RE: Introducing Mahakala omnogovae, little dromaeosaurid of Mongolia

[Tim Williams <twilliams_alpha@hotmail.com>]

The elephant in the room is the issue of where exactly in theropod phylogeny 
flight first evolved,  The title of the paper mentions avian flight, and the 
abstract states "The taxon?s [_Mahakala_'s] small body size and phylogenetic 
position imply that extreme miniaturization was ancestral for Paraves (the 
clade including Avialae, Troodontidae, and Dromaeosauridae), 
phylogenetically earlier than where flight evolution is strongly inferred."  
But I'm not sure when or where exactly "flight evolution is strongly 
inferred".

Birds can fly, and _Rahonavis_ could (presumably) fly.  As I see it, there's 
two possibilities.  Did flight evolve once, at the base of Paraves (i.e., 
was present in the most recent common ancestor of _Rahonavis_ and avialans)? 
 Or did flight evolve twice, in both birds (avialans) and the unenlagiines 
(as exemplified by _Rahonavis_)?  Flight evolving only once might appear to 
be the most parsimonious explanation; but the distribution of characters 
associated with flight might indicate otherwise.

If flight evolved only once, in a basal paravian (or lower), it requires 
that (a) there were multiple losses of flight in deinonychosaurs, and (b) 
that the aerodynamic abilities of microraptorines are not primitive 
(plesiomorphic) but in fact derived.  This might lend credence to the view 
that microraptorines could fly, in a four-winged "screaming biplane" 
fashion; but this is a can of worms, and I'm not looking for any trouble.  
;-)

Or maybe this entire issue has been cleared up already, and I'm the only one 
who's confused.

As for the phylogeny, Turner &c refer to the clade Microraptorinae rather 
than Microraptoria, although I wasn't aware that Microraptorinae had been 
formally defined (in paper form, anyway).  In the paper describing 
_Buitreraptor_, Makovicky et al. (2005) define Unenlagiinae, and they use 
the term Microraptorinae, citing Senter et al. (2004) for the definition of 
Microraptorinae; but Senter opted for Microraptoria over Microraptorinae.  
However, Sereno (2005; TaxonSearch) does provide a definition for 
Microraptorinae, that is in line with that employed by Turner et al. (2007). 
 (Sereno's definition of Microraptorinae is "The most inclusive clade 
containing _Microraptor zhaoianus_, but not _Dromaeosaurus albertensis_, 
_Velociraptor mongoliensis_ , _Unenlagia comahuensis_ , _or Passer 
domesticus_.")

Turner &c also find a Microraptorinae+Unenlagiinae clade.  The name 
Microraptoria is actually available for this clade, given Senter's original 
definition ("Taxa that are more closely related to _Microraptor_ than to 
_Velociraptor_ or _Dromaeosaurus.")  So Microraptoria and Microraptorinae 
could both be used, if we employ the emended (and narrower) definition of 
Microraptorinae.

Other minor details include the recovery of an _Archaeopteryx+_Jeholornis_ 
clade, as Tom mentioned.  No modern bird taxa were included in the analysis, 
so it'll be interesting what impact (if any) the inclusion of neornithean 
taxa would have on the position of _Rahonavis_ within the Dromaeosauridae, 
or on the _Archaeopteryx+_Jeholornis_ clade (and what this clade would be 
called).  (The name Archaeopterygidae is available, but as defined by Sereno 
(2005) this uses _Passer_ as a specifier - as do many definitions).  
Interestingly, Turner &c opt for the name _Jeholornis_ over 
_Shenzhouraptor_.  (For one perspective on why _Jeholornis_ might qualify as 
the senior synonym of _Shenzhouraptor_, see 
http://dml.cmnh.org/2006Apr/msg00228.html).

Also, _Rinchenia_ is changed back to _Oviraptor mongoliensis_ in the 
phylogeny.  I don't know if this is a nomenclatural decison (the authors 
aren't certain if it is a validly publsihed name) or a phylogenetic decision 
(_philoceratops_ and _mongoliensis_ are recovered as sister taxa).

Cheers

Tim

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