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DROMAEOSAURS AND ARCHAEOPTERYX
<<Does birds come from Archaeopteryx or late evolved small Dromaeosaurids,
I, at one time, thought that Archaeopteryx and Dromaeosaurids formed an
exclusive clade and that _Archaeopteryx_ was ancestoral to dromaeosaurs. In
light of the newly discovered theropod _Unenlagia_, it seems that that view
is incorrect for three reasons associated with the hips.
1) CRANIAL PROJECTION OF THE PUBIC BOOT: is a primitive character throughout
Tetanurae, but is subsequently lost in _Unenlagia_, _Archaeopetryx_, and all
other birds, as well as _Adasaurus_, the flying raptor, and "Linsterosaurus".
The cranial projection is still present in dromaeosaurids and (surprisingly)
Alvarezsaurids (well, _Patagonykus_ at least).
2) PROXIMODORSAL PROCESS OF THE ISCHIUM: is a small knob on the caudodorsal
surface of the illium near the suture with the ischium and is a derived
character uniting _Unenlagia_, _Archaeopteryx, and all other birds. I am
unsure of its presence in the flying raptor or "Linsterosaurus", and it is
probably not in _Adasaurus_. It is completely absent in dromaeosaurs and
3) DISTAL PLACEMENT OF THE OBTURATOR PROCESS: is found in _Archaeopteryx_ and
all other birds. I am unaware of the condition in "Linsterosaurus" and the
flying raptor. Only the proximal portion of the ischium is preserved in
_Patagonykus_, so it is unknown at this time if the obturator process is
distal or not (I suspect not). The obturator process is proximal in
_Unenlagia_ and dromaeosaurs.
For these three reasons, I believe that _Archaeopteryx_ is closer to modern
birds than dromaeosaurs. I am not saying however, that dromaeosaurs didn't
evolve from a tree-living 'flying' ancestor, I am sure they did, juts that
that ancestor is more 'primitive' than _Archaeopteryx_.
These are also some reason why I believe Alvarezsaurids are less birdy than
they are made out to be.
1) The sickle clawed foot is almost certainly primitive for the clade uniting
_Dromaeosaurus_ and _Corvus, and perhaps Maniraptoriformes as well since it
appears in Troodontids, Dromaeosaurs, "Linsterosaurus", the flying raptor,
_Adasaurus_ and _Archaeopteryx_.
2) _Archaeopteryx_ is the outgroup to all other birds, with _Unenlagia_ and
Dromaeosauridae as successive outgroups.
The flying raptor, "Linsterosaurus", and _Adasaurus_ fall somewhere in
between Dromaeosauridae and _Archaeopteryx_.
3) _Adasaurus_ IS NOT another species of _Dromaeosaurus_.
Thank you for your time, and be thankful I didn't use any big words like
postcrania this time :-)
Ya Ya! You best keep walkin' 'fya know what's good fo' ya!