User:Sceptic view/sandbox
Phylogenetic position
[edit]2006 - 2010
[edit]The phylogenetic analysis by Daeschler at al. placed Tiktaalik as a sister taxon to Elpistostege and directly below Panderichthys preceded by Eusthenopteron. Tiktaalik was thus inserted above Acanthostega and Ichthyostega as a transitional fossil[1] and a true "missing link"[2].
Such order of the phylogenetic tree was initially adopted by other experts, most notably by Per Ahlberg and Jennifer Clack[3]. However, it was questioned in a 2008 paper by Boisvert at al. who noted that Panderichthys, due to its more derived distal portion, might be closer to tetrapods than Tiktaalik or even that it was convergent with tetrapods[4]. Ahlberg, co-author of the study, considered the possibility of Tiktaalik's fin having been "an evolutionary return to a more primitive form."[5]
2010 - now
[edit]In January 2010 a group of paleontologists (including Ahlberg) published a paper[6] accompanied by extensive supplementary material[7] (discussed also in a Nature documentary[8][9]) which showed that first tetrapods appeared long before Tiktaalik and other elpistostegids. Their conclusions were based on numerous trackways (esp. Muz. PGI 1728.II.16) and individual footprints (esp. Muz. PGI 1728.II.1) discovered at the Zachełmie quarry in the Holy Cross Mountains (Poland). A tetrapod origin of those tracks was established based on:
- distinct digits and limb morphology;
- trackways reflecting quadrupedal gait and diagonal walk;
- no body or tail drag marks;
- very wide stride in relation to body length (much beyond that of Tiktaalik or any other fish);
- various size footprints with some unusually big (up to 26 cm wide) indicating body lenghts of over 2.5 m.
Track-bearing layers were assigned to the lower-middle Eifelian based on conodont index fossil samples (costatus Zone) and "previous biostratigraphic data obtained from the underlying and overlying strata"[6] with subsequent studies confirming this dating[10][11][12].
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Zachelmie_tracks_vs_selected_Devonian_fossils.svg/220px-Zachelmie_tracks_vs_selected_Devonian_fossils.svg.png)
Both Titaalik's discoverers were skeptical about the Zachelmie trackways. Edward Daeschler said that trace evidence was not enough for him to modify the theory of tetrapod evolution[13], while Neil Shubin argued that Tiktaalik could have produced very similar footprints[14] (in a later study Shubin expressed a significantly modified opinion that some of the Zachelmie footprints, those which lacked digits, may have been made by walking fish[15]). However, Ahlberg insisted that those tracks could not have possibly been formed either by natural processes or by transitional species such as Tiktaalik or Panderichthys[6][16]. Instead, the authors of the publication suggested ichthyostegalians as trackmakers, based on available pes morphology of those animals[6]. However, a 2012 study indicated that Zachelmie trackmakers were even more advanced than Ichthyostega in terms of quadrupedalism[17]. Grzegorz Niedźwiedzki's reconstruction of one of the trackmakers was identical to that of Tulerpeton[18][19].
Prof. Narkiewicz, co-author of the article on the Zachelmie trackways, claimed that the Polish "discovery has disproved the theory that elpistostegids were the ancestors of tetrapods"[20], a notion partially shared by Philippe Janvier[21]. There have been a number of new hypotheses suggested as to a possible origin and phylogenetic position of the elpistostegids (including Tiktaalik):
- their phylogenetic position remains unchanged and the footprints found in the Holy Cross Mountains are attributed to tetrapods but as a result there are at least six long ghost lineages separating Zachelmie trackmakers from various elpistostegalian and ichthyostegalian species[6];
- they were "an evolutionary dead-end"[23];
- they were a result of convergent or parallel evolution so that apomorphies and striking anatomical similarities found in both digited tetrapods and elpistostegalians evolved at least twice[24][25][26].
It should be noted that convergency is considered responsible for uniquely tetrapod features found also in other non-elpistostegalian fish from the period like Sauripterus (finger-like jointed distal radial bones)[27][28] or Tarrasius (tetrapod-like spine with 5 axial regions)[29].
Estimates published after the discovery of Zachelmie tracks suggested that digited tetrapods may have appeared as early as 427.4 Myr ago and questioned attempts to read absolute timing of evolutionary events in early tetrapod evolution from stratigraphy[25].
Until more data becomes available the phylogenetic position of Tiktaalik and other elpistostegids remains uncertain.
