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Re: Ouranosaurus' sail



----- Original Message ----- 
From: "Jonathan R. Wagner" <jonathan.r.wagner@mail.utexas.edu>
To: "Silvio Renesto" <silvio.renesto@uninsubria.it>; <dinosaur@usc.edu>
Sent: Friday, June 13, 2003 6:41 AM
Subject: Re: Ouranosaurus' sail


> >   but I was wondering if the sail of  Ouranosaurus, rather than a
> > termoregulatory device, could have been a sort of mimicry, which
rendered
> > the inoffensive plant eater similar,  when seen at a distance, to a more
> > dangerous spinosaur.
>
> This has been suggested on-list in the past (by someone... I forget who...
> :). Bill Clemens tells me that it has been suggested in-print for
> Dimetrodon/ Edaphosaurus. In the latter case, this might serve as an
> explananation for the difference in morphological complexity of the "sail"
> among these taxa. It does seem possible that elevated dorsal spines, which
> may in some cases be biomechanically favorable, may also be a common
"theme"
> in dinosaur display behavior. In the case of "high-spined" pairs, such as
> Ouranosaurus/ Spinosaurus and Dimetrodon/ Edaphosaurus, I am more inclined
> to attribute the display function to the herbivores, with the predator as
> the mimic.

I think the balance of the theoretical dynamics may have been in the
opposite direction (see earlier post)

It is also possible that there may have been some positive
> feedback in the evolution of this feature in both species,

The evolutionary dynamics could indeed become very complex, but it depends
upon the strength of the selection pressures.  There have been suggestions
(in the 'mimicry' literature) that the dynamics change significantly if the
predator responsible for the selective pressure for mimcry is also important
in the overall population dynamics of the prey species.  In other words, it
may be possible for a selection pressure for mimicry to be applied by a
predator which has no real affect on the overall population dynamics of the
prey species.

with elevated
> neural spines in the predators becoming a behavioral signal in that
species,
> and possibly a means of camouflage for isolated herbivores as outlined
> above.

This may be true, and it is entirely possible that these dynamics are in
play without ever becoming a causal factor in the evolutionary orgination of
the sail/hump structure.

Cheers
Colin