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The appearance of fish is theoretically considered to have occurred during the Cambrian explosion, about 530 million years ago. Chordates had the skull and the vertebral column, but no jaw. These jawless fish are classed as Agnatha, which included the Haikouichthys.[1][2] The Devonian period often dubbed the "Age of Fish", saw the first appearance of ray-finned and lobe-finned bony fish. By the start of the Early Devonian 419 mya, jawed fish had appeared into four distinct clades: the placoderms and spiny sharks, both of which are now extinct, and the cartilaginous and bony fish, both of which are still extant. During the Middle Devonian 393–383 Ma, the armoured jawless ostracoderm fish were declining in diversity. Most jawless fish are now extinct, because they had more difficulty surviving than fish with jaws. The Mesozoic jawed fish were thriving and increasing in diversity in both the oceans and freshwater since 247 Ma, the largest class being Teleosts, which are economically important to humans.[3]

Fish

DiversityEdit

Early Triassic—251.902 Ma / 247.2 Ma (million years ago)

See also (Day 5)

The largest most diverse class of fish appeared after the Permian–Triassic extinction event ("The Great Dying") of 252 Ma, in an explosion of a variety of fish called Teleosts, which have been economically important throughout human history.[4]

The teleosts or Teleostei (Greek: teleios, "complete" + osteon, "bone") are by far the largest infraclass in the class Actinopterygii, the ray-finned fishes,[fn 1] and make up 96% of all extant species of fish. This diverse group arose in the Triassic period, and members are arranged in about 40 orders and 448 families. Over 26,000 species have been described. Teleosts range from giant oarfish measuring 7.6 m () or more, and ocean sunfish weighing over 2 t (2.2 short tons), to the minute male anglerfish Photocorynus spiniceps, just 6.2 mm () long. Including not only torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take specialised shapes as in anglerfish and seahorses. Teleosts dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps.

The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth. In more derived teleosts, the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a lever, pushing and pulling the premaxilla as the mouth is opened and closed. Other bones further back in the mouth serve to grind and swallow food.[5] Another difference is that the upper and lower lobes of the tail (caudal) fin are about equal in size.[6] The spine ends at the caudal peduncle, distinguishing this group from other fish in which the spine extends into the upper lobe of the tail fin.[7]

See alsoEdit

NotesEdit

  1. The other two infraclasses are the Holostei (bowfins and garfish) and the paraphyletic Chondrostei (sturgeons and reedfish).

ReferencesEdit

  1. Shu, D-G.; Luo, H-L.; Conway Morris, S.; Zhang, X-L.; Hu, S-X.; Chen, L.; Han, J.; Zhu, M.; et al. (November 4, 1999). "Lower Cambrian vertebrates from south China". Nature 402 (6757): 42–46. doi:10.1038/46965. Bibcode1999Natur.402...42S. 
  2. Dawkins 2004, p. 357.
  3. "Capture production by principal species in 2012". Fishery and Aquaculture Statistics 2012. Food and Agriculture Organization. p. 12. 
  4. "Capture production by principal species in 2012". Fishery and Aquaculture Statistics 2012. Food and Agriculture Organization. p. 12. 
  5. Vandewalle, P.; Parmentier, E.; Chardon, M. (2000). "The branchial basket in Teleost feeding". Cybium 24 (4): 319–42. ISSN 0399-0974. http://www.vliz.be/imisdocs/publications/237770.pdf. 
  6. Benton, Michael (2005). "The Evolution of Fishes After the Devonian". Vertebrate Palaeontology (3rd ed.). John Wiley & Sons. pp. 175–84. ISBN 978-1-4051-4449-0. https://books.google.com/books?id=VThUUUtM8A4C&pg=PA175. 
  7. Moriyama, Y.; Takeda, H. (2013). "Evolution and development of the homocercal caudal fin in teleosts". Development, Growth & Differentiation 55 (8): 687–98. doi:10.1111/dgd.12088.