Cleveland-Lloyd Dinosaur Quarry, Utah -

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.