A snowmobiler was killed Monday night in a collision with a bison, Yellowstone National Park officials said Tuesday. Donald M. Anderson, 48, of Geraldine, Mont., died at a hospital shortly after the accident, which occurred while he was snowmobiling with several friends after dark, said park spokeswoman Joan Anzelmo. Anderson's friends, who lost sight of him, found him severely injured on the ground, with clumps of bison hair nearby. Anzelmo said rangers believe the bison may have walked away unharmed.