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Re: Armadillos at the K/T?
> Jamie Headen [sic] said:
> >Egg-eating is not a tenable solution to the K/T. It is unviable
> >ecologically, and untestable.
> >Egg-eating must be a global event, and this has not been at all supported
> >by the present data.
> Allow me to suggest that "egg eating" is a poor description of what I'm
> proposing. "Predation on offspring" is better. [...]
> Predation on offspring as a persistent selective force
> is a well accepted fact; [...] Even after extirpation of significant
> rhea suffer a heavy, heavy predation load.
And they are _still_ _not_ _extinct_. Are there any known cases of species
that died out because of nest predation?
(What significant predators, BTW?)
> Because they are easy to find (compared to small birds, at least, but
> not compared to much larger non-avian dinosaurs), they are subject to
> predation from several species on offspring at several stages, both in the
> egg and whilst proceeding through growth to adulthood.
And they have had a long time to evolve to cope with it.
> So, I'm not
> proposing that a single predator evolved and suddenly wiped out
> I am saying that there was an increase in potential predators on their
You say that there _might have been_ such an increase, based on more large
mammals known in one spot of the world in the Maastrichtian than before.
IMHO that's negative evidence...
> I would include birds and other mammals. And I would welcome
> the addition of another player-armadillos-especially one which is so
> devastating to extant large egg layers!
Which are, sorry for repeating, still not extinct...
> This hypothesis _is_ testable.
> That they _did_ prey dinos to death may not be testable. But so what?
So-called historical processes are never testable.
> There are some things we may never know. This should not mean that we
> accept one hypothesis over another unless there is a good reason to do so.
Search the archives to find _lots_ of _good_ reasons to prefer the impact...
> Many, if not most paleontologists find the bolide insufficient in
> the patterns of extinction.
1. untrue, as seen on this list 2. unimportant 3. the pattern here is that
there is practically no pattern, isn't it?
According to both phylogenetic brackets and molecular clocks, paleognaths
must have been present before the K-T and survived it. I can't possibly
claim that any of them looked or behaved like a rhea at that time, but rheas
evolved alongside armadillos...
> But I'm not sure why anyone would find predation on
> offspring "untenable" when it is such an obvious limitation on extant
Because, I repeat, it is _still_ such an obvious limitation on extant
species and has totally failed to kill them completely off. Rheas are, if
the newest molecular phylogeny is true (it fits paleogeography), the
basalmost ratites, they must have been together with armadillos for probably
as long as the latter exist.
> All we need to know to give the hypothesis some respect is whether
> or not there was an evolutionary change w/in K/T creatures which brought
> them into the size ranges and morphologies which today cause oviparous
> species much trouble.
Just confused -- how do you explain the marine K-T extinctions?
> The finding of K/T armadillos--if true--adds value to
> the hypothesis.
"Finding" is a big exaggeration IMHO. All that there is is one molecular
clock date. Not a single fossil. (IMHO molecular clocks are often unreliable
around the times of explosive radiations after mass extinctions, but this
assumption is based on negative evidence -- lack of K crown group
placentals, for example -- too.)