Except that it’s completely arbitrary how many layers of nesting you put in there. For that same comparison, I could also perfectly validly use the nested tree
Animalia
Chiroptera
E. helvum
D. rotundus
All four of those are clades, Chiroptera is nested in Animalia, and the two species are both nested in Chiroptera. I could also compare another pair of organisms, as follows:
Plantae
Spermatophyta
G. bilboa
T. officinale
Just from those two nestings, it looks like the ginkgo and dandelion are (or could be) as closely related as are those two bats you mentioned. On the other hand, if Spermatophyta is labelled as a superdivision, while Chiroptera is labelled as an order, then it’s clear which pair of species is closer.
Such divisions do serve as a sort of shorthand for biologists, but the names don’t really indicate which groups are more closely related except in a very general way. It is sometimes said that if birds were beetles, they would be considered to be a Family rather than a Class, just based on the degree of morphological diversity found in each group.
Among vertebrates, the Class Agnatha diverged long before the Classes Mammalia or Aves. Compared to Agnatha, birds are much closely related to mammals.
What “misconceptions about taxonomy”? Now, Darwins Finch prefers a Cladistic system, I used the Linnean System- which is still completely valid and used by most scientists. Whichever system you prefer, the use of one or the other is hardly a “misconception”.
If Birds are Dinosaurs, then Passeriformes can not be an Order of birds at all. Impossible. If birds are dinosaurs then Aves is a Infraorder of the Order Theropoda. A Infraorder cannot contain any Orders within it. As Darwin’s Finch put it “In order to make birds fit within their presumed evolutionary space in such a scheme, you need countless more subdivisions, since you now have to take what used to be a Class, shoehorn it into what used to be another Class (Reptilia), and even within a previous Order (Saurischia), and so on. Thus, you now need Supras Infras and Supers in order to make everything fit.” Clearly he prefers the cladistic system and that’s fine. But the Linnaen system is still 100% valid and is used by more scientists than cladistics, although I concde cladistics is gaining ground.
So which is it? Are Birds Dinosaurs or are Passeriformes a Order of birds? Both cannot be true, it is a contradiction in terms. If you prefer a pure cladistic system, then you’d pretty much ignore “Orders.”
This rather clearly shows how badly you misunderstand the terms of the discussion. As Polycarp said earlier, you mistake traditional taxonomic categories for the reality they are supposed to be describing. Your understanding of taxonomy seems to be a good 30 years out of date.
We should perhaps distinguish here between taxonomic methodology, and taxonomy as a system of organizing data.
Cladistics is a taxonomic methodology used to characterize the evolutionary relationships between organisms. As such, it is pretty much the only game in town right now. Linnean taxonomy as a methodology is in its essence non-evolutionary, grouping organisms by their overall similarity rather than by descent. Although a few taxonomists today may not use cladistic methods, they are a small minority and likely have difficulty getting articles published in mainstream journals.
But because cladistics recognizes many branching nodes, it does not provide an easy way of organizing data or pigeonholing organisms. Although there have been some attempts, such as Phylocode, to develop systems of cladistic classification, they are somewhat cumbersome and have not yet caught on.
The Linnean system of taxonomy as a way of organizing data continues to be used more as a matter of convenience than anything else. Books, databases, and references continue to use it largely out of inertia - people are familiar with it, and know how to use it to locate information on the groups they are interested in. This does not mean that scientists believe that the system indicates something basic about evolutionary relationships between groups. If I write a report on biodiversity surveys, I will include separate sections for Reptiles and Birds. This does not mean that I believe that Aves is a valid taxomic category of equal rank with reptiles; I do it merely out of convention. The idea that scientists might have a “preference” for Linnean taxonomy over cladisitics just because they happen to use Linnean categories in books and articles is off the mark.
Above, I referred to Passeriformes as an order merely because that is the convention. If it will make you happier, I can just refer to Passeriformes as a clade instead, rather than a named rank. It doesn’t change the fact that it is perfectly legitimate to refer to passerine birds as a member of that clade, vs non-passerines as members of the clade Aves (whether you call it a Class, Subclass, Superorder, or whatever) that are not members of the passerine clade. Likewise, one can refer to avian and non-avian dinosaurs in a similar manner, without specifying Linnean ranks for the avian and dinosaur clades.
