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Re: Coelurus a maniraptoran (for how long?)



David Marjanovic wrote-

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

But in oviraptorids, they seem to be foramina from at least the embryonic
stage.

> 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."

Maybe I was confused and they are credited with seven sacrals.  The comment
in Perle et al. (1993) seems to stem from GI N100/99.  This specimen has
been referred to Shuvuuia (Chiappe et al., 1998) and has not been described
in detail.  I will give them the benefit of the doubt and agree that
Shuvuuia has seven sacral vertebrae.

> 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?

The original description (Ji et al., 1998) states- "There are ten
amphicoelous cervical vertebrae and five sacrals as in most non-avian
theropods and Archaeopteryx."

> > In addition, Alxasaurus, Nanshiungosaurus? bohlini and Nanshiungosaurus
> > brevispinus have only five sacrals.
>
> :-(
> Reduction due to less running?

The dinosaur taxa with the most sacrals (ankylosaurs, hadrosaurs,
ceratopsids) weren't exactly cursorial.  And Segnosaurus did have six sacral
vertebrae.

> Is a sacrum known for *Oviraptor*?

Oviraptor is said to have six sacral vertebrae (Barsbold, 1976).  However,
the taxonomy of oviraptorids is horribly chaotic now, so I don't think we
can trust Barsbold's statements apply to Oviraptor.  As his paper is on new
specimens discovered in 1971 (the holotype of Oviraptor lacks sacral
remains) and the photos included are of GI 100/20 and GI 100/21 (the
holotype and referred specimen of Conchoraptor), it's perhaps better to say
that Conchoraptor has six sacral vertebrae.

> 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.

Regarding the transition point in theropods, I believe it is defined by the
absence of transverse processes.  In this case, Shuvuuia (the "Mononykus"
picture of Perle et al., 1993) shows a transition point after nine caudals.
Other characters (centrum elongate, neural spine absent, chevrons skid-like,
elongate prezygopophyses, etc.) may also be present, but this varies with
the taxon.  I don't think the fact the distal tail wasn't stiff would keep
alvarezsaurids from having a transition point.  You're right to state
alvarezsaurids lack elongate prezygopophyses on distal caudals.  This is a
synapomorphy shared with several other coelurosaurs (Coelurus,
Compsognathus, therizinosauroids, Microvenator, caenagnathoids, troodontids,
Rahonavis and Archaeopteryx), although I'm sure you would agree Coelurus,
Compsognathus, troodontids, Rahonavis and Archaeopteryx still have
transition points.  Therizinosauroids, Microvenator and caenagnathoids are
the only tetanurans without a transition point, even Caudipteryx and
Nomingia have one.

> Could you enlighten me on details?

