Talk:Evolution of tetrapods

Comments from Ecapelle

• Expansion on the origin could add to the history of the article. More evolution information on pre-tetrapods.

• Palaezoic tetrapods: citations needed.

• Add to Cenozoic tetrapods (empty).

• Pictures of fin versus bony foot and the evolution among them could supplement the article.

Ecapelle (talk) 04:12, 24 March 2014 (UTC)

Usefulness of this article?

Is the article in it's current form actually necessary? It seems to just copy content from the tetrapod article. IMO, 1 of the articles should be changed or this article should be deleted. Blaylockjam10 (talk) 05:45, 9 April 2014 (UTC)

Looking at Talk:Tetrapod/Archives/2023/December#Evolution_of_Tetrapods it seems like the intent was to spin off a section from the tetrapod article as a standalone article but the original article was never updated to summarise the spun-off section. I've made an attempt at that. To do things properly, the main "evolution of tetrapods" article will need its lead updated more in line with other "evolution of" articles and some of these changes should be merged in. On the other hand, I'm not sure this split really works as much of the remainder of the tetrapod article is about early tetrapods so needs the evolution section to put it in context.TuxLibNit (talk) 23:25, 29 May 2014 (UTC)

In this edit I merged in the changes others had made to the Tetrapod copy before I summarised it. In these edits I refactored the lead, section headings etc to fit a basic "Evolution of" style. So all the actions I identified above as "to do" are now done. I'm still not convinced that this split is working but at least both articles do now reflect the intent to split. TuxLibNit (talk) 00:28, 1 June 2014 (UTC)

Front page:

• Wikipedia:Today's featured article/April 25, 2015

Amphibians is running on the 25th, and this article is linked to in the blurb. It might make sense to improve the article before the 25th. --Harizotoh9 (talk) 13:23, 9 April 2015 (UTC)

First paragraph of lede needs work.

First it says "the earliest tetrapods derived from neither lobe-finned fishes nor ray-finned fishes." Everybody knows that humans, mammals, birds, dinosaurs, and all other tetrapods belong to the clade of lobe-finned fishes, also known as fleshy-limbed vertebrates. Even the reference cited says as much if you actually read it.

Next, the second footnote references a 1997 paper by Jenifer Clack which she has since retracted in light of the 2010 trackway discovery in Poland. Zyxwv99 (talk) 20:14, 2 May 2015 (UTC)

I have fixed the first error, but disagree with the second. I can find no formal retraction of Clack's 1997 paper, nor anything in the 2010 that contradicts either the paper or the statement on the page. Of the two trackways described in the 2010 paper, the authors explicitly hypothesize one is subaquatic, and make no mention of the other in that regard. However, the lack of tail or body drag suggests both are formed by aquatic walking. HCA (talk) 03:02, 3 May 2015 (UTC)

Two versions of the the 2012 edition of Clack's book Gaining Ground are available on Google Books. If you find the book on Google Books, then click on "more editions" you will see the 2002 and two 2012 editions. Try clicking on the bottom one of the 2012 editions. Then search on the word "Poland." Here you will see several pages updating and revising what she said in the 2002 edition, which was similar to the 1997 research paper. Fortunately, she didn't actually have to "retract" anything. That's because she never made any definitive claims to begin with. Instead, she criticized other paleontologists for over-interpreting the evidence, reading more into it than was there. She also acknowledged that future fossil finds could prove that they were right after all. In the 2012 editions she expresses astonishment at the new finds and acknowledges that the paleontologists she had criticized might not have been so wrong after all. She also mentions raindrop impressions and dessication cracks associated with the Polish tetrapod trackways, not something one would expect to find under water.

