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Re: Coelurus a maniraptoran (for how long?)



> > Does this refer only to real pneumatic foramina or does it include
> pneumatic
> > fossae (which I have done, assuming that the real character should be
the
> > extent of the air-sacs...)
>
> Only actual foramina that penetrate the central wall.  Using the character
> in a sense of how far the air sacks extend seems like a bad idea, as
> pneumatic air sacs can leave no trace on the bone at all.

However, pneumatic fossae are something that is either present or absent,
and ontogenetically p. foraminae develop from p. fossae, in chickens at
least.

> > That of *Velociraptor* is broad and V-shaped like that of allosaurids
and
> > *Scipionyx*. Should be a reversal, because more basal dromaeosaurs
> > (*Sinornithosaurus*, IIRC *Microraptor* and *Bambiraptor* have thicker
and
> > rounder ones (so does *Archaeopteryx*). Those of tyrannosaurids are
thin,
> > but round, which looks like reducing the boomerang shape

I mean: "reducing a boomerang-shaped furcula in relative size and thickness"

> > to me, and those
> > of oviraptorids... all illustrations I have show thick, compact, round
bones
> > that are indistinguishable from Archie's furcula (aka The Unbreakable
> > Wishbone ;-) ).
>
> Sinornithosaurus and Bambiraptor stand a good chance of being closer to
> birds than dromaeosaurids,

IMHO this is probably due to plesiomorphies that they share with
*Archaeopteryx*, respectively reversals in Dromaeosauridae sensu stricto.

> but in any case Microraptor's furcula is unknown.
> Because the furculae of tyrannosaurids isn't actually boomerang-shaped,
the
> character would be "fucula rounded ventrally" then?

Probably. "Boomerang-shaped" is just the phrase that is commonly used.

> > :-O My error!!! This should have been at Maniraptora, and could be
phrased
> > as "at least 7 sacral vertebrae". *Mononykus* has 7, Ornithothoraces at
> > least begin with 8; I can't find out how many *Caudipteryx*
> > and *Protarchaeopteryx* have...
> >
> > *Chirostenotes*, however, has only 6, as is mentioned several times in
the
> > following ref. So do any coelurosaurs outside my contents of Maniraptora
> > have 6
> > sacrals?
>
> Not a single complete alvarezsaurid sacrum has been described.  Mononykus
is
> generally credited with six sacrals (must be unpublished information), but
> there's certainly no evidence for seven.

Interesting. The information I have is not unpublished, just old:

Perle Altangerel, Mark A. Norell, Luis M. Chiappe & James M. Clark:
Flightless bird from the Cretaceous of Mongolia, Nature 362, 623 -- 626 (15
April 1993)

"The synsacrum (incorporating seven vertebrae) and caudal vertebrae are
procoelous."

> Caudipteryx has five,

Neither the original description of *C. zoui* in Nature nor that of *C.
dongi* in Vertebrata PalAsiatica mention any sacrum, and I can't see any in
the illustrations in these articles. Is this also based on ilial length?

> Several taxa
> outside your Maniraptora have six sacrals. Troodontids and Rahonavis do.
> Ornithomimids do, except possibly Garudimimus, but this is debatable.

Convergence :->
(this, of course, cries for a parsimony analysis! :-) )


> In addition, Alxasaurus, Nanshiungosaurus? bohlini and Nanshiungosaurus
> brevispinus have only five sacrals.

:-(
Reduction due to less running?

> Excluding pygostylians, only Avimimus,
> Ingenia and possibly Nomingia have seven sacral vertebrae.

Is a sacrum known for *Oviraptor*?

> > As someone remarked onlist last time, this feature was noticed first as
a
> > difference between tyrannosaurids (that have it) and *Allosaurus* (which
> > was said not to have it). So I really think this is a typo in a
character
> > matrix.
>
> I first saw this character mentioned by Dong and Currie (1993) in
reference
> to its absence in Sinraptor and presence in Allosaurus, so I don't think
> it's a typo.

Confusing...
(Thanks to HP Jaime A. Headden for enlightening on other taxa!)

> > The *Eotyrannus* paper makes that comparison to troodontids...
>
> Yes, I was confused when I read it, as it implies troodontids have fused
> interdental plates, while I thought they were absent.  Maybe all "absent"
> interdental plates are really indistinguishably fused to the jaw bone.

Sounds probable to me...

> > Better phrasing for the character: Maniraptorans lack a transition point
> and
> > have procoelous caudals? (May be applicable only to oviraptorosaurs,
> > alvarezsaurids and maybe segnosaurs...)
>
> Alvarezsaurids have a transition point.  Distal caudals are elongate,
> without transverse processes and have long prezygopophyses.

