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Archive 1

Image

With the Postosuchus image gone, I found a pretty nice looking shot of a crocodilian on stock.xchng (though a good photo incorporating both a croc and a bird would be ideal), but I'm not sure of the species. Maybe somebody who's up on crocs can fll in the caption.The Thagomizer 18:30, 27 January 2006 (UTC)

Crocs are birds?

I'm a layman, but this sentence bothers me: The only groups of archosaurs to continue through to the Tertiary and, ultimately, to the present day, are the birds, which are descended from the dinosaurs and crocodylians, which include all modern crocodiles, alligators, and gharials.

Birds are descended from Dinosaurs exclusively, are they not? The crocs and dinosaurs split off long before the first bird/dinos showed up. Saying that the only archosaurs are birds is rather silly considering that crocs are still extant.

Again, I'm just a (paleonerd) layman, so am I interpreting this correctly? --Shubbell 09:14, 15 August 2006 (UTC)

The sentence is poorly constructed, I'll clarify it M Alan Kazlev 03:19, 16 August 2006 (UTC)

Advantages; metabolism

The article says "Their 'reptilian' metabolism seem to have given them a clear advantage over the mammal-like therapsids..." This is ambiguous as it may give the impression that a sluggish metabolism was an advantage. One could argue that endotherms would be at a disadvantage in hot, dry conditions, but some parts of the Triassic world must have been cool; and since modern monotremes have lower, more variable body temperatures than most placentals (and some placentals such as tenrecs have unusually variable temperatures), one has to assume that therapsids also had lower, more variable body temperatures and therefore the heat would not have placed them at a major disadvantage. I remember from Kermack & Kermack's book on the mammal-like reptiles that living diapsids (lizards, crocs, birds, etc.) excrete uric acid while mammals excrete urea. Uric acid can be excreted as a paste while urea requires penty of water to keep it fully liquid. If Permian-Triassic diapsids excreted uric acid and mammal-like reptiles excreted urea (as seems likely), the diapsids would have had better water conservation and this was probably a major advantage in the arid interior of Pangaea.

It would be interesting if someone could add good material on archosaur metabolic rates. I think dinos had high metabolic rates (see my comments on Wikipedia's "dinosaur" page), and crocs, although cold-blooded, have features normally associated with high metabolic rates: a palate which enables them to breathe while eating (palates were the first stage in synapsids' evolution towards endothermy - Kermack & Kermack), a mechanism to pump the lungs while moving, and a four-chambered heart (but small, running at lower pressure and with a by-pass which converts it to 3-chambered while diving, presumably to conserve oxygen). Either dinosaurs and their close ancestors developed high metabolic rates in 10-20M years although the synapsids took about 65M years, or earlier archosaurs had fairly high metabolic rates and crocs are secondarily cold-blooded. The latter hypothesis is consistent with the fact that Triassic crocs were slim and leggy (e.g. Terristrisuchus) and look like cursorial predators (e.g. dogs). An abstract which was recent taken offline by CMNH (I got it from Google's cache) supports the view that crocs were originally endothermic, and I'm inserting a copy at the end of this post. I have been unable to find other good material online about archosaur metabolism. Can anyone else do better?

Philcha 18:02, 5 October 2006 (UTC)


6th International Congress of Comparative Physiology and Biochemistry: 23.5. A case for endothermic ancestors of crocodiles at the stem of archosaur evolution

Seymour, R.S. Department of Environmental Biology, University of Adelaide, Adelaide 5005, SA, Australia roger.seymour@adelaide.edu.au

In living endotherms, there is a functional nexus between high rates of metabolism, high systemic blood flow rates, and high systemic (but low pulmonary) blood pressures produced by thick-walled, four-chambered hearts. The hearts of crocodiles are equivocal: they are four-chambered, but are relatively small and feature low blood pressure and a capacity for right-to-left shunting. Recent crocodiles are definitely ectotherms, but there is paleontological, embryological, anatomical and physiological evidence that their ancestors may have been highly active, endothermic predators. By invading an aquatic, ambush predator niche, one descendent line may have become ill-suited for endothermy and reverted to ectothermy, which may have prevented their extinction at the end of the Mesozoic. Endothermy in stem archosaurs has implications for the metabolic status of both saurischian and ornithischian dinosaurs.

