  A comparison is presented between the observed surface density of extremely
red objects (EROs) and the densities of red high-z elliptical galaxies
predicted by Pure Luminosity Evolution (PLE) and by some CDM hierarchical
models. The analysis is based on the widest field survey for EROs available to
date (covering in total $\sim$850 arcmin^2), and it takes into account the
effects of ERO clustering. Good agreement is found between the observed surface
densities of EROs and those predicted by PLE models for ellipticals selected
using the same color and luminosity thresholds. Since there is evidence that
the bulk of EROs are passively evolving ellipticals, this result implies that
most field ellipticals were fully assembled at least by $z\sim$2.5. Existing
hierarchical models predict instead a surface density of red ellipticals that
is much smaller than that of the EROs.
