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

Re: sinosauropteryx



Nick Longrich wrote-

> 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?

Well, since GMV 2124 (which is what I took pictures of by the way, the
holotype is really hard to see any details in) hasn't been described in the
literature yet, I suppose it could always be a different species.
Protarchaeopteryx and Caudipteryx taught us that this can be a problem.  As
for the differences you mention, the chevrons do look more reduced in GMV
2124, although I don't think the neural spines can be seen well enough to
compare to the holotype.  Yes, the apparently complete tail of GMV 2124 only
has about 45 vertebrae.  And, yes, the skull is shorter in GMV 2124.  The
tibia is indeed almost 140% of the femoral length and the metatarsus much
longer than in the holotype.  Very good job finding these differences and
the two could always be different taxa (in fact, now that you mention these
I'm beginning to wonder...), but you're missing an important detail.  All of
the coelurosaurian features listed above (except for the obturator
placement) were described from the original two specimens (which are alike
in the limb ratios at least), not GMV 2124.  So even if they aren't the same
species, Sinosauropteryx is still a coelurosaur.  Also, GMV 2124 has some
primitive features like an expanded dorsal quadratojugal process and the
morphology of manual digit I seems similar to Sinosauropteryx, so they may
still be closely related.  Until GMV 2124 is described we have no certain
way of telling.

Mickey Mortimer