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Re: Mammal diversity takes a 20 milion year step backwards!



John Bois wrote:

>Egg-laying in crocodiles works because, sovereigns in their swampy
>habitat, they can guard their nest with ferocious efficiency, on
>their own terms.  Egg laying in most snakes is okay because the nest
>is either guarded by venomous parents, or the eggs are down some
>slithery hole which only the parent can reach.  Lizards are small
>and can hide their eggs well.  Turtles make a single stealthy trip
>to lay their eggs, then they forget them.  But dinosaurs, big and
>parentally invested, had no means of avoiding detection.  The only
>strategy they could resort to was defence of the nest.  This is an
>expensive strategy and violates the first law of self-preservation:
>it is better to run than fight.

So, if egg-laying works well for crocodiles, which can defend their nests
ferociously, why do you deny dinosaurs that same trait, which were, I think
it can be safely argued, soveriegns in their respective niches?  After all,
dinos and crocs are related.
  
>Anyway, I have never heard of any significant predation on pregnant
>females.  Derek, where did you get this idea from, or is it just
>gainsaying?  Predators target the young, the sick, and the old, not
>the pregnant.

Predators target whatever is an easy catch - the old, young, and sick tend
to be the easiest.  If it happened that somehow a pregnant female got
separated from the herd, you can bet that that pregnant female is now a target.

>     I agree with Derek when he notes that baby open-field mammals,
>precocial though they may be, are at risk.  But then elephants
>surround the calves for protection, zebras confuse predators with
>stripes, wilderbeasts threaten predators, and so on.  True, such
>tactics were available to dinosaurs.  But they were not as effective
>for a stationary offspring (the egg).  Ultimately, the dinosaurs had
>to resort to blood and guts, expensive defence.

You seem to have changed the entire scope of your arguement!  If
dinosaurs are resorting to "blood and guts" defense, it is against
another (carnivorous) dinosaur (which are usually not out to steal the
eggs), not an egg-stealing mammal (or any other potential egg-thief)!
I don't see how it is expensive to fend off such a critter, which is
usually much smaller than the parent dinosaur(s), and will gladly run
away rather than get munched/crushed/bashed by an irate parent.  The
above arguement applies when the eggs hatch and the parents have to
defend little dinosaurs - but, from your previous posts, you
practically deny the eggs from hatching at all because of the
overly-voracious mammalian egg-predators!  Not to mention the fact
that it would be no more expensive for dinosaurs to defend their young
than it would be for mammals to do likewise.  Why, when mammals resort
to a given tactic, is it "useful," but for dinosaurs, the same tactic
is "expensive"?

> Again, I would argue the _prima facie_ evidence of fecundity in
>modern herding mammals.  And I deliver the _coup de grace_ to
>Derek's _pregnancy liability_ argument thusly: Greg Paul, in
>_Dinosaur Eggs and Babies_ reports that dinosaurs were r-selected.
>That is, few reached adulthood.  In contrast, many if not most
>mammal babies do reach adulthood.  As a result, open-field mammals
>only need bear one or so offspring a year to maintain their
>populations at carrying capacity!  Indeed, the very term used to
>describe this sort of reproduction is _K- selection_ and it is
>itself defined as low mortality among offspring.  Dinosaur age
>structures were like those of an oyster, bottom heavy.  The strategy
>was to lay lots of eggs in the hope that some would live.  This,
>however, is less than just an alternative strategy.  It was, in a
>world full of increasingly adept egg and offspring predators,
>increasingly expensive.

And yet, there are far more egg-producers in the animal world than there are
live-bearers.  If such an alternative strategy is so expensive, and by your
reasoning, flawed, why have the live-bearers not completely taken over all
available niches, driving all such "unfit" egg-bearers into extinction?

>     But Derek uses the fiction of the _pregnancy liability_ to
>bolster another fiction, i.e., eggs have a shorter window of
>insecurity than foetuses.  This counter-intuitive claim rests on the
>assumption that time from fertilization to viability in mammals and
>dinos is roughly equivalent and that a pregnant female is at much
>greater risk for the duration of her long gestation period.  But
>common sense and science refute these claims.

I think I should point out that my claims about "pregnancy liability" refer
to the parents, not the offspring.  What I said was:

"Animals with low birth-to-viablity times tend to have long gestation times.
During this time, the mother is at a greater risk than when she is not
pregnant....Egg-layers, on the other hand, suffer no such period (or at
least, a much reduced one) of heightened vulnerability, except that
associated with protecting the young (which, as you recall, is something
that even live- bearer's have to deal with)"

>Derek also implies that the heightened risk during pregnancy
>"necessitates" the herding of mammals.  While it might be true that
>pregnant females get protection from this tactic, it is misleading
>to see herding only a temporary counter to the pregnancy liability.
>Plain mammals _always_ herd!

