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sinosauropteryx



>Ah, yes.  I remember this debate.  The large amount of caudals is probably
>an apomorphy, as even Dilophosaurus and Ceratosaurus have less (~45 and ~55
>respectively).  Other coelurosaurs like Alxasaurus also seem to lack
>expanded chevrons.  Sinosauropteryx is described as having four transverse
>processes, with bumps in more distal caudals that could be interpreted as
>transverse processes.  Thus, unless you have unpublished information,
>Sinosauropteryx has 4(+?) caudals with transverse processes and this feature
>cannot be used to argue the phylogenetic position of Sinosauropteryx.  Any
>robustness in the hindlimbs would have to be quantified to be useful.  I
>believe I listed these features previously to show why Sinosauropteryx is
>considered a coelurosaur:
>
>- amphicoelous cervical vertebrae
>- slender third metacarpal
>- fourth metacarpal absent (convergent in Allosaurus, note Sinraptor has all
>four)
>- dorsal margin of ilium slopes caudoventrally
>- obturator process placed more than 25% down the ischial shaft
>- triangular obturator process
>- ischium reduced in length compared to pubis

        Again, it sounds like these are mainly characters coded off of GMV
2124. How are we justified in doing this? I have no doubt that GMV 2124 is
a derived coelurosaurian. However, I am equally skeptical that
Sinosauropteryx is maniraptoriforme coelurosaur if it is even coelurosaur
at all. I would argue that there is no good reason to believe that GMV 2124
is, in fact, an individual of Sinosauropteryx. (GMV 2124 is the thing that
has a mammal jaw in its gut. The two described Sinosauropteryx specimens
include the type and its counterpart- the original furball theropod- and
the apparently egg-bearing female which to my knowledge has only appeared
in a few tiny ).
        What evidence do we have that GMV 2124 is Sinosauropteryx? It's
small, fuzzy, has long legs, short arms, a triangular skull, a long tail:
okay, we've just described the majority of all small coelurosaurs and maybe
even small neotetanurans. Teeth with unserrated anterior margins? Tooth
serration varies dramatically even within families (e.g. troodontidae,
which have teeth that are fully serrated, teeth lacking anterior
serrations, and teeth lacking serrations at all). Presence/ absence of
tooth serration is a pretty plastic thing; it might be useful for low level
(intergeneric) studies but it is  not a good character for higher-level
phylogeny like deciding what family something belongs in.
        Take a look at the distal chevrons in GMV 2124 and then in either
Sinosauropteryx specimen. Take a look at how far the neural spines go out
on the tail of Sinosauropteryx, and then look at GMV 2124. Take a look at
the proportions of the caudals. See if you think that GMV 2124 could have
had 65+ caudal vertebrae. Other things- Relative proportions and length of
the trunk- have a look at those. Compare the relative length of the neck,
either to the skull or to the back. Tibia/femur. It's about 115-112% in the
two specimens Sinosauropteryx and *140%* in GMV 2124. Metatarsus is 95% of
femur length in GMV 2124, roughly 75% in the smaller specimen of
Sinosauropteryx (again, Sinosauropteryx is a really stocky-legged, not
especially fleet-footed animal, *especially* when you consider the
allometric effects of its diminutive size). I could go on, but in short,
the numbers simply do not add up.
Is there any good reason not to separate these animals?

-N