Geoscience Reference
In-Depth Information
sight, then you should stop calling it a gastrolith and instead refer to it as an
exo-
lith
, as in “exotic.” Although this word has not yet caught on with dinosaur pale-
ontologists—let alone ten-year-old dinosaur enthusiasts—it does help paleontolo-
gists and geologists make a mental shift when thinking about these as trace fossils.
Unlike most other dinosaur trace fossils, such as tracks and nests, gastroliths might
have been transported far away from where a dinosaur originally lived. In other
words, whenever suspected gastroliths show up outside of a dinosaur skeleton, ser-
ious doubt tends to pummel any sunny optimism.
Yet another factor to consider with dinosaur gastroliths is that dinosaurs might
have been recycling gastroliths before they died. Recall how certain birds of prey
use rangle: they swallow a few rocks, use these to clean out the upper part of their
digestive tracts, then cough them out. If some dinosaurs similarly ate and regur-
gitated gastroliths, then these rocks would have been left behind and perhaps later
picked up by another dinosaur that thought “Hey, look—free gastrolith!” For ac-
cidentally ingested gastroliths, these might have passed through dinosaur bodies
and come out the other end, deposited along with their feces. However grotesque it
might seem to those of us who do not regularly gulp rocks, nor pick through feces
for little undigested treasures, these stones could have been removed or eliminated
and then ingested by other dinosaurs if no others were readily available.
What was the fate of gastroliths after the death of their host? Given that many
dinosaursanddinosaurpartsweredepositedafterfloatinginrivers,lakes,oroceans,
paleontologists have to keep in mind that gastroliths still in dinosaur body cavities
went along for the ride too. Even worse, after floating for a few days, these dino-
saur bodies could have burst open from decay. Given their greater density, gastro-
liths would have been among the first objects to leave a dinosaur body and sink to
the bottom of a lake, stream, or ocean. Millions of years later, geologists might find
them, scratch their heads, and wonder how these larger rocks got into such fine-
grained sediments.
