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Re: Revising Hou et al, 96 (very very long)



Fam Jansma wrote-

> If we happen to decide that propubic-mesopubic-opisthopubic must be based
on
> the angles the three elements make that compose the pelvis, wouldn't they
> just make things more complicated? For instance, there is in no way
possible
> to say when something is mesopubic based on angles, it would become
> something like a grade thing. But how would this seperation would be like?
> >From exactly what angles do we deceide when a pelvis is mesopubic or not.
> No, I fail to see why this simplified seperation needs to be altered when
it
> is still in good shape. Like they say: never change a winning team.

The point is that the pubic/ischial orientation is NOT simple.  It is a
grade, mesopubic Archaeopteryx's pubis is more opisthopubic than
Patagonykus, which is more so than Sinornithoides, which is more so than
Rahonavis, etc..  Just like our current separation of opisthopubic from
mesopubic from propubic is arbitrary, the angles we decide to use when
refining the character will be arbitrary.  Characters are all like that in
the end- you get a lot of intermediates and have to decide exactly where to
divide the grade into distinct states.  By refining them, we make our coding
a more accurate reflection of anatomy.

> Opisthopubic pelves was probably an ancestral character which was later
> reversed in the Troodontids, Oviraptorids, some Dromeosaurs for unknown
> reasons. This would make the opisthopubic pelvis an ancestral character
and
> therefore pretty useless in creating a tree about the Maniraptoriforms.

But then you have to take into account Bagaraatan's strongly propubic
pelvis, as it's close to or barely within the enigmosaur-paravian
divergence.  And explain why basal alvarezsaurids have mesopubic pelvises,
while derived ones have opisthopubic pelvises.  I find a mesopubic basal
maniraptoran far more likely, judging by the condition in caudipterids and
Patagonykus.

> But
> what you are implying with the segment "I think it's less likely that
> paravians or all maniraptorans were primitively opithopubic", does this
mean
> this family is polyphyletic or anything?

No, I meant that I don't think it is very likely that the first maniraptoran
or first paravian was opisthopubic.  I think they were more likely to be
propubic, or perhaps mesopubic.

> I am an advocate for HP G.S. Paul's
> theory that maniraptorids are secondarily flightless, meaning that
> Maniraptors evolved from an opisthopubic ancestor the likes of
> Archaeopteryx. Both Sinornithosaurus and Sinovenator are very much like
> Archaeopteryx, leading me to expect that the latter could be their sort of
> ancestor or sister group, and these two genera are the basal most genera
> known for two of the major families that comprimise the Maniraptors. Where
> Ovi's fit in is a complete mystery and are probably not closely related to
> either the Dromeosaurids or Troodontids. Their universally accepted
> similarities to Therizinosaurids, with the Early Jurassic representative
> Eshanosaurus, leads me to suspect that Ovi's evolved the semi-lunate
carpal
> convergently. Or.....Archaeopteryx is not the first of a new breed of
> animal, but more an intermediate step and related to an animal from the
> Upper Triassic.

I also think maniraptorans were probably secondarily flightless (or
neoflightless, as Paul says in DA).  That doesn't mean that the basal flying
maniraptoran had to be opisthopubic, nor does it mean Archaeopteryx has to
be very closely related to that basal maniraptoran.  In fact, I think Paul's
new "proavis" drawing (DA pg. 129) pretty accurately sums up what it should
have looked like, though I would give it longer arms, a longer coracoid,
deeper less proximally expanded chevrons and perhaps a propubic pelvis.  I
think Archaeopteryx is solidly placed in the Paraves, and has a very high
probability of being closer to birds than dromaeosaurids.  I'm also getting
irritated by people assuming Sinornithosaurus is a basal deinonychosaur, as
I feel it's quite likely an avialan (which goes a long way in explaining why
it is so birdlike).  I'm not sure how Sinovenator will affect things.
Finally, segnosaurs are not universally agreed to be the sister group of
oviraptorosaurs (eg. Sereno), though I feel that time is not long in coming,
and the segnosaurian status of Eshanosaurus is quite uncertain.  I do think
that the precise semilunate shape of oviraptorids' fused distal carpal was
probably convergent with paravians, but that the presence of such a large
bone formed by the fusion of distal carpals I and II is synapomorphic in
enigmosaurs and paravians.

Mickey Mortimer