(Seymour's web page http://www.ees.adelaide.edu.au/people/enviro/rseymo01.html indicates that the full paper appeard in Physiol. Biochem. Zool. 77: 1051-1067)

Ornithodira

The infobox on the right says that the clade ornithodira is extinct. But I think I saw a member of that clade in my back yard this morning. Or am I reading this incorrectly?--VAcharon 20:05, 20 July 2007 (UTC)

I think you're right - consensus among paleontologists is that birds are dinos and dinos are ornithodira. Philcha 17:37, 21 October 2007 (UTC)

Forelimbs

I think forelimbs are important too, but not mentioned still...89.189.179.81 (talk) 16:08, 7 May 2009 (UTC)

Archosaurs are "reptiles"

Should we use reptile in this article, reptile still has the Linnanean connotations.. (ie. cold-blooded sauropsid, non-avian). Should we change it to eureptile or some more cladistic term?

I never understood the 'Linnean connotations' thing. For one, Reptile has been defined as a clade. If you're really concerned about it, it can be changed to sauropsid, but still--why change the name? Why not change the connotations instead? We managed to change the public's image of dinosaurs as slow and cold-blooded without abandoning the word dinosaur. Maybe popular science like Life In Cold Blood can do th same for other reptiles. What's wrong with being cold-blooded anyway? Many reptiles are. At least some archosaurs probably were (and are, like crocs). So what? Dinoguy2 (talk) 04:40, 20 April 2008 (UTC)
Dinoguy2, I never expected to suspect you of violating WP:NOR :-)
Perhaps "sauropsids (commonly known as 'reptiles')"? Philcha (talk) 16:01, 20 April 2008 (UTC)
How is it OR to argue for keeping the term "reptile", which is still used widely in the lit? Here's a cite from just a few months ago that uses Reptilia right in the title: [1]. I'm not arguing that we should go back to using "reptile," I'm arguing that we've never stopped (and in my opinion, for what it's worth, shouldn't). Do a Google Scholar search for say, "(Crocodilia, Reptilia)" and a year. I get 14 hits for 2007 alone for just this one reptile group. The rumors of Reptilia's death re greatly exaggerated ;) Dinoguy2 (talk) 01:27, 21 April 2008 (UTC)
Did you miss the smiley at the end of my last comment? More seriously, "Why not change the connotations instead? We managed to change the public's image of dinosaurs as slow and cold-blooded without abandoning the word dinosaur" is at least flirting with OR - it's Wikipedia's job to report things ( including perceptions), not to change them.
Or are you somewhat Marxist, like Stephen Jay Gould? ("The philosophers have only interpreted the world, in various ways; the point is to change it." - Theses On Feuerbach, part XI) :-) :-) :-)
More seriously, "reptile" is confusing as it popularly implies cold-blooded, but phylogenetically birds are reptiles / sauropsids. That's why I suggested "sauropsids (commonly known as 'reptiles')". Philcha (talk) 09:24, 21 April 2008 (UTC)~
Both Sauropsida and Reptilia have different phylogenetic definitions, so saying "sauropsids (commonly known as 'reptiles;)" is technically incorrect. In addition, the general public already knows that dinosaurs are reptiles, while a great many of them know of the warm vs cold blooded debate. I doubt the whole "implies cold-blooded" is even an issue. Regradless of which ever way this article is written, archosaurs are both sauropsids and reptiles. Mark t young (talk) 13:08, 21 April 2008 (UTC)

