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Author Topic:   Birds and Reptiles
faith24
Junior Member (Idle past 2340 days)
Posts: 27
Joined: 09-10-2010


Message 1 of 135 (581893)
09-17-2010 11:25 PM


I am new to this so i'm sorry if this may sound stupid. I would appreciate if someone can answer this question.

How do scientists classify what a bird is and is not, particularly with regard to their possible evolution from dinosaurs? Some say that birds appear earlier in the fossil record than the dinosaurs.

Edited by faith24, : No reason given.

Edited by faith24, : No reason given.

Edited by Admin, : Rewrite to make the topic more clear.


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Admin
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Message 2 of 135 (581929)
09-18-2010 7:30 AM
Reply to: Message 1 by faith24
09-17-2010 11:25 PM


Hi Faith!

These are good questions, but they cover three or four different topic areas. Could you narrow it down to just one topic?


--Percy
EvC Forum Director

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faith24
Junior Member (Idle past 2340 days)
Posts: 27
Joined: 09-10-2010


Message 3 of 135 (581954)
09-18-2010 11:03 AM
Reply to: Message 2 by Admin
09-18-2010 7:30 AM


Sorry. There i changed it.

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Admin
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Message 4 of 135 (582035)
09-19-2010 8:06 AM
Reply to: Message 3 by faith24
09-18-2010 11:03 AM


When you say that they appear earlier in the fossil record, who are you saying they appear earlier than? The dinosaurs?


--Percy
EvC Forum Director

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faith24
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Posts: 27
Joined: 09-10-2010


Message 5 of 135 (582043)
09-19-2010 11:00 AM
Reply to: Message 4 by Admin
09-19-2010 8:06 AM


Yes.

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Admin
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Message 6 of 135 (582168)
09-20-2010 5:50 AM


*** Copied from Proposed New Topics Forum
*** copied here from the Birds and Reptiles *** in the Proposed New Topics forum.

  
Strongbow
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Posts: 26
Joined: 09-16-2010


Message 7 of 135 (582187)
09-20-2010 8:06 AM


Hi Faith,

This is a very interesting subject.

First let me correct a misconception. Birds do not appear earlier in the fossil record than dinosaurs. They do, however, overlap dinosaurs by quite a lot, which is a point some creationists use as "proof" that birds cannot have evolved from dinosaurs, though they look over the fact that this would not say they didn't evolve at all!

I am sure you can see the fallacy of such an argumnet... it's just another version of the old "If humans evolved from apes, why are there still apes?" argument.

Our knowlwdge about the evolution of birds from therapod dinosaurs is still very young... and we're learning more on an almost monthly basis.

The deabte about the exact evolutionary origin of birds is still fairly heated. Many argue that the Theropods are the ancestors of modern birds and that the earliest birds show clear evidence of such a relationship.... for example, scientists now know archaeoptyrex did not have an opposed rear toe, so it's feet looked exactly like a dinosaur's foot and not like a modern bird's foot.

http://news.nationalgeographic.com/...201_archaeopteryx.html

In fact, although archaeoptyrex has usually been considered a dinosaur-like bird, some now consider it a bird-like dinosaur.

Of course, we know about feathered dinosaurs, but the issue does get murkier.

The earliest "birds" seem to appear earlier in the fossil record than the best examples of unambigusously feathered dinosaurs, though cladisitc research indicates that many of the earlier fossil theropods we do have were probably feathered, but we just don't have the skin impressions to prove it. A small minority think the poorly preserved fossil of Longisquama insignis is evidence that birds and dinosaurs had a common ancestor, rather than birds descending from dinosaurs themselves. Those that are proponents of this idea hold that "feathered dinosaurs" are actually early flightless birds, though this idea has it's own complications.

Of course, this gets to your main question, which is one of classification. It's important to realize that classification is a tool invented by humans, and not imposed by nature. We find classifcation useful as a way of describing relatedness, but nature is not at all concerned about defining precise boundaries to assist us. And it only gets more complicated as we find more fossils which fill in the gaps of the record. So, is archaeoptyrex a bird-like dinosaur, or a dinosaur-like bird? It certainly has some features we simply don't usually associate with modern birds. But it is certainly more bird-like than what we tend to think of as a dinosaur.

So the short answer, I think, is that scientists are finding it difficult to draw a bright line between dinosaurs and birds. If you polled 10 paleontologists about this subject, you probably find 8 different answers and 2 who say it doesn't matter.

I hope I helped.


