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Birds are Dinosaurs

Birds are now generally believed to represent descendents of dinosaurs, and so are classed with them by those who believe groups should be monophyletic.

Can someone point to a reputable source that claims birds are a kind of dinosaur? - Tim

Just type "bird dinosaur site:.edu" into Google. Here's one that popped up: http://www.ucmp.berkeley.edu/diapsids/avians.html. "Kind of dinosaur" is of cause a matter of definition, but there is no questions that birds are the closest living relatives of the dinosaurs, closer still than the crocodiles and other reptiles. --AxelBoldt

The point is more than that. Birds are not just the closest living relatives of the dinosaurs, but are in fact closer to some dinosaurs than they are to others. As there has recently been a big push for monophyletic groups, the Dinosauria would either have to be broadened as a formal category or extended to include birds. In practice the latter approach seems to be the one taken. I can't name any particular source, though UCMP and the tree of life would be some of the first I check, but I have seen it in a few more recent books.

Birds are not dinosaurs. Even if dinosaurs evolved into birds (contentious) then it is still true to say that all dinosaurs became extinct. DJ Clayworth 20:21, 6 Feb 2004 (UTC)

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1) Theropod origins is not, I repeat, not contentious. The half-dozen vocal paleornithological holdouts does not a contentious position make.

2) Phylogenetically, Aves is a clade within Dinosauria, just like Hominidae is a clade within Mammalia. So yes, birds are dinosaurs just like we are mammals.

Pterosaur conflicts Dinosaur, as it places birds within the Dinosuar classification, which means they are more than just closely related, and they aren't extinct either. How do we resolve this? Aliter 17:12, 18 May 2004 (UTC)

Check some biology textbook. Or Google for a relevant and authoritative page on that. There probably is one right way to classify birds. I am just not sure about those Archosaurs - who they are, may be just an artificially defined group to have a place to put birds and dinos into? Paranoid 21:06, 28 May 2004 (UTC)

Archosaurs are a natural group including birds, dinosaurs, pterosaurs, and crocodylians, set apart by the appearance of socketed teeth and the like. The thing is this. Birds clearly belong to the dinosaur clade, and dinosaurs belong to the archosaur clade, but these are not the same thing as taxa. Traditionally birds have been considered a class ves, and the others tossed into the class Reptilia. More recently there has been a move towards having taxa that represent clades, and Archosauria is as standard a class as any for these new schemes. But ornithologists are still happy with Aves, and keeping a separate Aves renders the adoption of Archosauria as a class superfluous.

See also:

• Feathered dinosaurs
• Talk: Feathered dinosaurs

adaptability concern

On the main page there had been a comment that only the most adaptable animals survived the K-T extinction, like mammals. I don't believe this is concensus, and there is a lot of evidence against this. Dionsaurs were highly adaptable and diverse, as were ammonites and other groups that were devastated or destroyed, while crocodiles and other such forms managed to pull through. Indeed the placental mammals had not shown much diversity before the Cretaceous. If anything, then, I would say that the more conservative groups were the ones that faired better. If there is a kernel of truth in the statement, it will need considerable modification before it is true enough to replace.

"Adaptable" organisms tend to survive extinction events simply because, having already proved to be adaptable, they have filled many various ecological niches, a few of which are more likely to survive moderately intact, when the extinction dice roll. "Adaptability" is not neccessarily a virtue in the changed situations that characterize extinction events. Rather than "conservatives" etc. the survivors tend to be "generalists."Wetman 20:22, 17 May 2004 (UTC)

Well humans seem to be the best generalists. Lets see if we survive. 28 May 2004

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Okay, here?s my knowledge/reasoning on that:

In the Permian, the dominant phylogeny of large land animals was the Synapsida, (pelycosaurs, in particular) the ancestors of mammals, or in the case of the pelycosaurs, great-uncles more like. The end of the Permian was marked by the Permian-Triassic extinction event, largest mass extinction known, in which it is estimated that more than 90% of all animal species went extinct. Certainly at least part of the cause was the formation of Pangaea at that time and the climatic (climactic?;-) ) change that would have been caused. Because a) the land fauna had been devastated and b) there was only one continent, the early Triassic had pretty much only one set of land animals that was found all over the world. In the mid-Triassic, several new groups arose to move in the gaping holes. The foremost among these (again only speaking of terrestrial animals) were the crocodiles, the dinosaurs, and the mammals (and their close relatives among the therapsids).

