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tokens: ( UVJ colour selected) at = 1.6. They found a mean age of 1.1 Gyr. As stated by the authors, this value is in excellent agreement with the age of local counterparts, if high- massive quiescent galaxies evolve passively. We verified that more than 80 of their sample is composed of massive passive galaxies with pc, thus we can reasonably compare their results with ours. If we assume passive evolution between and , the mean age of their massive quiescent galaxies rises to 3.1 Gyr. This is in fair agreement with the mean age of high- MPGs we find at ( Gyr) (see also Whitaker et al. 2013 ). Different conclusions were reached by F16. Using stacked spectra, the authors constrained the stellar population ages for dense and less dense passive galaxies in the zCOSMOS sample from to . They found that the age of dense massive quiescent galaxies increases less than would be expected from passive evolution alone. Moreover, they found no correlation between the age of stellar population and the dimension of the source. The present analysis differs from the F16 analysis in a number of ways: the selection of passive galaxies (no emission lines plus no MIPS in F16 vs. NUV colour in our work); the selection of the dense sub-population (cut at fixed or along the SMR vs. cut at fixed ); and the procedure adopted to constrain the stellar population age. Unfortunately, we cannot exactly reproduce their analysis with our data set. In Appendix B, we checked how our results change if we adopt the same criteria used by F16 to select dense and less dense galaxies. We found that the mean age of dense MPGs is consistent with passive evolution and that less dense MPGs are younger than dense MPGs, independently of the criteria used to divide the sub-populations. However, as stated above, we stress that the previous checks rely on a sample of MPGs selected in a different way and adopt different techniques to constrain the stellar population age. In fact, we cannot repeat the same analysis with our data set, so we cannot fully account for the effect of these two factors on the results. Fig. 9 Evolution of the number density of MPGs (filled red circles) and of star forming massive galaxies (MSFGs, blue filled stars). Open circles show the expected growth in the abundance of MPGs below , assuming that this is fully due to the observed decline of MSFGs. Solid and open circles have been shifted for visualisation purposes. 6. Where do new large MPGs come from? The evidence that the new MPGs are systematically younger than high- MPGs contrasts with the hypothesis that all massive galaxies are assembled mostly through dry mergers (e.g. Hopkins et al. 2009 ; Cappellari et al. 2012 ). In fact, dry mergers should dilute any trend between stellar population age and time of appearance by mixing up the stellar population of pre-existing systems. In fact, more recently new pieces of evidence have come to light supporting a scenario in which PGs are mostly the final evolutionary stage of