A theoretical model of ultrafast dynamics in the optical Kerr effect in molecular liquids is developed. It assumes that for short times there exist dynamic quasicrystalline structures including a central molecule and its nearest neighbors. The interaction of such structures with a femtosecond laser pulse leads to excitation of vibrational modes (local phonons) which are responsible for subpicosecond nonlinear polarizability of the liquid. The results of numerical calculations performed for benzene show a very good agreement with the experimental data. The lifetime of the dynamic quasicrystalline structures in benzene, at room temperature, is estimated to be about 200 fs.