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Re: Arctometatarsalia



On Tue, 26 Feb 2002, Jaime A. Headden wrote:

> Mike Keesey (tmk@dinosauricon.com) wrote:
>
> <To belong to _Carinatae_ _sensu_ de Queiroz and Gauthier 2001, the
> organism must have a keeled sternum *synapomorphic with that character in
> _Vultur gryphus_*. Thus, pterosaurs do not belong, as they developed
> keeled sterna separately.>
>
>   Not so. They explicitly write (I have the paper) that the qualification
> for the sternal keel, as found in *Vultur*, pertains to a set of features
> to include attachment of the mm. scapulocoracoideus and pectoralis, as
> well as arising from the midline of the sternum itself. In almost every
> feature, the pterosaur sternum agrees with the avian sternum, and a
> separate core of ossification for the keel itself is even approximated in
> some birds, so this cannot be stated to be non-homologous.

I have the paper, too:

"'_Carinatae_' refers to the clade stemming from the first panavian with a
keeled sternum homologous (synapomorphic) with that of _Aves_ (_Vultur
gryphus_ Linnaeus 1758)."

"Note that although pterosaur sterna are also keeled, that keel is not
homologous to the keel of _Aves_, and therefore pterosaurs are not part of
_Carinatae_."

IOW, since pterosaurs developed their keeled sterna separately from the
ancestor of _Vultur gryphus_, they are not part of _Carinatae_. The only
way pterosaurs could be included is if the trait is a synapomorphy for
birds and pterosaurs, which could only be true if:

a) a number of lineages (_Marasuchus_, ornithischians,
sauropodomorphs, herrerasaurids, coelophysoids, carnosaurs, various
coelurosaur lineages, etc.) are all secondarily without sternal keels.

or

b) pterosaurs are more closely related to birds with keeled sterna than
the aforementioned taxa.

Both of which seem pretty unlikely.

(Note that alvarezsaurids might also not be carinates under this
definition, despite having keeled sterna.)

It does seem to me there are other problems with this definition (the
authors openly admit that whether certain taxa, such as _Confuciusornis_
and _Concornis_, have a "keel" or a "ridge" is open to interpretation),
but inclusion of pterosaurs is not one of them.

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