Geoscience Reference
In-Depth Information
gastroliths represent a great start in better understanding where the first large-bod-
ied dinosaurs lived and how they lived during the Late Triassic.
The second set of interrelated questions—where did these dinosaurs find the
originalrocks,andhowfardidtheytravelwiththeirrockypayloads—wasatougher
onetofigureout,butanswerablebylookingforsimilarstonesinotherLateTriassic
formations in the same area of Virginia-Maryland. The best match came from the
Manassas Sandstone, which has conglomerates; these are sandstones that also have
chunkybits,suchaspebbles,gravel,andcobbles.Itturnedoutthesecoarser-grained
sediments—most of which were also composed of quartz and quartzite—were a
good fit for the Bull Run Formation gastroliths. Assuming that the gastroliths are
gravestones, marking the final resting places of prosauropods, then these rocks
moved a minimum of about 20 km (12 mi) under dinosaur control, and probably
much further. If true, this would be a great example of how dinosaurs had already
begun changing their environments, transporting large sediments to places where
rivers did not reach.
This sort of study demonstrates the great potential of gastroliths as trace
fossils,fillinginthegapsinlieuofdinosaurbonesortracksandothertraces.Atfirst
glance, gastroliths might seem like the most boring and misunderstood of dinosaur
trace fossils, holding little of the aesthetic appeal of footprints or raw ferocity of
toothmarks.Butwhentreatedwithrespect,andthroughtheawesomehealingpower
of science, these humble rocks greatly extend our knowledge of dinosaur presence
and behavior. Despite all we know now about gastroliths, though, I still think back
to that summer of 1983 when I held that strange rock from the Morrison Formation
in Wyoming and later wondered whether it spent time inside a dinosaur before rest-
ing in my hand. One thing is for sure, though: if other paleontologists or I were to
go back to that same spot today and find that rock, I am confident we could better
answer that question.
