Though not well known, the Cleveland-Lloyd Dinosaur Quarry is one of the greatest
palaeontology discoveries of all time. The most concentrated collection of Jurassic
dinosaur bones ever found was unearthed here. It is also the world's only known
dinosaur "Predator Trap".
Located in the colorful and remote badlands of central Utah, Cleveland-Lloyd is miles from a paved
road, and many more miles from a large city. The area is accessible by a network of
fair-weather dirt roads. Besides the quarry, you may visit numerous other
natural landmarks in relative solitude. They all have exotic names such as
the San Rafael Swell, the Wedge, or the Jump (pictured, above right).
The first official dig took place in 1929 by the University of Utah, after
local ranchers found bones scattered on the surface. Since that time, more than
12,000 bones from 74 individual dinosaurs have been excavated. Amazingly, almost
all the bones have been found in an area no larger than a home lot. The two sheds
in the photo, left, house the principal excavation. Note the row of rocks in front
of the sheds (use the enlargement for a better view). That marks the edge of the
quarry. Virtually all of the bones have been found between that line and the base
of the hill just behind the structures! Tests have shown that many more bones
lie buried near the base of the hill.
Over 66% of the uncovered bones belonged to the meat eater, Allosaurus, the
primary predator of the Jurassic age. The Allosaurus skeleton shown right is
at the fine Museum of the San Rafael in the nearby town of Castle Dale. At left,
from nearby Dinosaur National Monument, the largest Allosaur skull ever found.
Having two-thirds of the bones come from a predator is an extremely unusual
circumstance. Scientists theorize that roughly ten percent of dinosaurs were predators.
That is about the ratio found in the modern animal kingdom. It is also the ratio
of predator bones found in most dinosaur digs. Something special happened here.
(Photo left, badlands. The quarry is at the base of the hill in center. The area was thought
to be a lake in Jurassic times.)
Scientists have devised a fascinating theory known as the "Predator Trap". The
bones of many creatures, including Jurassic mainstays like Stegosaurus and
Apatosaurus (Brontosaurus), were found here all mixed together. While the bones
were not articulated (connected together), the were also generally not smashed up
or otherwise damaged. Damaged bones might have indicated a trauma such as a dead
carcass being torn to pieces. This might have been expected with all the Allosaurs
around. But, not so. And what killed all the Allosaurs?
The theory goes like this: the quarry area was thought to be on the edge of a
lake. Scientists speculate that a swampy mud bog there would occasionally trap a large
plant eater grazing around the lake. The trapped animal would be struggling
and crying out, trying to get free. The noise and commotion would attract packs
of allosaurs who would all pounce on the helpless creature. And, in the end,
they all sank together!
The photo, right, shows the interior of one of the sheds. While there are no
active excavations in progress at this time, the site was left in a working condition.
A number of exposed bones (closeup, below right) were marked and left in place along
with some of the typical tools used by the diggers. A wall chart
identifies the visible bones.