Big Bang Nucleosynthesis (BBN) says that the amount of baryonic (i.e. usual) matter cannot be much higher than what we directly observe. However, it accounts fo

Big Bang Nucleosynthesis (BBN) says that the amount of baryonic (i.e. usual) matter cannot be much higher than what we directly observe. However, it accounts for only ~16% of the mass necessary to account for galactic rotation curves, gravitational lensing by galaxies etc. So the leftover must be non-baryonic dark matter. One can of course say that BBN is wrong but that's very unlikely as it has been tested to high precision from CMB study.