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have soaked into the underlying sand with first wetting, so the original volume was
probably more like 500 to 1,000 cc. Because these trace fossils were in the same
strata as ornithopod and theropod tracks, and those dinosaurs were the only anim-
als large enough to have produced such vigorous bursts of fluid, the paleontologists
concluded they were the most likely to have left such marks.
Nevertheless, Fernandes and his colleagues, just like McCarville and Bishop,
further tested their results by trying to make their own structures in sand. For-
tunately,thisdidnotrequireanyself-experimentation, suchaschuggingliquidsand
running to a nearby sand dune. Instead, they took two liters of water and poured
it from 80 cm (2.6 ft) above and onto a loose sand surface with a slope having
the same angle (about 30°) as the fossil ones. This procedure successfully created
a structure strikingly similar to the interpreted urolites, with an elongated central
craterandstreamlinescausedbywaterdrippingdownslope.However,theirtriumph
did not satisfy completely, so they then “cheated” by watching a modern dino-
saur urinate: an ostrich, that is. Like many countries, Brazil has ostrich farms, so
these researchers simply went to one and watched these big birds take a leak. Sure
enough, what they observed matched their interpretations.
Because ostriches and other ratites eliminate liquid wastes first, then solid
wastes, this also would explain how ornithopods and theropods could have made
both urolites and coprolites. That is if they had plumbing comparable to ostriches,
versus most other birds that only produce a mixture of the two. Also keep in mind,
though, that if dinosaurs peed more like birds and less like mammals, their liquid
waste would have been evacuated behind them, not in front; this is how ostriches
tinkle. Oh, and one more thing: Remember that modern male birds do
not
use their
tools to urinate. So even if a male dinosaur had a penis, you still would not be able
to tell whether a male or female dinosaur made a urolite, which is definitely not the
case with any mammal urination structures I have seen. Regardless, if paleontolo-
gists are lucky enough to find urolites directly associated with dinosaur tracks, they
must be careful in defining “pre-pee” and “post-pee” footprints in that trackway.
