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So did dinosaurs affect the courses of rivers with their trails, carving out new
routes for flowing water through avulsions, or connect previously isolated water
bodies? Given the known effects of much smaller modern large animals on rivers,
the probable effects of individual dinosaurs that weighed 10 to 20 tons or more,
herd sizes of these dinosaurs, and their geological longevity, I would be extremely
surprised if they did not. If so, these effects may be detectable by geologists by
morecloselyexaminingMesozoicriverdepositsthatalsocontainplentyofdinosaur
bones and trace fossils—such as those of the Late Jurassic Morrison Formation in
the western U.S.—for sauropod-width incisions in ancient river levees. They might
also reexamine crevasse splays to see whether these connect to such divots, and
whether these contain sauropod or other dinosaur tracks. In this respect, in 2006,
two geologists—Lawrence Jones and Edmund Gustason—did indeed propose that
avulsionfeaturesintheMorrisonFormationofeast-centralUtahwerelikelycaused
bysauropodtrailsthatcreated“channels”fortheflowoffloodwaters.Indeed,some
formerriver-channelsandstonesintheLateJurassicMorrisonFormationhavedino-
saurtracksontheirbottoms,whichmayhavebeenmadebytheropodsorsauropods
crossing rivers.
Amazingly, geologists have also determined that some modern rivers have
been flowing more or less in the same valleys since before and well into the Meso-
zoic Era. These rivers include the Nile in eastern Africa, the Amazon of South
America, the Macleay and Murrumbidgee of Australia, and the Colorado River
of the western U.S., among others. All of these rivers are in places where dino-
saurs—includingbigsauropods—usedtoroam,meaningatsomepointintheirgeo-
logical histories dinosaurs and previous versions of these rivers intersected. Con-
sidering the substantial human populations that settled along these rivers (some for
as long as 10,000 years or more) and have since depended on the rivers and their
floodplains for their lives, it is humbling to think that their present-day locations
may have been at least partially determined by dinosaurs. Also think of how the
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