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148 million years later, the Cleveland-Lloyd Dinosaur Quarry in Utah remains a cold case

July 10 , 2016


"An early researcher out here once stated that there are almost as many hypotheses for this site as there are annual visitors," said University of Wisconsin-Oshkosh assistant professor Joseph Peterson.

The quarry has proved a reliable source for the Allosaurus, which could grow 30 feet long and had knifelike teeth, razor-sharp claws and the general profile necessary to grab the attention of young museumgoers. Cleveland-Lloyd even has its own visitors center — complete with an assembled Allosaurus skeleton, which is Utah's state fossil — and would become Jurassic National Monument in the Public Lands Initiative proposed by Utah Reps. Rob Bishop and Jason Chaffetz.

Local paleontologists, however, have been less interested in hauling out a 50th Allosaurus than finding new dinosaurs at other sites. Peterson and Indiana University of Pennsylvania (IUP) assistant professor Jonathan Warnock were surprised to learn about five years ago that the historic quarry had no active digs, and they applied to the Bureau of Land Management for a permit to conduct a more technologically informed study of the fossil record.

The long-prevailing theory held that near the end of the Jurassic era, the quarry was a muddy pit. After one unfortunate soul became mired, others arrived to feed on it and met the same end, then lured more hopeful diners who didn't have the benefit, in those days, of Yelp.

That scenario neatly explained the prevalence of carnivores at Cleveland-Lloyd. The only problem: Almost no other evidence supports it.

This became clearer from 2001 to 2004, when a more sophisticated study from then-University of Utah master's student Terry "Bucky" Gates found that the quarry had little in common with other well-known predator traps, like the La Brea Tar Pits in Los Angeles.

Few bones had bite marks. There was not the number of shed teeth that would indicate a dinosaur feeding frenzy, nor the broken bones you'd expect from dinosaurs desperately writhing to free themselves. For that matter, the lower-leg bones discovered were flat, not vertical, as they would be if they'd been staked into mud.

Gates, who lectures at North Carolina State, thought they might have met their end at a watering hole during a drought, with the predominance of Allosaurus explained by the sickliness of plant-reliant herbivores, who dared not risk a showdown. An egg found at the site had an extra shell layer, Gates wrote, a telltale sign of stress in modern animals.

His theory was a better fit for the evidence, but it wasn't bulletproof. U. paleontologist Mark Loewen, who looked in vain for more bones from a Ceratosaurus skeleton at the site in 2007, observed that while some bones showed signs of having been trampled, there likely would have been more if skeletons had lain exposed at a watering hole frequented by 2-ton reptiles.

Loewen grew up in southern Missouri, and for him, the evidence recalled a Mississippi River floodplain, where he once saw a dozen cows floating in an eddy in the middle of a cornfield. The dinosaurs died elsewhere, Loewen thought, then inflated with gas and floated to Cleveland-Lloyd. The scattering of their bones — which Gates had attributed in part to scavengers' messy eating habits — might more simply be the result of decomposition in water.

Early returns from Peterson and Warnock's study support Loewen's hunch, though the so-called "float and bloat" effect might have worked in tandem with other causes of death. For instance: A large number of decomposing corpses would create a poisonous environment that might be responsible for the almost total absence of smaller vertebrates at the quarry. Peterson and Warnock hope a chemical analysis of the bones and sediment will reveal a fuller picture of what might have been a Jurassic cesspool.

Fossil preparator Steve Clawson, meanwhile, is overseeing an effort to map the site with three-dimensional photography as students remove sediment in 5-centimeter layers, providing a visual context that previously was muddled by the inconsistent record-keeping of excavators throughout the 20th century.

Mapping in the north building has shown at least three distinct orientations of the bones that may indicate three floods. Two-dimensional mapping had shown randomness.

Said Gates, who shared his data with Peterson and Warnock: "What [the] work is showing is that there's a lot more work to do."



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