Cleveland Lloyd Quarry and Photogammetry: New Look at Jurassic Predators

It's hard to imagine the last Ice Age without thinking of Los Angeles' La Brea Tar Pits, which trapped a number of prehistoric monsters in resin: giant sloths and smilodons so well-preserved that parasites in their fur could be analyzed to determine the time of year in which they died. The Jurassic period -- between 201 and 145 million years ago, doesn't allow quite the same opportunity for studying its animals with scrutiny, but the Cleveland Lloyd Dinosaur Quarry outside Price, Utah, does come close. Rather than providing answers, however, the pit in which a number of Jurassic predators were found buried together seems at first glimpse to be one giant enigma. What led these infamous prehistoric butchers to their deaths?

A team of paleontologists working from several different institutions may have the answer -- with poison playing a part in the story. The remains of 30-foot-long Allosaurs, the carnosaur made famous in Arthur Conan Doyle's novel The Lost World, have been found alongside remains of the undiscovered Marshosaurus and Stokesosaurus since the first expedition was established by the University of Utah in 1928. The site's earliest surveyors suspected that the quarry was the result of a large herbivore such as a Stegosaur trapped in mud, whose cries lured a number of pack-hunting allosaurs to the scene who then also became trapped. While there is little doubt that allosaurus (who actually graced the silver screen in movies nearly a decade before its descendant, the T-Rex) was the apex hunter in North America during the Upper Jurassic, we have little evidence that they hunted in packs like such modern predators as the African lion--apart from this quarry where the bodies have piled up.

The truth was likely not so simple, as the Utah pit shows no evidence of asphalt or other substances that would have trapped dinosaur feet. A new technology called photogrammetry has helped paleontologists like Joseph Peterson explore the mystery further -- allowing them to reconstruct Utah as it was during the Jurassic period in three-dimensional projections. Over 15,000 bones have been discovered in the plot so far, with nearly 50 allosaur skeletons excavated. Among new possible theories they are exploring is a buildup of poison in the water. This is based on new results that the rocks may have emitted gases such as radon, poisoning the water supply. Details from Peterson's crew are awaiting publication, with an abstract recently published on the new technology.

However, further evidence supports a "bloat and float" theory. In this theory, the animals died further from the site, then their bodies bloated with decaying gases and became buoyant. In this state, they floated on swift river currents to locations miles away. As morbid as that sounds, most dinosaur bones are discovered preserved in river sediments, with their bones replaced by minerals from the clay.

For more information about the Jurassic period in what is now Utah, see here.