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ontologists reporting these—Katherine McCarville and Gale Bishop—tried to rep-
licate this structure on a Georgia beach by using a combination of water buckets,
funnels, hosing, and ladders. The suspected Morrison urolite, which is preserved in
a former lakeshore limestone, is a shallow, oblong, trench-like depression, which
McCarville and Bishop described as “bathtub-shaped,” a descriptor that does not
sit well when imagining it occupied by liquid waste. Because this depression cuts
across bedding, scouring of some sort formed it, but in a specific spot on an other-
wise nearly flat surface.
Had paleontologists encountered this feature just by itself, most might have
shrugged, written “weird bathtub-shaped depression” in their field notebooks, and
moved on. However, additional trace fossil evidence led McCarville and Bishop to
consider sauropod pee as a possibility. The same limestone bed with the suspec-
ted urolite also holds more than eighty dinosaur trackways, divided almost evenly
between sauropods and theropods. Known as the Purgatoire site (after the Pur-
gatoire River, which runs through the area), it is one of the most spectacular dino-
saur tracksites in the western U.S., including some of the best-known examples of
herding-sauropod trackways. This circumstantial evidence meant that large poten-
tial peers were at the site, and the size of the possible urination structure pointed
toward a sauropod as the culprit.
Based on its present dimensions, it would have held about a cubic meter (265
gallons) of liquid, which would easily overflow a small wading pool. Even the
largest of Late Jurassic theropods living in this area, such as Allosaurus , would not
have had enough juice to produce such a huge structure, no matter how much they
drank and how long they held it. Also, an adult sauropod cloaca—especially those
of Apatosaurus or Diplodocus —would have been much higher off the ground (3-6
m,or10-20ft)thanthoseofcontemporarytheropods(1-2m,or3.3-6.6ft).Hence,
their liquid wastes would have generated more force and imparted greater erosion.
How likely is it that this enigmatic feature is a urolite? I rate it a definite
“maybe.” Fortunately, I have seen it in person and did not have to rely just on
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