The protofeathers like the ones on the Sinosauropteryx appear to be covered with hollow filaments. These may have been the forerunners of bird feathers; or, as some scientists believe, feathers used for insulation, not the precursors to flight. Dinosaurs like the Sinosauropteryx, other similar dinosaurs, and fossil feathers from the same period, give scientists a better idea about the evolution of feathers. In particular, it is thought that feathers evolved rapidly in terms of geologic time. Feathers possessed properties that were highly advantageous to survival; they gave the animals an aerodynamic body and provided insulation for warmth, two features needed to survive a tough, predator-ridden world.