The list of Fortran 2008 features in gfortran 4.5 (http://gcc.gnu.org/wiki/GFortran#GCC4.5) says: Add ATAN(Y,X) as alias for TAN2(Y,X). This must be ATAN2, not TAN2, as stated in http://gcc.gnu.org/onlinedocs/gfortran/ATAN.html#ATAN
Fixed in wiki by reporter.