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Diggin' For Dinosaurs - Cleveland-Lloyd Dinosaur Quarry

Updated on March 30, 2010

Cleveland-Lloyd Dinosaur Quarry, Utah

A lumbering Camarasaurus wades into a shallow pond to slake its thirst. As the massive dinosaur drinks, its stout, elephantine legs sink into the viscous clay. Struggling to extract its limbs only buries them deeper. The beast bellows an alarm call, which lures a trio of hungry allosaurs to the pond. The carnivores rush in to chomp the flanks of their prey, but before they can reach the helpless camarasaur, they notice their pace slowing. Each step mires the predators deeper in mud until only their thrashing heads remain above water.

Whether or not this scene played out some 147 million years ago is a matter of speculation, but a similar scenario likely did. The Cleveland-Lloyd Dinosaur Quarry in central Utah constitutes one of the most puzzling and dramatic dinosaur death traps ever excavated. Unlike the floods that formed the mass dinosaur graveyards at sites such as Ghost Ranch or Dinosaur National Monument, the deposits at Cleveland-Lloyd formed in still water. And unlike most dinosaur deathbeds, where herbivores dominate among the deceased, nearly three-quarters of the bones pulled from the Cleveland-Lloyd quarry come from meat-eating dinosaurs.

The bounty of bones numbers more than 12,000 from a dozen kinds of dinosaurs and represents at least 70 individuals, including 44 Allosaurus fragilis. The top predator of the middle Jurassic, Allosaurus was widespread and abundant. Some palaeontologists suggest that the high numbers found at Cleveland-Lloyd might be because they hunted in packs, at least as juveniles. Though smaller than Tyrannosaurus, Allosaurus had beefier arms and bigger claws (with three on each hand to T. rex's two), so just one out stalking would have inspired intense fear. Smaller carnivores, Ceratosaurus, Stokeosaurus, and Marshosaurus, hunted or scavenged here as well.

The dinosaur bones, stained jet black from manganese oxide in ancient groundwater, were scattered but otherwise preserved remarkably intact and unweathered. Excavation started in 1929, and discoveries began soon after William Lee Stokes, a Princeton student from nearby Cleveland, Utah, and the future state geologist, arrived at the site in 1939 with some shovels and a poorly paid assistant. Various teams worked off and on until 1990. Fossils removed from Cleveland-Lloyd have stocked museum displays worldwide, and an unknown number of bones are still buried here.

Two metal sheds cover the quarry site, where visitors can still see original fossils in place and casts of other bones from a metal walkway just above the excavation. The yard-wide pelvis of Camarasaurus on display has dinosaur tooth marks carved into it.
More bones, and a mounted Allosaurus skeleton, can be seen in the small visitor center on site. There's a cast of the probable Allosaurus egg found in 1987, next to a CAT scan that appears to show a tadpole-shaped embryo inside; an abnormal shell layer indicates that the egg was retained within the mother as she succumbed in the Cleveland-Lloyd sediments. A site map on the visitor center wall, with thousands of bones outlined, reveals the remarkable density of dinosaur fossils in the surprisingly small site.

Visitors with spare time should enjoy meandering among the red-tinged deposits of the Morrison Formation, the richest repository of dinosaur remains in the United States, on the 1.5-mile Rock Walk Nature Trail. Or one can take a worthwhile excursion 30 miles north to the College of Eastern Utah Prehistoric Museum, in Price. There, four dinosaur skeletons from Cleveland-Lloyd - Allosaurus, Camarasaurus, Camptosaurus, and Stegosaurus - take center stage, and surrounding cases display deformed toe bones and injured ribs and arm bones from Allosaurus (apparently life was tough atop the Jurassic food chain). Upstairs, be sure to see an impressive collection of dinosaur footprints found in the ceiling of coal mines in Carbon County, Utah. The foot bones of two track makers, Chasmosaurus and Prosaurolophus, have been mounted above their respective prints, and a nearby footprint cast measures nearly four and one-half feet long.

Continued in: Diggin' For Dinosaurs - Berlin-Ichthyosaur

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