We present estimates of CN and Mg overabundances with respect to Fe for early-type galaxies in 8 clusters over a range of richness and morphology .
Spectra were taken from the Sloan Digital Sky Survey ( SDSS ) DR1 , and from WHT and CAHA observations .
Abundances were derived from absorption lines and single burst population models , by comparing galaxy spectra with appropriately broadened synthetic model spectra .
We detect correlations between [ Mg/CN ] and [ CN/Fe ] and cluster X-ray luminosity .
No correlation is observed for [ Mg/Fe ] .
We also see a clear trend with the richness and morphology of the clusters .
This is interpreted given varying formation timescales for CN , Mg and Fe , and a varying star formation history in early-type galaxies as a function of their environment : intermediate-mass early-type galaxies in more massive clusters are assembled on shorter timescales than in less massive clusters , with an upper limit of \sim 1 Gyr .