Again, I said:

"It seems to me that the decreased time from bearing to viability
almost necessitates, rather than permits, the development of complex
social behaviors."

This brings in an entirely new potential discussion, one which may or may
not belong here: the evolution of herding behavior.  Perhaps herding began
as a behavior that was limited to the breeding season - observe animals such
as seals which normally hang out by themselves, or in small groups.  During
breeding season, however, they gather in huge groups, so the males can argue
about who gets which females, and the females can then bear and protect
their offspring until such time as the offspring can fend for themselves.
Then everybody goes home until next year.  
Some animals, however, may have found that it was useful to stick around
even after the breeding season, simply because there's safety in numbers.
Thus, herding becomes a year-round thing, but was initially developed from
breeding behaviors.  
Keep in mind that this is, of course, mere speculation, and my opinion.  I
did not claim as fact many of the things which you claim I did.  This whole
discussion is really nothing more than speculation.

>     Moving now to speculation: 

See?  :o)

>But even the juveniles, who likely had quite different niches from
>their parents

Why is that?  Do plains-mammal offspring occupy different niches than their
parents?

> would eat down their range, especially since (as trackway evidence
>shows, I think) they ranged with the adults staying close-by for
>protection.  And now factor in the predators.  Big predators,
>stealthy predators, small predators, flying predators, burrowing
>predators (perhaps), predators on juveniles, predators on eggs,
>predators on hatchlings, predators on adults.  Again, the dinosaurs
>had no flexibility of response.  They must stand and fight.

And where is the evidence for this?  Dinosaurs were very diverse, like
mammals are today.  To claim that they must all respond the same way in a
crisis is nonsense.  Is the only option available to mammals to stand and
fight?  Of course not.   

>  And the predators could stake out the nest area.  Unlike the
>relatively simple life of a large and vigilant herd of mammals,
>dinosaurs were required to return to the same place, to stay within
>a certain range, to protect a large number of juveniles as best they
>could from a ferocious gang of predators who knew where they were at
>every minute of the day!!!!

And yet, they survived.  Amazing, given the fact they should have all been
consumed in a feeding frenzy by all those voracious predators, from the
land, sea and air.

>     Derek says that dinosaurs suffering intense predation at one
>site can simply abandon the nest and move to a new one.  "After
>all," he says, "there's always next year."  This sounds like one of
>those "Famous Last Words" jokes, perhaps said on the last day of the
>K/T.  Small deficits in fitness can lead, in a short time, to
>extinction!

Animals do not plan ahead to prevent possible extinction.  They know nothing
about deficits in fitness.  They only "know" that if they are in danger if
they remain in a given area, it is best to move on.  They do not stop to
think, "But, oh, what of my poor babies?"  With the high young mortality
rate inherent in being r-selected, losing an entire litter is part of the
deal.  I seriously doubt the dinosaurs lost much sleep over it.

>     But then Derek challenges me to argue the benefits of mammalian
>reproduction in a _carnivorous_ territorial mammal.  Again, this is
>a situation which never existed, i.e., carnivorous mammals
>vs. carnivorous dinos in the open-field.

I don't know that hadrosaurs ever had to compete with wildebeest, either.

[...]

>But unlike the other extinction scenarios, mine also kills off the
>small (chicken-sized) dinosaurs.

It does not, however, account for the rest of the extinctions during
that time.

>After all, in a bolide-winter _some_ small dinos should be able to
>survive on rotting dino carcasses, small mammals, birds, lizards,
>and snakes.  But none did.  In my non-stealthy nest idea, small
>dinos are lumped in with the rest.

The so-called "bolide winter," I think, does not explain things any
better than egg-eating scenarios.  I don't think we really know what
would happen if a large object struck the Earth.  Sure it would be
devastating.  But what EXACT effects would it have, and how long would
they last?  We don't know this.  However, the collision-scenario at
least accounts for planet-wide devastation.  Egg-eating is an ad-hoc
explanation, which requires ad-hoc explanations to account for the
other affected groups.

As an aside, does anyone (I'm sure someone out there, does, actually)
have a comprehensive list of what groups bought it, or at least took a
severe beating, at the K/T?

Derek Smith
djsmith@ccnet.com
DSmith0531@AOL.com