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Re: Big = Old = Advanced?




On Thu, 4 Sep 1997, Dann Pigdon wrote:

> John Bois wrote:
> > <snip>
> > Maybe dinosaurs could let the hatchlings scurry into
> > brush for hiding and then call them into the open for feeding.  Does this
> > work for any creature today?  
> 
> There are so many examples of this I couldn't hope to list them all.
> Foxes, hyaenas, wolves, and many den birthing species leave their
> young underground while they go out foraging, calling to them to
> come out when all is clear. 

Yes. These are all good examples.  But now I will criticize them on the
basis of their applicability to dinosaurs.  For example,
I think there is general agreement that dinosaurs could not burrow.

> Harp seal pups with their white fur
> lie still in the snow until their mother returns. 

Probably not an option for dinosaurs since 1. Hatchlings were
unlikely to accumulate sufficient fat reserves for insulation, i.e.,
there is more time to do this inside a uterus, and 2. Seal
mothers utilize swimming ability to reach such inhospitable places.  This
is a skill differential of a magnitude that one dinosaur prey is unlikely
to have over its predator. I don't know of any fossilized swimming
structures, such as flippers.  Though _some_ swimming ability was almost
certain.

> Many species of
> deer, antelope and the like will leave their young in long grass
> while they draw predators away, only returning when it is safe.

Again, I think this technique tends to depend on the animal's ability to
conceal itself, or move quietly through dense forest.  Though bigger
animals than deer live in the forest, they don't, as far as I know (at
least the forest elephant) rely on hiding their young.  This is the
critical point.  The Sumatran Rhino and the forest elephant babies follow
their mother around (or so I have read).  

A very interesting related question is whether or not a big animal should
_nest_ in deep cover.  Ostriches, emus, and rheas use open space cover
(grass).  The only animal of any size that does this today is the
cassowary of NG and NE Aust.  And I am stumped as to how it is able to get
away with deep-cover nesting given its size.  I have been told that the
male has amazing crypticity as it stays with the nest (possibly in
torpor!).  But I wonder why this strategy is so little converged to?  Is
it only the special biogeographical history of New Guinea and Australia
that allows this?  

> I'm sure there were as many infant raising techniques
> amongst the dinosauria as there are in most extant 
> lineages. 

While I agree that infant raising techniques among dinosaurs were
diverse, I think we do better looking at their extant forms rather than
the extant forms of other lineages.  For example, nursing provided
opportunities for rearing that they simply could not have had (just as egg
laying provides opportunities that mammals cannot have!).

> I doubt we can generalise on any particular sub-order, or even genus,
> of dinosaurs in this way.

Maybe not.  But discussions of possible limitations may be valuable.
Specifically, while recognizing exceptions, we _can_ generalize that
dinosaurs were relatively large animals with a fixed-site baby.  And we
may have some confidence that this placed some constraints on them.  It
may also have provided a selective force to come up with solutions that
cannot even be imagined here.