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Re: Amargasaurus (but rules can change)


Mike,
I agree that is how evolution "usually" works. But then comes along a big bad bolide, and neither spines nor armor are worth diddly. Then it is often a matter of dumb luck----lucky to be on the other side of the globe, lucky to be a small ground dweller, and/or a low-maintenance scavenging generalist. Or in a resting-state of torpor or a hardy spore.
Then the best overall strategy is almost totally up to chance---and no "strategy" will work if the bolide falls anywhere near you. All the normal "rules" evolution are smashed by a preponderance of sheer dumb luck, especially for specialized metazoans. But noone ever said mother-nature was fair, and all the regular "rules of the game" can sometimes change drastically in an instant. That's when the meek finally get their chance to inherit the earth, at least for a while. :-)
---Ken
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From: "T. Mike Keesey"
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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