No, I am not confusing anything. I am using the Linnean system of taxonomy, which most scientists still use, and science still supports. Are you claiming they really secretly don’t beleive in it, they just use a system that is wrong and outdated due to convention?? :dubious: Give me a break. :rolleyes:
I also know full well that for some purposes, cladistics is more useful. This may well be one of them.
Look I know perfectly well there is a large dicotomy beteen Cladistics and Linnean system of taxonomy- that dicotomy is exactly what I was trying to point out. I understand that “Birds is dinos” currently really makes sense only in a cladistic sense, and creates a dicotomy with the Linnean system of taxonomy. The point remains that Science still uses the Linnean system of taxonomy all the time. “Birds is Dinosaurs” is something that although it currently has the majority of adherants, it is not so firmly accepted that Biologists wish to change the Linnean system of taxonomy to match. It can be done, and *if *and when it becomes completely accepted, it likely will be done. But it hasn’t been done, and IMHO he likely reason why Biologists leave the dicotomy there is because the evidence is still slim, and things may change back. Or not.
Which is why I still ask the question:
*Are the Passeriformes an Order or aren’t they?
*
Knowing that the answer is “Yes, they still are, because Ornithologists still haven’t agreed that “birds is dinos” is going to be the final answer”.
And you know that also. All these little digs about my “misconceptions about taxonomy” are just pissing contests. There are likely Scientists your superior who use the Linnean system of taxonomy, and I don’t think you make snarky comments about their outdated knowledge. Nor is the Linnean system of taxonomy “outdated”. It is a perfectly good tool for many purposes.
Once again, DrDeth, you seem to have completely missed my point. It really does seem to be hopeless discussing this you, since you have absolutely no idea what you are talking about.
This is completely nonsensical, and an utter non sequitur. One statement has nothing to do with the other. The fact that you would even state it this way shows that you don’t understand the discussion.
**DrDeth, ** you frequently come into GQ and post all kinds of incorrect information and ill-informed opinions based on an extremely superficial knowledge of biology. This really isn’t useful, and I would suggest that you improve your knowledge of these subjects before venturing to post on them.
It’s not completely arbitrary; you should include as many nodes as will get your point across regarding the relationships you are discussing. Most folks wouldn’t simplify things down to the level you mentioned simply because it is such a vast oversimplificiation and would really only serve to muddy the taxonomic waters for the groups in question.
But, regardless of that point, your objection would apply to any hierarchical taxonomic scheme. I’m sure there are some taxonomists out there who would love to be able to apply a name to each and every fork in the evolutionary tree (note that this would not include me!). The sane ones would likely prefer to use only as many as are necessary for describing a group (that is, if there are X nodes in clade A and Y nodes in clade B, there is no reason to expand the number of nodes in one clade or the other in order to have them “match up” rank-wise) in a particular context.
Well, sorry, but I do understand the discussion. Show me where I have made an error.
Ah, one of your famous Ad hominem attacks. Look you know your stuff, but for some reason you hate it whenever anyone disagrees with you in the slightest and you get into Ad hominem attacks. Where, here, in this thread have I posted “incorrect information”? Rather than start with the Ad hominem attacks, why not debate the point at hand?
My knowledge may not be as up to date as yours, but I have fact checked twice every point I made here.
Bypassing the cladistics argument, a first cut at a practical answer to erie’s basic question would be:
Those species survived which met some or all of the following criteria:
[ol][li]Relative smallness.[/li][li]Low metabolism, or ability to lower one’s metabolism (e.g., estivation).[/li][li]Econiche that involved taking shelter.[/li][li]Generalist rather than specialist. This may include diet, lifestyle and habits, minimal environmental demands for survival, etc.[/li][li]Wide tolerance for changes in environmental conditions (e.g., salinity of water, ambient temperature, etc.).[/ol][/li]
Not all these criteria needed to be met, but the better you were at each, the better your chances of survival. Lizards in general tended to be small, could estivate, had a wide range of dietary preferences, were used to reduced metabolism, and (the survivors, at least) did not have specializations. Mosasaurs, giant varanoid lizards specialized for high-level predation in a marine environment, didn’t fit the criteria and went extinct. Three of four latest-Cretaceous marsupial families went extinct, but the survivors, Didelphidae, were consummate generalists with the ability to adapt to nearly any climatic condition and food source – to the point that they are the oldest surviving family of mammal today, by at least an order of magnitude over the others. There are a variety of other examples exemplifying this.
