The skull and horns of a "gigantic" Ice Age bison were uncovered Saturday afternoon at Ziegler Reservoir, the fossil dig site near Snowmass Village.Dr. Ian Miller, curator of paleontology and chairman of the Earth Science Department at the Denver Museum of Nature & Science, spotted a bison horn core, uncovered by a heavy equipment operator. The horn was so large, Miller initially mistook it for a mammoth or mastodon tusk, according to the museum's daily e-mail update on Sunday.After another careful pass by the bulldozer, a second exposed horn core led scientists to the spot where the skull was located. The span of the horns was more than six feet."I'm trying to think of a cooler fossil that I've ever seen in my life," said Dr. Kirk Johnson, the museum's chief curator and vice president of research and collections, in the update. "This is the iconic fossil recovered thus far in the excavation."The size of the skull and horns indicates the animal was twice as large as modern bison. The horns of prehistoric bison extended straight out from their heads before curving at the tips, unlike present-day bison.Similar species found elsewhere in the western United States indicate extremely large bison are often found in sediments as old as 30,000 to 50,000 years. If the Snowmass site contains fossils from a range of ages, it would greatly increase its significance, Johnson said in the update.Scientists had said they believed at least some of the animals being found in Snowmass Village dated back 12,000 to 15,000 years. The bison skull was encased in plaster in the field, then the 250-pound specimen was carried to a truck to be transported to the museum for preparation and preservation. Scientists will collect samples from the skull and attempt to radiocarbon date it to determine its age, and to extract ancient DNA.Another bison found at the dig may have been a juvenile of the same species as the large one found Saturday, according to the museum. Proper identification awaits cleaning the skull and comparing it to other specimens in the museum and university collections.A museum crew is racing against winter to recover prehistoric animals from the reservoir. The first find, a mammoth uncovered by a bulldozer operator on Oct. 14, has been followed by a multitude of discoveries. Evidence of bison, a deer-like animal, mammoth, mastodon and a giant ground sloth have all been discovered.The reservoir, at one time the site of a glacial lake, according to scientists, is being enlarged by the Snowmass Village Water and Sanitation District at a cost of $6 million.