.jpg

Osteichthyes

Actinopterygii Atlantic sturgeon flipped.jpg

Sarcopterygii Tetrapoda

Amphibia Deutschlands Amphibien und Reptilien (Salamandra salamdra).jpg

Amniota Sauropsida

Sauropsida Description des reptiles nouveaux, ou, Imparfaitement connus de la collection du Muséum d'histoire naturelle et remarques sur la classification et les caractères des reptiles (1852) (Crocodylus moreletii).jpg

    Synapsida

Mammalia Phylogenetic tree of marsupials derived from retroposon data (Paucituberculata).png

                 

References

  1. ^ a b Zaccone, Giacomo; Dabrowski, Konrad; Hedrick, Michael S. (5 August 2015). Phylogeny, Anatomy and Physiology of Ancient Fishes. CRC Press. p. 2. ISBN 978-1-4987-0756-5. Retrieved 14 September 2016.
  2. ^ Cooper MD, Alder MN (February 2006). "The evolution of adaptive immune systems". Cell. 124 (4): 815–22. doi:10.1016/j.cell.2006.02.001. PMID 16497590.
  3. ^ a b New study showing pelvic girdles arose before the origin of movable jaws
  4. ^ The first vertebrate sexual organs evolved as an extra pair of legs
  5. ^ Keating, Joseph N.; Sansom, Robert S.; Purnell, Mark A. (2012). "A new osteostracan fauna from the Devonian of the Welsh Borderlands and observations on the taxonomy and growth of Osteostraci" (PDF). Journal of Vertebrate Paleontology. 32 (5): 1002–1017. doi:10.1080/02724634.2012.693555. ISSN 0272-4634.
  6. ^ Sansom, R. S.; Randle, E.; Donoghue, P. C. J. (2014). "Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history". Proceedings of the Royal Society B: Biological Sciences. 282 (1800): 2014–2245. doi:10.1098/rspb.2014.2245. ISSN 0962-8452. PMC 4298210. PMID 25520359.
  7. ^ Scientists make jaw dropping discovery
  8. ^ Zhu, Min; Yu, Xiaobo; Choo, Brian; Qu, Qingming; Jia, Liantao; Zhao, Wenjin; Qiao, Tuo; Lu, Jing (2012). "Fossil Fishes from China Provide First Evidence of Dermal Pelvic Girdles in Osteichthyans". PLOS ONE. 7 (4): e35103. Bibcode:2012PLoSO...735103Z. doi:10.1371/journal.pone.0035103. PMC 3318012. PMID 22509388.
  9. ^ a b Min Zhu; et al. (10 October 2013). "A Silurian placoderm with osteichthyan-like marginal jaw bones". Nature. 502 (7470): 188–193. Bibcode:2013Natur.502..188Z. doi:10.1038/nature12617. PMID 24067611.
  10. ^ Choi, Charles Q. (17 October 2012). "Evolution's Bite: Ancient Armored Fish Was Toothy, Too". Live Science.
  11. ^ ScienceShot: Ancient Jaws Had Real Teeth
  12. ^ Hanke, Gavin F.; Wilson, Mark V. H. (2004). "New teleostome fishes and acanthodian systematics." (PDF). Recent advances in the origin and early radiation of vertebrates. pp. 189–216. ... record of acanthodian fishes is limited to microremains from the latest Ordovician (JANVIER 1996)
  13. ^ Sansom, Ivan J.; Smith, Moya M.; Smith, M. Paul (February 15, 1996). "Scales of thelodont and shark-like fishes from the Ordovician of Colorado". Nature. 379 (6566): 628–630. Bibcode:1996Natur.379..628S. doi:10.1038/379628a0.
  14. ^ "Fossil reveals oldest live birth". BBC. May 28, 2008. Retrieved May 30, 2008.
  15. ^ Bony fishes Archived 2013-06-06 at the Wayback Machine SeaWorld. Retrieved 2 February 2013.
  16. ^ Jaws, Teeth of Earliest Bony Fish Discovered
  17. ^ Clack 2012 harvnb error: no target: CITEREFClack2012 (help)

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Gnathostomata (echinoid)

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The Gnathostomata are a superorder of sea urchins, including the familiar sand dollars.

Gnathostomatans are irregular in shape, but unlike other irregular sea urchins, possess a feeding lantern. The mouth is located in the centre of the lower surface, as it is in most other sea urchins, but the anus is found to one side of the upper surface, rather than being central. The members of the group are adapted for burrowing in soft-bottomed marine environments.

References

  • Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 981. ISBN 0-03-056747-5.
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Gnathostomata (echinoid): Brief Summary

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The Gnathostomata are a superorder of sea urchins, including the familiar sand dollars.

Gnathostomatans are irregular in shape, but unlike other irregular sea urchins, possess a feeding lantern. The mouth is located in the centre of the lower surface, as it is in most other sea urchins, but the anus is found to one side of the upper surface, rather than being central. The members of the group are adapted for burrowing in soft-bottomed marine environments.

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Wikipedia authors and editors
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visit source
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wikipedia EN

Gnathostomata: Brief Summary

provided by wikipedia EN

Gnathostomata /ˌneɪθoʊstoʊˈmɑːtə/ are the jawed vertebrates. The term derives from Greek: γνάθος (gnathos) "jaw" + στόμα (stoma) "mouth". Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates. In addition to opposing jaws, living gnathostomes have teeth, paired appendages, and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons. Another is an adaptive immune system that uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene.

It is now assumed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins. Until recently these ancestors, known as antiarchs, were thought to have lacked pectoral or pelvic fins. In addition to this, some placoderms were shown to have a third pair of paired appendages, that had been modified to claspers in males and basal plates in females—a pattern not seen in any other vertebrate group.

The Osteostraci are generally considered the sister taxon of Gnathostomata.

It is believed that the jaws evolved from anterior gill support arches that had acquired a new role, being modified to pump water over the gills by opening and closing the mouth more effectively – the buccal pump mechanism. The mouth could then grow bigger and wider, making it possible to capture larger prey. This close and open mechanism would, with time, become stronger and tougher, being transformed into real jaws.

Newer research suggests that a branch of Placoderms was most likely the ancestor of present-day gnathostomes. A 419-million-year-old fossil of a placoderm named Entelognathus had a bony skeleton and anatomical details associated with cartilaginous and bony fish, demonstrating that the absence of a bony skeleton in Chondrichthyes is a derived trait. The fossil findings of primitive bony fishes such as Guiyu oneiros and Psarolepis, which lived contemporaneously with Entelognathus and had pelvic girdles more in common with placoderms than with other bony fish, show that it was a relative rather than a direct ancestor of the extant gnathostomes. It also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes. Fossils findings of juvenile placoderms, which had true teeth that grew on the surface of the jawbone and had no roots, making them impossible to replace or regrow as they broke or wore down as they grew older, proves the common ancestor of all gnathostomes had teeth and place the origin of teeth along with, or soon after, the evolution of jaws.

Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians or "shark-like fishes", may mark Gnathostomata's first appearance in the fossil record. Undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian, and become abundant by the start of the Devonian.

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