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Re: Arctometatarsalia



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.

  The keel in *Vultur* was explicityly defined, and in this,
*Rhamphorhynchus* agrees to every point. That was my point. A keel, as
found in *Vultur*, is known in forms that no one currently supports as
being members of a clade known as Carinatae, except that now, this is no
longer the case, and Carinate under this definition is broader than
previously considered. This is why homologies must be fully considered in
other forms to clarify structure of apomorphies and therefore
distributions and utility of the definition. The assumption that the
sternal keel in *Vultur* _is not homologous_ to that of *Rhamphorhynchus*
doesn't meet the criteria by which Gauthier and de Queiroz define the
carinate sternal keel.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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