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Vestigial Arms != Big Jaws (Was: Theropod limbs - how mobile?)



> Date: Thu, 16 May 2002 08:38:27 +0200
> From: "Fam Jansma" <fam.jansma@worldonline.nl>
> 
> Large theropod evolution, wether you are talking about Carnosaurs or
> Tyrannosaurs, seems to be focussing one increase in body size and
> decrease the size of the forelimbs (Giganotosaurus in the
> Carnosaurs, Tyrannosaurs in general).

... so that more mass can go into the head and particularly the jaws,
yes.  That's what I assumed.  Makes perfect sense.

The fly in this particular ointment, to my mind, is _Carnotaurus_.
This critter has ludicrously attenuated forearms -- I mean, it makes
_T. rex_ look like _Deinocheirus_.  Yet its head is also relatively
puny: it has one of the shortest heads (relatively) of all theropods.
And worse, it has a long trunk and neck.  All that precious body-mass
wasted when it could have gone into the jaws!

Illustrative skeletal reconstructions at
        http://www.netlaputa.ne.jp/~pantheon/carnotaurus1.jpg
        http://www.netlaputa.ne.jp/~pantheon/carnotaurus2.jpg
        http://www.nhm.org/journey/prehist/saur/carnotaurus.html
and a full-flesh rexstoration at
        http://dinosauricon.com/images/carnotaurus-ms.html
if you prefer that kind of thing.

So I think the simple smaller-arms-for-a-bigger-head model,
intuitively appealing though it appears, is flawed.

 _/|_    _______________________________________________________________
/o ) \/  Mike Taylor   <mike@miketaylor.org.uk>   www.miketaylor.org.uk
)_v__/\  "Too many people on the bus from the airport, too many
         holes in the crust of the earth: the planet groans every
         time it registers another birth" -- Paul Simon, "Born at
         the Right Time"