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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)
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)
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:
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
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, 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
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
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)
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)
I don't have the knowledge to improve it, but this biggest dinosaur bit is unclear.
Aliter 17:12, 18 May 2004 (UTC)
Should this be ordered more like:
? Aliter 17:12, 18 May 2004 (UTC)
What defines the difference between a reptile and a dinosaur? -Rob May 28, 04
MWAK
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)
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)
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)
MWAK
MWAK
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)