At the end of the Triassic, another mass extinction (the Triassic-Jurassic extinction event), wiped out the major contenders from Crocodilia and Mammalia. This left the dinosaurs to inherit all the Earth. Since Pangaea was still all together they spread across the whole continent, leaving no place a competing group might be able to develop from. So the dinosaurs were extremely succesful and utterly dominant as land animals for the 130 odd million years, while the crocodiles and the mammals hung on on the margins by staying out the way of the dinosaurs, concentrating on semi-aquatic ambushing, and nocturnal insectivory, respectively.

The Dinosaur species were thus able to monopolize abundant resources and grow big, and specialize. The other groups, did not have access to the abundant resources and had to remain flexible enough to utilize anything that came their way, and generally stayed rather smaller and/or slower metabolismed than the dinosaurs.

Thus when the disruption that caused the Cretaceous-Tertiary extinction event, probably significantly including the Chixculub meteor, the dinosaurs fared worse.

That is, the dinosaurs, being succesful, were able to be phylogenetically adaptable, which made them individually more conservative.

The crocodiles and mammals, on the other hand, having lost out in the Triassic-Jurassic lottery, had never had the opportunity that the dinosaurs had to be phylogenetically adaptable and diverse, had retained relatively conservative body plans throughout the Jurassic and Cretaceous, but had to be individually more adaptable in more precarious niches than those enjoyed by many dinosaurs.

Which is all to say, yes there is a kernel of truth to the statement, and yes it does need considerable modification.. But all this should probably be put in the Cretaceous-Tertiary extinction event article, which I have just added links to from Dinosaurs. I hope to put up some of this information in when I actually have some references handy. Or someone else can.

old talk

Old talk, moved here from Talk:Dinosaurs:

Therepoda are a subgroup of Saurischia, so that change is not correct --Arco Scheepen

That seems to be the current best guess, but there is not a huge amount of evidence and it is possible opinions might change. In any case Therepoda are sufficiently different to the other Saurischia that i thought they needed a mention on the front dinosaur page. I am happy with the arrangement there now.

245M years ago is *way* too early.

Permian ended 230M years ago, and there were certainly no dinosaurs at that time. And they didn't appear until middle Triassic.

So correct number is most probably somewhere between 220M and 210M years ago.

What about reptiles relationship to dinosaurs? --rmhermen

Interesting question. Does it belong here or in reptiles? Of the surviving reptiles they should be closest to crocodiles, but of course they are even closer to birds. The statement about thecodonts on the page is interesting. My understanding is that thecodonts are supposed to be the common ancestor of dinosaurs birds and crocodiles. Some experts now regard thecodonts as a very dubious grouping, with some of the supposed thecodonts now believed to be not closely related to the others, and much disagreement about what actually are and are not thecodonts. What is the current concensus about this?

Current concensus is that the thecodonts are simply the basal Archosaurs, and so form a group paraphyletic to the dinosaurs-and-birds, pterosaurs, and crocodylians, in the same way that the reptiles are simply the basal amniotes and form a group paraphyletic to birds and mammals. Whether or not you accept either as a valid grouping depends on whether you restrict groups to monophyly. There is an increasing tendency to do this, but I don't think it's near universal yet.

"Thecodontia" is used only by a handful of holdouts; the same folks who question theropod origins. It is, without a doubt, a polyphyletic garbage-bag for non-dinosaur, non-pterosaur, non-crocodylomorph archosaurs.

As for Reptilia, sensu Gauthier, its perfectly monophyletic. See for example my page of the EvoWiki here for characters supporting it. -GFA

recent lecture

At a recent lecture I went to the current evidence is that dinosaurs were not reptiles at all. This is because a large number of them were too large to have been cold-blooded unless they ate huge, huge amounts. Secondly some dinosaurs had very advanced, large brains. Thirdly their is even some evidence that dinosaurs could have had wings as the fossil of arceopteryx is identical to that of another dinosaur except for the feathurs. Dinosaurs should be considered as a seperate group and not reptiles

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The dinosaurs, being succesful, were able to be phylogenetically adaptable, which made them individually more conservative. This is not necessarily so. Diversification creates specialists as well as generalists. Populations of generalists survive sudden change better than specialists. Wetman 20:22, 17 May 2004 (UTC)

Taxonomy

The listed classification does not seem to match any of the cladograms in the external references. I will work over the next few days to come up with something that is representative of the external data. - UtherSRG 12:15, 17 May 2004 (UTC)

Biggest

I don't have the knowledge to improve it, but this biggest dinosaur bit is unclear.

