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Re: Preview of new stegosaur plate paper

Replies interspersed below--

--- Mike Taylor <mike@miketaylor.org.uk> wrote:
> > Date: Wed, 18 May 2005 07:28:07 -0700 (PDT)
> > From: don ohmes <d_ohmes@yahoo.com>
> > 
> > If plate size scales with body size in accordance
> with
> > thermoregulatory function, I personally find that 
> > compelling evidence that thermoregulatory
> selection is
> > the primary driver of plate size.
> Not necessarily; it could easily happen that the
> allometric
> exponential for thermoregulatory function (=~
> metabolic rate, I guess)
> is the same as that for some other variable.  It
> would be a clue, but
> far from conclusive.

Did not say "conclusive". That trend across numerous
taxa through time I find compelling, not conclusive.
What other variable? (Also, >= MR is my guess.)
> > Engineering and mass allocation considerations
> indicate that the
> > relative size of passive defense structures must
> scale negatively
> > with body size.
> How so?

Muscle-to-mass ratios decrease with body size.
Assuming mass specific power is equal, as mass
increases, the relative muscle power available to
"tote that bale", or shield, or armor plate, or shell,
or .45 ammo, or anything with mass decreases. Big guys
tote bigger shields than small guys, but small guys
can carry more shield per kilo. 
> > Intuitively, it seems to me that the relative size
> of display
> > structures might scale negatively with body size.
> Does anyone have
> > enough data from extant animals to comment on
> this?
> I don't have references to my fingertips, but I do
> recall that,
> surprisingly, this is often incorrect.  For example,
> the ludicrously
> big antlers of the recent deer _Megaloceros_ ("Irish
> Elk") scale
> _positively_ with body size, so that large specimens
> have
> proportionally larger antlers than smaller
> individuals.

Megaceleros' antlers may not have been even partially
for display... deer in rut are EXTREMELY aggressive.
What evidence do you have that the (I grant you)
apparently ridiculous size of irish Elk antlers is a
"display" trait? They certainly did not begin as
display traits. Don't forget interspecific

> This is, IIRC, discussed in one of Chris McGowan's
> books, quite
> possibly _A Practical Guide to Vertebrate Mechanics_
> as this has a
> _Megaloceros_ skeleton on the front cover:
> To bring the discussion back to sauropods (hey,
> that's while we're all
> here, right?) it appears that many of the very large
> sauropods seem to
> have long necks even by sauropod standards.  Among
> these I cite
> _Supersaurus_, _Brachiosaurus_ and (even more so)
> _Sauroposeidon_.  By
> contrast, smaller sauropods such as _Saltasaurus_
> seems to have
> proportionally short necks.  Clearly this is only
> anecdotal, and
> someone ought to take a stab at analysing this
> statistically.  But if
> this positive allometry is real, then it could be
> read as an
> indication in favour of the idea that those big ol'
> necks were nothing
> more than penis substitutes (i.e. sexual display
> organs).

>  _/|_ 
> /o ) \/  Mike Taylor  <mike@miketaylor.org.uk> 
> http://www.miketaylor.org.uk
> )_v__/\  "When the substitute enters the field of
> play [...] the player
>        whom he is replacing ceases to be a player" --
> FIFA law 3,
>        paragraph 5.6