Geoscience Reference
In-Depth Information
record revealed, which was not readily apparent from contemporary examples of
walking down dunes, is that outlines of the dinosaur feet were preserved below the
surfaces of the original grainflows. In cross-sections of the sandstone, Loope found
theropod and prosauropod tracks directly associated with grainflows, in which the
dinosaurscauseddownslopemovementswitheachstep,thensteppedintothegrain-
flowdeposittheyhadjustmade.Thedinosaurshadcausedsmallavalanches,which
then buried their tracks, leaving behind the most important clues needed to determ-
ine what caused these grainflows in a Jurassic dune field.
Withthisexampleinmind,wemightwonderhowelsedinosaurs,throughtheir
walking on slopes, might have wrought other changes in their landscapes, such as
triggering mass movements of materials in upland areas. For example, did dino-
saurs that lived in mountainous regions ever start an avalanche by walking across
a rocky slope? Did polar dinosaurs ever start snow avalanches? Both of such ex-
amples are extremely unlikely to have been preserved in the geologic record: for
one, snow tends to melt, which was also true of Mesozoic snow. Nonetheless, sand
dunes and other sedimentary deposits could reveal more secrets of how dinosaurs
modified their environments, step by step.
Nesting Grounds: Turning Flat into Bumpy
As we learned from the Late Cretaceous titanosaur nests in Argentina, sauropod
nesting grounds probably changed the appearances of their landscapes, especially
because they kept coming back to the same area over generations. This meant that
sauropod nests, which were probably made by scratch digging, were placed above
the graves of former nests, eggs, and embryos. In Montana, the Late Cretaceous
hadrosaur
Maiasaura
and theropod
Troodon
also seemed to nest in the same places
over time, implying that these dinosaurs also may have habitually used nesting
grounds. High concentrations of dinosaur eggs elsewhere in the world, such as in
South Africa, Spain, and India, likewise point toward how dinosaur parents kept
choosing the same places over generations for their nesting. All of this nesting over
timemeantmanygroundnests,someofwhichmayhavebeenreused;butoncebur-
