Ichthyostegalia

Source: Wikipedia, the free encyclopedia.

Ichthyostegalia
Ma

 Possibly emerged 395 Ma
Ichthyostega, the nominal genus.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Superclass: Tetrapoda
Order: †"Ichthyostegalia"
Säve-Söderbergh, 1932
Genera

See text

Ichthyostegalia is an

amphibians, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade.[1] While the group are recognized as having feet rather than fins, most, if not all, had internal gills
in adulthood and lived primarily as shallow water fish and spent minimal time on land.

The group evolved from elpistostegalian fish in the late Devonian,[2] or possibly in the middle Devonian.[3][4] They continued to thrive as denizens of swampland and tidal channels throughout the period. They gave rise to the Temnospondyli and then disappeared during the transition to the Carboniferous.[5]

Classification

Description

As first described, the order's sole member was

Stegocephalians, in that it combines a flat, heavily armoured stegocephalian skull with a fishlike tail bearing fin rays.[6] Later work on Ichthyostega and other Devonian Labyrinthodonts shows that they also had more than 5 digits to each foot, in fact the whole foot being fin-like.[7] Acanthostega, later found in the same locations, appears to have had a soft operculum and both it and Ichthyostega possessed functional internal gills as adults.[8][9]

The feet are only known from Ichthyostega, Acanthostega, and Tulerpeton, but appear to be polydactyl in all forms with more than the usual five digits for tetrapods and were paddle-like.[10] The tail bore true fin rays like those found in fish.[11]

The Ichthyostegalians were large to medium-sized, with an adult size form most genera on the order of a meter or more. Their heads were flat and massive, with a host of

arthropods and other invertebrate life along the tidal channels of the coal swamps. The vertebrae
were complex and rather weak. At the close of the Devonian, forms with progressively stronger legs and vertebrae evolved, and the later groups lacked functional gills as adults. As adults, the animals would have been heavy and clumsy on land, and would probably appear more as fish that occasionally went ashore rather than proper land animals. All were however predominately aquatic and some spent all or nearly all their lives in water.

Genera

The order Ichthyostegalia was erected for Ichthyostega, and contained until the 1980s only three genera (Ichthyostega,

cladistic
analyses indicate they are more advanced than Tiktaalik, though whether they actually had feet rather than fins is unknown. In order of discovery:

References

  1. ISBN 978-0-03-910754-3.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  2. ^ "Fossil Record of the Amphibia". ucmp.berkeley.edu. Retrieved 2022-10-03.
  3. S2CID 4428903
    .
  4. ^ Uppsala University (2010, January 8). Fossil footprints give land vertebrates a much longer history. ScienceDaily. Retrieved January 8, 2010, from https://www.sciencedaily.com/releases/2010/01/100107114420.htm
  5. S2CID 205212809
    .
  6. ^ Jarvik, E (1996). "The Devonian tetrapod Ichthyostega". Fossils & Strata. 40: 1–213.
  7. S2CID 4319165
    .
  8. S2CID 31298396
    .
  9. S2CID 4411060
    .
  10. S2CID 4319165
    .
  11. ^ Jarvik, E. (1996). "The Devonian tetrapod Ichthyostega". Fossils & Strata. 40: 1–213.
  12. Science Daily
    . Retrieved 28 February 2012.
  13. ^
    doi:10.1111/j.1475-4983.2011.01117.x
    .
  14. doi:10.1111/j.1475-4983.2004.00435.x
    .
  15. ^ Jarvik, E. (1952). "On the fish‐like tail in the ichthyostegid stegocephalians". Meddelelser om Grønland. 114: 1–90.
  16. ^ Lebedev, O.A. (1984). "The first find of a Devonian tetrapod vertebrate in the USSR". Doklady Akademii Nauk SSSR. Palaeontology (in Russian). 278: 1470–1473.
  17. doi:10.1080/03115517708527771
    .
  18. ^
    S2CID 4344655
    .
  19. S2CID 4364221
    .
  20. S2CID 2835592
    .
  21. doi:10.1111/j.1463-6395.2008.00361.x
    .
  22. S2CID 4420615
    .
  23. ^ Lebedev, O.L. (2004). "A new tetrapod Jakubsonia livnensis from the Early Famennian (Devonian) of Russia and palaeoecological remarks on the Late Devonian tetrapod habitats". Acta Universitatis Tatviensis. 679: 79–98.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Ichthyostegalia&oldid=1215519348"