[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Sauroparental care

On Mon, 22 Dec 2003, Graydon wrote:

> > 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?

Maybe not.  But generally.  But even with sauropods what alternatives is
anyone suggesting?

> 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.

But the bracket is important.  How do you rate such brackets?  I imagine
the bracket is strong enough for you to agree that sauropods had red blood
without any direct evidence.  Parental care isn't as strong of course--but
it _is_ strong.  If you see parental care in the larger phylogenetic
context as an important watershed: as part of the evolutionary canon.
Having derived such an important and time tested and ubiquitous ability,
why would a species _not_ employ it?  Why would a species give it up?
Certainly there are exceptions--megapodes are presumably secondarily non
parental (right?)--so what is the argument for sauropods as an exception?
Which is the "little green men" argument: parental or non-parental?

> > 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.

I'm missing the point--frogs have little investment in either eggs or
baby, right?  They are beyond the bracket.

> 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.

I think this is not borne out.  It seems to argue that sauropods could
never experience reproductive failure, that they had landed themselves the
perfect strategy.  Predators know better.  Making more unprotected babies
is simply setting new places at the predator table.  The offspring must
have predator-resistant strategies.  The idea that they could be like mass
hatching turtles is unlikely.  Surely predators may be locally
or temporarily swamped--but these babies cannot resort to any refugium
remote from regular "lawn mower" predators--or, if they could, where is
it?  What hypothesis could one derive to test this?

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

Firstly, "R-strategy" is only a relative term.  To a crab turtles look
like K strategists.  Secondly, as argued above, if turtles stayed on land
they would not survive.  So really, if one is to make a non-parental
arguement, one has to explain how?  I mean, I'm happy to say "we just
don't know for sure".  But I'm not willing to accept nonparental as a
default hypothesis--either hypothesis needs testing/support.

> 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.

So how do you explain the wild success of elephants?