Geoscience Reference
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ing ad in which a person misleadingly underreports his or her age. These bones are
very likely recycled, having been eroded out of older rocks, re-deposited, and bur-
ied a million years or more after the dinosaur originally died. On the other hand, a
single dinosaurtrack in64-million-year-oldrockswouldbehard-to-refute evidence
that at least one dinosaur was walking around after they supposedly all died.
So although dinosaur trace fossils certainly can answer questions that range
fromwhatanindividualdinosaurwasdoingatagivenmomentduringtheMesozoic
to the big picture of how dinosaurs originated, evolved, and went extinct, paleon-
tologists still hope for more. For instance, some of the trace fossils on their “wish
lists” are those that flesh out some of the more dramatic encounters dinosaurs very
likely had. One that comes to mind would be more trace fossil evidence support-
ing the oft-depicted scene of large predatory theropods stalking other dinosaurs, or
pack-hunting behavior in theropods of all sizes. The first scenario is portrayed in
our story toward its end as the tyrannosaur, after her botched attack on the hadro-
saur,followsitandtherestofthehadrosaurherd.Asimilarbehaviorcanbeinferred
from tracks in Early Cretaceous rocks of east Texas, in which the footprints of a
large theropod paralleled and then crossed those of a sauropod, apparently shadow-
ing it. Other compelling theropod trackways include some from the Cretaceous of
Chinathattellofsixtheropods,equallyspacedandallmovinginthesamedirection,
whichverymuchlookslikeevidenceofpackhunting.Moreevidenceofpack-hunt-
ing theropods is suggested by parallel trackways in Early Jurassic rocks of Utah.
Oh,andIshouldalsomentionthatthetwo-toedtracksleftbytheChinesetheropods
showtheyweredeinonychosaurs,sickle-clawedtheropodsrelatedto
Dromaeosaur-
us
and
Velociraptor
.Youcanbetthesetheropodsweren'tdiggingfortheirfoodthat
day.
Lamentably, trace fossils clearly illustrating dinosaur mating, like those con-
jectured for an amorous pair of
Ankylosaurus
, have not yet been recognized. Be-
cause we don't know for sure what “dinosaur whoopie” trace fossils might look
like,thesewillrequireanactive (perhapsoveractive) imagination todetect them,as
