ristic stellar mass from the mass function of the GOODS-MUSIC sample is shown as a dashed line [@fon06], although we warn that the GOODS-MUSIC masses are calculated using a @salp55 IMF, which will give a systematic 0.25 dex overestimate in $\log$M$_s$ with respect to our choice of IMF. Our sample is safely away from the limit imposed by the cut in apparent magnitude ($i_{AB}\leq 24$). The curved solid lines give that limit for two extreme star formation histories, corresponding to the “old” and “young” populations as defined above. Notice that within our sample of massive early-type galaxies there are NO galaxies whose colours are compatible with young stellar populations (i.e. open circles).

The evolution of massive galaxies {#sec:evol}
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The redshift evolution of the comoving number density is shown in figure \[fig:logn\] (black dots). The ($1\sigma$) error bars include both Poisson noise as well as the effect of a 0.3 dex uncertainty in the stellar mass estimates. These uncertainties are computed using a Monte Carlo run of 10,000 realizations. The figure includes data from GOODS-MUSIC [@fon06], COMBO17 [@Bell04] and Pal/DEEP2 [@con07]. At z=0 we show an estimate from the segregated 2dFGRS luminosity function [@crot05]. We take their Schechter fits for early-type galaxies within an environment with a mean density defined by a contrast – measured inside radius $8h^{-1}$ Mpc – in the range $\delta_8=-0.43\cdots+0.32$ (black open circles). In order to illustrate possible systematic effects in 2dFGRS, we also include the result for their full volume sample as grey open circles. The 2dFGRS data are originally given as luminosity functions in the rest-frame $b_J$. We took a range of stellar populations typical of early-type galaxies in order to translate those luminosities into stellar masses. The error bars shown for the 2dFGRS data represent the uncertainty caused by this translation from light into mass over a wide range of stellar populations (with typical M/L($b_