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Re: Sauroparental care



On Mon, Dec 22, 2003 at 09:54:40PM -0500, John Bois scripsit:
> On Sun, 21 Dec 2003, Ken Carpenter wrote:
> > Again, I raise the point of how do you test your hypothesis? I can
> > just as as well say that little green men come to earth and took
> > care of the babies.
> 
> I agree that at the present state of evidence we can only make
> inferences about parental care.  I must disagree about the _strength_
> of the inference.  In my view parental care is a strong inference--so
> strong that we can assume it happened.

In sauropods?

I don't think we've got anything more than the phylogenetic bracket and
the existence of eggs in clutches, which is a reason not to dismiss the
idea out of hand, but which is also not any kind of positive evidence.

> Behaviors don't fossilize.  Maybe we can never prove it.  However, in
> terms of helping us derive hypotheses, I wonder at what point does an
> inference become so strong that a broad consensus exists that we can
> assume it happened?  I'm trying to think of an analogy.  Parental
> care--i.e., increasing investment in egg and therefore baby (once an
> organism has invested considerable time and effort in an egg it pays
> to maintain investment in baby!) seems to have increased over
> evolutionary time. 

News to all those frogs, that.

There isn't any way to make ~50 2kg eggs a big investment to a 20 ton
parent.  (Unless mating is really, really risky, but that's not likely.)

That hypothetical clutch is 100 kg out of 20,000 kg; half a percent of
body mass for fifty chances to successfully reproduce.  Lay eggs at that
rate once per wet season over a fifty year reproductive life and you
have 2,500 chances.  If _two_ offspring, less than one per thousand,
succeed in reproducing themselves, you're fine, in a proper Darwinian
reproductive sense.

That looks like sauropods could be as completely R-strategist as sea
turtles.

Small creatures have to be in a hurry; they have short lifespans and a
high risk of predation.  Gibberingly enormous creatures that live a long
time don't have to be in a hurry to reproduce, and can successfully take
a statistical approach.

> I realize that this is not necessary in all species.  But it is in
> most terrestrial quadrupeds over a certain size.

Mammals are hardwired K strategists; you more or less can't have an R
strategist mammal.  Viviparity and lactation preclude it.  In that
sense, *all* mammalian models will be wrong.  (and most modern bird
models are probably wrong, too, since they're all small.  Even moa were
small by the standards of the full Dinosauria.)

> If one cannot have direct evidence of something, what is the next best
> thing?  And at what point does the need for empirical evidence become
> superceded by the quality of indirect evidence?

First, you need something to explain. 

Sauropod reproductive success doesn't appear to need any particular
effort to explain that would require invoking parental care.

-- 
oak@uniserve.com | Uton we hycgan    hwaer we ham agen,
                 | ond thonne gedhencan    he we thider cumen.
                 |   -- The Seafarer, ll. 117-118.