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{{short description|The state of having more than five digits in ancient fish and tetrapods}}
{{short description|The state of having more than five digits in ancient fish and tetrapods}}
[[File:Fishapods tetrapods.JPG|thumb|right|500px|Limb evolution: A. ''[[Eusthenopteron]]'', B. ''[[Gogonasus]]'', C. ''[[Panderichthys]]'', D. ''[[Tiktaalik]]'', E. ''[[Acanthostega]]'', F. ''[[Ichthyostega]]'' ( hindleg ), and G. ''[[Tulerpeton]]''. ]]
[[File:Fishapods tetrapods.JPG|thumb|right|500px|Limb evolution: A. ''[[Eusthenopteron]]'', B. ''[[Gogonasus]]'', C. ''[[Panderichthys]]'', D. ''[[Tiktaalik]]'', E. ''[[Acanthostega]]'', F. ''[[Ichthyostega]]'' ( hindleg ), and G. ''[[Tulerpeton]]''. ]]
'''Polydactyly in stem-tetrapods''' should here be understood as having more than five digits to the finger or foot, a condition that was the natural state of affairs in the very first [[Stegocephalia|stegocephalians]] during the [[Vertebrate land invasion|evolution of terrestriality]]. The polydactyly in these largely [[aquatic animal]]s is not to be confused with [[polydactyly]] in the medical sense, i.e. it was not an anomaly in the sense it was not a [[congenital disorder|congenital condition]] of having more than the typical number of [[digit (anatomy)|digit]]s for a given [[taxon]].<ref name=hall>''Evolutionary developmental biology'', by Brian Keith Hall, 1998, {{ISBN|0-412-78580-3}}, [https://books.google.com/books?id=JhSwumfgTQ4C&pg=PA262&dq=polydactyly+tetrapods p. 262]</ref> Rather, it appears to be a result of the early [[evolution]] from a limb with a [[fin]] rather than digits.
'''Polydactyly in stem-tetrapods''' should here be understood as having more than five digits to the finger or foot, a condition that was the natural state of affairs in the very first [[Stegocephalia|stegocephalians]] during the [[Vertebrate land invasion|evolution of terrestriality]]. The polydactyly in these largely [[aquatic animal]]s is not to be confused with [[polydactyly]] in the medical sense, i.e. it was not an anomaly in the sense it was not a [[congenital disorder|congenital condition]] of having more than the typical number of [[digit (anatomy)|digit]]s for a given [[taxon]].<ref name=hall>{{cite book |last1=Hall |first1=Brian K. |title=Evolutionary Developmental Biology |date=1998 |publisher=Springer Science & Business Media |isbn=978-0-412-78580-1 |page=262 }}</ref> Rather, it appears to be a result of the early [[evolution]] from a limb with a [[fin]] rather than digits.


