Geoscience Reference
In-Depth Information
gastroliths.Inresponse,othergeologistsandpaleontologists wouldscoffatthesug-
gestion, as if I had asked about Bigfoot, aliens, or Bigfoot aliens.
Were these skeptics completely or partially right, or should they have been
laughing at themselves for being gastrolith deniers? But maybe they had a point.
After all, what exactly were gastroliths? How could a mere rock tell us whether a
dinosaur had been on or near a given spot in the western U.S.? Moreover, if gast-
roliths were real, how could these curios actually be trace fossils, supplying deep
insights on dinosaur behavior and evolution?
Between a Rock and a Soft Place
Starting nearly 200 million years ago, well before our ancestors were attracted to
certain rocks, chose them with care, and began using them as tools, dinosaurs had
their own rock collections. Some of these rocks even had fossils in them, which
meantthatdinosaursmighthavebeenunwittinglythefirstfossilcollectors,too.The
biggest difference between these dinosaur- and human-made assortments of stones
isthatdinosaurscarriedthemontheirinsides.“Gastrolith”literallymeans“stomach
stone”(inGreek,
gastros
=stomach,
lithos
=stone),andtheythusrefertorocksthat
somehow made it into the digestive tract of an animal. Because many modern an-
imals—from invertebrates to vertebrates, marine to terrestrial—have rocks in their
innards, no one questions the physical reality of gastroliths. Nevertheless, with di-
nosaurs of the long-lost past, disagreement stems from exactly how those rocks got
there in the first place, whether they served any purpose, and if so, their intended
functions. Thus it becomes easy to see why these are among the most controversial
of dinosaur trace fossils.
Ifonecanstomachit,alittlebitofjargongoesalongwayinbetterunderstand-
ing these enigmatic trace fossils. For one, they can be divided into two categories:
bio-gastroliths
and
geo-gastroliths
. As these hyphenated prefixes imply, biologic-
al processes make one of them, whereas the other is formed by geological means.
However,thelattertypecertainlyhastoinvolveananimalatsomepointinagastro-
lith'slifecyclebymakingitswayintoagut.Sothesecouldbecalledgeo-bio-gastro-
