CLEVELAND-LLOYD DINOSAUR QUARRY, Utah - For the first time since the 1960s, researchers are excavating this quarry. University of Utah geologists are not simply searching for more Allosaurus bones - they are digging for answers about how the creatures ended up here.
This prodigious paleontological dig, a national historic site that sits 30 miles south of Price and 12 miles from the nearest paved road, yielded more than 10,000 bones between the 1920s and the 1960s. Researchers from the university are questioning the accepted explanation that the site near the San Rafeal Swell was a predator trap.
Paleontologists have held that carnivorous dinosaurs in search of dinner were lured to this mud-filled death pit. A single stranded plant-eating dinosaur might call for help, attracting multiple predators. The colossal hunters would die after becoming bogged down in muck.
Scott Sampson, a geologist and curator of vertebrate paleontology at the Utah Museum of Natural History, and Bucky Gates, a master's degree student, say the evidence they are unearthing may not support the predato-trap explanation. After analyzing all of the data, they plan to publish their findings in a scientific journal.
The quarry work, which began in May and covers an area of 2 square meters, stems from Gates' thesis work. Gates said the quarry data does not match up with his examinations of evidence from the La Brea Tar Pits, a predator trap, in Los Angeles.
Sampson said clues in this 150-million-year-old murder mystery point to another, as of yet undetermined, solution.
For starters, the quarry would be filled with shed dinosaur teeth. Dinosaurs tended to lose teeth during meals, Sampson said. Few such teeth were found.
Bones in a predator trap would be broken from dinosaurs struggling to escape. Also, many bones would feature teeth marks. The bones from here are pristine, indicating they were buried quickly.
Drought and volcanic activity are among the possible explanations for what killed off these dinosaurs.
Research crews are now gathering bits of evidence to figure out which theory is most viable. While field techniques have changed little from those that 19th-century fossil hunters employed, the scope of the detail recorded has expanded.
Sampson said the crews today are as concerned about finding bones as they are about placing them in context. All specimens, as well as the surrounding sediment and microfossils, from this dig will be placed on a three-dimensional map.
Dig crews work inside moveable open-floored metal huts that shield their material from weather as well as vandals. Bones down to a millimeter in thickness - material that earlier fossil hunters might have ignored as debris - are being noted. Intact bones of this size show that the bodies did not travel far to reach the quarry.
Sampson said bloated, dead dinosaurs carcasses could have floated in from another location to their final resting place. The quarry is located in a depression on what would have been a flood plain in the arid region.
Mike Getty, paleontology collection manager at the museum, explained that heavy tools were used to carve trenches into the limestone. Once they reached the bone level, smaller hammers, awls and dental picks were brought in for precision work.
Crew members sit or kneel in the 4-foot-deep trenches. Upon discovering a fossilized bone, which appears black, workers will attempt to carve around it. Cheesecloth or burlap dipped in plaster is placed on the bones, forming a cast like the kind a person would wear on a broken leg.
More than 50 volunteers have participated in this university-funded project. Many of the volunteers have spent time in the trenches. Crews will be periodically working the quarry over the next several years
Gates said he is attempting to gather all possible evidence in order to publish findings on such a storied and well-mined dinosaur site.