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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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    $\begingroup$ 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. $\endgroup$ – Remi.b May 21 '14 at 21:21
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    $\begingroup$ 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 $\endgroup$ – Songo May 22 '14 at 15:44
  • $\begingroup$ Related: If dinosaurs could have feathers, would they still be reptiles? $\endgroup$ – Remi.b May 28 '18 at 22:08
  • $\begingroup$ If there were, would they be known as flying dynosaucers? $\endgroup$ – user1136 Jun 3 at 19:43
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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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  • $\begingroup$ 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.) $\endgroup$ – Sparhawk May 22 '14 at 5:32
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    $\begingroup$ "Flying reptile" is often used not to mean "a reptile which flies" but instead as a synonym for Pterosaur. $\endgroup$ – Noah Snyder May 22 '14 at 10:41
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    $\begingroup$ 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. $\endgroup$ – Matt Thrower May 22 '14 at 10:58
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    $\begingroup$ 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. $\endgroup$ – Steve Jessop May 22 '14 at 19:03
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    $\begingroup$ @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. $\endgroup$ – Sparhawk May 23 '14 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

By any reasonable definition, T. Rex is more closely related to sparrows than to Stegosaurus.

  • Separation by time
  • Phylogenetic distance
  • Physical similarity

Birds aren't descended from dinosaurs, they are dinosaurs.

Which means the fastest animal alive today is a small carnivorous dinosaur, Falco Peregrinus.

It preys mainly on other dinosaurs, which it strikes and kills in midair with its claws.

This is a good world.

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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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Asides from flight-capable modern birds and their early ancestors1, there are several other therapod dinosaurs which palaeontologists suspect were capable of flight, "but in a manner substantially different from that of modern birds":

Dromaeosaurids

enter image description here

enter image description here

  • Sinornithosaurus
    Feathered coelurosaurs from China: new light on the arboreal origin of avian flight, Feathered dragons

enter image description here

enter image description here

  • Rahonavis
    Glorified Dinosaurs: The Origin and Early Evolution of Birds, Sydney
    Gravity-defying Behaviors: Identifying Models for Protoaves, American Zoologist
    Avian ancestors. A review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, Anchiornis and Scansoriopterygidae, SpringerBriefs in Earth System Sciences
    The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar, Science

enter image description here

  • Zhenyuanlong
    A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution, Scientific Reports

enter image description here

Troodontids

enter image description here

Paraves (basal)

enter image description here

Scansoriopterygidae

And interestingly, not using feathered wings but membranous ones similar to bats or pterosaurs:

enter image description here

enter image description here


Sources:

 • 1. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds, Nature
 • Wing bone geometry reveals active flight in Archaeopteryx, Nature Communications
 • The wings before the bird: an evaluation of flapping-based locomotory hypotheses in bird antecedents., PeerJ

Note: flight in Anchiornis only suspected of being possible in juveniles

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