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DROMAEOSAURS AND OVIRAPTOROSAURS ARE NOT IN AVES!
I had to fight off a thread like this earlier this year....
| | +--Dromaeosauridae
* elongate coracoids, retroverted pubes, lunate carpal, and a few
others ** de-retroverted pubes significant (look at _Ingenia_ in _The
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
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.
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
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.
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
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.
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