The main problem I guess is the confusion with the original linnean paraphyletic Reptilia, colloquial "reptile" not including the birds. —Preceding unsigned comment added by 76.64.53.236 (talk) 02:15, 30 April 2008 (UTC)

Gizzards

Is the gizzard a defining feature of archosaurs? Crocs, birds, and at least some sauropods have them, so isn't it more than likely the gizzard was present in their common ancestor? Virginia-American (talk) 06:02, 5 April 2009 (UTC)

Archive 1

Birds

If archosaurs are reptiles, how can birds be living representatives of them?--94.7.0.72 (talk) 02:24, 4 August 2010 (UTC)

Birds are a group of dinosaurs, which are group of archosaurs. The other group of archosaurs that still live to-day are crocodilians. --Philcha (talk) 02:56, 4 August 2010 (UTC)
Several other pages (Birds, Vertebrate) put birds under "Aves", an order on an equal level to "Reptilia". This article is placing birds and Aves seven levels below Reptilia. I know taxonomy isn't always clear-cut, but this seems like a pretty big contradiction? Naleh (talk) 09:38, 13 August 2010 (UTC)
The problems is the conflict is Linnean and phylogenetic taxonomy. The Linnean is the convenience of been stability, but scientists doing real work use phylogenetic taxonomy. From that point of view "Reptilia" is ambiguous and useless, and a summary of the useful approach would be:

If by "real work" you mean "phylogenetic work" you are right, although it makes you sound a little bit conceited. You could also simply observe that some terminology is paraphyletic. That's because some things, even if they grow out of a phylogenetic unity become so different it makes sense to consider them a new semantic unit. Saying humans aren't apes isn't "useless", nor is it wrong, it's simply a case of using paraphyletic terminology for excellent reasons. We even have an image explaining this, it's called File:Traditional Reptilia.png and it's duly transculded at the reptiles article. --dab (𒁳) 11:06, 23 January 2011 (UTC)

I think by real work he's referring to peer-reviewed papers, rather than summaries in popular or university textbooks that synthesize work originally done in a phylogenetic context into a Linnean scheme. I haven't seen and primary sources use Linnean ranks in ages but feel free to point to some and cite them in the article. MMartyniuk (talk) 23:46, 23 January 2011 (UTC)

What goes into Archosauria?

This article lacks a straight up list of what animals goes into this unit and who are excluded. The phylogenetic tree contain a number of names, but the tree itself is not sourced. Even a cursory glance at literature (I'm by no means an archosaur expert) indicate that bout pterosaurs and champsosaurs may fall well outside Archosauria (champsosaurs are even listed as outside Archosauromorpha by deBraga, M & O Rieppe, 1997). This should be an important article, and needs a bit of going through and sourcing. Petter Bøckman (talk) 21:51, 19 August 2010 (UTC)