As I said, that’s a first cut at a coherent answer – others may want to refine it in much more detail and correct any misapprehensions I have perpetuated.
That’s more or less it, and although I said something close “Generally, smaller and more adaptable species survived” but your answer is far better worded than mine. Thank you.
Dudes- sorry about the silly-assed hijack/argument between Colibri and me. It has now turned into a hijack, and thus I should not have continued this after it got into a hijack. But it- and Darwin’s Finch’s excellent contibutions- have shown there are interesting points and differences between cladistics and the Linnean system of taxonomy.
This just shows a very naive understanding of classification schemes and what their significance is. Virtually any scientist will acknowledge that a taxonomic scheme doesn’t reflect reality with complete accuracy. Taxonomy is used for two major things: to express evolutionary relationships, and also as method of organizing data for retrieval. Linnean taxonomy has been modified to better express evolutionary relationships, but it really can’t do a very good job of it. As I have already explained, it continues to be used by practicing biologists largely for historical reasons and as a matter of convenience for organizing data.
This isn’t an either/or question. Cladograms most fully express evolutionary relationships. Linnean hierarchies are often a more useful way of organizing data.
No, the “birds are dinosaurs” question has absolutely nothing to do with whether one uses a Linnean or cladistic system. If you use Linnean methodology, you might recognize birds and dinosaurs as separate taxonomic categories by considering the paraphyletic group of non-avian dinosaurs to be a formal named taxonomic category. According to cladistic methodology, paraphyletic groups are not permitted, so one would not be recognized. However, there is nothing inherent in a Linnean classification scheme that would prevent birds from being recognized as a named clade within a larger clade comprised of dinosaurs.
As one hypothetical example, the following Linnean hierarchy would express this relationship. It is not too dissimilar to what some taxonomists have suggested:
Class Archosauria (including crocodiles, dinosaurs with birds included, and some other groups)
Subclass Saurischia (including saurischian dinosaurs and birds, the other major Subclass being Ornithischian dinosaurs)
Infraclass Theropoda (including theropod dinosaurs, another Infraclass being sauropod dinosaurs)
Superorder Aves (including just birds, with other theropods being included in other Superorders)
Order Passeriformes (plus the other orders of birds)
There really isn’t any formal standard that dictates what each hierarchical category represents. A taxonomist can shift them up and down and subdivide them to a considerable extent.
By removing the named Linnean ranks, you would simply have a sequence of named clades.
Except that there is absolutely nothing that requires that Theropoda be considered an Order instead of some larger category. While it often has been, that has no bearing whatever on whether or not Passerines could be considered to be a clade within it at some level.
No, the evidence is very strong that birds are a subclade of theropod dinosaurs. While it is not absolutely beyond question, this relationship is accepted by the vast majority of taxonomists working in the field. Last year I attended a session on the subject at the North American Ornithological Congress in Mexico, and there really wasn’t any dissent on the issue.
And what do you mean by “it hasn’t been done?” There isn’t any formal body that endorses or approves higher-level taxonomic schemes that must be followed by biologists. Most taxonomists recognize birds as a subclade of theropod dinosaurs. Biologists certainly don’t “leave the dichotomy there” - most don’t recognize it.
You frequently make this error in other threads as well. You presume that there is some “official” position on taxonomic schemes endorsed by scientists as a group. There is not; rather there are taxonomic schemes that are followed by varying numbers of taxonomists. You will scarcely find two taxonomists that adhere to exactly the same scheme.
Your errors have been pointed out by both me and others in previous posts.
I’m perfectly willing to debate an issue when someone has an informed opinion on a subject. And I have pointed out where you have posted incorrect information. What I really hate is not disagreement, but when someone repeatedly posts wrong information in GQ, and persists in the argument even when it’s clear they are ill-informed on the subject.
