[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: New alvarezsaurid
Oviraptors and alvarezsaurs do not share any major
>characters.>
>
>No, they don't. They do share closer osteology than alvarezsaurids do
to
>various other theropod groups, with the exception of the dromies' and
>Archie's group.
This osteology seems to be one more of convergence then anything
else. Alvarezsaurs have many cranial apomorphies that ally them with
birds that oviraptorosaurs lack. As listed by Chiappe et al.:
1) Absense of contact between the postorbital and jugal.
2) Loss of contact between the squamosal-quadratojugal bar.
3) Movable joint between the quadrate and quadratojugal.
4) Seperate squamosal and prootic articulations of the quadrate.
5) Confluence betweem the caudal tympanic recess and columellar recess
( stapes ).
6) Triradiate palatine.
7) Large foramen magnum.
8) Loss of coronoid in the lower mandible.
Oviraptors lack all of these characters.
>Relationships cannot be derived from one or two ambiguous characters,
>but in basic osteology, myology, life histories, behaviors, and DNA.>
>
>Only the first (osteology) can be usefully diagnosed unless we do find
>DNA for a dino (and that depends upon _which_ dino, for it is hardly
>conclusive except for the are-birds-dinos? thing if we get it from a
>hypsie or the like).
I was listing all the tools for determining relationships. Myology
can be, and is useful ( loss of the M. cuppedius is one of the features
that ally dromaeosaurs with birds ).
>Now, how did one bird develop the streptostylic quadrate or
tripalatine?
>They just didn't appear in one dino, and you've got a bird, or the
>bird's got it and then the theropod derivative looses the darned thing.
>The fact is, Aves converges greatly within its own groupings to make
>them barely distinguishable from one another except by very distinct
>features (beaks, ornamentation, even ratios [dare say] are not
>conclusive enough).
Yes, there is a lot of convergence in Aves. But these convergences
are explanable and traceable. Take Apatosagittarius. This bird is very
similiar to Sagittarius ( the secretary-bird ) in its general body form.
However, it is a remarkable case of convergence. It is allied with
accipitirid hawks in its pes proportions and pedal morphology. It does
not lose its derived features and its ancestry is traceble through many
characters. With alvarezsaurs and oviraptorids this is not the case. You
seem to be saying, " Since there is a lot of convergence in Aves, then
any relationships are viable." This is not so.
>... I need to wait till I get the *Shuvuuia* article in my
>hands or someone can post the data on the skull...
See above.
MattTroutman
______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com