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Huntard
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Posts: 2870
From: Limburg, The Netherlands
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Message 8 of 135 (582190)
09-20-2010 8:29 AM
Reply to: Message 7 by Strongbow
09-20-2010 8:06 AM


Strongbow writes:

They do, however, overlap dinosaurs by quite a lot, which is a point some creationists use as "proof" that birds cannot have evolved from dinosaurs, though they look over the fact that this would not say they didn't evolve at all!


Even worse, they still could've evolved from dinosaurs even if they are overlapping.

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Strongbow
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Posts: 26
Joined: 09-16-2010


Message 9 of 135 (582194)
09-20-2010 9:34 AM
Reply to: Message 8 by Huntard
09-20-2010 8:29 AM


Quite right, of course.

I take that for granted, but forgot that many do not.


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jar
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From: Texas!!
Joined: 04-20-2004
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Message 10 of 135 (582195)
09-20-2010 9:58 AM
Reply to: Message 9 by Strongbow
09-20-2010 9:34 AM


We should also point out that there are examples today of a trait like flight evolving, being lost, and being reacquire so it is entirely possible that dinosaurs could have evolved into flying birds that then evolved into flightless birds.


Anyone so limited that they can only spell a word one way is severely handicapped!

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Strongbow
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Posts: 26
Joined: 09-16-2010


Message 11 of 135 (582254)
09-20-2010 2:26 PM
Reply to: Message 10 by jar
09-20-2010 9:58 AM


Also an excellent and often overlooked point. Thanks!

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Dr Adequate
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Posts: 16112
Joined: 07-20-2006


Message 12 of 135 (582286)
09-20-2010 5:26 PM
Reply to: Message 1 by faith24
09-17-2010 11:25 PM


How do scientists classify what a bird is and is not, particularly with regard to their possible evolution from dinosaurs?

Currently, a bird is Archaeopteryx or anything that is more like a modern bird than Archaeopteryx is.

Of course, this is very arbitrary, and will have to be rethought when someone finds something which is only very slightly less like a modern bird than Archaeopteryx is.

The problem with any system of classification is that nature doesn't make jumps. The current solution depends on the fact that our present knowledge of the fossil record does make jumps.

Some say that birds appear earlier in the fossil record than the dinosaurs.

And my, how very wrong they are. By about 70 million years.

Edited by Dr Adequate, : No reason given.


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caffeine
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Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 13 of 135 (582421)
09-21-2010 10:09 AM
Reply to: Message 12 by Dr Adequate
09-20-2010 5:26 PM


Currently, a bird is Archaeopteryx or anything that is more like a modern bird than Archaeopteryx is.

More accurately, 'bird' is not a scientific term, but a common one, and doesn't have any clear scientific definition. From an eviolutionary point of view, recognising that change is gradual, it's not too important where the exact line is between protobird and bird.

In scientific nomenclature, the birds are 'Aves', and the most common definition of Aves is the one that Dr. Adequate says - the common ancestor of Archaeopteryx and modern birds and all its descendants. This isn't the only definition though, and to try and clarify issues like this and give us clear, unambiguous definitions of groups of organisms, a mighty project is under way called the Phylocode. This will give a standard definition for each taxon so that, in theory at least, anyone working in biology would be able to check exactly what you do and don't mean by 'Aves' (when it will ever be ready is an open question).

Under some of the proposed definitions, Archaeopteryx wouldn't make it into Aves, but whether or not you wanted to carry on calling it an early bird is a matter of taste. Common terms for animals always hit problems when you go back towards distant ancestors, that's why some bioogists decided they needed this unambiguous series of definitions for scientific nomenclature.

Edited by caffeine, : No reason given.


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faith24
Junior Member (Idle past 2340 days)
Posts: 27
Joined: 09-10-2010


(1)
Message 14 of 135 (582498)
09-21-2010 4:44 PM


This article seem to say otherwise about dino-bird evolution. Maybe it was the other way around?

http://www.physorg.com/news184959295.html

There are many differences between birds and dinosaurs. Their lungs, reproductive system, etc. Birds breathe more because they have special lungs. They're incapable of moving their thigh bones like that of dinosaurs, so their lungs will collapsed if they do.

Edited by faith24, : No reason given.

Edited by faith24, : No reason given.

Edited by faith24, : No reason given.


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jar
Member
Posts: 33343
From: Texas!!
Joined: 04-20-2004
Member Rating: 3.0


Message 15 of 135 (582499)
09-21-2010 4:55 PM
Reply to: Message 14 by faith24
09-21-2010 4:44 PM


Actually that doesn't say that birds came before dinos or that dinosaurs evolved from birds, just that the split may well have been earlier and some of the finds may have been misidentified.

This is another example of why Science will work. As more information is learned, even strongly held opinions get challenged.


Anyone so limited that they can only spell a word one way is severely handicapped!

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