• Is the Sauropodus Argentinosaurus the biggest or isn't it? If we think Brachiosaur Ultrasaurus is bigger, why is it not the record holder? Is this because we've never seen a whole one? (But did we ever see a whole Argentinosuarus?)
• If only one certain species of whale is bigger, then it should be possible to name it. (Bigger than Argentinosaurus or than Ultrasaurus?)
• Throw a scale of cmparison around. We mention the weight of Ultrasaurus. What about Argentinosaurus and the whale? Put in T-Rex for comparison, as that's what people think of as the biggest dinosaur, even if it isn't. (Is it still called T-Rex? I thought it was discovered to already have been named differently a few decennia earlier.)

Aliter 17:12, 18 May 2004 (UTC)

Structure

Should this be ordered more like:

1. Overview
   1. Characteristics (Common or Diversity)
   2. Saurischians
   3. Ornithischians
   4. Related classes
2. Collected Knowledge
   1. Warm-blooded dinosaurs
   2. Feathered dinosaurs
   3. Surmises about dinosaur behavior
   4. Extinction
3. Classification of dinosaurs
4. Dinosaurs in culture
5. External links

? Aliter 17:12, 18 May 2004 (UTC)

I think we should make each link to a dinosaur species in the same format. Obviously, pages for each would be ideal, but instead of simply linking to Abelisaurus, we should linke to Dinosaur_Abelisaurus, or maybe Abelisaurus_(dinosaur). If we do this for more things, lists will be less cluttered. Lockeownzj00 21:27, 18 Jun 2004 (UTC)

Well, the idea is to use a distinct term as the title, so the term can be used in text and so people can jump to the page by typing in that term. Only when this purpose is defeated by the fact that there is more than one concept with the same name, specifications are added. So [[Abelisaurus]] would be OK, and [[Abelisaurus (dinosaur)]] would only be used if Abelisaurus meant something else as well. Aliter 20:22, 28 Jun 2004 (UTC)

reptile v dinosaur

What defines the difference between a reptile and a dinosaur? -Rob May 28, 04

I Dinosauria is factually within Reptilia, so the proper question should be: what differentiates Dinosauria?

II Reptilia itself is not defined by morphology or characters, but by ancestry. The same is true for Dinosauria. So there is a difference by definition, in that there is a difference of definitions. So no matter how birdlike the dinosaurian, it will always be dinosaurian - and thus reptilian, if Dinosauria is factually within Reptilia.

III Given these definitions, the differentiation of Dinosauria within Reptilia is not a matter of definition, but of empirical fact. The known facts show that Dinosauria is within Reptilia.

IV Go back to I.

MWAK

I'm feeling a bit confused about the reason for removing this. It is the accepted scientific opinion on the matter - and quite informative, if only you try to understand it. Be not afraid of either science or logic. :O)

MWAK

I'd removed it for it being a bad answer. Yes, the clade of Dinosauria is within the polyphyletic grouping called reptilia (please don't capitalize it...). Your answer does nothing to explain the differences between reptiles and dinosaurs, tries to use smoke and mirrors to make it look like you have an answer and a clue, and then gets obnoxious with "Go back to I". (To paraphrase: You don't answer the question, you pretend to answer the question, then you get obnoxious.) I figured these were fair grounds for removing your response. - UtherSRG 12:06, 4 Jun 2004 (UTC)

Well, maybe my answer was very bad. Then expose it. But don't remove it. Allow others to judge for themselves!

