Re: eggs with thin shells

[Mike Bonham <bonham@jade.ab.ca>]

> Neil Clark <NCLARK@museum.gla.ac.uk> wrote:
>> One thing that worries me is how the eggs are laid in the first place.  If 
>> the eggs are so thin it is likely that the parent would have to squat to 
>> lay (because if it were dropped from any height, it would break!).  If 
>> the dinosaur had to squat, it is difficult for it to produce regular lines 
>> of eggs without the tail breaking them.  Even more difficult for a 
>> sauropod, I imagine :-)  I believe they may have dug a hole, or 
>> trench?, and squatted over it to lay the eggs.  I'm just thinking aloud 
>> here, but I have trouble imagining how the eggs are physically laid.

and Crpntr@ix.netcom.com (Kenneth Carpenter) wrote:
> 
> I agree, it is a problem that I have not satisfied myself with.  
> However, we do know they did it.  They must have squatted, or 
> kneeled back on their haunches.  Also, crocs and turtles sometimes 
> cushion the fall of the eggs with their hind feet.
> 

How about a thick gelatinous secretion from the cloaca during egg-laying,
that lets the egg dangle in a big droplet of goo or foam, slowly and
gently drooping down to the ground?  The goo probably would have to
de-gel-ify and run off, disintegrate or evaporate porously soon after
laying, to allow air to reach the egg.  Footage of sea turtles dropping
eggs into their deep sandy pits shows a pretty gooey liquid going along
with the eggs.

Perhaps a linear row of eggs would not be crushed by the tail if the
mother dino `scootched' herself backwards as each egg is laid.  That allows
the mother to crouch over the eggs already deposited, protecting them
with her body and forelegs until she was all done.  The forelegs (if long
enough -- sorry Mrs. Rex!) would be in a good position to cover up the
trench as she went.

Alternatively, perhaps a linear row of eggs is consistent with the eggs
(and their gelatinous goo) sticking to the tail and sliding down along
the underside to a precision landing!

I just remembered noticing how much `leaner' the modern reconstructions
of dinosaurs -- theropods especially -- are, compared to earlier ones.
Instead of a fat tail whose bulk completely hides the ischial process
(the long pointy bone projecting down and backward under the base of the
tail) and the pubis (the canoe-paddle-handle-shaped bone that projects
forward and down between the legs of saurischians), dinosaurs are now
commonly shown with slender tails and taut, muscled abdomens that leave
the ischial and pubic processes sticking out from the main body line.
Could eggs have slid down one of those protrusions, to a nice soft
landing?  What good are the pubic processes structurally anyway?
Would they have made a good `mounting point' (so to speak :-) for the
genital organs of both male and female, and have allowed a smaller drop
height for the eggs?

-- Mike Bonham        bonham@jade.ab.ca