Geoscience Reference
In-Depth Information
scope, you will also see tiny grooves and scratches. You have such wear on your
teeth, too, especially if you are in the habit of eating mineral-laden plants.
These marks, called
microwear
, were scored on dinosaur teeth when they
chewedplantscontainingsilicaorplantswithgritonthem.Thegritalsowouldhave
consistedofsilica-richmineralssuchasquartz.Asanygeologymajorwillgleefully
tell you, quartz is harder than the mineral apatite, and the latter is what composes
vertebrate teeth and bones. Hence, silica in plant tissues or silica-rich grit on plants,
combined with dinosaurs chewing those plants, would have caused more scratches
than if the dinosaur had either swallowed those plants whole without chewing or
eaten plants with less silica. On the other hand, browsing on plants growing well
above the ground should have resulted in fewer scratches.
To better understand how silica was included in some plant tissues, we look
to evolution. Plant-eating dinosaurs may have left few bite marks on fossil plants,
but plants certainly “bit back.” Thorns or spikes, toxins, or indigestible parts be-
came common in some plant lineages as a consequence of dinosaurs treating them
likeindiscriminateitemsonasaladbar.Amongthesedefenseswere
phytoliths
,tiny
grains of silica precipitated in plant tissues. Phytoliths represent a war of attrition,
which, through sheer numbers and high abrasiveness, slowly wear down herbivore
teeth. Hard seeds and nuts are more overtly offensive, inflicting breakage in teeth
and thus forming pits.
Phytoliths are common in many plants today, especially monocotyledons,
which include all grasses, orchids, bamboo, palm trees, and many others. Mono-
cotyledons also got their start in the middle of the Mesozoic Era. Coincidence?
Maybe, but the evolution of the largest land herbivores of all time surely resulted
in land plants responding ferociously; after all, plants have no moral compulsion to
fightfair,andtheywanttosurviveandreproduce,too.Thus,itcomesasnosurprise
thatsauropods,hadrosaurs,andotherherbivorousdinosaursalsoevolvedfast-repla-
cing teeth (in sauropods) and dental batteries (in hadrosaurs) to more easily replace
teeth worn down by insidiously vicious plants.