References
[edit]- ^ Daeschler, Edward B.; Shubin, Neil H.; Jenkins, Farish A., Jr (6 April 2006). "A Devonian tetrapod-like fish and the evolution of the tetrapod body plan" (PDF). Nature. 440 (7085): 757–763. Bibcode:2006Natur.440..757D. doi:10.1038/nature04639. PMID 16598249.
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: CS1 maint: multiple names: authors list (link) - ^ Rex Dalton (5 April 2006). "The fish that crawled out of the water". Nature. doi:10.1038/news060403-7.
- ^ Ahlberg, Per Erik; Clack, Jennifer A. (6 April 2006). "A firm step from water to land". Nature. 440 (7085): 747–749. Bibcode:2006Natur.440..747A. doi:10.1038/440747a. PMID 16598240.
- ^ Boisvert, Catherine A.; Mark-Kurik, Elga; Ahlberg, Per E. (4 December 2008). "The pectoral fin of Panderichthys and the origin of digits". Nature. 456 (7222): 636–638. Bibcode:2008Natur.456..636B. doi:10.1038/nature07339. PMID 18806778.
Given that recent phylogenies consistently place Panderichthys below Tiktaalik in the tetrapod stem group, it is surprising to discover that its pectoral fin skeleton is more limb-like than that of its supposedly more derived relative. [...] It is difficult to say whether this character distribution implies that Tiktaalik is autapomorphic, that Panderichthys and tetrapods are convergent, or that Panderichthys is closer to tetrapods than Tiktaalik.
- ^ Ker Than (September 24, 2008). "Ancient Fish Had Primitive Fingers, Toes". National Geographic News. National Geographic Society. Archived from the original on September 27, 2008.
Curiously, the radial bones of Panderichthys are more finger-like than those of Tiktaalik, a fish with stubby leg-like limbs that lived about five million years later. Many scientists regard Tiktaalik as a "missing link": the crucial transitional animal between fish and the first tetrapods. One possibility, Ahlberg said, is that finger development took a step backward with Tiktaalik, and that Tiktaalik's fins represented an evolutionary return to a more primitive form.
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- ^ a b c d e Niedźwiedzki, Grzegorz; Szrek, Piotr; Narkiewicz, Katarzyna; Narkiewicz, Marek; Ahlberg, Per E. (7 January 2010). "Tetrapod trackways from the early Middle Devonian period of Poland". Nature. 463 (7277): 43–48. Bibcode:2010Natur.463...43N. doi:10.1038/nature08623. PMID 20054388.
- ^ Niedźwiedzki, Grzegorz; Szrek, Piotr; Narkiewicz, Katarzyna; Narkiewicz, Marek; Ahlberg, Per E. (2010). "Tetrapod trackways from the early Middle Devonian period of Poland. Supplementary information". Nature. 463 (7277). Archived from the original on September 1, 2014.
- ^ Walking with tetrapods. Nature. January 6, 2010. Archived from the original (FLV) on December 20, 2014.
- ^ Jonathan Amos (6 January 2010). "Fossil tracks record 'oldest land-walkers'". BBC. Archived from the original on January 7, 2010.
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(help) - ^ Narkiewicz, Katarzyna; Narkiewicz, Marek (1 March 2010). "Mid Devonian carbonate platform development in the Holy Cross Mts. area (central Poland): new constraints from the conodont Bipennatus fauna". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 255 (3): 287–300. doi:10.1127/0077-7749/2009/0025.
- ^ Niedźwiedzki, Grzegorz; Narkiewicz, Marek; Szrek, Piotr (2014). "The age of the oldest tetrapod tracks from Zachełmie, Poland". Bulletin of Geosciences. 89 (3): 593–606.
- ^ Narkiewicz, Katarzyna; Narkiewicz, Marek (January 2015). "Middle Devonian invertebrate trace fossils from the marginal marine carbonates of the Zachełmie tetrapod tracksite, Holy Cross Mountains, Poland". Lethaia. 48 (1): 10–12. doi:10.1111/let.12083.
- ^
"Trace evidence is not enough for me to change my mind about accepted theories on tetrapod evolution"
- Edward Daeschler as quoted in Rex Dalton (January 6, 2010). "Discovery pushes back date of first four-legged animal". Nature. doi:10.1038/news.2010.1. Archived from the original on March 8, 2014.{{cite journal}}
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(help)"I am not ready to discard the established paradigm for the fish-tetrapod transition"
- Edward Daeschler as quoted in Jef Akst (January 6, 2010). "Tetrapods' old age revealed". The Scientist.{{cite news}}
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(help)"With all respect to the scientists involved in this study, there may be other explanations for these suggestive tracks."
