Exporting Animated Model from blender to assimp

What is the proper way to export a Rigged and animated model to be used with assimp in a openGL program.

No matter what I do scene->mNumAnimations is always =0 ;
and mesh->mNumbones is also always zero.

What am I Missing?
is it related to a particular blender exportation option?

      static const int assimpFlags = aiProcess_Triangulate | 
      aiProcess_PreTransformVertices | 
	scene = importer.ReadFile(getDiskFile(), assimpFlags);

aiProcess_PreTransformVertices is the problem.
Removing it makes assimp load bones and animations normally