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Re: Spinosaurs as what?



My assumed scenario for evolution:
1. Fortuitously advantageous trait.
2. Directional selection.
3. Stabilizing selection.

Note that a trait can have a suite of advantages and
disadvantages. Therefore, I prefer to visualize
selection pressure as a vector sum. When the sum
equals zero, stabilizing selection is occurring. 

Organisms exposed to water (i.e. while acquiring
resources) reach thermal equilibrium with it quickly.
If water temperature is below the optimum for the
organism, responses include reduced surface/mass
ratio, and insulation. If water temps are high,
increased surface/mass ratio is a response. If air
conditions are such that evaporative cooling occurs,
increasing the exposure of surface area to air is
advantageous, hence the sail.

With the possible exception of the last sentence, this
is all pretty standard stuff. I?ve assumed (and read)
that sails in quadrupeds large enough to have problems
dumping heat evolved more or less in this fashion
(i.e., hot, swampy, sunny environments wtih large
expanses of sallow water). So yes, cooling.

My question is, ?What dry savannahs??

--- David Marjanovic <david.marjanovic@gmx.at> wrote:

> > Amen to the study! Increasing your surface-to-mass
> > ratio to increase core body temp seems
> self-defeating
> > to me.
> 
> Increasing core body temperature seems lethal to me
> -- in the shade-poor 
> equatorial dry-savanna-kind-of-environment in which
> all those sailed dinos 
> lived! It was seemingly too hot for rainforests! Of
> course the idea exists 
> that the function of the sail was in cooling... 
> 
>