::sigh::
Here's your proof:
[quote:251b1]One entry found for fossilise.
Main Entry: fos·sil·ise
chiefly British variant of FOSSILIZE
[/quote:251b1]
http://www.m-w.com/cgi-bin/dictionary?va=fossilised
There you go.
British version: fossilise.
American version: fossilize.