[[Tetrapod]]s evolved from animals with fins such as found in [[lobe-finned fish]]es. From this condition a new pattern of limb formation evolved, where the development axis of the limb rotated to sprout secondary axes along the lower margin, giving rise to a variable number of very stout skeletal supports for a paddle-like foot.<ref>Coates, M.I. and Clack, J.A. (1990): Polydactyly in the earliest known tetrapod limbs. ''[[Nature (journal)|Nature]]'', 347, pp.66-69.</ref> The condition is thought to have arisen from the loss of the [[Fish anatomy#Spines and rays|fin ray]]-forming proteins [[actinodin 1]] and [[actinodin 2]] or modification of the expression of [[HOXD13]].<ref name="zhang2010">{{Cite journal | last1 = Zhang | first1 = J. | last2 = Wagh | first2 = P. | last3 = Guay | first3 = D. | last4 = Sanchez-Pulido | first4 = L. | last5 = Padhi | first5 = B. K. | last6 = Korzh | first6 = V. | last7 = Andrade-Navarro | first7 = M. A. | last8 = Akimenko | first8 = M. A.| title = Loss of fish actinotrichia proteins and the fin-to-limb transition | journal = Nature | volume = 466 | issue = 7303 | pages = 234–237 | year = 2010 | pmid = 20574421 | doi = 10.1038/nature09137|bibcode = 2010Natur.466..234Z }}</ref><ref>{{cite journal|last1=Schneider|first1=Igor|last2=Shubin|first2=Neil H.|title=Making Limbs from Fins|journal=Developmental Cell|date=December 2012|volume=23|issue=6|pages=1121–1122|doi=10.1016/j.devcel.2012.11.011|pmid=23237946|doi-access=free}}</ref>
[[Tetrapod]]s evolved from animals with fins such as found in [[lobe-finned fish]]es. From this condition a new pattern of limb formation evolved, where the development axis of the limb rotated to sprout secondary axes along the lower margin, giving rise to a variable number of very stout skeletal supports for a paddle-like foot.<ref>{{cite journal |last1=Coates |first1=M. I. |last2=Clack |first2=J. A. |title=Polydactyly in the earliest known tetrapod limbs |journal=Nature |date=September 1990 |volume=347 |issue=6288 |pages=66–69 |doi=10.1038/347066a0 }}</ref> The condition is thought to have arisen from the loss of the [[Fish anatomy#Spines and rays|fin ray]]-forming proteins [[actinodin 1]] and [[actinodin 2]] or modification of the expression of [[HOXD13]].<ref name="zhang2010">{{cite journal |last1=Zhang |first1=Jing |last2=Wagh |first2=Purva |last3=Guay |first3=Danielle |last4=Sanchez-Pulido |first4=Luis |last5=Padhi |first5=Bhaja K. |last6=Korzh |first6=Vladimir |last7=Andrade-Navarro |first7=Miguel A. |last8=Akimenko |first8=Marie-Andrée |title=Loss of fish actinotrichia proteins and the fin-to-limb transition |journal=Nature |date=July 2010 |volume=466 |issue=7303 |pages=234–237 |doi=10.1038/nature09137 |pmid=20574421 }}</ref><ref>{{cite journal |last1=Schneider |first1=Igor |last2=Shubin |first2=Neil H. |title=Making Limbs from Fins |journal=Developmental Cell |date=December 2012 |volume=23 |issue=6 |pages=1121–1122 |doi=10.1016/j.devcel.2012.11.011 |pmid=23237946 }}</ref>