The champsosaur thing was weird, I didn't know they were considered archosaurs by anyone. Non-archosaurian pterosaurs is a fairly minority view, and seems to only be held by David Peters who also thinks they were frilled viviparous marsupial analogues. Also vampires. MMartyniuk (talk) 22:27, 19 August 2010 (UTC)
Good grief! Well, Benton has pterosaurs outside Archosauria, see Benton (1985): Classification and phylogeny of the diapsid reptiles summary. Do yo know if he has left than view? Petter Bøckman (talk) 22:51, 19 August 2010 (UTC)
Not sure if Benton specifically has left that position, but it was 25 years ago so it wouldn't be too surprising. But I can't personally think of any papers with pterosaurs outside Archosauria in the past 10 years or so. Could be missing something though. I know a few like Unwin (2006) suggested there could be an affinity with Sharovipteryx, but I'm not sure if they endorsed this and supported it with an analysis or just suggested it as a possibility. MMartyniuk (talk) 23:27, 19 August 2010 (UTC)
For what it's worth, here's a 2007 Benton paper which concludes the non-ornithodiran phylogenies are in error, and with current evidence pterosaurs should be considered ornithodiran archosaurs. [2] MMartyniuk (talk) 23:35, 19 August 2010 (UTC)
Well, that should settle Bentons view then. The back-and-forth status of pterosaurs should be mentioned, and I'd still like to see a section devoted to "who is who" among the archosaurs.--Petter Bøckman (talk) 06:38, 20 August 2010 (UTC)
Regarding the tree, it might be better to replace it with a few from recent studies, because this one seems a little old to me. The phylogeny of crurotarsans in particular isn't that certain. The tree[3] in Brusatte et al. (2010)[4] is the most recent one I know of that deals with Archosauria as a whole. Smokeybjb (talk) 20:46, 20 August 2010 (UTC)
That certainly looks thorough to me, but the discussion highlights that even this phylogeny should not be seen as the definitive word. I think tis article should reflect that the internal who-is-who of Archosauria, and particularly the Crurotarsi is not entirely well understood. Petter Bøckman (talk) 21:38, 20 August 2010 (UTC)
Yes, I agree. I think if we are going to include new trees, there should be several showing different hypotheses. Smokeybjb (talk) 23:42, 20 August 2010 (UTC)
Either that, or the strict consensus tree from the article, with most of the Crurotarsi sprinnging from a single unresolved node. --Petter Bøckman (talk) 06:43, 21 August 2010 (UTC)

I just noticed that this line is under the "Main types of archosaurs" heading: "In the late Triassic, the ornithodires diversified to produce dinosaurs and possibly pterosaurs, though it is uncertain if the latter is actually a part of Archosauria.[6][7]" I'm not aware that there's any good evidence as of the present that pterosaurs lie anywhere outside Avemetatarsalia, well within Archosauria, apart from a few minority experts (and David Peters). The first link is dead and the second is a fairly old paper that, as mentioned before, no longer even reflects the position of the scientist who wrote it. I think this line should be removed from the end of this section. Gruekiller (talk) 00:45, 27 December 2013 (UTC)

Name

Are we sure about "Cope 1869", and that the name is supposed to mean "ruling lizards"? I am asking because I get a google snippet here suggesting "Cope 1891". And the "ruling" translation appears to be unsubstantiated. The name could just as well mean "ancient lizards", which would seem to make a lot of sense. --dab (𒁳) 10:26, 23 January 2011 (UTC)

this seems to suggest that Cope first introduced the term in 1869, but then kept fiddling with its definition until 1891, so that the current grouping may be argued to date to 1891. --dab (𒁳) 10:28, 23 January 2011 (UTC)

Right, I figured it out. As I suspected, the "ruling" is spurious. Here is an 1878 reference that complains about Cope's term being a Greek-Latin hybrid, and suggestive of "ruling" while in fact Cope simply wanted to refer to the cranial arches. As it were, Arch-o-saurus. It is not helpful to "reference" such artificial taxonomical terms by linking standard dictionaries of Classical Greek. --dab (𒁳) 10:44, 23 January 2011 (UTC)

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Subgroups

Shouldn't the subgroups be only Avemetatarsalia and Pseudosuchia, from the definitions of these and Archosauria? Taxa incertae sedis are not independent subgroups, just subgroups that we don't know which subgroup they belong to. Lavateraguy (talk) 19:07, 25 July 2018 (UTC)

Bipedal locomotion? New trackways study, proposed new species

"Giant Crocodile Ancestor Walked Around on 2 Legs, Ancient Footprints Suggest [5] Science Alert, June 11, 2020

Interesting photos & commentary. Naming a species from tracks alone is... fraught. But the prints certainly look crocodilian, and bipedal. The news article concludes: "Except for a few early Mesozoic reports, to date no such bipedal crocodiles have been reported from the Cretaceous. Maybe we've been misinterpreting their footprints." Likely premature for our purposes? --Pete Tillman (talk) 04:59, 15 June 2020 (UTC)

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