  Massive galaxies are key probes to understand how the baryonic matter evolves
within the dark matter halos. We use the "archaeological" approach to infer the
stellar population properties and star formation histories of the most massive
(M > 10^10.75 Msun) and passive early-type galaxies (ETGs) at 0 < z < 0.3,
based on stacked, high signal to noise ratio (SNR), Sloan Digital Sky Survey
spectra. We exploit the information present in the full-spectrum by means of
the STARLIGHT public code to retrieve the ETGs evolutionary properties, such as
age, metallicity and star formation history. We find that the stellar
metallicities are slightly supersolar (Z ~ 0.027 +/- 0.002) and do not depend
on redshift. Dust extinction is very low, with a mean of Av ~ 0.08 +/- 0.03
mag. The ETGs show an anti-hierarchical evolution (downsizing) where more
massive galaxies are older. The SFHs can be approximated by a parametric
function of the form SFR(t) \propto \tau^-(c+1) t^(c) exp(-t/\tau), with
typical short e-folding times of \tau ~ 0.6 - 0.8 Gyr (and a dispersion of +/-
0.1 Gyr) and c ~ 0.1 (and a dispersion of +/- 0.05). The inferred SFHs are also
used to place constraints on the properties and evolution of the ETG
progenitors. In particular, the ETGs of our samples should have formed most
stars through a phase of vigorous star formation (SFRs > 350-400 Msun yr^-1) at
z ~ 4 - 5, and are quiescent by z ~ 1.5 -2. Our results represent an attempt to
demonstrate quantitatively the evolutionary link between the most massive ETGs
at z < 0.3 and the properties of suitable progenitors at high redshifts, also
showing that the full-spectrum fitting is a powerful approach to reconstruct
the star formation histories of massive quiescent galaxies.
