Are birds dinosaurs? Discuss

[Tin Pot]

T Rex

 

[Profpointy]

Birds are not dinosaurs. Birds and one branch of dinosaurs shared a common ancestor before about 167 million years ago. At this point the phylogenetic tree branches and they take their respective paths.
I'm still obsessed with dinosaurs (and as a biologist, I'm allowed to be even though I am over the age of 5!)

All my half dozen dinosaur books say birds are dinosaurs. They do allow non-avian dinosaurs as a term for traditional dinosaurs, but scientifically you can't really have a category ( dinosaurs) which only misses out a whole group of descendents but includes others far less closely related. If you say birds are not dinosaurs but are descended from dinosaurs its akin to saying monkeys aren't mammals but are descended from mammals. A bird doesn't stop being a sub-category of the larger group.

Reptiles of course become problematic, as it becomes a bit of a mish-mash group if it includes dinosaurs, and only very distantly related things like snakes or crocodiles but somehow misses out descendants of dinosaurs. I believe modern thinking is to try an avoid the term reptile if talking of evolution rather than merely naming, or even to expand to include birds.

A trickier question might be "is a cow a fish?" and in one sense maybe the answer is "yes" although a step too far for some

 

[Profpointy]

View attachment 416793

Yebbut are pliesiasaurs dinosaurs though?

 

[swansonj]

All my half dozen dinosaur books say birds are dinosaurs. They do allow non-avian dinosaurs as a term for traditional dinosaurs, but scientifically you can't really have a category ( dinosaurs) which only misses out a whole group of descendents but includes others far less closely related. If you say birds are not dinosaurs but are descended from dinosaurs its akin to saying monkeys aren't mammals but are descended from mammals. A bird doesn't stop being a sub-category of the larger group.

Reptiles of course become problematic, as it becomes a bit of a mish-mash group if it includes dinosaurs, and only very distantly related things like snakes or crocodiles but somehow misses out descendants of dinosaurs. I believe modern thinking is to try an avoid the term reptile if talking of evolution rather than merely naming, or even to expand to include birds.

A trickier question might be "is a cow a fish?" and in one sense maybe the answer is "yes" although a step too far for some

So can I ask you again: do you think these definitions have any absolute meaning, or are they just arbitrary?

 

[Tim Hall]

I read that. Loved it. I don't think it was Bradbury, but I was a Bradbury completest so maybe ...

Edit: found it!

That's the one. I was going to post but the thread was locked when I got here.

 

[classic33]

Yebbut are pliesiasaurs dinosaurs though?

By being waterbournne not landbourne, no.

 

[Julia9054]

So can I ask you again: do you think these definitions have any absolute meaning, or are they just arbitrary?

It's arbitrary. Why pick dinosauria when you could just as easily pick archosauria, diapsida (the clade which includes all reptiles) or tetropoda - all pylogenetic clades which also contain birds? It's because people have heard of dinosaurs.

 

[Profpointy]

So can I ask you again: do you think these definitions have any absolute meaning, or are they just arbitrary?

I think they have absolute meaning.
The answer may change with evidence, but they are not arbitrary, an absolutley not social constructs

 

[Profpointy]

It's arbitrary. Why pick dinosauria when you could just as easily pick archosauria, diapsida (the clade which includes all reptiles) or tetropoda - all pylogenetic clades which also contain birds? It's because people have heard of dinosaurs.

Well that's kind of muddying the waters isn't it? Tetrapods are a thing, diapsids, synapsyds, archasaura, dinosaurs and so on. One can argue based on evidence if the lesser spotted toad whippet is or isnt in one of these cateogries, but it is surely dead wrong to claim any are arbitrary.

 

[Julia9054]

Well that's kind of muddying the waters isn't it? Tetrapods are a thing, diapsids, synapsyds, archasaura, dinosaurs and so on. One can argue based on evidence if the lesser spotted toad whippet is or isnt in one of these cateogries, but it is surely dead wrong to claim any are arbitrary.

Perhaps i didn't make myself clear. Of course the categories are not arbitary but phylogenetics as we currently understand it. The fact that people are saying "birds are dinosaurs" rather than naming any other clade that birds are part of is arbitrary and based on the fact that "dinosaur" has a specific meaning within popular culture that people understand. I am certainly not claiming that birds are not members of that clade.

 

[Pat "5mph"]

@Julia9054 you're a good teacher: I can understand your posts even though I know nothing of the subject.
Well, I know a bit more now!

 

[Profpointy]

Perhaps i didn't make myself clear. Of course the categories are not arbitary but phylogenetics as we currently understand it. The fact that people are saying "birds are dinosaurs" rather than naming any other clade that birds are part of is arbitrary and based on the fact that "dinosaur" has a specific meaning within popular culture that people understand. I am certainly not claiming that birds are not members of that clade.

Ok I think I see what you are getting at. Choosing to say "birds are dinasaurs" rather than "birds ar diapsids" or "birds are archosaurs" is the arbitrary choice

(hopefully thw above are right rather than a new unintended controversy born of ignorance: I didn't double check)

For all that, i was amazed and delighted when I recently learnt "birds are dinosaurs" and by implication reptiles aren't really a thing in that crocodiles are closer to birds than to lizards or whatever.it is. . And me more of a physics geek too

 

[Julia9054]

It's really a question of semantics. I would argue that birds have come far enough down their evolutionary pathway to say that birds are birds. Does a statement like birds are dinosaurs help or hinder the general public's understanding of how evolution works.

 

[Profpointy]

It's really a question of semantics. I would argue that birds have come far enough down their evolutionary pathway to say that birds are birds. Does a statement like birds are dinosaurs help or hinder the general public's understanding of how evolution works.

Helped me I think. The whole cladistics thing just seems so much more logical. A cow really is a sort of fish it seems. Unless.you follow this path aren't you in danger of Rutherford's comment "there is only physics, the rest is stamp collecting"

As an aside one of my current books is "Rise of thr fishes", having worked back through dinasours, amphipians, via digressions into Trilobytes (Fortey) and so on

 

[swansonj]

I think they have absolute meaning.
The answer may change with evidence, but they are not arbitrary, an absolutley not social constructs

In that case, may I ask you
(A) is marmalade jam?
(B) does that have an absolute meaning or is that arbitrary definition?

Then we might move on to how many continents there are?