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Spinosaur skull mechanics (Was: Dinosaur diversity analysed)



Denver Fowler writes:
 > > [...] including an excellent presentation by Emily Rayfield,
 > > showing that the snouts of baryonychines are functionally
 > > equivalent to those of gavials rather than alligators or
 > > "classic" theropods.
 > 
 > Is this really all that surprising? I mean, it's not as if they are
 > morphologically similar to other theropods or alligators, and they
 > do look very like gavials. You can see the similarity just looking
 > at the bones.

OK, I oversimplified pretty drastically here.  Let's see how well I
can remember Emily's talk.

Unsurprisingly, it was based on FEA.  It used four skull models: an
extant alligator, extant gavial, _Baryonyx_ and a sort of idealised
generic theropod.  Among these animals, the extant crocodylians and
_Baryonyx_ have secondary palates IIRC, whereas the typical theropod
lacks them.  Further, the crocs have lost their antorbital fenestra,
which is retained in generic theropods and greatly reduced in
_Baryonyx_ (I think -- as I write this, I don't have access to any
materials.)

The study consisted of testing the peak loads induced by biting both
symmetrically and asymmetrically (only one side of the jaw) at three
different places; and then re-running the analyses having added
palates to those models that lacked them and taken them out from those
that had them; and then doing the same with the AOFs.  Emily showed
graphs indicating how much difference the presence and absence of
these two features makes to the skull's resistance to symmetrical and
asymmetrical bending in each of the four taxa.

I didn't take notes so I can't give you full results; but I can tell
you that they were surprising.  Adding a palate or filling in the AOF
of the generic theropod would significantly improve strength, yet
these animals did not evolve such features.  Conversely, removing the
palate or adding an AOF to alligators did NOT significantly reduce
strength, yet they _did_ evolve them.  Garials and _Baryonyx_ did gain
significant strength from the addition of the palate, and from the
absence or reduction of the AOF, so in this sense they are similar.

There's a lot more, but that's the outline.  I have to stop now, my
plane's about to land :-)

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  Archosaurs rule!