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Re: Limusaurus Inextricabilis

2009/6/20 David Marjanovic <david.marjanovic@gmx.at>:
>> I suppose gastroliths may be useful to crush a rat-sized prey in an
>> alligator-sized predator
> ...but that's not what happens. The alligator that was filmed was in fact
> fed a dead rat with stones sewed into it. As the film shows, the rat was
> digested, and the stones just lay around and did nothing.

Ok., so apparently there is no evidence for carnivorous archosaurs
(although to be fair, the fact that new films indicate the stones do
not crush a rat do not invalidate Bakker's 1986 observations of the
contrary -and would mean that both things can happen, perhaps under
different conditions not considered-, unless we hypothesize technical
inferiority for Bakker's means of observations).

Now, more speculation on gastroliths and carnivores:

Wings (2007, Acta Paleont. Polonica) writes that in pinnipeds there
are strong contractions of the stomach wall which suggests gastroliths
can be used to process food, although apparently he means there are no
observations of such use in food processing (sidenote: one may suppose
these mammals with haplodont molariforms would be more in need of such
alternative "mastication" than other mammals, although gastroliths are
not known for also haplodont-toothed cetaceans).

Xenarthran anteaters have also a muscular stomach which is said to
crush ants (according to Grassé's Traité de Zoologie). I do not know
if there are gastroliths in anteaters, but suppose it will be
difficult for the anteater to avoid ingestion of say, ant-sized rocks,
which may stick to their tongue as well as the insects, and help
crushing the insects via stomach contractions. However, as they are
far from archosaurs, the condition in them would be less applicable to
dinosaurs than that in crocodiles.

Gastroliths may be more useful in aquatic predators of relatively
small hard-shelled molluscs and arthropods, where rocks may be
apparently more useful. This would require proof, however.

Alternatively, if there is no way for gastroliths in processing animal
food, they may suggest obligate omnivory in at least an epoch of the
year. There are, according to Wings (2007), crows which need a more
herbivorous diet in some epoch of the year, and eat many gastroliths
in this time, but not when the animal food is more abundant. May
gastroliths help theropods with carnivorous teeth to eat somewhat else
than flesh, at least in hard times?