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Re: The Final Days




From: "Adam Britton" <abritton@wmi.com.au>
Reply-To: abritton@wmi.com.au
To: <dinosaur@usc.edu>
Subject: Re: The Final Days
Date: Sun, 17 Nov 2002 13:12:20 +0930

From: "David Marjanovic" <david.marjanovic@gmx.at>
>
> Crocs are ectothermic and can therefore fast on end, more or less.
Endotherms
> can't do that without special adaptations (e. g. hibernation). And who
says
> that any adult croc survived, BTW. Maybe the only surviving individuals
were
> insect-eating babies of 1/10 or less adult length.

But adult crocs have significantly lower food requirements per unit body
mass than juveniles: a good-sized adult can fast two to three times as
long as a juvenile (approximately 18 to 22 months versus 6 to 8 months).
Also bear in mind that adults (of extant species at least) _primarily_ eat
small prey (fish, crustaceans, small mammals, even large insects) so their
food supply in freshwater may have been more reliable. Being generalist
predators certainly helped,

Apparently not in the case of dyrosaurs which, judging by their slender snouts, were probably specialized fish eaters.




but it depends on the time scale they had to
survive through. A mature female of the larger extant crocs has a
reproductive life of roughly 40 to 50 years (reproductive senescence kicks
in eventually), which assuming she could survive that long would certainly
help overcome problematic times. There are examples of extant croc species
not breeding for over 30 years, then being placed with a male and producing
viable eggs.

Another thing: small juvenile crocs are finger food for a wide range of
critters.

Varanids, birds, felines,turtles, even carnivorous fish. It is true that at the K-T, there were no likely mammalian predators, and some other predators might have suffered temporary losses. Still, predation from some source was virtually certain, and likely intensified in the hypothesized, energy depleted environment.


If food were scarce, you'd have thought the juveniles would be at
even greater risk of predation.

Right, especially in the absence of any parental protection, if the adults had been wiped out. The survival rate of baby crocs is very low even with such protection, it could have been zero without it.

Adam Britton


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