A treasure trove of fossils uncovered in Utah is helping paleontologists understand why some meat-eating dinosaurs evolved into vegetarians. The bones represent a new species belonging to a group known as the therizinosaurs, plant-eating cousins of Jurassic Park's Velociraptor.

Scientists unearthed some 1,700 bones, which date to 125 million years ago, from the base of the Cedar Mountain rock formation in Utah. According to James Kirkland of the Utah Geological Survey, hundreds to thousands of individual dinosaurs could have perished at the two-acre dig site. The researchers recovered bones representing about 90 percent of the skeleton of the new species, Falcarius utahensis, which walked on two legs and stood over four feet tall. Although no feathers turned up, the team posits that the beast was covered in shaggy protofeathers because direct evidence for feathers has been discovered on fossils of its close relatives in China.

Indeed, most of the fossils of other known therizinosaurs have come from China and Mongolia, with just one 90-million-year-old specimen hailing from New Mexico. "Falcarius utahensis shows the beginning of features we associate with plant-eating dinosaurs, including a reduction in size of meat-cutting teeth to leaf-shredding teeth, the expansion of the gut to a size needed to ferment plants, and the early stages of changing the legs so they could carry a bulky body instead of running fast after prey," Kirkland explains. This discovery thus places the most primitive therizinosaurs in North America. Study co-author Scott Sampson of the University of Utah notes that the rise of plant-munching therizinosaurs in Utah "may have been directly linked to the spread of flowering plants about 125 million years ago."