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

Re: Chilantaisaurus maortuensis/sibiricus

Ekaterina Amalitzkaya wrote-

> Do the species  maortuensis and sibiricus have nay relationship to the
> species of Chilantaisaurus? Serreno et al in the Afrovenator paper state
> that Chilantainsaurus is a Torvosaur. Is there any suppor t for this
> After all the post-crania I am aware of are very fragmentary and may not
> allow a direct linkage with the Torvosaurs like Torvosaurus or
> Eustreptospondylus.

"Chilantaisaurus" maortuensis is maniraptoran according to Chure's new
analysis that will soon be published.  It is known from a posterior section
of skull, maxilla, axis and six caudal vertebae, and will recieve a new
generic name soon.  Features Chure (1998) notes include twleve maxillary
teeth, a large pneumatic nasal chamber, small invasion of frontals by the M.
pseudotemporalis, a frontoparietal saggital crest, small fused interdental
plates, lack of groove for interdental artery (is this the Mackelian
groove?) and a highly pneumatized and shortened basicranium. The fused
interdental plates are only known in dromaeosaurids among coelurosaurs, so
perhaps "C." maortuensis belongs to that family.  Chure says it shares
synapomorphies with dromaeosaurids, troodontids, tyrannosaurids and
Chilantaisaurus tashuikouensis is known from a humerus, first manual ungual,
fragmentary ilium, femora, fibula and metatarsus.  It has been allied with
basal tetanuraens, allosaurids segnosaurs and tyrannosaurids.
C. sibiricus should be left in Chilantaisaurus for the time being, as it is
said to be nearly identical to C. tashuikouensis.  It is only known from a
distal fourth metatarsal however.
On to your second question. Sereno et al. (1994) classifies Chilantaisaurus
as a torvosauroid (Afrovenator, Eustreptospondylus, Torvosaurus,
spinosaurids) and renamed the clade Spinosauroidea for their 1996 and 2000
papers.  Of the torvosauroid synapomorphies listed by Sereno et al. (1994,
1996), none can be determined in C. tashuikouensis as they are all cranial.
The torvosaurid + spinosaurid subgroup is diagnosed by "manual ungual I
elongate (three times height of proximal articular end)", which is present
in C. tashuikouensis.  Also, in 2000, Sereno added deltopectoral crest more
than 45% of humeral length, which is almost true of C. tashuikouensis.
Although these two characters are present in Chilantaisaurus, it is
debatable if they imply a relationship to torvosauroid/spinosauroid taxa.
If Sereno's manual ungual length is along the curve (as it must be for
Baryonyx to exhibit the trait, so I assume it's implied), Chilantaisaurus
has a ratio of 3.17, while Baryonyx has a ratio of 3.2 and Torvosaurus has a
ratio of 3.4.  Neither Herrerasaurus, coelophysoids, Dilophosaurus,
Afrovenator or Allosaurus show these proportions, although abelisaur and
carcharodontosaurid (maybe in the new Acrocanthosaurus skeleton?) unguals
are undescribed and I lack an illustration of "Szechuanosaurus's" unguals.
However, several basal coelurosaurs have the derived condition
(Nqwebasaurus, Dryptosaurus, most ornithomimids), although others don't
(Compsognathus, Scipionyx, tyrannosaurids).  This shows the character
distribution to be more complex than previouly thought.
Chilantaisaurus's deltopectoral crest extends 44% of humeral length.  This
compares to 37 in Allosaurus, 40 in Liliensternus and Dilophosaurus, 41 in
Ceratosaurus, 42 in Segisaurus and Elaphrosaurus "philtippettorum", 43 in
Eustreptospondylus and Baryonyx, 46 in Torvosaurus and 51 in Carnotaurus.
Thus, if the synapomorphic percentage is moved from over 45 to over 42, the
character still holds (allowing convergence with abelisaurs), but I don't
think a one percent difference from other theropods means much.  Because of
this extremely minor difference in length between torvosauroids and other
theropods, I wouldn't trust this character.
So there's your evidence for Chilantaisaurus tasuikouensis being a
torvosauroid.  I don't think it's very strong, but I don't have a competing
hypothesis (I haven't read the original description, which I hear is
incorrect in many areas anyway, or studied basal tetanuraen relationships
yet).  I trust Chure will have something to say about it's affinities in his
new paper and I look forward to reading it.

Mickey Mortimer