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Re: New paper on pre-Archaeopteryx coelurosaurian dinosaurs



010/10/29 Tim Williams <tijawi@gmail.com> wrote:
>
> Yep, the claim is dubious.  I'll fess up and say that I was kind of
> just stirring things up when I called _Gigantoraptor_ "the largest
> known theropod".
>
In my view, the assertion is more likely erroneous. Even when absolute
certainty is difficult as many large theropods which contest for the
title of the largest are incompletely known (as Giganotosaurus,
Spinosaurus), I think that the femur of Giganotosaurus measuring 143
cm, and being more robust than that of "Sue", while that of
Gigantoraptor measures 110 cm and is more lightly built than that of
tyrannosaurs, suggests Giganotosaurus is larger. Furthermore, judging
from the published drawings (Xu et al., 2009, Nature 447: 844-847) and
the scales they include, the entire lower jaw of Gigantoraptor is
scarcely longer than 44 cm, while just the dentary of Giganotosaurus
measures 120 cm according to the figure and scale in Coria and Salgado
(1995, Nature 377: 224-226) (Calvo, 1989, in an abstract in
Ameghiniana 26(3-4): p. 241, claims that an incomplete dentary
-similar to that of Giganotosaurus- measures 63 cm, larger than the
entire jaw of Gigantoraptor). Sadly, I cannot see many other shared
elements which can be compared, except ofr the caudal vertebrae,
because of Coria and Salgado's drawing being too small.

You may be right regarding the size of the guts, but even admitting
strict herbivory (which thus cannot be used with certainty), it is not
a very compelling argument because of two reasons. First, some
quantification is in order if we are to see to which degree gut size
related to herbivory provides mass capable of surpassing that of
carnivores with a larger skeletal frame. Second, the apparent
diversity of relative gut sizes among herbivores. Herbivory does not
oblige to have a large, heavy gut of the kind of that of a Megatherium
or other ground sloths. For example, cervids and gazelles are way
slimmer, even if their gut is larger than that of carnivores with a
similarly sized skeletal frame. And, as it seems, Gigantoraptor more
resembles a gracile large herbivore than something like a
therizinosaur or a titanosaur, at least as far as the limb is
involved. Also, as far as it is stated by Osmóslka et al. (2004) in
the chapter on oviraptorosaurus in the second edition of "The
Dinosauria", the pubic apron is narrow in oviraptorosaurus (p. 178),
which may suggest a not so wide body cavity (I do not know of the
state in Giganotosaurus, for there is no cranial/caudal view or
assertion in the text). Even if we admit a proportionally larger gut
in Gigantoraptor, we likely have a proportionately and absolutely
larger skull in the basal tetanuran, a less pneumatic skeleton
compared to the oviraptorosaur (if we measure size from mass instead
of volume), and, accepting from estimation based on the closer
relatives with well-preserved tails, a longer tail. These may in
principle counter the effect of the larger gut... However, admittedly,
the proportionally larger forelimb may relatively increase the size of
the oviraptorosaur, although I do not know which one is absolutely
larger among both scapulocoracoids. In any case, quantification should
also be in order to indicate to which degree the relative increase in
each body part surpasses (or is surpassed by) the other.

Sorry for not talking too much about Spinosaurus, the interest with
Giganotosaurus is not because of chauvinism of considering the
birthplace of the largest theropod, but because the former does not
have a measured complete femur (at least not in Strömer's paper),
which is the only explicitly measured bone of Gigantoraptor. And,
although the dimensions of both jaw and femur are also larger in "Sue"
than in Gigantoraptor, as Giganotosaurus was larger in these
measurements than in "Sue" I did not considered it.