Geoscience Reference
In-Depth Information
Utah at and near the St. George site that also has the dinosaur-sitting traces men-
tioned earlier. The next year (2007), dinosaur swim tracks were again interpreted
from long linear marks on an expansive surface of Early Cretaceous rock in Spain.
In 2013, yet more dinosaur swim tracks were reported from another Early Creta-
ceous site in Queensland, Australia. Suddenly, dinosaurs seemed to be swimming
everywhere.
How would you know whether a dinosaur was swimming by looking at its
tracks? Well, for one thing, you wouldn't know it at all unless its feet touched the
bottom of the water body it crossed. If the water were too deep, buoyancy would
have kept dinosaur bodies—along with their feet—above any sediment surface that
would have recorded their tracks. But through a combination of legs long enough
to reach the bottom and water shallow enough to allow this, they would have made
tracks.
Why should a dinosaur swim at all? Or as an actor might ask, what was their
motivation? Getting from one place to another is a likely reason, instead of walking
aroundashallow lake orstream, ortheold“togettotheotherside” answer.Yetan-
otherargumentrelatestotheirattractiontoaquaticenvironmentsasgreatsourcesof
food.Fortheropods,thismighthavebeenfish,butotheraquatic animals alsomight
have served as tasty treats. For hadrosaurs and sauropods, though, which were (as
farasweknow)allherbivores,thisisnotsuchagoodexplanation.Notsurprisingly,
recreational purposes have never been suggested for swimming dinosaurs, but who
knows whether an occasional dip might have also relieved any dinosaurs suffering
from skin parasites or a hot day in the Mesozoic.
The Not-So-Secret Social Lives of Dinosaurs
Tracks also tell us about dinosaur social lives, and thanks to these trace fossils we
are confident that many dinosaur species moved together as herds, packs, flocks,
congresses, murders, or whatever group name seems appropriate. Assemblages of
dinosaur bones composed of many individuals but only representing one species
also support this idea, and we now take for granted that the stereotype of the “lone
