utahraptor
January 7, 2015

Mass Utahraptor grave may prove pack-hunting hypothesis

Chuck Bednar for redOrbit.com - Your Universe Online

A nine-ton block of sandstone recovered from a Utah mountain in late 2014 contained an astonishing cache of six Utahraptor specimens, making it the largest fossil find of this feather-covered predator to date.

The Utahraptor, which National Geographic said resembles “a pumped-up version” of the Velocipator of Jurassic Park fame, and has the trademark large sickle claw on each second toe, may have hunted their prey in packs like wolves. This follow may prove this hypothesis true.

“If the dinosaurs died together, they might provide some long-sought evidence of group hunting,” the website explained. “The densely packed dinosaurs (in some places, fossils are stacked three feet thick) may have died at different times as they blundered into quicksand, or perhaps they died together in a social supper gone horribly wrong.”

The remains were excavated as part of a decade-plus long effort led by Utah state paleontologist James Kirkland. According to the Daily Mail, a total of six specimens have been recovered from the rock, including a 16-foot long adult, four juveniles and a baby, and there may be more.

Included among the fossils already recovered include never-before-seen bones that is altering their understanding of the dinosaur’s anatomy. Kirkland explained that they now believe that young Utahraptors were about the size of a turkey, that the adults were more heavily muscled.

He was first told about the site by a geology student in 2001 after that student discovered what originally appeared to be a human arm bone amongst early Cretaceous rocks in Utah. The bones appeared to be contained in a sandstone blob that would once have been quicksand, and after looking at the bone, Kirkland found that it was not human, but part of a dinosaur foot.

Additional work at the site revealed more fossils. By chipping off smaller pieces of the block, he and his colleagues found the remains of the six dinosaurs, including a baby that would have been only three feet long from snout to tail, National Geographic said. The site also contained remains of  a beaked, bipedal herbivore called an iguanodont, which may have been their prey.

Kirkland believes that the iguanodont may have accidentally entered the quicksand, and its struggles (as well as its smell) likely attracted the predatory Utahraptors. Once they arrived on the scene, one after another would have tried to dine on the stranded dinosaur, only to become trapped in the quicksand themselves, thus attracting others also looking for an easy meal.

“We believe it's going to be the first example of dinosaurs trapped in quicksand en masse in the fossil record,” he told Nat Geo. To investigate the idea, however, he and his colleagues first had to remove the massive sandstone block. “We didn't want to take out a nine-ton block,” he said, “but every time we tried to cut in, we kept hitting legs and vertebral columns.”

They ultimately were able to transport them to the Salt Lake City's Department of Natural Resources with the help of heavy machinery, and they will now attempt to determine if the block is representative of a pack of Utahraptors, or a group of individual predators that all happened to become trapped in the quicksand individually.

According to University of Maryland paleontologist Thomas Holtz, Jr., “if the skeletons show some interweaving,” with arms and legs tangled together, that would “be a good clue” that they were hunting as a pack. In addition, the degree to which each of the bones were damaged by sun and weather exposure prior to burial could indicate if they became trapped at the same time.

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