- Edward Daeschler as quoted in Dan Vergano (January 6, 2010). "Four-legged finding muddies paleontological waters". USA Today. Archived from the original on December 24, 2014.{{cite news}}
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(help) - ^
[Neil Shubin] says that a model of Tiktaalik’s skeleton would produce a print much like the one in the paper if it’s mushed into sand, and different consistencies or angles would produce an even closer match. He adds, "There is nothing in Tiktaalik’s described anatomy that suggests it didn’t have a stride."
in Ed Yong (January 6, 2010). "Fossil tracks push back the invasion of land by 18 million years". Discover. Archived from the original on May 16, 2010.{{cite news}}
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(help) - ^ King, Heather M.; Shubin, Neil H.; Coates, Michael I.; Hale, Melina E. (December 27, 2011). "Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes". PNAS. 108 (52): 21146–21151. doi:10.1073/pnas.1118669109.
It follows that the attribution of some of the nondigited Devonian fossil trackways to limbed tetrapods may need to be revisited.
- ^
"You can see anatomical details consistent with a footprint, including sediments displaced by a foot coming down", "There is no way these could be formed by a natural process."
- Per Ahlberg as quoted in Rex Dalton (January 6, 2010). "Discovery pushes back date of first four-legged animal". Nature. doi:10.1038/news.2010.1. Archived from the original on March 8, 2014.{{cite journal}}
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(help) - ^ Pierce, Stephanie E.; Clack, Jennifer A.; Hutchinson, John R. (28 June 2012). "Three-dimensional limb joint mobility in the early tetrapod Ichthyostega" (PDF). Nature. 486 (7404): 523–526. doi:10.1038/nature11124. PMID 22722854.
- ^ a b Niedźwiedzki, Grzegorz; Szrek, Piotr (2010). "Way to Go!" (PDF). ACADEMIA. 2 (26). Polish Academy of Sciences: 28–31. ISSN 1731-7401. OCLC 786293607. Archived from the original (PDF) on January 19, 2015.
- ^ The 2007 artistic restoration of Tulerpeton by Dmitry Bogdanov available at Wikimedia is virtually identical to the 2008 rendering of a Zachelmie trackmaker by Grzegorz Niedźwiedzki.
- ^ W.Ż. (February 4, 2010). "A Creature That Time Forgot". The Warsaw Voice. Warsaw. Archived from the original on December 22, 2014.
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(help); "W Polsce odkryto ślady najstarszych kopalnych czworonogów" [Oldest tetrapod fossil footprints discovered in Poland]. Science & Scholarship in Poland (Polish Press Agency) (in Polish). Warsaw. January 7, 2010. Archived from the original on December 22, 2014. - ^
"We now have to invent a common ancestor to the tetrapods and elpistostegids."
- Philippe Janvier as quoted in Karen McVeigh (January 6, 2010). "Footprints show tetrapods walked on land 18m years earlier than thought". The Guardian. London. Archived from the original on March 2, 2014.{{cite news}}
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(help) - ^ "Four feet in the past: trackways pre-date earliest body fossils". Nature. 463 (7277). 7 January 2010. Archived from the original on November 3, 2012.
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ignored (help) - ^ "Ancient Four-Legged Beasts Leave Their Mark". Science. 6 January 2010. Archived from the original on September 30, 2013.
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(help) - ^ Janvier, Philippe; Clément, Gaël (7 January 2010). "Muddy tetrapod origins". Nature. 463 (7277): 40–41. doi:10.1038/463040a. PMID 20054387.
- ^ a b Friedman, Matt; Brazeau, Martin D. (7 February 2011). "Sequences, stratigraphy and scenarios: what can we say about the fossil record of the earliest tetrapods?". Proceedings of the Royal Society B. 278 (1704): 432–439. doi:10.1098/rspb.2010.1321. PMID 20739322. Archived from the original on December 22, 2014.
- ^ Gee, Henry (January 6, 2010). "First Footing". SciLogs. Archived from the original on December 22, 2014.
It is possible that the close similarity between elpistostegids and tetrapods might have been the result of evolutionary convergence. The common ancestor of elpistostegids and tetrapods wouldn't have to have looked like Tiktaalik – it could have been a more undifferentiated, tetrapodomorph fish. Elpistostegids and tetrapodomorphs, each following their own paths, grew to look more and more like one other.
