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Re: gigantism as liability

----- Original Message ----- From: "Graydon" <oak@uniserve.com>
To: <dinosaur@usc.edu>
Sent: Saturday, November 08, 2008 9:42 PM
Subject: Re: gigantism as liability 
Newly hatched sea turtles are effectively defenceless.  (Swallowed whole
by gulls, etc. = effectively defenceless.)

By analogy, just getting bigger involves incremental predator immunity;
remember that there are many fewer large predators than small predators,
just on trophic web/food pyramid grounds; get too big for the 10 kg
predators and your risk drops by an order of magnitude, and this keeps
happening until you're eventually not worth the bother for the 2,000 kg
predators.

The initial argument here is that I claimed that simply being an r strategist was not enough for sauropods, that they needed defence of young in addition to producing lots of them. I don't believe turtles are a good comparison because 1) they have a body plan specialized for predator defence; the shell effectively limits predation soon (relative to non-shelled creatures) after hatching, and 2) they live in a vast 3 dimensional medium that affords protection not available to terrestrial animals...if sauropods relied strictly on numbers it is hard (for me) to come up with a scenario whereby babies who are defenseless at chicken size, who would have had predators at least all the way up to elephant size, could avoid total reproductive failure. The argument on "web/food pyramid grounds" doesn't work so well when the whole ecology is scaled up relative to the size of today's animals. Predators were larger, yet babies were smaller...meaning that mesozoic babies had to pass through more predatory classes than babies of today's mammals. Turtle hatchlings had a mad scramble to the ocean, sauropod hatchlings had a mad scramble to predator immunity, a scramble to get big. In the meantime, I believe, they needed considerable protection from their massive parents.

Whales, rhinos, horses, elephants, pretty much all ungulates, it's
single births with rare twins.  This is probably -- but I don't know
that it has been definitively demonstrated -- due to a cost/benefit case
with investment in offspring.  (Your best odds of success are dependent
on the ability of the offspring to keep up with the herd, so the
larger/fitter it is at birth, the better the odds are.)


Yes...a case of one full glass rather than two half empties.

> The putative 20 ton parent is defending 2 kg eggs. How -- what possible 
mechanism -- does it do that, against the 5kg mammal digging away on top
of the nest?  Or the ~100 kg juvenile allosaur standing among the
hatchlings?

While I deeply relish the image you have presented, I am reminded of the exceptional tenderness of croc parents in bringing hatchlings to the water. And I imagine that even the 20 ton parent could deliver a nasty bite to either of these nest predators. But I agree that large size is not helpful here. It is helpful against predation of adults at the nest however.