The problem is not so much the “facts,” but your interpretation of them. And many things you have posted are not actually facts, but opinions based on misinterpretations of the status of knowledge on the subject.
Essentially, then, a diverse clade of higher-than genus level (e.g., a Linnean Family), as well as a geographically disbursed one, will have better chances of having some species survive than more focused ones (be they sparse in terms of diversity, or more geographically localized). So, one could add yet another bullet to Polycarp’s list of points: cosmopolitan clades tended to fare better than more localized clades. The more spread out the group is, the more likely it is that at least some subgroups will survive.
Where “suborder Theropoda” got 106 hits and “Infraclass Theropoda” got 0. So your hypothetical is very very hypothetical, some might call it “imaginary”. (“Order Saurischia” got 461 hits on Google Scholar, btw.)
Aves would come below Suborder: Theropoda, which some call an “infraorder”.
True - there *is *absolutely nothing that requires that Theropoda be considered a (SUB)Order instead of some larger category- except the facts. The facts are that Theropoda currently is a Suborder. True that might change but so might the current relationship between dinos and birds. And of course Passeriformes is a clade within it at some level, but you are being disengenous when you infer that clade might be an Order, as you know that as long as Theropoda currently is a Suborder (and Saurischia is an Order), the Passerines can not be an Order within it.
I ask again- What error *here, *on this page in this thread? So far, not one single error of fact has been posted- by me.
Again you continue with the Ad hominem attacks whenever your Seat of King of biology in GQ gets a little unstable. Look dude, we all know you are an expert, so you don’t have to get with the personal Ad hominem attacks whenever anyone deigns to post an opinion or fact that isn’t 100% in agreement with yours. If I am wrong, then just crush me with the facts, backed up with lots of spiffy cites, instead of more Ad hominem attacks. Facts, not attacks, OK? I am willing to be crushed under your superior knowledge and whatever Search skills you may have. Go for it. Crush me, dude. But stop with the baseless Ad hominem attacks, OK? You’re better than that.
Again, dudes, I apologize for the continued hijack. I tried to stop it, really I did.
Great cite!
I like this from that cite, too: *“This is not to say that traits favored under low extinction intensities were never advantageous during mass extinctions: resting stages in phytoplankton, occupation of unperturbed habitats or regions, physiological tolerances that happened to match the extinction-driving stresses, and perhaps particular ecological strategies, all might play a role in survivorship (10–12). Further, the broad correspondence between survivorship during mass extinction and long-term clade volatility (variance in standing diversity, i.e., net diversification rates rather than per-taxon origination or extinction rate) (13–15) suggest that other intrinsic biotic factors (6) carry over from low to high extinction-intensity regimes…Given that some clades show consistently severe or mild responses to extinction events, which suggests that intrinsic biotic factors are important determinants of survivorship, why does the vulnerability of other clades appear to vary significantly among extinction events (6, 16)? This question bears critically on the evolutionary consequences of extinction events but has received little attention. Potential explanations range from long-term hardening of clades by the removal—and failure to re-evolve—extinction-prone constituents, to contrasting forcing mechanisms in the different extinction events, to fortuitous trait combinations evolved under “background” extinction regimes. Such analyses also are needed to make better biological sense out of apparent selectivity against major clades (e.g., ammonites, mosasaurs, dinosaurs etc. at the K-T boundary) when other selectivities appear indifferent to clade membership [e.g., widespread vs. restricted-range bivalves and other taxa at many extinction events (2, 4)].”
(and this on birds)"To drive home these important but somewhat abstract points on the long-term prospects for evolutionary replacements, consider the Cenozoic history of birds. The large, flightless phorusrhacid and diatrymid birds, probably the top carnivores of early Cenozoic terrestrial communities (62, 63), interfered with the triumphant mammalian ascent to center stage in the postdinosaurian world, and probably were not replaced by an exact mammalian analog once they disappeared. Note also that these carnivorous birds opportunistically converged on theropod dinosaurs rather than adhering to the pterosaur models that might have been the most likely targets for convergence given a flying avian starting point (62). …
*
Again thank you, this one cite has IMHO answered the OP’s question.