There are quite a few characters that support the Metornithes in Chiappe et
al.'s (1998) matrix.  However, most of these are problematic.
6.   Postorbital-jugal contact: present (0), absent (1).
The postorbital bar is complete in Confuciusornis, suggesting Shuvuuia
developed it in parallel.
9.  Quadrate articulating only with the squamosal (0), or with both prootic
and squamosal (1).
This is a fine metornithine character, although oviraptorids have it too.
15.  Carotid processes in intermediate cervicals: absent (0), present (1).
Although Chiappe et al. code this as unknown in Alvarezsaurus, it is absent
in that genus (Novas, 1996).  It is also present in ornithomimids,
troodontids and Avimimus.
16.  Prominent ventral processes on cervico-dorsal vertebrae: absent (0),
present (1).
Again, Chiappe et al. code this as unknown in Alvarezsaurus, when the first
three dorsals of that genus have very small hyapophyses, if any (Bonaparte,
1991).  The authors code it as absent in dromaeosaurids, as the processes in
Deinonychus are only moderate in size.  The hypapophyses of Nomingia,
Chirostenotes, Sinornithoides, Avimimus and Rahonavis are at least as large
as Mononykus, while Ornitholestes, Caudipteryx, Saurornitholestes,
Velociraptor and oviraptorids are also said to have prominent processes.
18.  Wide vertebral foramen in thoracic vertebrae, vertebral
foramen/articular cranial facies ratio (vertical diameter) larger than 0.40:
absent (0), present (1).
This is a valid metornithine character too, though it is also present in
Avimimus and Rahonavis.
19.  Hyposphene-hypantrum accessory intervertebral articulations in dorsal
vertebrae: present (0), absent (1).
Although Chiappe et al. code Patagonykus as having this character, it is
absent in this genus(Novas, 1997).
39.  Sternum subquadrangular to transversally rectangular (0) or
longitudinally rectangular (1).
I think basal pygostylian sterna are more hexagonal, but for the sake of
arguement, we can assume the character is indicating if they are tranversely
or longitudinally elongate.  As can be seen from the following list, this
does not support Metornithes.  The numbers indicate width divided by length.
Spinosauridae (95), Sinraptoridae (200), Tyrannosauridae (277), Caudipteryx
(160-250, depending on which way sternal plates are oriented), Oviraptoridae
(94-138), Mononykinae (51), Velociraptor (92-105), Bambiraptor (91),
Sinornithosaurus (90), Yandangornis (70), Confuciusornis (109), Protopteryx
(115), Longipteryx  (90), Eoenantiornis (78), Concornis (95), Liaoningornis
(93)
Indeed, it can be seen that Mononykus has an exceptionally narrow sternum,
while the proportions in basal pygostylians are similar to those in
dromaeosaurs.  I think you'll agree there is no support for Metornithes
here.
40.  Ossified sternal keel: absent (0), present (1).
Confuciusornis only occasionally has a faint keel (two specimens), while the
keel is caudally restricted in Protopteryx and absent in Changchengornis.
So whether this is a good metornithine character or not is very debatable.
45.  Humeral distal condyles mainly located on distal (0), or cranial (1)
aspect.
Also known in tyrannosaurids, segnosaurs and troodontids.
51.  Distal end of ulna subrectangular and transversely compressed (0), or
subtriangular in shape (1).
This is fine.  Also known in Rahonavis by the way.
54.  Distal carpals and proximal portion of metacarpals unfused (0), or
fused forming a carpometacarpus (1).
An extremely variable character.  Mononykus has all metacarpals and the
semilunate completely fused.  Confuciusornis only fuses metacarpal I with
the semilunate.  Jibeinia, Protopteryx, possibly Longipteryx, Sinornis,
"Archaeoraptor", Cathayornis? caudatus and Longchengornis have unfused
metacarpi.  Thus, I think Mononykus developed this in parallel to the
partial development in confuciusornithids, the development within
enantiornithines and the development in euornithines.
64.  Prominent antitrochanter: absent (0), caudally directed (1), or
dorso-caudally directed (2).
This is fine, though also present in Avimimus.
70.  Ischium less than two-thirds (0), or two-thirds or more of pubis length
(1).
Confuciusornithids have the primitive state (44%), again suggesting the
character developed in parallel between mononykines and ornithothoracines.
75.  Pubic apron more than one-third the length of the pubis (0), shorter or
absent (1).
This is fine too, although present in Avimimus and Bagaraatan too.
85.  Proximal end of fibula prominently excavated by a medial fossa (0), or
nearly flat (1).
This is also true of a large variety of maniraptorans- Bagaraatan,
Segnosauria, Nomingia, Microvenator, Velociraptor, Troodontidae and
Rahonavis.  Thus, the authors coded dromaeosaurids incorrectly and the
distribution would suggest this is a maniraptoran synapomorphy.
86.  Fibula with tubercle for M. iliofibularis anterolaterally (0),
laterally  or caudolaterally or caudally (1) directed.
This is true, but also occurs in troodontids.
So out of the sixteen metornithine characters, seven are valid, assuming
some parallel development or close relationship of a few taxa (usually
Rahonavis, troodontids or Avimimus).  All of these are included in my
analysis, and dromaeosaurs, Rahonavis and Archaeopteryx are always closer to
pygostylians than alvarezsaurids are.

> 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. :-)

I really don't see the resemblence between the distal tails of Nomingia and
Caudipteryx you cite, but you lack confirming evidence in any case.  The
most you could get away with would be coding Caudipteryx as "?" for
pygostyle present.

Mickey Mortimer