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Re: Armadillos at the K/T!


Brian,
Perhaps it would be better to say that the bolide was the "ultimate" cause of the mass extinction, but not necessarily the "primary" or "sole" cause (terms which would be more likely to get us into semantic difficulties).
The bolide impact itself would have been the direct cause of an enormous amount of loss of life within minutes and hours just from the energy release in the initial blast (vaporization and massive injury), boulders falling from the sky and massive fires even further out, massive tidal waves, and other primary effects. The Americas bore the brunt of the primary effects (but I would think coastal areas worldwide would have been flooded by tidal waves).
All these primary effects would trigger secondary and tertiary effects (and so on) in a cascading domino effect. Blocking of the sun shutting down photosynthesis, triggering of mud slides, volcanic eruptions, flooding, and further ecological disasters, and so on----which in turn trigger other problems globally (disease and rotting, starvation, acid rain, etc.).
Blast, fire, and even starvation would have been less of an immediate problem in the oceans than on land, but even all ammonites would succumb to starvation and eventual extinction since their young in particular are so dependent on plankton. On land the ecological systems would have collapsed much more quickly (immediately in Mexico and Central America). Disease and starvation spreading worldwide, by secondary, tertiary, and more remote effects.
I don't think egg predation would have been a major factor in any dinosaur extinction, and many buried eggs would have succumbed to flooding, heat, acid rain, or no adults left to guard them (dinosaurs with big appetites were doomed, herbivores and then those that preyed on them). Those that did manage to hatch would be vulnerable to disease, starvation, or predation. However, such eggs may have been a help to some predators (even if they were generalists) that might have otherwise starved (we may never know for sure).
But if you were in torpor underground (frogs, birds, mammals, or whatever), you could have slept through the worst of the starvation (frogs can remain in torpor for years under adverse conditions and then emerge when things get better). On land in particular, torpor among animals (and similar resting stages like seeds, cysts, spores, and so on) is what got many of the surviving groups through times of reduced sunlight and collapsing food supplies.
Ultimately, in my opinion, virtually all of the extinctions at K-T were caused by the bolide impact, whether it was primary and quick, or secondary and tertiary (and somewhat delayed). And extinction was probably widespread even among most of the groups that survived, so I find it easier to look at why the survivors managed to squeak through, and write off the rest as simply failing to survive the devastation that the bolide caused (primarily, secondarily, or on down the line). So in a sense, the bolide was "ultimately" the trigger (but not necessarily the sole or primary trigger depending on how you define "sole" or "primary") which resulted directly or indirectly in virtually all the mass extinctions which occurred in the days, months, and years which followed. The radiation of successful survivors may have caused further extinctions on a smaller scale down the road (but even then probably more by competitive exclusion than predation on eggs or young). There are bound to be exceptions to such general trends however, but it is obviously far more difficult to speculate or test about exceptions than it is for trends in general.
But in fairness to John, I would say that things like increased predation on eggs and young could have conceivably weakened the populations and survivability of some groups during the Late Cretaceous that might have otherwise squeaked through the K-T disaster (but whether any of those might have been non-avian dinosaurs would be difficult to ever prove with any certainty---but who knows what techniques future generations of paleontologists will be able to come up with to study such things). I guess we should never say never.
---Cheers, Ken
P.S. My apologies to Ray for inadvertently responding to a personal message on the list. Apparently my brain was still half asleep this morning, but that is certainly no excuse for my being so careless (shame on me). I even managed to mangle the spelling of irrelevant. Feel like banging my head on the table a few more times, but I guess a good night sleep would be healthier and more effective. Been a long day, not to mention a Monday.
******************************************** 
From: <philidor11@snet.net>
To: "Ken Kinman" <kinman@hotmail.com>
CC: <dinosaur@usc.edu>
Subject: Re: RE: Armadillos at the K/T!
Date: Mon, 1 Oct 2001 19:27:26 -0400

Ken, you ask if the bolide hypothesis isn't broken, why try to
fix it?
I agree with you that a bolide is obviously the primary cause.
 But when you look at how widespread and thorough the extinctions
were, all around the globe, can you be confident that a single
event with effects lasting for a comparatively brief time must
have produced them all?
That seems an assertion which requires proof more than the idea
that there was one primary cause and also a number of secondary
causes.  Would the secondary causes (including egg predation)
have been sufficient?  That's more unlikely than the bolide as
sole cause.
Because bolide-as-sole-cause cannot be falsified as compared
to bolide-and-secondary-causes, I'd argue that bolide-as-sole-cause
isn't a full scientific hypothesis.  Now there's a statement
I'd appreciate your comments about!


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