Re: Amargasaurus...

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Thu, 26 Apr 2001, Marcel Bertolucci wrote:

>     I think just like you: if it was for protection, why it didn't evolved
> like _Saltasaurus sp._ or others Titanosaurids? It's better to be protected
> by an amrour, then by spinal spikes.

Evolution doesn't always happen in the best way possible. Animals don't
plan out their evolutionary strategies. Variations occur randomly, and
natural selection weeds out the unfit variations. The ancestors of
_Amargasaurus_ may not have been "lucky" enough to have an armor-producing
mutation. Instead they had mutations leading to high cervical spines, and
these variations were, for some reason, naturally selected for. The ones
with higher spines were more likely to survive and/or breed than those
without. As I said before, protection along the top of the neck is better
than no protection at all. Furthermore, spines are more visible than
scutes, and thus may have been more visually effective in warding off
predators.

As I also mentioned before, though, armor may indeed be a better overall
"strategy". Hence the survival of _Titanosauria_ after the demise -
_Amargasaurus_' line (as far as we know). (There may even be a parallel
here in _Stegosauria_ vs. _Ankylosauria_, although the full truth is
probably more complicated). In my understanding, that's how evolution
often works -- several methods arise, and, among competing lineages, the
best one overall eventually wins out.

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T. MICHAEL KEESEY
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