So, DrDeth, you’re saying that the internally-inconsistent hierarchy is the one true absolute correct one, and the alternate one which has been modified to correct the inconsistency is the “completely fantastic and false” one? If you want to hold onto something resembling the structure Linneaus used, then you’re kind of forced to use a modification like the one *Colibri posted. Or, of course, you could completely discard the premise that you’re sticking to Linneaus, but you seem even more averse to that option.
No, as I have said several times, Cladistics is perfectly valid and even often a better tool than Linnean system of taxonomy, depending on what you want to show. However for many other things, Linnean system of taxonomy is a better tool. Indeed for this debate- cladistcs are better. I just wanted to show the dicotomy where Paleontologists list Theropoda as a Suborder, but Ornithologists continue to list Aves as a Class. There is a dicotomy there, and I think it is both interesting and telling.
It is perfectly OK to say that birds are a named clade within a larger clade comprised of dinosaurs. Fine by me. But once you start using the Linnean system of taxonomy and it’s named hierarchies, then you can’t just make shit up. Thus under cladistics “birds are a named clade within a larger clade comprised of dinosaurs” or even “Passeriformes are a named clade within a larger clade comprised of dinosaurs” are perfectly fine. But saying “Under the Linnean system of taxonomy, Theropoda is an Infraclass” is completely false. No one claims that.
There’s nothing false about it. It’s a perfectly valid Linnean hierarchy that represents the actual cladistic groupings.
No, it is not “really” anything. As I have repeatedly pointed out to you, there is no “official” higher classification of these groups. I don’t know why you have so much trouble grasping this simple fact.
This is completely irrelevant to my point. It doesn’t matter what the common classification is; what I wrote is a valid Linnean hierarchy.
Once again, the idea that “Theropoda is currently a Suborder” presupposes that there is some objective standard or official endorsement that makes it a Suborder. There is none. It is not a “fact” that Theropoda is a Suborder; this is an opinion that can vary between taxonomists.
I have repeatedly pointed them out, as have others. You have made repeated errors concerning taxonomic standards and practice. You have also stated that the evidence for birds being dinosaurs is “slim” when in fact it is voluminous. There are many others.
It isn’t an ad hominum attack when I point out that most of what you have posted is based on a complete misunderstanding of the key issues involved. I haven’t made any remarks about you personally, other than commenting on the level of knowledge that is evident from your posts. This is relevant to the discussion.
You know, when you get expert opinion on a subject, you might actually try to learn from it, rather than Googling random references and basing your opinion on those.
You could quite easily stop it by refraining from posting nonsense. As long as you continue to do so, I’ll continue to refute it, per GQ practice.
To clarify a bit, the hierarchies that I posted and the one that DrDeth did are consistent with one another. The only real difference is which particular hierarchical names one applies to the particular branching nodes. (Sauropsida is a level above Archosauria; either could be called a Class.) Both the hierarchies are Linnean, but both follow cladistic principles rather than the Linnean one of recognizing paraphyletic groups (assuming Aves are included within Theropoda and not recognized as a Class).
You know, it gets much, much worse. Impose cladistic findings (which are acknowledged as accurate for defining lines of descent even among those who don’t espouse the cladistic taxonomy of Darwin’s Finch, and you get:
(And have fun fitting all tetrapods into a single family, and all dinosaurs and birds into a single supergenus.)
On the other hand, regarding “Dinosauria” as part of “Reptilia” (or even Sauropsida, which I’ll bet most readers of this thread had never heard of), with Reptilia or Sauropsida as a Class and Aves as another class, obscures the extremely clear biological relationship between the smaller theropod dinosaurs and early birds.
And I frankly see no reason not to regard “dinosaur” as “a paraphyletic grouping of the tetrapodal land-living and amphibious members of Clade Dinosauria, which went extinct at or before the end of the Cretaceous, explicitly excluding crown group Aves” vs. “birds” as “the feathered, winged and flying or sedcondarily flightless members of Clade Aves, a subclade of Clade Dinosauria.” Which eliminates the irony implicit in “non-avian dinosaurs” or the jokes about “the dinosaurs are migrating north for the spring.”
But stop with the baseless Ad hominem attacks, OK? You’re better than that.