But was my answer so bad? You seem to think so - and in a way you're absolutely right. The answer you think I gave is indeed utterly incoherent. That is because you assumed that I used the name Reptilia in the traditional sense. But of course I didn't. It's not my habit to give incoherent answers. I obviously, as any good taxonomist would, referred to Gauthiers crown-clade definition. Yes, perhaps that name is redundant, what with Eureptilia and Sauria or even Amniota. But whether it is, is a matter of fact, not definition. Just as the differences between a "dinosaur" and a "reptile" are factual, and not a matter of definition. That is the dangerous misunderstanding, implied in mr May's question, that I tried to make explicit. And though I am often ironic, I, it goes without saying, am never obnoxious. Step IV simply makes the framework of my reasoning coherent. Or not?

MWAK

No, you are certainly obnoxious. Stating just that the difference between reptile and dinosaur is factual doesn't say *what* those differences are. Certainly the differences are factual (as opposed to fictional), but the question was *what* are the differences. Also, this doesn't preclude the differences being a matter of definition either....although the definition comes from those factual differences. So.... do you *have* an answer to the original question, or are you going to simply act in an obnoxious, condescending manner? - UtherSRG 21:38, 4 Jun 2004 (UTC)

Perhaps we can all agree I'm a pedant. So allow me to condescend a bit more. Indeed Rob May probably asked for just that: those "differences being a matter of definition". And he probably thought, as you do, that in turn "the definition comes from those factual differences". Within traditional taxonomy this question makes sense. It can only be answered by: "No such list of characters is known to us, nor is it even possible to give one". This is because traditional taxonomy itself makes no sense within the concept of evolution. That is why a better instrument was created: cladistics. Now it must be admitted that for a painfully long time the cladistic praxis was just as foolish as that of traditional taxonomy, in that clades were defined by synapomorphies. Science progresses however, and we now "all" define clades by ancestry - although it is sometimes useful to apply a secondary synapomorphic taxonomy to the primary systematics. A "dinosaur" is then just a member of the clade formed by the last common ancestor of Iguanodon and Megalosaurus and its descendants. This definition isn't based on the morphological facts (just on the factual ancestry), so we can never directly infer that a species is dinosaurian from its morphology: we have to show it is by way of cladistic analysis. This analysis does give us - and is in turn based on - a list of valid synapomorphies of Dinosauria as against some turtle, but, though proud to be one, I'm not enough of a pedant to provide it. It would be a bit long. :O)

MWAK

I've added the simple distinction. I've also removed a lot of chaff from the taxobox, though I would argue strongly that it should give the class as Reptilia (is a taxon, may be capitalized). Archosauria would be better, since it is a clade, but only if it's also applied to birds, which it doesn't look like it will be any time soon. In fact, since it wasn't even used for crocs, I'm going to make the change. Josh 07:26, 5 Jun 2004 (UTC)

Reptilia sensu Gauthier is a clade too. Isn't it a bit tricky to mix both systems? Why not simply explain the facts to the reader? Embarassing as they might be... :oS

MWAK

We should, and to some extent do. Unfortunately the taxobox only displays a single system.

- How is it that the explanation here on the talk page page is more informative than the one that was intended to go to the page?
- The impression one gets here is quite different from the "Dinosaurs are an extinct superorder of reptiles" on the page, where the fact that the dinosaurs are the super-order and the reptiles are not, suggests the reptiles are an order within the otherwise extinct superorder of dinosaurs.
Could someone who knows what he's talking about rephrase this so the layman will understand it as well? Aliter 10:26, 5 Jun 2004 (UTC)

Eh, Reptilia is supposed to be a "Class", higher in rank than an "Order". It's really all nonsense anyway...

MWAK

OK, if you know how to word that, can you please adapt the first sentence of the article to indicate the dinosaurs fall within the reptiles? (Unless it's that much nonsense that it ought to be removed.) Aliter 01:54, 6 Jun 2004 (UTC)

The problem this article has is that the opening para is trying to do two different jobs: (a) introduce dinosaurs, and (b) deal with complex and confusing taxonomic matters. The answer is to avoid dealing with taxonomy in the first para. Just say "Dinosaurs were creatures that blah blah blaw:. Then have a seperate paragraph saying somethbning like "The traditional classification, now regarded as incorrect is ABCXYZ. Other proposed classifications ... blah blah blah. Tannin 04:00, 6 Jun 2004 (UTC)