Archosauromorpha classification

[Rossano]

Dear all, I am at my first visit here after a few months frequenting the twin ATF.

I am really new (less than one year) at collecting animal figures, and began buying the first dinos just few months ago. The Rhamphorhynchus by Safari that my son insisted to buy against my suggestion for another shark (Megamouth) triggered an unsuspected interest for those animals that before then I had always perceived as odd and nearly non-real creatures mainly living into blockbuster movies and the like.

Now, the problem is: I have quite a taxonomist mind, and after realizing that "prehistoric animals" and "Dinosaurs" where not really the same thing, I browsed some wiki pages and realized where the main taxons of extinct animals inserted into the Animalia tree. Things looked very stimulating and easy to chart into my excel file, until I came to the Archosauromorpha group.

There are some groups that I can hardly fit bewteen the levels.

- Archosauromorpha are a Diapsid infraclass, together with Lepidosauromorpha, and this is ok.
- Where do I put Archosauriformes?
- Archosauria, with its two groups Crurotarsi and Ornithodira, are at a lesser level of infraclass, since they are into the Archosauromorpha, but at an higher level of Superorder, since into Ornithodira there are Crocodylomorpha, that are a superorder.

As far as I know there are no intermediate levels of classification between infraclass and superorder, so all these groups should be clades, but I can't understand clearly what's into what. Can you help me?

[Lanthanotus]

Welcome to the forum,...

...nice and challenging intro question, unfortunately I am not capable of answering them without any extended search , but I am sure you'll find some help here

[Jose S.M.]

Welcome to the forum! I can't help you either since sometimes I read that some species belongs to an X "group" and I have to go on the Internet to find where said group is! specially with extinc animals, but I guess that's a way of learning, good dinosaur and animal figures are educative for people of all ages hehehe.

[Halichoeres]

Nesbitt 2011 (Bulletin of the American Museum of Natural History 352) is, as far as I know, the best sampled systematic study of the archosaurs and their relatives. Nesbitt defines Archosauriformes as the least inclusive clade that includes both the Nile crocodile and Proterosuchus. This is a less inclusive clade than Archosauromorpha; that is, it is nested inside of Archosauromorpha and includes the archosaurs (crocodiles, dinosaurs, etc.), phytosaurs, Euparkeria, and a handful of other taxa. Other sources place proterosuchids outside of Archosauriformes, but they would still be included in the Archosauromorpha.

I wouldn't worry too much about ranks. They're all clades. I hope that helps!

[Rossano]

Thanks Halichoeres for the indications, I will check them out as soon as I get to my pc.

Now the point with clades is, if I got it right, that they are variable subsets of the steady classification structure, so that I can position any animal into the classification tree without considering the clades, and relying only on the varous levels of the basic taxonomy.

If that is the way it is, what are the superorders that are into the Archosauromorpha infraclass? I found just the two superorders of Crocodylomorpha and Dinosauria, that I believe are both into Archosauria. But maybe there are other superorders, or at least other groups that are into Archosauromorpha but out of Dynos and Crocs, and out of any other superorder?

[Halichoeres]

Thanks Halichoeres for the indications, I will check them out as soon as I get to my pc.

Now the point with clades is, if I got it right, that they are variable subsets of the steady classification structure, so that I can position any animal into the classification tree without considering the clades, and relying only on the varous levels of the basic taxonomy.

If that is the way it is, what are the superorders that are into the Archosauromorpha infraclass? I found just the two superorders of Crocodylomorpha and Dinosauria, that I believe are both into Archosauria. But maybe there are other superorders, or at least other groups that are into Archosauromorpha but out of Dynos and Crocs, and out of any other superorder?

Clades are hypotheses about how things are related. The taxonomy isn't static or steady, but usually reflects the clades. A clade is a group composed of one common ancestor and all of its descendants. Usually the common ancestor isn't known but inferred from a numerical appraisal of similarity among organisms such as what Nesbitt produced. Archosauria, Archosauromorpha, Aves, Ornithodira--these are all taxonomic labels that correspond to the hypothesis that everything circumscribed by them is more closely related one to another than to anything thought of as outside of the group. Taxonomists, both of fossil and living organisms, try to have the taxonomic groupings be natural groups (aka clades, or monophyletic groups), but sometimes non-natural groups are used for convenience. Usually they are grades (aka paraphyletic), but occasionally they are polyphyletic. The old taxonomic group "Pisces" was a grade, because it excluded tetrapods, which is a problem because tetrapods are more closely related to some fish than some fish are to one another.

