  There have recently been many predictions of "superdiffusion" in
two-dimensional strongly coupled Yukawa systems, both by computer simulations
and in dusty plasma experiments, with substantially varying diffusion
exponents. Here we show that the results crucially depend on the strength of
dissipation and the time instant of the measurement. For sufficiently large
friction even subdiffusion is possible. However, there are strong indications
that, in the long-time limit, anomalous diffusion vanishes for dissipative as
well as for frictionless systems.
