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Re: *Aucasaurus garridoi* and Some Stuff on Halluces (Just in Time, Too!)



Jaime Headden wrote-

> Interestingly, in *Carnotaurus* and
> *Majungatholus*, the first caudal as in other theropods is straddled by
> the ilia, and lacks the cranial "awls"; in *Aucasaurus*, these processes
> begin on the first caudal, not the second, and the first caudal is behind
> the ilia, rather than between them; furthermore, there is a caudal
> (posterior) notch in each caudal iliac blade which in *Aucasaurus* is
> articulated with the "awl" of the first caudal, while this is apparently
> connected to the second caudal's awl in other taxa. This may further be
> considered an ambiguous synapomorphy of carnotaurines (pers. obs.).

Although Carnotaurus does have the first caudal completely between the
postacetabular processes, the transverse processes project posteriorly
enough to laterally embrace the ilia.  Coria et al. support this when they
say "Although these projections are not preserved in the first caudal of
Carnotaurus, notches for their reception are visible on the lateral surface
of the dorsocaudal corner of the ilia (MACN-CH-894)."  I assume the
arrangement in Majungatholus also involved the first caudal, though the
region is undescribed.

> the
> manus is wierd. It apparently lacked articulations for any phalanges on
> metacarpals I and IV. Distal ends of metacarpals II and III are associated
> with phalanges, the third digit known with two bones. This also suggests
> the spur like bone of the hand of *Carnotaurus* may not be a metacarpal,
> but could be a variable carpal element (pers. obs.). I have reconstructed
> it as such here (http://qilong.8m.com/Carnotaurus_sastrei_manus.jpg) last
> year.

I provisionally disagree (haven't seen the illustrations yet).  Coria et al.
describe the first and fourth metacarpals of Aucasaurus as roughly conical
structures that carry no phalanges.  This sounds much like the supposed
fourth metacarpal of Carnotaurus, so I think there is good evidence is was
not a carpal element.  As metacarpal I of Aucasaurus is said to be largest,
perhaps the element in Carnotaurus is metacarpal I instead of IV.
Interestingly, digits II and III (containing one and two phalanges
respectively) may not have had unguals.  If what I've heard is true,
Aucasaurus lacks ossified carpals entirely, further evidence against Jaime's
hypothesis.  The carpals of Carnotaurus are suggested to be phalanges by
Coria et al..

> There is a first
> metatarsal that is (get this, avian freaks) J-shaped, with the distal end
> projecting _laterally_ on a perpendicular.

That's it!  Confuciusornis and avisaurids are derived abelisaurs, proving
Raath was right in his ceratosaurian origin for birds! ;-)

> The hallux was at least
> laterally oriented; metatarsal II is almost as long as IV, and not much
> shorter than III; the proximal morphology of metatarsal III is avian in
> that is expands mediolaterally behind IV and thus buttresses it
> (typically, theropods broaden the IVth, not the IIIrd).

And the metatarsus lacks the slender second and fourth metatarsals seen in
several abelisauroids.  Metatarsal IV is actually much broader than III
(sort of like troodontids).  So this settles the debate as to whether
abelisaurids have this character, allowing it to be used to group Noasaurus,
Masiakasaurus and Velocisaurus in a Noasauridae to the exclusion of
abelisaurids.  Whether Ligabueino, Elaphrosaurus, Laevisuchus or
Chuandongocoelurus are noasaurids too, or somewhere else in the Ceratosauria
remains to be clarified.

Bagaraatan is referred to as a troodontid by Coria et al..  An interesting
hypothesis, given my analyses placing it as a basal paravian.  Can't say I
agree with them though, given the unfused interdental plates, lack of a
lateral dentary groove to contain foramina, proximal caudals with oval
centra, fourteen caudals with transverse processes, propubic pelvis and
fibula contacting the tarsus.  The troodontid-like trochanteric crest and
fused astragalocalcaneum (assuming the calcaneum was present in troodontids)
are seen as convergences.

Mickey Mortimer