RE: Pterosaur origins

[Tim Williams <twilliams_alpha@hotmail.com>]

The same volume also includes a revised phylogeny of coelurosaurs by Phil 
Senter.  The phylogeny contains a few surprises (or maybe not, in some 
cases)...

_Coelurus_ and _Tanycolagreus_ form a clade (Coeluridae) at the base of the 
Tyrannosauroidea.  (No mention of _Stokesosaurus_.)

_Deinocheirus_ is found to be a basal ornithomimosaur ("arctometatarsalian" 
in Senter's system).

A monophyletic Compsognathidae is recovered, containing _Compsognathus_, 
_Sinosauropteryx_ and _Huaxiagnathus_.

No support is found for a unique Therizinosauroidea-Oviraptorosauroidea 
clade (i.e., to the exclusion of deinonychosaurs, birds, and 
alvarezsaurids).

A unenlagiine clade turns up, which includes _Unenlagia_, _Buitreraptor_ and 
_Unenlagia_.  Unenlaginae comes out at the base of the Dromaeosauridae; but 
Senter rejects the idea that dromaeosaurids were secondarily flightless.  
Instead, the traits common to unenlagiines and birds (ornithurans) - and 
also present in microraptorans too - are interpreted as convergent in all 
three clades.  (I'm not sure what this means for the flight abilities of 
_Rahonavis_.)

_Epidendrosaurus_ is found to be a bird.  Well, it's inside Avialae but 
outside Aves, which has _Archaeopteryx_+_Wellnhoferia_ as its most basal 
clade.  Senter defines Avialae as "all taxa more closely related to birds 
than to Deinonychosauria", whereas Aves is defind as "all taxa 
phylogenetically bracketed by _Archaeopteryx_ and Neornithes".  I know 
neither definitions conform to PhyloCode, since individual species are not 
used.  But I like the spirit behind both definitions, especially Avialae 
being stem-based (must exclude deinonychosaurs), and Aves being node-based 
(must include _Archaeopteryx_.


Sener, P. (2007). A new look at the phylogeny of Coelurosauria (Dinosauria: 
Theropoda). Journal of Systematic Palaeontology.  Published online.

Abstract: "The most comprehensive phylogenetic analysis of the theropod 
clade Coelurosauria to date, is presented here, with 85 coelurosaurian 
ingroups and 360 characters, using _Allosaurus_ and _Sinraptor_ as 
outgroups. The strict consensus tree is highly resolved and has the 
following topology: Tyrannosauroidea + (Compsognathidae + (Arctometatarsalia 
+ (_Ornitholestes_ + (Therizinosauroidea + (Alvarezsauridae + 
(Oviraptorosauria + (Avialae + (Troodontidae + Dromaeosauridae)))))))). The 
analysis places _Coelurus_ and _Tanycolagreus_ at the base of 
Tyrannosauroidea, _Deinocheirus_ within Arctometatarsalia, 
_Protarchaeopteryx_ within Oviraptorosauria and _Epidendrosaurus_ at the 
base of Avialae. The analysis results in wide phylogenetic separation 
between _Caenagnathus_ (close to the base of Oviraptorosauria) and 
_Chirostenotes_ (placed within a clade of crested oviraptorids), casting 
doubt on their synonymy. All taxa with an enlarged, trenchant ungual on the 
second toe are placed within Troodontidae or Dromaeosauridae; at the base of 
the latter is an unenlagiine clade that includes _Unenlagia_ and 
_Rahonavis_. The hypothesis that dromaeosaurids are secondarily flightless 
birds is not supported."

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