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Re: Sundry responses of Bois



John Bois wrote:

>>Yes.  Varanids must also be considered.  But my argument is that the guild
membership increased such that the predation load became overwhelming.  As
you know, most oviparous--especially large oviparous creatures--suffer
very high predation.<<

I was not seriously suggesting that varanids played a role in dinosaur 
extinction. I was merely using them as an example to illustrate a point, that 
if we're going to start pointing fingers at egg-eaters as potential agents of 
extinction (which we shouldn't), that varanoids (and snakes, and troodontids, 
and oviraptorids, and insects, and so forth), should look equally guilty.

> >>In addition to size increase, dentition diversity increases.<<
> 
> Can you demonstarte a connection between more complex mammalian teeth and 
> ovivory?

No.<<

If specialized dentition cannot be demonstrated to be specialized for 
ovivory, than don't site it as evidence in your favor.

>>By far, the most important locally documented change
among vertebrate assemblages at and soon after the boundary involved
non-avian dinosaurs and (the invasion of) condylarthran mammals."<<

I don't have this paper in front of me, but it seems clear that the authors 
are speaking of the K/T event as it appears in the Ferris Formation, i.e., 
"locally," *not* in general. Likewise, when I'm collecting in the Prairie 
Bluff Chalk and Clayton Fm., which span the K/T event in western Alabama, the 
"most important locally documented change among vertebrate assemblages" is 
the sudden disappearance of mosasauroids and certain families of marine 
turtles. Same event. But dinosaurs aren't *locally* a part of the equation.

>>We are talking about reproductive failure, right?  Or does the Alvarez
model posit a clean wiping out of all non-avian dinosaurs without
regard to their reproduction?  I mean, it is in these details that the
Alvarez model has no clothes.<<

If you die in a firestorm, or starve during an "impact winter," or drown in a 
tsunami, or by sulfuric rainstorms, there's not much need to worry about 
reproductive failure. At least in North America, after the Yucatan impact, 
*if* there were breeding populations of dinosaurs left to lay eggs, and *if* 
enviromental conditions (temperature, etc.) would have permitted those eggs 
to hatch, it's probable the hatchlings would have starved. So, at this point, 
it really does not matter if your eggs are eaten, or by whom your eggs are 
eaten, because the reproductive cycle (from mating to adult, 
reproductively-viable offspring) has already been so profoundly and 
irrevocably altered.

>>And a reasonable assumption is that the two taxa are not equally gifted in 
this regard.<<

*Why* is this a reasonable assumption? 

>>> And what about _Megalania prisca_ in Australia? How did it survive to 
become 
> a top-level predator with so many marsupial egg-eaters, not to mention 
murid 
> rodents?

Can you suggest a reason?<<

Yes (though I'm not the one that needs to). Clearly, ovivory did not pose an 
extinction-level threat to _Megalania_ (and please don't plead grasslands; we 
have no evidence that _Megalania_ nested in grassy places, since we have no 
fossil _Megalania_ eggs) and extant varanids, even the big ones, don't rely 
on the cover of grasses to save their eggs.

>>I'm not picking on you Caitlin<<

I was starting to think it might seem the other way round.

>>> We have a set of explanations that already work far better 
> than your hypothesis (whether they're the truth or not).

I don't see _any_ explanations.  Whether or not my hypothesis is viable,
at some point those who advocate the bolide as a cause must tell us what
the mechanism was.  The fact that this does not seem to be an important
requirement may be an indication that the hypothesis is not that robust.<<

The mechanisms (and I assume you mean the actual agents of direct extinction) 
should be fairly obvious. Fire, flood, darkness, cold, famine, disease, etc. 
But at this point, I'm choosing to bow out of this dialogue. I honestly don't 
think you're looking at your own ideas, much less anyone else's, objectively. 
You change your hypothesis whenever someone pokes a hole in it, so that it is 
infinitely elastic and vague and impenetrable, which makes any serious 
discussion exceedingly difficult.

Caitlin R. Kiernan