The theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The motion through the fission barrier is followed by a fast, nonadiabatic descent of the potential between the fragments. The latter stage is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained from the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258 Fm nucleus are studied. The resulting fission fragment characteristics show good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle and quasiparticle picture is emphasized and qualitatively studied.