[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Moroccan noasaurid?



Jaime A. Headden wrote-

> <... "bone taxon A" of Russell 1996.  This is based on two skull roofs
> (NMC 50807- frontals and parietals; NMC 50807- frontals) from the Albian
> Gres Rouges Infracenomaniens of Morocco.  They are rather small (frontal
> lengths of 50 mm and 65 mm), but firmly coossified.  What intrigued me was
> the fact there is a sagittal crest on the parietals.  This character is
> otherwise only known in abelisaurids, "Alas.... er "Chilantaisaurus"
> maortuensis :-) , tyrannosaurids and some more derived coelurosaurs.>
>
>   Actually, some basal oviraptorids have strong sagittal crests, as well,
> only some abelisaurids have the crest and these are generally carnotaurine
> (specifically, *Aucasaurus,* *Majungasaurus,* *Carnotaurus,* and
> *Indosaurus*), or are tapered from the interparietal plateau caudally (as
> in "abelisaurines" like *Abelisaurus* and *Indosuchus*. This occurs in
> some allosauroids, as well. Many of these taxa have robust jaw muscles and
> the condition of an advanced sagittal crest is often correlated (at least
> in mammals) to jaw size, function, and even ontogeny -- -this has been
> explicitly tested in many carnivoran mammals, especially hyaenids,
> ursines, and cats.

I said some derived coelurosaurs have sagittal crests, didn't I?  This is
not only found in oviraptorids, but also troodontids, Avimimus,
dromaeosaurids and perhaps Ornitholestes.  Which abelisaurids lack sagittal
crests, if "only some" includes Aucasaurus, Majungatholus, Carnotaurus,
Indosaurus, Abelisaurus and Indosuchus?  There don't seem to be any
abelisaurids left with known parietals.  Allosauroids lack sagittal crests
(Holtz, 2000).

>   The frontals have advanced stereoscopic properties, with the preserved
> orbital rib having features of a maniraptoran quality, so that the
> interorbital margins are parallel, only just wider than long, with a
> caudal margin turned laterally at around 45 degrees to the midline. the
> olfactory bulbs preserved at the very rostral end of the frontal,
> underlying the scarf joint with the nasals, are very broad and elongated,
> and the caudal margin displays complex supracranial sinuses along the
> contact with the laterosphenoid, suggesting the latter was pneumatic as
> were other portions of the braincase. The orbital margin is deflected
> dorsally and it is clear that it would have provided a shallow arch for
> the eyeball, and that this organ was fairly large. The animal was probably
> maniraptoriform, and the lateral and dorsal orientation of the lateral
> wings of the frontals suggest it was maniraptoran.

Wouldn't the "broad elongated" olfactory bulbs suggest a non-maniraptoran,
as maniraptorans were reducing these structures (Wharton, 2001).  Also, you
don't explain why the cerebral hemispheres are so small if this is a
maniraptoran.  It has been shown these structures are much larger in
relation to size in coelurosaurs (Larsson, 2001).  I would assume
development of binocular vision would be common in small theropods and
Majungatholus also has pneumatic frontals.  The large orbits are a
size-related feature common in small basal theropods too (eg.
coelophysoids).

>   As for NMC 41873, this bone possesses a distal end whose shape is
> ginglymoidal in aspect with a length and width of the articular end being
> much narrower than expected for its length. What may be a supracondylar
> crest (ent- or ectepicondylar) is present on one side, and the other has a
> flange that is probably the rim of the condyle and not a crest. The distal
> end bears a ligamental pit not found on humeri, and this data suggests
> that the bone is either a metacarpal or metatarsal bone of some length.

Russell can't tell a humerus from a metatarsal, eh?  The latter seems
possible at least.

Mickey Mortimer