Line-strength gradients versus central velocity dispersion. Black triangles show the observed FCGs while grey squares and triangles are index measurements from Kobayashi & Arimoto (1999) and Rawle et al. (2010). Dashed lines represent the average gradient for all observed fossils while short-dashed lines indicate zero gradients. The Hβ gradient is not shown for RX J0752.7+4557 since the line is seen in emission. The very steep Mgb gradient of RX J1548.9+0851 has been excluded for the estimation of the average Mgb gradient.