[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: szechuano- & yangchuanosaurus
I've been staying away from John's questions, because he
specifically requested _professional_ input, but I'm gonna throw in my
tupence on this one. Be forewarned, I am not a professional...
John R. Hutchinson wrote:
> I've forgotten... what's the current status of Szechuanosaurus and
>Yangchuanosaurus (besides being hard to pronounce)?
>I remember hearing that Szech. was of dubious validity, but I'm not sure
>where I heard that.
_Szechuanosaurus_? Which one? Dr. Holtz has mentioned on this list
that the skeletal remains of two animals have been ascribed to this genus,
which was origionally based on a tooth (Paul, _PDW_, 1988). One is a
carnosaur, which shows some affinities with _Yangchuanosaurus_ (Paul 1988,
various list members including Nick Pharris, and pers. obs.). One has been
described (by Holtz, this list) as a coelurosaur.
The carnosaur does show a strong similarity to yangchuan, and is
found in the same formation. No teeth with roots have been recovered, and
the safe bet is to regard it as a new taxon. Paul (1988) refers it to
_?Szechuanosaurus_. My nacient taxonomic instincts suggest that it should
either be sunk into _Yanchuanosuarus_ (the "lumper" approach, and of dubious
monophyly), or named as a new genus and species (my preferance would be
_Dongzhimingsaurus szechuanensis_. George, feel free to go wild with this).
In either case, it seems clear that this taxon needs more study.
I have no knowledge of the coelurosaur, but unless teeth were
recovered in place, its assignment to _Szechuanosaurus_ must be considered
suspect. In any case, the presence of an advanced carnosaur and a
coelurosaur in the same genus is clearly unacceptable.
_Yanchuanosaurus_ seems to be considered valid by most workers now.
Paul's (1988) lumping of it into _Metriacanthosaurus_ seems to have been
widely rejected, although it certainly does not refute the possibility of a
close relationship. Metria seems to have several derived characters in
common with several different carnosaurian taxa (Sinraptoridae,
_Neovenator_). IMHO we will not achieve any real progress on this matter
unless more metria material is found. Three species of _Yangchuanosaurus_
are named (that I know of). One has been referred to _Sinraptor_ (see
below), and one is based largely on larger size and differences which may be
ontogenetic. Paul concluded that _Y. magnus_ and _Y. shanyouenensis_ [sic?]
are respectively older and younger members of the same species.
As an aside, Currie and Xiao (1993) note that the shape of the ilium
in yangy as origionally depicted is very different from those of
_Sinraptor_, and suggest that the origional illustrations may be in error.
Paul based his famous reconstruction (1988) of this taxon on the origional
illustrations, and noted (I believe, correct me if I'm wrong here, GSP) that
the shape of the ilium conformed to _Metriacanthosaurus_ (although this was
not, contra earlier comments by me, the basis of his referral of yangy to
metria). Examination of photos of the ilium of _Y. magnus_ show an ilium
much closer to the general shape of _Sinraptor_, and further call into
question the origional illustrations. If the origional reconstruction is
accurate, it may represent a pathological or incompletely ossified bone.
This may lend further weight to Paul's synonymization of the two species of
yangy known at the time.
One thing that no one seems to have commented on is the relatively
more "primitive" looking pelvic morphology of _Yangchuanosaurus_ and
"_Szechuanosaurus_" as compared to _Sinraptor_. The pelves of the former two
taxa appear generally more similar to _Monolophosaurus_, while the latter
taxon exhibits an _Allosaurus_-like pelvis. This may be due to errors in
reconstruction (as postulated for the ilium), but IMHO becomes possibly less
surprizing if one exmaines potential mis-polarizing of certain
long-established characters in the pelvis.
>Currie mentioned in the Sinraptor paper that Yangchuanosaurus might be
>synonymous with Sinraptor; any developments on that front that I've missed?
I am afraid you misremember the paper. One recently described
species of _Yangchuanosuarus_, certainly not the type, was interpreted as
belonging to _Sinraptor_. As the type was accepted as a different genus by
Currie, he did not advocate the synonymization of the two genera. Indeed,
were the two to be considered synonyms, it is _Sinraptor_ (Currie and Xiao
1993) which would be synonymous with _Yangchuanosuarus_ (Hu? 1964?).
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock TX 79409
"The cost of living hasn't affected its popularity." - Unknown