Early groups like ''[[Acanthostega]]'' had eight digits, while the more derived ''[[Ichthyostega]]'' had seven digits, the yet-more derived ''[[Tulerpeton]]'' had six toes.<ref name=hall/> ''[[Crassigyrinus]]'' from the fossil-poor [[Romer's gap]] in early [[Carboniferous]] is usually thought to have had five digits to each foot. The [[Anthracosauria|Anthracosaurs]], which may be stem-tetrapods <ref>Laurin, M. 1998. The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I. Systematics, middle ear evolution, and jaw suspension. Annales des Sciences Naturelles, Zoologie, Paris, 13e Série 19:1-42</ref><ref>Marjanović, D. and M. Laurin. 2009. [https://doi.org/10.1007%2Fs11692-009-9065-8 The origin(s) of modern amphibians: a commentary. Evolutionary Biology 36:336–338].</ref> or reptiliomorphs,<ref>Gauthier, J., A. G. Kluge, and T. Rowe. 1988. The early evolution of the Amniota; pp. 103-155 in M. J. Benton (ed.), The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds. Clarendon Press, Oxford</ref> retained the five-toe pattern still found in [[Amniotes]], while further reduction had taken place on other [[Labyrinthodont]] lines, leaving the forefoot with four toes and the hind foot with five, a pattern still found in [[Lissamphibia|modern amphibians]].<ref>[[Michael Benton|Benton, M.]] (2005): [[Vertebrate Palaeontology (Benton)|Vertebrate Palaeontology]] 3rd edition. Blackwell Publishing</ref> The increasing knowledge of Labyrinthodonts from Romer's gap has led to the challenging of the hypothesis that [[pentadactyly]], as displayed by most modern tetrapods, is [[plesiomorphic]]. The number of digits was once thought to have been reduced in [[amphibians]] and [[reptiles]] independently,<ref name=hall/><ref>Coates, M. I. 1991. New palaeontological contributions to limb ontogeny and phylogeny; pp. 325-337 in J. R. Hincliffe, J. M. Hurle, and D. Summerbell (ed.), Developmental Patterning of the Vertebrate Limb. Plenum Press in cooperation with NASO Scientific Affairs Division, New York</ref> but more recent studies suggest that a single reduction occurred, along the tetrapod stem, in the Late Devonian or Early Carboniferous.<ref>Laurin, M. 1998. [https://www.jstor.org/stable/2411316 A reevaluation of the origin of pentadactyly. Evolution 52:1476-1482]</ref><ref>Ruta, M. and M. I. Coates. 2007. Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology 5:69-122</ref> However, even the early [[Ichthyostegalia]]ns like ''Acanthostega'' and ''Ichthyostega'' appear to have had the forward ossified bony toes combined in a single stout digit, making them effectively five-toed.
Early groups like ''[[Acanthostega]]'' had eight digits, while the more derived ''[[Ichthyostega]]'' had seven digits, the yet-more derived ''[[Tulerpeton]]'' had six toes.<ref name=hall/> ''[[Crassigyrinus]]'' from the fossil-poor [[Romer's gap]] in early [[Carboniferous]] is usually thought to have had five digits to each foot. The [[Anthracosauria|Anthracosaurs]], which may be stem-tetrapods<ref>{{cite journal |last1=Laurin |first1=Michel |title=The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I. Systematics, middle ear evolution and jaw suspension |journal=Annales des Sciences Naturelles - Zoologie et Biologie Animale |date=January 1998 |volume=19 |issue=1 |pages=1–42 |doi=10.1016/S0003-4339(98)80132-9 }}</ref><ref>{{cite journal |last1=Marjanović |first1=David |last2=Laurin |first2=Michel |title=The Origin(s) of Modern Amphibians: A Commentary |journal=Evolutionary Biology |date=September 2009 |volume=36 |issue=3 |pages=336–338 |doi=10.1007/s11692-009-9065-8 }}</ref> or reptiliomorphs,<ref>{{cite book |last1=Gauthier |first1=J. |first2=A. G. |last2=Kluge |first3=T. |last3=Rowe |year=1988 |chapter=The early evolution of the Amniota |pages=103-155 |editor1-last=Benton |editor1-first=Michael J. |title=The Phylogeny and Classification of the Tetrapods: Amphibians, reptiles, birds. Vol. 1 |publisher=Systematics Association |isbn=978-0-19-857705-8 }}</ref> retained the five-toe pattern still found in [[Amniotes]], while further reduction had taken place on other [[Labyrinthodont]] lines, leaving the forefoot with four toes and the hind foot with five, a pattern still found in [[Lissamphibia|modern amphibians]].<ref>[[Michael Benton|Benton, M.]] (2005): [[Vertebrate Palaeontology (Benton)|Vertebrate Palaeontology]] 3rd edition. Blackwell Publishing{{pn}}</ref> The increasing knowledge of Labyrinthodonts from Romer's gap has led to the challenging of the hypothesis that [[pentadactyly]], as displayed by most modern tetrapods, is [[plesiomorphic]]. The number of digits was once thought to have been reduced in [[amphibians]] and [[reptiles]] independently,<ref name=hall/><ref>{{cite journal |doi=10.1007/978-1-4615-3310-8_43 |s2cid=86020906 }}</ref> but more recent studies suggest that a single reduction occurred, along the tetrapod stem, in the Late Devonian or Early Carboniferous.<ref>{{cite journal |last1=Laurin |first1=Michel |title=A Reevaluation of the Origin of Pentadactyly |journal=Evolution |date=1998 |volume=52 |issue=5 |pages=1476–1482 |jstor=2411316 }}</ref><ref>{{cite journal |last1=Ruta |first1=Marcello |last2=Coates |first2=Michael I. |title=Dates, nodes and character conflict: Addressing the Lissamphibian origin problem |journal=Journal of Systematic Palaeontology |date=January 2007 |volume=5 |issue=1 |pages=69–122 |doi=10.1017/S1477201906002008 }}</ref> However, even the early [[Ichthyostegalia]]ns like ''Acanthostega'' and ''Ichthyostega'' appear to have had the forward ossified bony toes combined in a single stout digit, making them effectively five-toed.


== See also ==
== See also ==

Revision as of 22:28, 5 October 2020

Limb evolution: A. Eusthenopteron, B. Gogonasus, C. Panderichthys, D. Tiktaalik, E. Acanthostega, F. Ichthyostega ( hindleg ), and G. Tulerpeton.

Polydactyly in stem-tetrapods should here be understood as having more than five digits to the finger or foot, a condition that was the natural state of affairs in the very first stegocephalians during the evolution of terrestriality. The polydactyly in these largely aquatic animals is not to be confused with polydactyly in the medical sense, i.e. it was not an anomaly in the sense it was not a congenital condition of having more than the typical number of digits for a given taxon.[1] Rather, it appears to be a result of the early evolution from a limb with a fin rather than digits.

