The new 12um deep galaxy survey ISO-ESS on the ESO Sculptor survey area, allows a coherent analysis of optical-to-IR faint galaxy counts. Dust and star emissions are both interpreted by galaxy type with the evolutionary code PEGASE. We predict the number density excess revealed at ~0.3mJy from ISO (12um, 15um) and MIPS/Spitzer(24um) is due to a few dusty ellipticals ultra-luminous in the IR and apparently normal in the optical. No need of arbitrary high-z starbursts.
The resulting star formation history is high at early epochs, due to z>4 ellipticals. Their common properties with distant radio sources is discussed (Rocca-Volmerange, de Lapparent, Seymour, Fioc 2007, AA, 475, 801).