Although the 2010 paper from Poland is behind a paywall, the supplementary material is freely available. here "Trackway of a walking animal preserved on a semi-dry surface with raindrop structures" "tracks preserved on thin and dry microbial mats" "probably made by walking animals in subaerial conditions" "Trackway of a walking animal preserved on a semi-dry surface with raindrop structures". Zyxwv99 (talk) 21:32, 3 May 2015 (UTC)

So, there's a number of problems with the referenced statement. First, I think the statement about the inability to move on land is almost certainly incorrect, based on a variety of extant organisms which manage just fine with less specialized morphologies (e.g. walking catfish), as well as a forthcoming (but as yet unpublished) paper. That said, current trackways are highly ambiguous - even the cracked mud could have formed *after* the subaquatic trakcway bed was exposed due to tide or drought. On top of that, I'm extremely suspicious of any putative subaerial trackway that doesn't have belly/body drag or at least tail drag, as it would require not just the strength and morphology to lift the entire body clear of the substrate but also the entire tail. I propose we dodge the entire issue for now, and state something to the effect of how known trackways are ambiguous and the extent of the terrestrial locomotion of early tetrapods is unknown. HCA (talk) 22:29, 3 May 2015 (UTC)

You seem to be confusing "early" with "basal." Although the tetrapods that made the Polish trackways are chronologically early, the are universally accepted as nowhere near basal (and therefore not necessarily belly-draggers). The discovery of these trackways has revolutionized tetrapod studies in the same way as the asteroid theory has revolutionized our understanding of how the non-avian dinosaurs became extinct. If you want to sidestep the modern scientific consensus and continue with you own original research, please feel free. Zyxwv99 (talk) 20:50, 4 May 2015 (UTC)

I used the term "early" because that's a word in the sentence we're discussing; I am perfectly aware of the differences between early and basal, as well as the implications of these tracks. The sentences under discussion claim that "...little evidence supports the idea that any of the earliest tetrapods could move about on land..." because "...the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water." Now, logically think it through: If the Poland tracks were formed subaquatically, they do not refute that sentence. If the Poland tracks were made subaerially, the lack of a body drag suggests they were made by more morphologically derived tetrapods (in spite of their early date), which, in turn, means that they must have been preceded by more morphologically primitive (and yet undiscovered) forms of uncertain terrestrial capabilities. Again, the sentence is technically correct, because, while the trackway makers would be both terrestrial and chronologically early, they must have been preceded by still earlier undiscovered forms, unless you wish to argue that the Poland tracks (and tetrapod evolution) are the product of a Hopeful Monster.

The sentence could clearly be revised and clarified, but without leaping to conclusions not supported by the text of the suggested citation. HCA (talk) 02:51, 6 May 2015 (UTC)

You're right. Now I'm looking at this part of the first paragraph: "While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water." The first part makes total sense, just not for the reasons given. Tetrapod trackways in Scotland show belly-dragging alongside tracks made without belly-dragging. This is generally understood to mean that belly-dragging occurred when the tide was lower, while non-belly-dragging occurred with the tide was higher and much of the animal's weight was supported by water. Zooming out and looking at the big picture, we have no fossils or tracks of the first tetrapods. They are thought to have been fully aquatic, using their "four legs bearing digits" mainly as paddles, and only occasionally venturing onto land or water so shallow that they might have used their paddles in the manner of a seal with it's flippers. For the earliest tetrapods it's more a question of definition than evidence. Tetrapods are defined (by paleontologists, apomorphically) as tetrapodomorphs with four legs bearing digits, with the understanding that digits are found in fully aquatic animals (various ray-finned fishes) that don't use them for walking, much less on dry land. Zyxwv99 (talk) 18:43, 6 May 2015 (UTC)

IMHO, the problem is how to convey this simply and clearly in one or two sentences, without getting bogged down in details, since it's a lede. Maybe something like "While most modern tetrapods are terrestrial, the early tetrapods and their relatives may have had significant difficulty moving on land." It's a bit weasel-wordy, but it also captures that there's a range of terrestrial locomotion difficulty and outcomes, from "stuggles to make any progress at all" to "effective and consistent but slow and lumbering". It also avoids a definitive declaration (always trouble in paleo), but can be generally considered self-evident since terrestrial locomotion is so different from aquatic locomotion. HCA (talk) 19:53, 6 May 2015 (UTC)

As far as I can see, you have not corrected the first error in the lead. And a sole reference to a site with unknown authors is not adequate. Macdonald-ross (talk) 19:42, 3 July 2015 (UTC)

Harvard references

The Harvard references in this article are all dead. Zyxwv99 (talk) 02:34, 5 June 2015 (UTC)

Which ones are those? I don't see any URLs directed to harvard.edu, though reference 24 is dead ( Geological Survey of Canada (2008-02-07). "Past lives: Chronicles of Canadian Paleontology: Eusthenopteron - the Prince of Miguasha". Retrieved 2009-02-10.) HCA (talk) 14:21, 5 June 2015 (UTC)