At this point I don't commit to memory the ranks of large clades such as Archosauromorpha. The ranks themselves are to some extent relics of a pre-cladistic taxonomy. You are correct that there are animals in the Archosauromorpha that are neither within Dinosauria nor Crocodylomorpha. Some of them are closer to crocodiles than to birds and could therefore be called "stem-crocodiles" because they are on the branch that gave rise to crocodiles. Similarly, all dinosaurs and pterosaurs can be thought of as "stem-birds" because they are more closely related to birds than to anything else now living. Many others are "stem-archosaurs," because they are more closely related to the group (birds + crocodiles) than to anything else now living. Often it is these animals that people have in mind when they talk about archosauromorphs--protorosaurs, phytosaurs, proterosuchids. It's true that these hypothetical clades change names sometimes in the face of new evidence--that's as it should be. Just remember that clades are real, but our names for them--the taxonomic levels--are our hypotheses about which things actually constitute a clade.

[Dinoguy2]

You might be getting confused because there are many conflicting ways to label things. Is Archosauromorpha an infraclass or a subclass? Depends who you talk to. Most paleontologist no longer even use ranks like subclass or infraclass and just leave these unlabeled to avoid confusion since those ranks are meaningless anyway.

[Rossano]

Halichoeres thanks again for the detailed answer, I am beginning to better move within the logics of classification.

In the meanwhile I found a site that gathers what seems to be a complete taxonomy of the whole extinct species, fossilworks.org, I think you already know it.

I find it very useful but there is a problem, it does not show the classification of the groups that contain a high number of elements into it. In this case the site simply lists the subtaxa in alphabetical order, all togeteher (subspecies genus tribe subfamily family and so on), without showing the position of each of them. Does anyone know if the classification can be downloaded in some way from the site?

[bmathison1972]

Also, when using Wiki pages for taxonomy, different pages might be edited by different people and may not match up. For example, some anomalacarids might be considered Arthropoda and others in Pan-arthropoda. Also some pages break down subtaxa better than others. For the most part Wiki pages are fairly up-to-date but you might find inconsistencies or omissions here and there.

[Neosodon]

Looks like there are some more complicated definitions but I've thought of it as a term referring to all all the animals in the reptile-dinosaur-bird lineage not counting lizards, snakes and turtles. So it basically includes a ton of miscellaneous Triassic reptiles, Crurotarsi, dinosaurs, birds, pterosaurs and marine reptiles.

If this is correct it would be a great term to sum up my collection. Since the vast majority of prehistoric figures are in this category we could just change the forum name to the Archosaur Toy Forum!  It may seem a little geeky at first but I think it could work.

[Halichoeres]

Looks like there are some more complicated definitions but I've thought of it as a term referring to all all the animals in the reptile-dinosaur-bird lineage not counting lizards, snakes and turtles. So it basically includes a ton of miscellaneous Triassic reptiles, Crurotarsi, dinosaurs, birds, pterosaurs and marine reptiles.

If this is correct it would be a great term to sum up my collection. Since the vast majority of prehistoric figures are in this category we could just change the forum name to the Archosaur Toy Forum!  It may seem a little geeky at first but I think it could work.

As a prehistoric fish enthusiast I am very offended! 

There's a decent chance that Archosauromorpha contains turtles, but it would exclude a whole bunch of Permian and Triassic amniote lineages that would have looked quite reptilian. Sadly, most of those never get made as toys. I think most people here (even me) have mostly archosaurs in their collections.

[Dinoguy2]

You should be aware that the vast majority of scientists who study the various groups of archosauromorphs abandoned taxon ranks and any label besides clade long ago. Some popular web sites still attempt to shoehorn ranks like "infraclass" or "superorder" into the taxonomy, but they are all going to conflict with each other because it's just random people making up their own schemes with no basis in current science. So when wading into the world of archosaur taxonomy, any time you see a rank label or term, just ignore it.

As of right now, the Wikipedia taxonomy looks good and mostly current, so I'd follow that. Just go to the Archosauromorpha page and follow the info box links plus the various family tree diagrams. Often they will present various alternate hypotheses.

Turtles as archosauriformes is a near certainty. DNA evidence consistently proves it. Analysis using fossils only often finds other results: what that means is that studies using only fossils are often wrong. Any study using primarily fossils that does not force the result to conform to DNA analysis, like the Ezcurra 2016 study shown in the Wiki article, is trash and should be ignored.

The first family tree shown on Wiki was a fossil based study that forced the results to follow DNA results, so it's much more reliable even though it's a few years older and is missing some newer fossil species. The most interesting result is that it suggests plesiosaurs, nothosaurs, and placodonts are actually archosauromorphs related to early turtles. Many fossil only studies have found those to be lizard relatives or more primitive reptile relatives.

