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RE: Theropod Forelimb Reduction



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=A0 Practical experiments on crocs or cats would prove fruitful for this co=
ncept. The relation to incrassate lateral teeth away from thinner=2C blade-=
like teeth (even if the incrassate teeth are ziphodont=2C they are not as n=
early narrow) rely on a different strategy for dealing with prey or foodtst=
uffs in general (where "prey" requires a living organism to kill). Large la=
teral teeth realtive to short anterior/mesial teeth are related to renderin=
g/processing=2C whereas the anterior teeth and their size relate to how the=
 prey is acquired: if small=2C these teeth are less related to acquisition =
of the prey but function more like processing "grips"=3B if large=2C they a=
re primarily involved in the purpose of prey acquisition=2C and are not use=
d in the processing of the prey afterward (generally).=20

=A0 I made a comparison to the dental equipment of cats before=2C where the=
 incisors are very short=2C generally of the same saize=2C and arranged in =
a largely transverse arcade. They are furthermore also transversely broad=
=2C with two large carinae on the mesial and distal margins=2C producing a =
serrate=2Cd shearing margin on the jaws. The premaxillary teeth of tyrannos=
aurids are very similar=2C albeit produced into a curving arcade rather tha=
n being nearly straight across=3B the D-shaped structure of the teeth are a=
lso similar=2C although not identical to the incisiforms of cats. The condi=
tion in crocs is similar=2C although the teeth are conical=2C in that a sho=
rt anterior arcade is used to nip a large animal.

=A0 Practical experiments to test this hypothesis including testing the gri=
pping=2C processing (shearing=2C sawing)=2C or nonfunctionality of differen=
t sets of teeth including in taxa with homogenous premaxillary/maxillary te=
eth to those with heterodont arrangements. The same tactic can also work fo=
r accessing how the premaxillary arcades work in ornithischians=2C where te=
eth are often absent but the jaw morphology is nonetheless approximate. The=
 hypothesis suggested above that tyrannosaurids were better processers than=
 acquirers with thei anterior jaws implicates a less-head-first concept of =
prey capture and more like a processing suite in the jaws with less emphasi=
s on hunting than grabbing and suppressing (head first).


Cheers=2C

Jaime A. Headden

"Innocent=2C unbiased observation is a myth." --- P.B. Medawar (1969)


"Human beings=2C who are almost unique in having the ability to learn
from the experience of others=2C are also remarkable for their apparent
disinclination to do so." --- Douglas Adams (Last Chance to See)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things=2C the human race
has had a dream: to kill him=2C so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion=
 Backs)





----------------------------------------
> Date: Thu=2C 22 Oct 2009 08:47:24 +1100
> From: dannj@alphalink.com.au
> To: dinosaur@usc.edu
> Subject: Re: Theropod Forelimb Reduction
>
> On Wed=2C Oct 21st=2C 2009 at 12:15 PM=2C "Thomas R. Holtz=2C Jr."  wrote=
:
>
>> Given that Raptorex was only approximately 3 m long as an adult and has
>> highly reduced forelimbs=2C while larger more primitive tyrannosauroids
>> (Eotyrannus=2C Guanlong=2C etc.) have proportionately longer forelimbs=
=2C the
>> new guy actually throws a monkey wrench into this idea. If the reduced
>> arms of Raptorex represent the same reduction present in Tyrannosauridae=
=2C
>> then it evolved in small body size.
>>
>> Indeed=2C the presence of large theropods with big forelimbs (Gigantorap=
tor=2C
>> Therizinosaurus=2C Deinocheirus=2C etc.) shows that it is possible to be=
 long
>> armed and big at the same time.
>
> Raptorex had the characteristic 'D-shaped' teeth (in cross section=2C tha=
t is) seen in later
> tyrannosaurs. Could it be that a move away from relatively fragile=2C nar=
row=2C blade-like teeth
> towards something more capable of withstanding lateral movement meant tha=
t the jaws took over
> some (or even most) of the role previously played by the forelimbs during=
 prey capture?
>
> --
> _____________________________________________________________
>
> Dann Pigdon
> GIS / Archaeologist Australian Dinosaurs
> Melbourne=2C Australia http://home.alphalink.com.au/~dannj
> _____________________________________________________________
>
                                         =20
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