In the skeletal reconstruction in the abovementioned paper (which is not
very detailed) I at least can't see long prezygapophyses. The transverse
processes do indeed disappear gradually from proximal to distal, but they
are still present on vertebrae that apparently have no neural spines. A
chevron is preserved between the last two preserved vertebrae. Procoelous
instead of amphiplatyan or whatever is the plesiomorphy :-] are AFAIK
thought to confer greater mobility, while the region behind a transition
point is considered to be stiffened.

>From the *Chirostenotes* paper I cited --
"The five preserved caudal vertebrae all have well-developed transverse
processes and anteroposteriorly relatively short centra. Unlike the caudals
in other coelurosaurian taxa, they do not exhibit major changes other than
decreasing in overall size towards the distal tip of the tail. [...] The
other four caudal vertebrae are much smaller than the anterior one and
comparable in size to each other; this indicates that the tail of
*Chirostenotes* may have lacked a transition point (sensu Gauthier, 1986) [I
haven't read that paper], as in Oviraptoridae but unlike the condition in
most other theropod taxa. The best preserved of these vertebrae [...]
differs from the caudals of other non-avian theropods except Oviraptoridae
[...] in the presence of several presumably pneumatic foramina in the neural
arch. The asymmetrical distribution and form of some of these openings on
this and the other caudal vertebrae is consistent with their inferred
pneumatic origin. The amphicoelous centrum [...]" -- you're right with the
following:

> Neither
> segnosaurs, Caudipteryx, Microvenator, caenagnathids, oviraptorids,
> Yandangornis, enantiornithines or ornithurines have procoelous caudals.
> Only alvarezsaurids and Patagopteryx do.

> > BTW, the description of *Shuvuuia* mentions some characters that unite
> > Alvarezsauridae and other birds and can only be found in the
Supplementary
> > information... :.-( I have yet to spend a few hours at the Nature
> website...
>
> Well, I've included all their characters in my analysis, so whatever
uniting
> they're doing, it's not working. :-)

Could you enlighten me on details?

> > >From the comparisons -- "It is still uncertain whether the quadrate
head
> > (caput quadrati) [...]
>
> How very interesting.  Confuciusornis has a double-headed quadrate
(Chiappe
> et al., 1999).  Apparently derived hesperornithiformes reversed then (as
> Enaliornis is a basal member).

Seems to me that the second head evolved once and was then reduced very
often, and sometimes even lost.

> If Gobipteryx has a damaged quadrate, someone needs to look
> at Protopteryx, Eoenantiornis, the Spanish hatchling or Liaox[i]ornis.
Perhaps
> other Liaoning taxa (Cathayornis, etc.) would be useful as well.....

Sure!

> > Are any segnosaur tail ends known?
>
> Nope.

Ah, sweet negative evidence... makes speculation so much easier ;-)

Regarding the "proto-pygostyle", I have looked once more at the original
Nature paper on *Nomingia*:

Rinchen Barsbold, Philip J. Currie, Nathan P. Myhrvold, Halszka Osmólska,
Khishigjaw [the high art of transcription...] Tsogtbaatar, Mahito Wanabe: A
pygostyle from a non-avian theropod, Nature 403, 155f. (13 January 2000)

"The number of fused vertebrae is the same as the number of caudals
supporting tail feathers (rectrices) in *Caudipteryx* and modern birds."
"Birds generally have 18 [...] to 23 [...] caudal vertebrae, although most
are fused into the synsacrum and pygostyle, leaving between five and nine
free caudals." *Nomingia* has 24, and the last one is totally microscopic
compared to number 22.
"Although the terminal vertebrae of *Caudipteryx* are not fused [IMHO its
number 22 may be a composite of 22-24, because it looks much like this
region in the pygostyle of *Nomingia*, but it shows no suture lines], they
do seem to form a stiffened rod. [...] Pygostyle-like structures [that's the
term! :-) ] could have evolved independently at least three times in
theropods, although the presence of rectrices in [at least] two of these
taxa suggests a functional associaton."

Together with the embryology abstract, this sounds like evidence. It would
mean, however, that the condition in oviraptorids is a reversal: "The
minimum caudal counts are 32 for *Conchoraptor* [...], 27 for *Ingenia* and
27 for *"Oviraptor" mongoliensis*." (same ref) Loss of the pygostyle has
occurred IIRC several times among flightless birds, but always connected to
a reduction of the tail, not to an enhancement. I speculate therefore that
the reason for this is the loss of the need to firmly support the rectrices,
and that oviraptorids didn't have rectrices. :-)

Well, I must have the description of *Yandangornis*, and what will soon be
published on *Avimimus*... *withdrawal symptoms from waiting-for-the-paper*
:.-(