Tetrapods evolved from animals with fins such as found in lobe-finned fishes. From this condition a new pattern of limb formation evolved, where the development axis of the limb rotated to sprout secondary axes along the lower margin, giving rise to a variable number of very stout skeletal supports for a paddle-like foot.[2] The condition is thought to have arisen from the loss of the fin ray-forming proteins actinodin 1 and actinodin 2 or modification of the expression of HOXD13.[3][4]

Early groups like Acanthostega had eight digits, while the more derived Ichthyostega had seven digits, the yet-more derived Tulerpeton had six toes.[1] Crassigyrinus from the fossil-poor Romer's gap in early Carboniferous is usually thought to have had five digits to each foot. The Anthracosaurs, which may be stem-tetrapods[5][6] or reptiliomorphs,[7] retained the five-toe pattern still found in Amniotes, while further reduction had taken place on other Labyrinthodont lines, leaving the forefoot with four toes and the hind foot with five, a pattern still found in modern amphibians.[8] The increasing knowledge of Labyrinthodonts from Romer's gap has led to the challenging of the hypothesis that pentadactyly, as displayed by most modern tetrapods, is plesiomorphic. The number of digits was once thought to have been reduced in amphibians and reptiles independently,[1][9] but more recent studies suggest that a single reduction occurred, along the tetrapod stem, in the Late Devonian or Early Carboniferous.[10][11] However, even the early Ichthyostegalians like Acanthostega and Ichthyostega appear to have had the forward ossified bony toes combined in a single stout digit, making them effectively five-toed.

See also

References

  1. ^ a b c Hall, Brian K. (1998). Evolutionary Developmental Biology. Springer Science & Business Media. p. 262. ISBN 978-0-412-78580-1.
  2. ^ Coates, M. I.; Clack, J. A. (September 1990). "Polydactyly in the earliest known tetrapod limbs". Nature. 347 (6288): 66–69. doi:10.1038/347066a0.
  3. ^ Zhang, Jing; Wagh, Purva; Guay, Danielle; Sanchez-Pulido, Luis; Padhi, Bhaja K.; Korzh, Vladimir; Andrade-Navarro, Miguel A.; Akimenko, Marie-Andrée (July 2010). "Loss of fish actinotrichia proteins and the fin-to-limb transition". Nature. 466 (7303): 234–237. doi:10.1038/nature09137. PMID 20574421.
  4. ^ Schneider, Igor; Shubin, Neil H. (December 2012). "Making Limbs from Fins". Developmental Cell. 23 (6): 1121–1122. doi:10.1016/j.devcel.2012.11.011. PMID 23237946.
  5. ^ Laurin, Michel (January 1998). "The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I. Systematics, middle ear evolution and jaw suspension". Annales des Sciences Naturelles - Zoologie et Biologie Animale. 19 (1): 1–42. doi:10.1016/S0003-4339(98)80132-9.
  6. ^ Marjanović, David; Laurin, Michel (September 2009). "The Origin(s) of Modern Amphibians: A Commentary". Evolutionary Biology. 36 (3): 336–338. doi:10.1007/s11692-009-9065-8.
  7. ^ Gauthier, J.; Kluge, A. G.; Rowe, T. (1988). "The early evolution of the Amniota". In Benton, Michael J. (ed.). The Phylogeny and Classification of the Tetrapods: Amphibians, reptiles, birds. Vol. 1. Systematics Association. pp. 103–155. ISBN 978-0-19-857705-8.
  8. ^ Benton, M. (2005): Vertebrate Palaeontology 3rd edition. Blackwell Publishing[page needed]
  9. ^ . doi:10.1007/978-1-4615-3310-8_43. S2CID 86020906. {{cite journal}}: Cite journal requires |journal= (help); Missing or empty |title= (help)
  10. ^ Laurin, Michel (1998). "A Reevaluation of the Origin of Pentadactyly". Evolution. 52 (5): 1476–1482. JSTOR 2411316.
  11. ^ Ruta, Marcello; Coates, Michael I. (January 2007). "Dates, nodes and character conflict: Addressing the Lissamphibian origin problem". Journal of Systematic Palaeontology. 5 (1): 69–122. doi:10.1017/S1477201906002008.
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