Jawed vertebrates
Temporal range:
Early SilurianPresent, (Possible Late Ordovician record, 444 Ma)[1]
Example of jawed vertebrates: Dunkleosteus (Placodermi), Spotted wobbegong (Chondrichthyes), Silver arowana (Osteichthyes) and a Nile crocodile (Tetrapoda).
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Olfactores
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Gegenbauer 1874

Gnathostomata (/ˌnæθˈstɒmətə/; from Greek: γνάθος (gnathos) "jaw" + στόμα (stoma) "mouth") are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living gnathostomes have true teeth (a characteristic which has subsequently been lost in some), paired appendages (pectoral and pelvic fins, arms, legs, wings, etc.),[2] the elastomeric protein of elastin,[3] and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons, and an adaptive immune system that has the discrete lymphoid organs of spleen and thymus,[4] and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene.[5]

It is now assumed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins.[6] Until recently these ancestors, known as antiarchs, were thought to have lacked pectoral or pelvic fins.[6] In addition to this, some placoderms (extinct fish with bony plates) 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.[7]

The Osteostraci (bony armored jawless fish) are generally considered the sister taxon of Gnathostomata.[2][8][9]

Jaw development in vertebrates is likely a product of the supporting gill arches. This development would help push water into the mouth by the movement of the jaw, so that it would pass over the gills for gas exchange. The repetitive use of the newly formed jaw bones would eventually lead to the ability to bite in some gnathostomes.[10]

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.[11] 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.[12] It also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes.[11] Fossil 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.[13][14]

Late Ordovician-aged microfossils of what have been identified as scales of either acanthodians[15] or "shark-like fishes",[16] 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.

  1. ^ a b Brazeau, M. D.; Friedman, M. (2015). "The origin and early phylogenetic history of jawed vertebrates". Nature. 520 (7548): 490–497. Bibcode:2015Natur.520..490B. doi:10.1038/nature14438. PMC 4648279. PMID 25903631.
  2. ^ 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.
  3. ^ Rodriguez-Pascual, Fernando (27 October 2021), "The Evolutionary Origin of Elastin: Is Fibrillin the Lost Ancestor?", in Sashank Madhurapantula, Rama; Orgel P.R.O., Joseph; Loewy, Zvi (eds.), Extracellular Matrix - Developments and Therapeutics, Biochemistry, vol. 23, IntechOpen, doi:10.5772/intechopen.95411, ISBN 978-1-83968-235-3, S2CID 233943453
  4. ^ Mitchell, Christian D.; Criscitiello, Michael F. (December 2020). "Comparative study of cartilaginous fish divulges insights into the early evolution of primary, secondary and mucosal lymphoid tissue architecture". Fish & Shellfish Immunology. 107 (Pt B): 435–443. doi:10.1016/j.fsi.2020.11.006. PMID 33161090. S2CID 226284286.
  5. ^ 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.
  6. ^ a b Zhu, Min (4 January 2012). "An antiarch placoderm shows that pelvic girdles arose at the root of jawed vertebrates". Biology Letters. 8 (3): 453–456. doi:10.1098/rsbl.2011.1033. PMC 3367742. PMID 22219394 – via Research Gate.
  7. ^ "The first vertebrate sexual organs evolved as an extra pair of legs". Archived from the original on 20 December 2016. Retrieved 4 July 2014.
  8. ^ 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. S2CID 32317622.
  9. ^ 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.
  10. ^ Gridi-Papp, Marcos (2018). "Comparative Oral+ENT Biology" (2018). Pacific Open Texts. 4. Pacific Open Texts.
  11. ^ 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. S2CID 4462506.
  12. ^ 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.
  13. ^ Choi, Charles Q. (17 October 2012). "Evolution's Bite: Ancient Armored Fish Was Toothy, Too". Live Science.
  14. ^ Rücklin, Martin; Donoghue, Philip C. J.; Johanson, Zerina; Trinajstic, Kate; Marone, Federica; Stampanoni, Marco (17 October 2012). "Development of teeth and jaws in the earliest jawed vertebrates". Nature. 491 (7426): 748–751. Bibcode:2012Natur.491..748R. doi:10.1038/nature11555. ISSN 1476-4687. PMID 23075852. S2CID 4302415.
  15. ^ Hanke, Gavin; Wilson, Mark (January 2004). "New teleostome fishes and acanthodian systematics". Journal of Vertebrate Paleontology: 187–214 – via Research Gate.
  16. ^ Sansom, Ivan J.; Smith, Moya M.; Smith, M. Paul (15 February 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. S2CID 4257631.

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