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Cladistic relatedness of Aves and Reptiles

Discussion of everything related to the Theory of Evolution.

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Cladistic relatedness of Aves and Reptiles

Postby Weston » Sat Oct 16, 2010 8:30 pm

I've recently become extremely interested in the evolutionary relation between aves and reptiles. My girlfriend and brother butt heads over the topic. My girlfriend works with reptiles in a zoo setting, and claims that birds are reptiles. My brother just finished his undergraduate degree in biology and is adamant that although birds share the same common ancestry as modern reptiles, that they are not, in fact, reptiles themselves.

All the research I've done shows that aves and reptiles differ on the class level! Despite all of the anatomical similarities between them, the only thing the two taxa have in common is that they're chordates?

Does anyone know or have access to any information on the topic?

I'd love to get my grubby hands on a phylogram or a chronogram.
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Re: Cladistic relatedness of Aves and Reptiles

Postby StevePush » Mon Oct 18, 2010 2:27 pm

Your girlfriend is right. The scientific concensus is that birds evolved from dinosaurs (in fact, are dinosaurs) and thus birds are reptiles. But because all of the other dinosaurs are extinct, birds are not closely related to any other living reptiles.

Source: Evolution by Douglas J. Futuyma, 2005, Sinauer Associates, Inc.
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Postby Darby » Tue Oct 19, 2010 2:22 am

Birds are generally considered paraphyletic to dinosaurs, which themselves are probably paraphyletic to reptiles - they share derivation, but the newer group is considered separate.
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Re: Cladistic relatedness of Aves and Reptiles

Postby StevePush » Tue Oct 19, 2010 3:02 pm

I stand by my position that Weston's girlfriend wins the argument. Reptilia is a monophyletic group that includes all birds and extinct dinosaurs. Excluding birds because they are the only extant warmblooded, feathered members of the clade represents historical bias rather than evolutionary relatedness.

See http://en.wikipedia.org/wiki/Monophyletic for diagrams showing both the monophyletic and paraphyletic groups.
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Re: Cladistic relatedness of Aves and Reptiles

Postby Weston » Tue Oct 19, 2010 4:39 pm

I appreciate the notation of a source other than wikipedia backing your point, Steve. Does the textbook make note of the primary source for the statement? I'd really like to find a journal article on the topic, but my ability to search scholarly articles efficiently is gone now.

$130,000 for an education, and the university doesn't even allow you to use their science-dedicated search engines after you graduate. Some deal, eh?

Google scholar makes me cry.

Anyway, if there was a citation for that, it would be nice to see.

Thanks.
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Re: Cladistic relatedness of Aves and Reptiles

Postby StevePush » Tue Oct 19, 2010 5:22 pm

According to L.M. Chiappe and G.J. Dyke (2002), "most researchers agree that birds are theropod dinosaurs." Even before this consensus formed, the other candidates for birds' ancestors were all reptiles, specifically turtles, lizards, crocodylomorphs, pterosaurs, and other kinds of dinosaurs.

Source: L.M. Chiappe and G.J. Dyke. The Mesozoic radiation of birds. Annu. Rev. Ecol. Sys. 2002, 33:91–124. http://biology-web.nmsu.edu/houde/Chiap ... e_2002.pdf

If this argument involved a bet, I want a cut. :)
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Re: Cladistic relatedness of Aves and Reptiles

Postby Weston » Tue Oct 19, 2010 8:13 pm

Steve, thanks very much for the information and quick replies.

Unfortunately, there was no bet over the matter. My girlfriend and I would very much enjoy a night on the town at my brother's expense! :lol:
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