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STONES & BONES: GASTROLITH FUNCTION
Ralph Miller posted a useful summary of some thoughts on gastrolith
distribution and utilisation in dinosaurs. Here are some additional
Something we've mentioned on this list before is that gastroliths can
apparently be distinguished from non-gastoliths by firing laser beams
at them: the light-scattering effect of gastoliths differs from
non-gastroliths and can be detected. The paper that first reported
this (the technique was first used on moa gastroliths) was in
_Journal of Paleontology_: I don't have the citation with me now, but
it has been posted on the list.
It may also be of interest that some work on bird gastroliths - it is
cited in Anderson's book on moa but I cannot recall the author
off hand - indicates that gastrolith replacement is actually very
much rarer than was supposed. As acid etching and abrasion increases
the number of microscopic worn faces on each gastrolith, it is
apparently advantageous for the animal to be in possession of very
old gastroliths. The more 'gastricised' the stone, the better. This
only goes for those taxa that use gastroliths for digestion: don't
forget that many aquatic animals - pinnipeds, plesiosaurs, crocs,
etc. - use them as ballast.
Exactly how gastroliths, and, indeed, gizzards, do function in many
extant taxa is still controversial. Efforts to create an artificial
goose gizzard and then test its function and abilities were published
in _Journal of Zoology_ last year.
It is unfortunate that many of Bakker's (1986, 1987) statements are
not supported by reference to primary literature. As Ralph noted,
much of what he says about moa gastroliths seems to be speculation
that is not based on published work (also, in attempting to
demonstrate that the small sauropod head does not necessitate a
non-endothermic physiology, Bakker (1986) makes out that dinornithid
moa heads were smaller than they actually were).
Bakker wrote that x-rays of a croc gizzard showed how the animal used
gastroliths to help break down a dead mouse. But, in everything
written about the function of gastroliths by Mike Taylor, it is
emphasised that carnivorous animals do not use gastroliths for
digestion: it simply would be maladaptively risky to break up bones
in their stomachs. I will have to read up on crocodile digestion,
this is something I cannot claim to know much about.
Finally, Bakker also mentioned that Ken Carpenter had found
gastroliths in a nodosaur. Can't recall if this was ever written up.
"Right now, we don't know what it is. But that doesn't mean we
*can't* know what it is"