Silicon Graphics, a pioneering giant in creating computer-generated special effects for the motion picture industry, filed for bankruptcy protection on Monday. The Mountain View, CA company, which astounded audiences with the dinosaurs it created for Jurassic Park, listed $397 million in assets and $650 million in debt. In a statement on Monday Silicon Graphics said that it plans to reduce its work force by about 12 percent by the end of the year as part of a plan to cut $150 million in annual costs.