[albertonykus]

Turtles as archosauriformes is a near certainty. DNA evidence consistently proves it. Analysis using fossils only often finds other results: what that means is that studies using only fossils are often wrong. Any study using primarily fossils that does not force the result to conform to DNA analysis, like the Ezcurra 2016 study shown in the Wiki article, is trash and should be ignored.

That's a bit harsh. The Ezcurra study was intended to test the relationships of archosauromorphs belonging to entirely extinct groups (i.e.: groups without any molecular data). It doesn't even include any members of the living archosauromorph groups (Testudines, Crocodylia, and Neornithes). A molecular constraint can't be implemented if one doesn't exist for the taxa included in an analysis.

I concur that a molecular scaffold should be used if there is a robust molecular framework that conflicts with morphology-based topologies for the taxa being studied (as was the case for the Halliday et al. study on Paleocene placentals and the recent description of Tsidiiyazhi), but Ezcurra (2016) wasn't one of those studies.

Would Ezcurra have found a different topology if turtles had been included? Maybe. But that hardly makes his study worthless. It has more morphological characters and greater taxon sampling by far than any other study that has focused on the same groups, and would make an excellent starting point for anyone who wants to test what does happen if turtles are thrown into the mix.

Consider also that, other than the position of turtles and sauropterygians, Lee (2013) found the exact same topology for archosauromorphs with and without the molecular scaffold, so any topological differences between Lee (2013) and Ezcurra (2016) have nothing to do with whether a molecular scaffold was implemented or whether turtles were included.

Additionally, turtles are probably archosauromorphs but we don't know if they're archosauriforms. That is something a study using molecular scaffolding can help us tease out. So far, even Lee (2013) didn't find them as archosauriforms.

[Halichoeres]

Molecular trees consistently recover turtles as sister to the living archosaurs, and I agree that where genes conflict with fossils, the genes should be trusted. At the same time, it doesn't necessarily follow that they're particularly close to archosaurs, as many extinct lineages could theoretically lie on the turtle stem or the archosaur stem. A morphological analysis that samples broadly among sauropsids and only constrains the turtles to lie closer to birds than to lizards would be the most explicit way to recover the turtles' sister group. I think it's pretty likely that they're in Archosauromorpha, based, for example, on the Pappochelys paper that recovered them within sauropterygians. But there are people arguing for a thalattosaurian affinity for turtles, a hypothesis that doesn't have any explicit test that I'm aware of (although if anyone has tested that, please let me know!).

[Dinoguy2]

Turtles as archosauriformes is a near certainty. DNA evidence consistently proves it. Analysis using fossils only often finds other results: what that means is that studies using only fossils are often wrong. Any study using primarily fossils that does not force the result to conform to DNA analysis, like the Ezcurra 2016 study shown in the Wiki article, is trash and should be ignored.

That's a bit harsh. The Ezcurra study was intended to test the relationships of archosauromorphs belonging to entirely extinct groups (i.e.: groups without any molecular data). It doesn't even include any members of the living archosauromorph groups (Testudines, Crocodylia, and Neornithes). A molecular constraint can't be implemented if one doesn't exist for the taxa included in an analysis.

I concur that a molecular scaffold should be used if there is a robust molecular framework that conflicts with morphology-based topologies for the taxa being studied (as was the case for the Halliday et al. study on Paleocene placentals and the recent description of Tsidiiyazhi), but Ezcurra (2016) wasn't one of those studies.

Would Ezcurra have found a different topology if turtles had been included? Maybe. But that hardly makes his study worthless. It has more morphological characters and greater taxon sampling by far than any other study that has focused on the same groups, and would make an excellent starting point for anyone who wants to test what does happen if turtles are thrown into the mix.

Consider also that, other than the position of turtles and sauropterygians, Lee (2013) found the exact same topology for archosauromorphs with and without the molecular scaffold, so any topological differences between Lee (2013) and Ezcurra (2016) have nothing to do with whether a molecular scaffold was implemented or whether turtles were included.

Additionally, turtles are probably archosauromorphs but we don't know if they're archosauriforms. That is something a study using molecular scaffolding can help us tease out. So far, even Lee (2013) didn't find them as archosauriforms.

Actually, now that I double check (which I should have done before running my mouth off...), I was thinking specifically of this 2015 analysis by Sues, not last years' by Ezcurra. The phylogeny from Sues 2015 is currently being presented on Wikipedia as an "alternate hypothesis" on the placement of turtles and is presumably why Pantestudines is listed as "disputed" on the Archosauromorpha page. Which is extraordinarily misleading to say the least.

https://en.wikipedia.org/wiki/Pantestudines

[albertonykus]

Ah, that makes more sense. I agree, the Schoch and Sues analysis would have benefited from molecular scaffolding.