Nanotyrannus Rig
I imported the FBX (or OBJ) files and don't see the feathers
The particle systems for the feathers are only available in the BLEND file, to be opened in Blender. They are not included in the OBJ and FBX files.
I opened the BLEND file and don't see the feathers particles systems
The particles systems are turned off by default to avoid lagging the Viewport. Select the main Nanotyrannus model and navigate to the modifier stacks to see them and turn on the feathers.