Geoscience Reference
In-Depth Information
the north and south islands of New Zealand up until less than a thousand years ago,
which is about when the Maori people arrived and found them far too delicious for
theircontinuedexistence.Thescientists,RogerJohnstonandtwoothers,againused
laserreflectancetolookfordifferencesinpolishbetweenmoagastrolithsandbeach
rocks. However, they also employed a video instrument that recorded the reflect-
ance in three dimensions, rather than just a horizontal plane. They concluded that
themoagastrolithsweremorepolishedthanbeachrocks,statingthatitwas“fairly”
successful. This faint praise came with an admission that the amount of polish on a
gastrolith may have depended on the time these gastroliths spent in a moa's gizza-
rd. This meant former beach rocks, swallowed by a moa but only put to work for a
few weeks before that moa's death, would be nearly indistinguishable from unused
beach rocks.
In 2000, scientists Christopher Whittle and Laura Onorato used a scanning
electron microscope (SEM) to peer more intensely at gastroliths in general. In their
study, they picked out a variety of gastroliths from dinosaurs, plesiosaurs, birds,
and alligators, and then calculated percentages of areas that were pitted or gashed.
At a magnification fifty times what we would see with unaided eyes, they found
thesegastrolithsweremostlysmooth,butalsohadagoodnumberofpitsandgashes
on about 20% of gastrolith surfaces. In contrast, rocks that had been polished by
waves, river flows, or wind were much less pitted or gashed than the gastroliths.
These dinks and nicks on otherwise smooth surfaces are assumed to have come
fromrock-to-rockcontactsmorefrequentthanthoseinoutsideenvironments.These
were promising results, and even though Whittle and Onorato used such expensive
equipment for this study, they also pointed out that paleontologists could use nor-
mal binocular microscopes at the same magnification to look for these diagnostic
features.
These outcomes also point to how gastroliths and microwear in dinosaur teeth
tend to overlap in a few ways. Recall that minerals harder than apatite tend to
scratch teeth, whether as quartz sand onplant surfaces orphytoliths in plant tissues.
