RE: New gliding reptile: Mecistotrachelos

[Tim Williams <twilliams_alpha@hotmail.com>]

Paula Goodman wrote:

> *how do the wings of this new fossil relate to the 
> maybe-feathers/maybe-scales wings of the Longisquama?

In their description of _Mecistotrachelos_ Fraser &c leave open the question 
of where exactly _Mecistotrachelos_ might lie in diapsid phylogeny, though 
they tentatively suggest it is an archosauromorph (i.e., closer to birds and 
crocodiles than to lizards and snakes).  It might even be closely related to 
_Sharovipteryx_

The kuehneosaurs, another group of extinct gliding diapids, are usually 
regarded as lepidosauromorphs (i.e., closer to lizards and snakes than to 
birds or crocodiles).

_Longisquama_ isn't mentioned in the description, but an analysis of 
_Longisquama_ a few years back (Senter, 2004) recovered _Longisquama_ in a 
group he called the Avicephala, which also includes drepanosaurids and 
coelurosauravids.  This group lies somewhere near the base of the Diapsida, 
outside both the archosauromorphs and lepidosauromorphs.

So to answer your question, at the moment there does not appear to be any 
unique connection between _Mecistotrachelos_ and _Longisquama_.  Gliding 
abilities appear to have evolved several times independently among small 
diapids.  Having said that, the precise function and arrangement of the 
dorsal structures of _Longisquama_ is not known; it could be a single file, 
or a paired structure like _Coelurosauravus_ or _Mecistotrachelos_ or 
keuhneosaurs.

Nor does there appear to be any connection at all between _Longisquama_ and 
birds; the dorsal structures present in _Longisquama_ (which *might* have 
been used for gliding) do not appear to be homologous to bird/theropod 
feathers.  _Longisquama_ is only distantly related to birds; if Senter's 
analysis is correct, _Longisquama_ is no more closely related to birds than 
to lizards or snakes.

Cheers

Tim

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