Geoscience Reference
In-Depth Information
Near the
Dromaeosaurus
couple and next to the river levee, a few other thero-
pods (
Troodon
) shifted anxiously on their sediment-rimmed ground nests. Several
weeks earlier,
Troodon
mothers had laid eggs in the nests two at a time, a function
of their dual oviducts. Some had deposited as many as two dozen eggs, a dinosaur-
ian form of labor that took about a week and a half to complete. After laying, each
mother
Troodon
vertically oriented the eggs in the center of the doughnut-shaped
nest. Now it was the job of the male to sit above and otherwise guard the precious
egg clutch for nearly fifty days. Almost nothing could motivate them to leave their
nests, so they continued to squat above them, albeit nervously.
Two smaller feathered theropods, potential egg predators and only a few
metersaway,gavethe
Troodon
fathersfurtherincentivetostayput.Thesedinosaurs
gnawed on a recently dead pterosaur, scraping their teeth across its limb bones to
strip whatever flesh was left. One of them, though, unsettled by the ripple effects of
the dinosaur duel below, succumbed to caution and scrambled up a tree, her hands
and feet imparting sets of scratch marks on the smooth bark.
The spreading disturbance initiated by the
Triceratops
provoked several small
ornithopod dinosaurs, distantly related to
Thescelosaurus
, to retreat into their bur-
rows. The burrows, which they had dug previously into the banks of the levee, had
entrances only slightly wider than the ornithopods' bodies, making for a tight fit
as they scrambled inside. These burrows twisted to the right and then left as they
descended, making S- or Z-shapes, before expanding into a main living chamber at
their ends. This zigzag design effectively deterred predators while maintaining liv-
able temperatures and humidity in each burrow, essential features for these ornitho-
pods to safely raise their young.
Several hundred meters downstream from the two
Triceratops
—which were
only seconds away from ramming each other—a group of ostrich-like theropods
(
Struthiomimus
) walked along a gravel bar at the edge of the river. They stopped
every now and then to swallow pea- and marble-sized quartz-rich rocks. These
“stomachstones,”alsoknownasgastroliths,wouldlodgeinamusculargizzardjust
