DROMAEOSAURS AND OVIRAPTOROSAURS ARE NOT IN AVES!

["Matthew Troutman" <m_troutman@hotmail.com>]

I had to fight off a thread like this earlier this year....

<<Maniraptora
|--Compsognathus
+--Paraves
   |--Protarchaeopteryx
   |--Troodontidae
   +--Aves*
      +--+--+--Archaeopteryx
         |  |--+--Rahonavis
         |  |  +--Dromaeosauridae
         |  +--Ornithoraces
         +--Oviraptosauria**

*  elongate coracoids, retroverted pubes, lunate carpal, and a few 
others ** de-retroverted pubes significant (look at _Ingenia_ in _The
Dinosauria_)>>

I really do not like dinosaurs being put into Aves because their is no 
real evidence for a scenario like this.  First let me battle off some of 
these features...

<<Elongate coracoids>>

In the cladogram above it is claimed that Protarchaeopteryx does not 
have this feature. I have seen pictures of the new specimen of it and 
there do seem to be elongate coracoids.

<<Retroverted pubes>>

Protarchaeopteryx also appears to have retroverted pubes.  

<<Lunate (semilunate?) carpals>>

This is not clear.  Maniraptoriforms all have semilunate carpals.  You 
may also be referring to the cuneiform (ulnarae) and the scapholunar 
(radiale) in the avian wrist which are probably present in troodontids 
and Protarchaeopteryx.  

<<De-retroverted pubes>> 

Wouldn't this feature sort of disprove your hypothesis?

I have argued against similiar scenarios such as this one in the past.  
Let me argue against this one point by point.

ARCHAEOPTERYX=>RAHONAVIS=>DROMAEOSAURS

Well first of all Forster et al. have argued that the features that are 
supposedly the evidence for this scenario might be primitive in 
dromaeosaurs.  The features that supposedly make Rahonavis the ancestor 
of dromaeosaurs are as follows:

1)  Large trechent ungual on hyperextendable second toe.
2)  Elongate chevrons and prezygapophyses.  

However, these features might be primitive.  Gautheir (1986) and Paul 
(1988) have argued that the second pedal digit of Archaeopteryx was 
hyperextendable and Archaeopteryx appears to have a similiar 
construction in the tail.  

The features that argue against Rahonavis being ancestral to 
dromaeosaurs are:

A)  Outwardly facing glenoid.
B)  Reverted hallux.
C)  Dorsal ischial processes.

Let me explain "A".  If Rahonavis was ancestral to dromaeosaurs, then a 
loss of flight would have to occur.  In flightless birds the outwardly 
facing glenoid is still present.  
Let me explain "B".  Dromaeosaurs do not have the same type of hallucal 
arrangements that birds and Rahonavis has.  Norell and Makovicky (1997) 
showed in their description of a perfectly preserved pes of a 
dromaeosaur that the hallux was not reverted.
Let me explain "C".  Primitively birds have dorsal ischial processes; 
these are not seen in dromaeosaurs (admittedly this is the weakest 
arguement against the scenario.  

OVIRAPTOROSAURS IN AVES

Oviraptorosaurs (or Oviraptoroids)  do show some birdlike 
characteristics.  They have a furcula with a low interclavicular angle 
and some quadrate features that are shared with "ornithothoracine" birds 
(Maryanska 1997).  However, these features can be described as 
convergent or feeding adaptations ("ornithothoracine" quadrates are 
streptostylic whereas oviraptorosaur quadrates are monoistylic; 
Maryanska 1997 respectively).  Besides these features, there are no 
other uniquely birdlike features in oviraptorosaurs.

THE COUP DE GRACE

Dromaeosaurs and oviraptorosaurs are not in Aves because they lack these 
advanced features of Aves:

I)  Loss of ascending process of the squamosal.
II)  Lack of ascending process of the jugal bar.
III)  Confluence between orbit and lateral temporal fenesta.
IV)  Crocodilian-type teeth with triangular crown and a waisted crown 
with distinct replacement pits for teeth.
V)  Elongate coracoids (more so than dromaeosaurs and oviraptorosaurs) 
than fit in a socket of the sternum.
VI)  Single sternum.
VII)  Heart-shaped ulnarae.  
VIII)  Hypopubic cup.
IX)  Dorsal ischial processes.
X)  Reverted hallux.
XI)  Caudal vertebrae count reduced to around 20.

Matt Troutman

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