Harvard referencing is a style of reference used in the Tetrapod article. Some references in this style were imported into this article, but without the second part that goes at the bottom of the article. For example, if you look at the first paragraph of the lede in Tetrapod then click on footnote number 2, you will come to a reference that just says "Clack 2012, pp. 125–7". If you click on that, it takes you down to the Literature section (below References) where it says "Clack, J.A. (2012). Gaining ground: the origin and evolution of tetrapods (2nd ed.). Bloomington, Indiana, USA.: Indiana University Press." If you click on the book title, it takes you to the book on Google Books. The advantage is that people can reference the same source multiple time, but each time with different page numbers.

Harvard referencing is explained at WP:HARVARD and Template:Harvard citation documentation#Author-date citation templates. If you look at this article in edit mode and search on "harv" you will see quite a few instances. If you try clicking on any of them, it only gets you to the first step, but not the second one where the main publication info is supposed to be located.

This style of referencing was already being used both in this article and the Tetrapod article before I got here. I expanded it a little in the Tetrapod article so that the literature section there now includes some of the more widely referenced books. I'd like to add Benton's Vertebrate Palaeontology (2009) to the list. Right now this article uses Benton (2005) which is a little dated and impossible to find in Google Books. Much of the 2009 edition is visible in Google Books preview mode. There is also a 2014 edition, but in preview mode it doesn't show the page numbers. For this reason, I would use 2009 wherever possible and 2014 only when necessary.

Zyxwv99 (talk) 19:43, 6 June 2015 (UTC)

Merging?

Sorry if I missed any fragment here touching on this, but I don't see the question of merging this with the "skeletal changes..." article covered here, so I'm making this subheading for it... and regarding which, I would humbly vote... Nay. To me, these are two topics which, though related, are absolutely not equivalent in either scope or focus, and I very much hope shall not be combined. Indeed, it's somewhat puzzling why the proposal was made in the first place. Saturn comes back around (talk) 22:01, 17 June 2015 (UTC)

The Discuss links on both merge banners should now link here. Talk:Skeletal_changes_of_organisms_transitioning_from_water_to_land#Article title misleading might be related to the original merge proposal, in particular, the Skeletal article is more specific to tetrapods than the wordy (and improbably general) title implies. I think the scope of the Evolution article contains that of the Skeletal article and on that basis the Skeletal article could be merged into this one but not the other way around. Whether it should be depends on size and personal preference for split vs merge. I agree not to merge but in that case I think there is a need to link the articles together, eg by See also or Main article links.TuxLibNit (talk) 21:23, 5 December 2015 (UTC)

Agree with the suggestion of 'see also' and not merging;

Resolved

Klbrain (talk) 20:33, 12 October 2017 (UTC)

Huge contradiction

The tetrapod article says "Tetrapods evolved from the lobe-finned fishes". The first sentence of this article says "the earliest tetrapods derived from neither ray-finned nor lobe-finned fishes." Is that not a huge contradiction? Makes me wonder whether this article has suffered some vandalism.75.163.204.203 (talk) 05:31, 10 July 2015 (UTC)

Fixed. HCA (talk) 13:52, 10 July 2015 (UTC)

Proposing Merge with "Vertebrate land invasion"

The topic is already covered in some depth on this page. I think any additional details could be added here. If instead that article were to be significantly expanded, much of the relevant content on this page could be moved there to reduce excessive redundancy. EAR47 (talk) 03:49, 4 June 2016 (UTC)

Agreed, I think the content from that page should be moved here. HCA (talk) 18:16, 4 June 2016 (UTC)

Oppose merge: The land invasion is very important part of the Evolution of tetrapods, and is therefore independently notable. I suggest keeping the two pages, but linking as a summary/main, perhaps from Evolution of tetrapods#From water to land. Klbrain (talk) 19:23, 30 March 2018 (UTC)

Section Titles

I won't change them again, but thought I'd bring up the issue here. Sure, they don't have to be "dry and academic" -- and perhaps the ones I suggested were too much so -- but I still believe the current section titles are much too informal. Thoughts? EAR47 (talk) 01:02, 15 June 2016 (UTC)

@EAR47:When I reverted, I recall having some additional concerns:

• That the older section content worked together with the section titles so that a larger rewrite was needed to keep the article coherent.
• That some of the new section titles were duplicating other existing section titles, again implying that a larger rewrite was needed to keep the article coherent.

