Re: Big = Old = Advanced?

[Ronald Orenstein <ornstn@inforamp.net>]

John Bois writes:
>This is true.  And I know it.  All I meant above was that _regarding that
>particular strategy_ non-avian dinosaurs were at a relative disadvantage.
>As you know, I also believe that regarding the strategy of being cryptic,
>non-avian dinosaurs (generally) were at a relative disadvantage. 

Maybe.  But remember that we do not know what they actually did in detail.
And remember also that for many birds predation may well be higher after
hatching than before (there are a lot more baby bird-eating snakes than
egg-eaters, for example) and we do not know how altricial baby dinosaurs
were.  We also do not know how long it took the eggs to hatch (do we?) -
the longer it takes the more vulnerable they are, especially if the young
could scurry off to hide in the brush shortly after hatching.

>Maiasaura, though, didn't appear to have a way of distancing themselves
>from their worst predators.  The nasties could, for all we know, just
>follow the herds up and down the continent--at least their pred./prey
>system is not analagous the kind of territoriality shown in the
>lion/wildebeest system and the consequent predator territoriality. 

Remember that we don't know what their "worst predators" were - only that
there were some potential candidates.  We certainly don't know which were
the most frequent egg-eaters as opposed to hunters of hatchlings, etc.  For
all we know there could have been something about the siting of Maiasaur
colonies that related to mortality factors we have yet to guess.

>Why do the vast majority of birds stay with there nests?
>I think megapodes are the only exception to this.

Actually male megapodes do stay with the nest mound until hatching.  They
do not incubate, though.  Your question is a good one - I wonder if this
has something to do with the thermodynamics involved, or the amount of
energy that must be conveyed to the egg in the form of brooding heat to
permit development of an animal which, after all, is or is about to become
homeothermic.  I don't know the answer, though.  Of course crocodilians,
some snakes, many fishes, some frogs etc also guard their nests or clutches.

>Turtles can also hatch at a relatively immature stage--presumably because
>they need less complex wiring and they have protective shells that give
>them a margin of protection.  

Actually many birds hatch at a much less developed stage than any turtle.
I know of no altricial turtle (or reptile, for that matter) - that is, none
that is incapable of feeding itself at birth.  Of course many birds,
including all songbirds, are altricial.  What I think you mean is that
there is less need for imprinting or other forms of early-stage learning in
turtles than in birds; we know that songbirds in the nest learn aspects of
song, navigation etc before fledging.

This means that they can lay more, smaller
>eggs, i.e., their eggs are less expensive.  

I would say that most dinosaurs I have heard of lay remarkably small eggs
in comparison to their body size.  In birds, the smallest egg in relation
to size belongs to the largest living bird, the ostrich, which may tell you
something, but I'm not sure what.  Anyway, the amount of investment a
maiasaur put into a single egg may have been a lot less for its size and
metabolism than with modern birds.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net