  [abr] We report the analysis of three galaxies selected in the Hubble Deep
Field South at Ks<22 on the basis of their unusually red near-IR color J-K>3.
We have used population synthesis models to constrain their redshifts and their
stellar masses. One galaxy is at redshift z_p~2.4 while the other two are at
z_p~2.9-3.0. All three galaxies have already assembled a stellar mass of about
10^{11} M_sun at the observed redshift placing the possible merging event of
their formation at z>3.5. The inferred mass weighted age of their stellar
populations implies that the bulk of the stars formed at z_f>3.5. The resulting
co-moving density of M_{stars}>10^{11} M_sun galaxies at <z>~2.7 is
rho=1.2(+-0.7)x10^{-4} Mpc^{-3}, about a factor two higher than the predictions
of hierarchical models. The comparison with the local density of galaxies
implies that the three galaxies must have already formed most of their stellar
mass and that they cannot follow an evolution significantly different from a
passive aging.The comparison with the density of local L>L* early types
(passively evolved galaxies) suggests that their co-moving density cannot
decrease by more than a factor 2.5-3 from z=0 to z~3 and that up to 40% of the
stellar mass content of bright (L>L*) local early type galaxies was already in
place at z>2.5.
