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RE: tiny-armed theropods

  Understand that I am making an assumption here that the oversized skull and 
neck of a tyrannosaur is not as "massive" as may be assumed. That is, the skull 
and neck are very pneumatic, and in many cases, the additional volume of the 
skull from, say, a similar-sized carnosaur is likely to be filled with air and 
muscle, on top of the wide throat and vaulted palate. One may then consider 
than the "massiveness" of the skull in some taxa is over-exaggerated and that 
the balancing effect made up for by the reduced limbs is not substantial at all.

  Yes, increased use of the head for acquisition leads to reduced use of the 
limbs for same. The other features of taxa that show this trend (shorter, more 
robust hind limbs, increased shoulder girdle and pelvic girdle) may indicate 
that forelimb reduction is an effect with just one functional cause. That's an 
hypothesis, though, and certainly testable.


  Jaime A. Headden
  The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 

> Date: Fri, 7 Oct 2011 21:13:48 -0300
> Subject: Re: tiny-armed theropods
> From: augustoharo@gmail.com
> To: qi_leong@hotmail.com
> CC: d_ohmes@yahoo.com; Tim@listproc.usc.edu
> 2011/10/7 Jaime Headden <qi_leong@hotmail.com>:
> >
> >   It is actually unreasonable to show that the reduction of arms simply 
> > reduces mass over all to allow greater pitch alleviation during 
> > accelleration, when some of these taxa are expanding the size and mass of 
> > their heads and necks in comparison. This is most evident when considering 
> > that the scapulae of smaller-armed theropods tends to be more robust and 
> > larger (and fused!) then those of larger-armed theropods. This is evident 
> > especially in the two key clades being discussed here, *Abelisauroidea* and 
> > *Tyrannosauroidea*.
> I do not know if such a word as "unreasonable" is deserved. For the
> animal with a massive skull and neck may help its weight problem by
> reducing size in some other less useful organ, and some other animal
> with smaller skull mass may conceivably also counter a mass problem by
> reducing useless appendices, for example casuariforms. I mean,
> selective pressure to reduce size or organs with little use does not
> contradict selective pressure to actually increase mass of other
> organs (for example, big heads). Increased selection to reduce
> forelimbs may actually be a consequence of the pressure to increasse
> the mass of the head, at least in certain lineages, as you proposed
> before.