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I've seen some articles which came in contradiction with each other.

The first article was talking about flying dinosaurs, dinosaurs with feathers and so on.

A couple of other articles are talking about misconceptions about dinosaurs one of them being that there are no flying dinosaurs but just flying reptiles (from scholastic.com and livescience.com).

So, which one is right? Also if possible please provide a source for argument.

I cannot find the first article again.

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Can you also provide the articles that you have read? –  golgicik May 21 at 16:17
    
Which articles have you been reading? Can you link them here please (use the edit button below your question). –  Chris May 21 at 16:42
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Beside the question of "Could the Pterodactyle fly?", there is the second "What is a dinosaur?". This question is related to the second one. But anyway, @kmm already provided a very good answer that you could accept. –  Remi.b May 21 at 21:21
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The title of the question is a little bit scary u know. I was under the impression that there is currently no flying dinosaurs :D –  Songo May 22 at 15:44
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3 Answers 3

Birds are both flying dinosaurs and flying reptiles. Yes, that's potentially confusing.

To understand the apparent contradiction, you have to understand how modern classification of organisms works (phylogenetic systematics). Under the old (Linnean) classification system, Reptilia (reptiles) was an order and Aves (birds) was a separate order. Phylogenetic systematics, which has completely replaced the Linnean system, views all organisms as interrelated in a nested set of monophyletic groups (clades). It's like a set of venn diagrams, where all organisms fall into a giant circle and then successively smaller circles classify more and more specific groups.

The clade Reptilia includes snakes, lizards, crocodiles, and lots of extinct groups, including dinosaurs. So all dinosaurs are reptiles. The clade Dinosauria includes all the extinct dinosaurs (Stegosaurus, Triceratops, sauropods, etc.), including theropod dinosaurs, which include well known dinosaurs like Tyrannosaurus and Allosaurus. Based on a mountain on anatomical evidence, including lots of transitional fossils, living birds are a sub-group of theropod dinosaurs.

So all birds (Aves) are theropod dinosaurs (Dinosauria: Theropoda). All dinosaurs are reptiles. Therefore, birds are dinosaurs and reptiles. They are just more closely related to dinosaurs than to other reptiles.

The tricky part is that most people have an intuitive idea of what "reptiles" and "dinosaurs" are. To a systematist, whose job it is to classify organisms, these terms don't mean the same thing as they do to most people. Systematists think about groups like Reptilia and Dinosauria and how those groups are related to one another. So they have no problem saying that birds are dinosaurs and reptiles, because birds are nested within both of those groups.

A few words about pterosaurs

Along with birds and bats, pterosaurs are the other clade of vertebrates capable of powered, flapping flight. Pterosaurs fall within Reptilia (and Diapsida and Archosauria) along with Dinosauria, which includes birds. There are a lot of other extinct lineages in the tree that are not shown, e.g., ornithodirans that are not dinosaurs and not pterosaurs. Pterosaurs and birds share anatomical features that all reptiles, diapsids, archosaurs, and ornithodirans have, which is how we know that they are more closely related to each other than to other groups, like crocodiles. But their flight structures evolved independently and are anatomically distinct fro one another. So pterosaurs are flying reptiles but not flying dinosaurs.

These images might help you understand the above explanation.

enter image description here

enter image description here

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Nice answer, but having said that, there's no reason why dinosaurs can't be a paraphyletic group. (I don't know if they are, but it's potentially a taxonomic leap to equate monophyly with calling them the same name.) –  Sparhawk May 22 at 5:32
    
"Flying reptile" is often used not to mean "a reptile which flies" but instead as a synonym for Pterosaur. –  Noah Snyder May 22 at 10:41
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This is a good comprehensive answer - but I think the OP needs to also understand that pterosaurs are not dinosaurs, and that this is a separate question from whether birds are flying dinosuars. You might want to edit your answer to include this information, since it's also a matter of systematics. –  Matt Thrower May 22 at 10:58
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The most important take-away being that ostriches (Struthio camelus) are the largest remaining dinosaurs :-) And sure @Sparhawk, dinosaurs can be a paraphyletic group in the sense that you can define a jargon term any way you like. But cladists will refuse to utter the word with such meaning. –  Steve Jessop May 22 at 19:03
    
@SteveJessop I'm an evolutionary biologist (amongst other things), primarily in protists, a polyphyletic group. There are certainly other poly/paraphyletic groups that are defined as such (e.g. fish), although I agree that most of them are not useful from a classification perspective. I am unfamiliar with dinosaur taxonomy, but I was just making the point that birds being nested in the dinosaur clade doesn't necessarily imply that they are dinosaurs. I think the answer has to explicitly mention the claim that dinosaurs are monophyletic. –  Sparhawk May 23 at 0:39
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In addition to kmm's excellent answer, I'd like to present the xkcd point of view.

xkcd/1211

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I'm not an expert, but I think that you have to be specific about the flying animals to which you are referring. Pterosaurs are not classed as dinosaurs, whereas modern birds are descended from theropod dinosaurs which is where feathers appeared.

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