- ^ Daeschler, Edward B.; Shubin, Neil (8 January 1998). "Fish with fingers?". Nature. 391 (6663): 133–133. doi:10.1038/34317.
- ^ Davis, Marcus C.; Shubin, Neil; Daeschler, Edward B. (2004). "A new specimen of Sauripterus taylori (Sarcopterygii, Osteichthyes) from the Famennian Catskill Formation of North America". Journal of Vertebrate Paleontology. 24 (1): 26–40. doi:10.1671/1920-3.
- ^ Sallan, Lauren Cole (22 August 2012). "Tetrapod-like axial regionalization in an early ray-finned fish" (PDF). Proceedings of the Royal Society B. 279 (1741): 3264–3271. doi:10.1098/rspb.2012.0784. PMID 22628471. Archived from the original (PDF) on January 3, 2015.
Comparison of with tetrapod-like features
[edit]A number of fish, both extant and prehistoric, have featured some characteristics typical of tetrapods.
Species | venturing onto land | tetrapod-like spine | tetrapod-like appendages | digit-like bones | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
5 axial regions | interlocking vertebrae | fully ossified vertebrae | shoulder & skull separation | functional 'intra-fin' joints | fins adapted for walking rather than swimming | strong & muscled fins | humerus, radius & ulna bones | differentiated distal radial bones | jointed distal radial bones | ||
Panderichthys rhombolepis † | ? | No | No | No | No | ? | No | Yes | Yes | Yes[1] | No |
Sauripterus taylori † | ? | No | No | No | No | ? | No | Yes | Yes | Yes | Yes[2] |
Tarrasius problematicus † | ? | Yes[3] | No | No | No | No | No | No | No | No | No |
Tiktaalik roseae † | ? | No | No | No | Yes | Yes | No | Yes | Yes | No | No |
Atractosteus spatula | No | No | Yes | No | No | No | No | No | No | No | No |
Leptolepis koonwarriensis † | ? | No | No | Yes[4] | No | No | No | No | No | No | No |
Eastmanosteus pustulosus † | ? | No | No | No | Yes[5] | No | No | No | No | No | No |
Periophthalmus papilio | Yes | No | No | No | No | Yes[6][7] | No | No | No | No | No |
Brachionichthys hirsutus | No | No | No | No | No | No | Yes | No | No | No | No |
Ogcocephalus darwini | No | No | No | No | No | No | Yes | No | No | No | No |
Antennarius maculatus | No | No | No | No | No | No | Yes | No | No | No | No |
Protopterus annectens | Yes | No | No | No | No | No | ?[8] | No | No | No | No |
Latimeria chalumnae | No | No | No | No | No | No | No | Yes | No | No | No |
Polypterus bichir lapradei | Yes | No | No | No | No | No | No | Yes | No | No | No |
References
[edit]- ^ "The pectoral fin of Panderichthys and the origin of digits". Nature. 456 (7222): 636–638. 4 December 2008. Bibcode:2008Natur.456..636B. doi:10.1038/nature07339. PMID 18806778.
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ignored (help) - ^ "Fish with Fingers?". Nature. 391 (6663): 133–133. 8 January 1998. doi:10.1038/34317.
{{cite journal}}
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ignored (help) - ^ "Tetrapod-like axial regionalization in an early ray-finned fish" (PDF). Proceedings of the Royal Society B. 279 (1741): 3264–3271. 23 May 2012. doi:10.1098/rspb.2012.0784.
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ignored (help) - ^ Shukla, J.P. (2007). Fish & Fisheries. Rastogi Publications. pp. 24–25. ISBN 81-7133-800-3.
- ^ "Fossil Musculature of the Most Primitive Jawed Vertebrates". Science. 341 (6142): 160–164. 12 July 2013. doi:10.1126/science.1237275.
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ignored (help) - ^ "Propulsive Forces of Mudskipper Fins and Salamander Limbs during Terrestrial Locomotion: Implications for the Invasion of Land" (PDF). Integrative and Comparative Biology. 53: 283–294. August 2, 2013. doi:10.1093/icb/ict051. PMID 23667046.
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ignored (help) - ^ "Mudskipper pectoral fin kinematics in aquatic and terrestrial environments" (PDF). The Journal of Experimental Biology. 212: 2279–2286. July 15, 2009. doi:10.1242/jeb.029041. PMID 19561218.
{{cite journal}}
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ignored (help) - ^ "Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes". PNAS. 108 (52): 21146–51. 27 December 2011. doi:10.1073/pnas.1118669109.
{{cite journal}}
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ignored (help)