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Re: spikes



(veni, vidi, concreti) wrote:

> So far we have (if I read aright) no evidence of a firmly fixed plate;
> they are just overblown scutes embedded in the skin (whether standing
> up or laying flat).  Now, the problem with this is that you have a
> large mass attached by a (relatively) weak attachment. It would surely
> not take much (relatively) leverage to tear the off, and I would have
> thought (no calculation) any respectable size tyrannosaur could have
> done it (some one must have studied jaw strength etc).  So, could they
> really have been much use as armour? I think not. Therefore the tails
> spikes must play a very important defensive role, and I could envisage
> a S. stenops turning tail toward an aggressor and waving his spikes
> around in a threatening way; maybe even raising it up to cover his
> back?

I've never seen the conflict between the relative weakness 
of the plates and their use as defensive structures.

After all, the spikes are only modified plates (or v.v.  At 
least, this would be my interpretation after looking at
_Kentrosaurus_), so either the spikes derived from defensive 
plates, or we have to accept that plates which were forming 
some other function were modified to perform a defensive 
role.  The second choice is, of course, perfectly possible.  
But it seems to me that having all these structures 
performing the same task is a simpler explanation.

Looking for modern analogs, there are certainly many fish
which have weak, or even soft, fin structures which are
still called on to form defensive roles.  There are also
several examples of animals which shed body parts when 
under attack.  I seriously doubt that "any respectable size
tyrannosaur" ever had an opportunity to have a go at _S. 
stenops_ (or any other Stegosaur, at least in N. A.), but 
your statement may well have covered exactly what did 
happen when Stegosaurs encoutered large carnosaurs.

Perhaps the plates were designed to break away, leaving
an Allosaur with a nice cruncy tidbit while the Stegosaur
took an opportunity to slip away.  Yes, I realize these
plates were highly vascularized.  But if we can accept the
idea that the blood flow could be regulated for cooling
purposes, which not shut off?  Go catch a skink by the 
tail and see how quickly they shed a large, highly
vascular chunk of their body.  Plates might be so poorly
rooted because they were designed as break-away defenses.

There's my heresy of the week.  Stegosaur plates as
defensive structures first, break off body parts second.
And tail spines paired above and below instead of side
by side.

And now, like a Stegosaur shedding a plate, I slip off to 
the Hell Creek for a couple of weeks of extracting 
crumbly things.

Mark
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