If I understand well, Planck units are fundamental in the sense that they don't depend on any arbitrary choice of measurement scale, but they emerge directly from the laws of physics. For Planck lenght and Planck time, this seems to fit with the widespread belief that they may well also be fundamental in the sense that they are the smallest, indivisible units, below which the terms space or time don't have meaning anymore. Indeed it seems natural to expect that the fundamental unit emerging from the laws is the smallest possible one, otherwise we would need another smaller unit (or, of course, measure smaller things as fractions of the unit, but that does not feel so "fundamental" anymore) However, Planck mass is very big by subatomic standards, we know of many things with much smaller mass, so it is not fundamental in the second sense. Why is it so? Does it have any significance the fact that Planck mass is so big? Shouldn't the fundamental unit of mass be the smallest possible mass?