  Hierarchical models predict that massive early-type galaxies (mETGs) are the
latest systems to be in place into the cosmic scenario (at z<~0.5), conflicting
with the observational phenomenon of galaxy mass downsizing, which poses that
the most massive galaxies have been in place earlier that their lower-mass
counterparts (since z~0.7). We have developed a semi-analytical model to test
the feasibility of the major-merger origin hypothesis for mETGs, just
accounting for the effects on galaxy evolution of the major mergers strictly
reported by observations. The most striking model prediction is that very few
present-day mETGs have been really in place since z~1, because ~90% of the
mETGs existing at z~1 are going to be involved in a major merger between z~1
and the present. Accounting for this, the model derives an assembly redshift
for mETGs in good agreement with hierarchical expectations, reproducing
observational mass downsizing trends at the same time.
