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Re: Sundry responses of Bois



John Bois wrote:

>>Caitlin R. Kiernan said:
> It certainly seems unlikely  that mammals posed no large-scale threat to 
> dinosaurs until the Latest Cretaceous, when, you suggest, they somehow, 
> suddenly, engaged in a world-wide egg-devouring binge.

This assumes that without an extra-terrestrial event, the paleo biota
should remain in unpunctuated equilibrium.<<

No, it doesn't, actually. 

It's fairly obvious that populations are dynamic enough phenomena, without 
the aid of cataclysmic extraterrestrial influences. Predation does occur and 
it is relevant to the process of natural selection. However, that said, 
demonstrating that egg-eating mammals played a role in the extinction of 
non-avian dinosaurs is another matter. As I said, I don't think anyone here 
will argue that there were not Maestrichtian mammals that ate dinosaur eggs, 
but that's a long, long way from their being a potential factor in 
dinosaurian extinction.

Why suspect mammals as the agent? It seems rather arbitrary. For example, why 
not varanoid lizards? We know that extant varanids are ovivorous, and the 
varanoids experienced their first success in the Late Cretaceous (hence they 
lack the much longer, problematic coexistence with dinosaurs that mammals 
exhibit). If ovivory was the culprit, don't varanoids make a better 
candidate? And if not, why?

>>However, some evidence suggests
the following sequence of events: 1. small dinosaurs disappear towards the
end--a reasonable hypothesis is that this was due to competition or
predation from new mammals and birds; 2. In any case, now that traditional
tormenters were gone, there was relaxation on size constraint for
mammals.<<

What do you mean by "small."? Has anyone ever demonstrated that smaller 
dinosaurs posed more of a threat to mammals than larger dinosaurs? There are 
fairly large carnivorous mammals today (such as wolves) that prey on fairly 
small mammals (such as lemmings). Maestrichtian troodontids surely would have 
found even lemming-sized mammals fair game.

And why do larger mammals pose a greater threat to nesting dinosaurs?

>>In addition to size increase, dentition diversity increases.<<

Can you demonstarte a connection between more complex mammalian teeth and 
ovivory?

Eggs are easy things to break into, even relatively large eggs. Complex teeth 
simply aren't a prerequisite. I'll cite varanoids again. Very good 
egg-eaters; very simple teeth.

>>Lillegraven and Eberle comment in 1999 paper, that in the cross K/T strata
that they studied, the _only_ apparent change was the disappearance of
non-avian dinosaurs.<<

???? Quote Lillegraven and Eberle to this effect. I'm certain they were not 
making a generalization about the whole K/T transition. Unless I've somehow 
missed all those Paleocene ammonites and rudistids . . . 

>>I, and many paleontologists, find the Alvarez
explanation of dinosaur extinction very unsatisfying.<<

Why? Whether it's true or not, the model satisfies the criteria that would 
have to be satisfied to explain such a global event.

>>My claim that an important
synergistic effect was predation is controversial.  But I'm not sure why.<<

Because there's no evidence to support your claim. I'm not being flippant. 
It's just that simple.

>>If someone discovered big terrestrial egg layers and mammals (particularly 
placentals) living in harmony--without having to hide, I would run away
forever. <<

I'm uncertain as to why marsupials make poorer egg-eaters than placentals, 
but . . . what about the phorusrhacids and diatrymatids? They coexisted with 
far larger mammals than those that tyrannosaurs and ceratopsians would have 
had to contend with. And while I'm sure these large birds probably did have 
eggs eaten by mammals (and reptiles, for that matter) - almost all birds do - 
there seems little reason to suspect ovivory as a casual factor in their 
eventual extinction. If your hypothesis is correct, why were the 
phorusrhacids ever able to *become* dominant predators, after the blow dealt 
to the dinosaurs by the Maestrichtian egg-eaters?

And why do we exclude crocodilians and turtles from the threat of extinction 
by ovivory? There are plenty of extant mammals larger than the largest 
Maestrichtian mammals that inhabit the wetlands where crocodilians lay eggs, 
and even larger predatory mammals have access to the beaches where sea 
turtles lay eggs. 

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?

You can't protect your hypothesis by pleading special cases for these obvious 
problems.

>>As far as I know, the "out-dated" version was rather perfunctory (mammals
eat dino eggs).  My version has many more bells and whistles.  In any case,
age of an hypothesis is only relevant if new information has made it
illogical.<<

The earlier version of this idea was largely based on a) a need to explain 
the disappearance of dinosaurs, b) a mistaken view of dinosaurs as 
"reptiles", and c) the idea that mammals are innately "superior" to 
dinosaurs. We now have new data that does, indeed, render the hypothesis 
positing ovivorous mammals as the culprit in dinosaurian extinction obsolete. 
As the evidence of a cosmological and/or cataclysmic geological agent/s grows 
more weighty, the need to search for other causes diminishes, especially 
causes as far-fetched as sudden, worldwide predation by Maestrichtain 
egg-eating mammals.

In short (again), you have no new evidence to present (or you aren't 
presenting it). We have a set of explanations that already work far better 
than your hypothesis (whether they're the truth or not). Therefore, there is 
no need to take this idea, of extinction via egg predation, off the shelf and 
dust it off for reconsideration.

Caitlin R. Kiernan