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Re: Tall Croc Tales (was Sauropod Necks As Weapons)

From: "Dann Pigdon" <dannj@alphalink.com.au>
> To be serious for a moment (no, really) I found it interesting that all
> salties have gastroliths once they reach at least 2m in length, yet
> below this length stones don't seem to be required at all (crocs without
> them survive just as well as those with them).

We've found stones in crocs smaller than 2 metres, though they're slightly
less common. Their size and overall mass are also proportional to the croc's
size, which probably reflects the size of their stomach. The function of
gastroliths in crocs has been long debated, but my feeling is they reflect
dietary preferences and assist digestion. A study we did a couple of years
ago, with temperature loggers held in the stomach to measure internal body
temperature, revealed that crocs with gastroliths successfully smashed the
casing and began to digest the loggers (not the intended outcome!) whereas
those with few to no stones left loggers unscathed. These were all
wild-caught animals. What that indicates is that stones are very good at
breaking up solid objects, perhaps increasing digestion efficiency if
hard-shelled prey are common. Salties have a particular taste for mud crabs
in some estuarine areas.

> Either it is
> related to the changes in diet as crocs get bigger, or larger crocs
> desperately need balast (or a combination of both).

As there are large crocs without stones, the idea that stones are necessary
for ballast seems undermined. It may, however, reflect possible differences
in diet or simply reduce digestion efficiency where stones aren't available.
Regarding ballast, I've removed gastroliths from 4 metre adults and it makes
zero difference to their ability to float, dive, or otherwise control
themselves in water. If the weight of stones in the stomach were so vital
for ballast, then what would the crocodile do after eating a heavy wallaby
that increased its ballast significantly? Crocodiles can compensate easily
for changing ballast, so why would they need a few stones? Questions! There
are a number of straightforward studies that could be done to answer the
gastrolith question more clearly. Hopefully Santa will bring me some more
funding. Uh oh...

> You lie! You'll be saying there's no Santa Claus next.

Why, I would never disappoint you on Christmas Eve!

Adam Britton