Going back to the point about heading style, I think the original intent was that these rather chatty headings told a little "just so" story by themselves, so the lazy reader gets some value just by reading the list of section headings. I don't think this works very well in the current implementation and I'm not sure if there is currently enough scientific certainty in the story it is telling, but in principle I think it is a legitimate approach for an article to take (particularly in the early sections, which should be as accessible as possible to lay readers.

I hope that helps. I'm not particularly trying to defend the existing content it is just that I felt that your edit wasn't a good next step. I also think that the issue here is a choice between two legitimate styles, not a question of "encyclopaedic" vs "unencyclopaedic" content. Feel free to have another go if you still feel inspired.

TuxLibNit (talk) 23:05, 24 June 2016 (UTC)

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Excretion of Urea

I have removed the excretion section, preserved below for reference. My reasons for doing so will follow the preserved text.

″The common ancestor of all present gnathostomes (jawed-vertebrates) lived in freshwater, and later migrated back to the sea.[citation needed] To deal with the much higher salinity in sea water, they evolved the ability to turn the nitrogen waste product ammonia into harmless urea, storing it in the body to give the blood the same osmolarity as the sea water without poisoning the organism, rather than directly shedding the ammonia through their gills, which is possible in fresh water. This is the system currently found in cartilaginous fishes. Ray-finned fishes (Actinopterygii) later returned to freshwater and lost this ability, while the fleshy-finned fishes (Sarcopterygii) retained it. Since the blood of ray-finned fishes contains more salt than freshwater, they could simply get rid of ammonia through their gills. When they finally returned to the sea again, they did not recover their old trick of turning ammonia to urea, and they had to evolve salt excreting glands instead. Lungfishes do the same when they are living in water, making ammonia and no urea, but when the water dries up and they are forced to burrow down in the mud, they switch to urea production. Like cartilaginous fishes, the coelacanth can store urea in its blood, as can the only known amphibians that can live for long periods of time in salt water (the toad Bufo marinus and the frog Rana cancrivora). These are traits they have inherited from their ancestors.

If early tetrapods lived in freshwater, and if they lost the ability to produce urea and used ammonia only, they would have to evolve it from scratch again later. Not a single species of all the ray-finned fishes living today has been able to do that, so it is not likely the tetrapods would have done so either. Terrestrial animals that can only produce ammonia would have to drink constantly, making a life on land impossible (a few exceptions exist, as some terrestrial woodlice can excrete their nitrogenous waste as ammonia gas). This probably also was a problem at the start when the tetrapods started to spend time out of water, but eventually the urea system would dominate completely. Because of this it is not likely they emerged in freshwater (unless they first migrated into freshwater habitats and then migrated onto land so shortly after that they still retained the ability to make urea), although some species which never left, or returned to, the water could of course have adapted to freshwater lakes and rivers.″

Unfortunately, no sources were cited for this section, so I am unable to say for sure where the contributor got this information. Based on research into the topic, it seems that parts of the section were sourced from an encyclopedia Britannia article, which on its own makes no reference to the argument for tetrapods needing to remain in saltwater before colonizing land. There are also claims in the section that, based on the fossil record of fishes evolving in freshwater (which is mentioned in the encyclopedia article I’ve linked to), they lost their ability to produce urea. The article I’ve linked and I assume was being used for reference mentions the evolution of urea production evolved in Chondrichthyes after returning to the ocean in the Carboniferous (after the first tetrapods appeared). Colonization of the ocean by Chondrichthyes in the Carboniferous aside, research suggests that multiple - though not all - lineages of Actinopterygii retain the genes required for urea production, and it is triggered by environmental stressors. Stressors mentioned in the study include embryonic development, high ph, presence of high levels of ammonia, and bodies of water drying up, the latter of which would be a similar stressor to an organism going on land. — Preceding unsigned comment added by Luxquine (talk • contribs) 01:05, 26 May 2021 (UTC)

Whoops! Forgot to sign that previous message. Luxquine (talk) 08:20, 26 May 2021 (UTC)

References