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Re: Triassic Crurotarsi vs Ornithodira in latest Science



David Peters wrote:
>
> Haven't seen the article yet.
>
> Does it speak to the subject of dinosaur ancestry among the
> 'crurostarsi'?

_Crurotarsi_. Depending on the definition used, this may or may not be
impossible. The history of definitions for this clade name can be
found here: http://taxonsearch.org/dev/taxon_edit.php?Action=View&tax_id=365

Under some of the node-based definitions, including _Dinosauria_ in
_Crurotarsi_ is possible, but unlikely. It would only happen if one of
the specifiers used (e.g., phytosaurs, ornithosuchids, etc.) turned
out to share closer ancestry with dinosaurs than with crocodylians (in
which case _Crurotarsi_ would be a synonym of _Archosauria_), or fell
outside of _Archosauria_ (crown group sense) altogether. Some older
studies placed ornithosuchids closer to dinosaurs than to
crocodylians, but my understanding is that this placement is very much
out of date. The analysis by Brusatte et al. (2008) certainly doesn't
find this, either -- they have ornithosuchids as sister clade to
poposaurids, well inside the crocodylian total group.

But Brusatte et al.seem to be using a branch-based definition for
_Crurotarsi_, which makes it identical to the crocodylian total group.
Under this definition, it would be pretty much impossible for
dinosaurs to be crurotarsans, unless avians are not dinosaurs.

-- 
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California