print

map {
    $_->[0]
}

grep {
    if ($previous eq $_->[1]) {
        $previous = $_->[1];
        0;
    } else {
        $previous = $_->[1];
        1;
    }
}

sort {
    $a->[1] cmp $b->[1] or $b->[2] <=> $a->[2]
}

map {
    (undef, undef, undef, $date, $magnitude) = split ',';
    $date =~ m/(\d{2})-(\d{2})-(\d{4}) (\d{2}:\d{2}:\d{2})/;
    $date_sort = "$3$2$1$4";
    [$_, $date_sort, $magnitude]
}

<DATA>;

__DATA__
2550,531,66,10-12-2007 07:03:08.069,2
2549,529,62,10-12-2007 07:03:08.151,1
2550,531,66,10-12-2007 07:03:09.069,1
2549,529,62,10-12-2007 07:03:09.151,10
2549,529,62,10-12-2007 07:03:09.151,2
2549,529,62,10-12-2007 07:03:09.151,7
2549,529,62,10-12-2007 07:03:09.151,2
2549,529,62,10-12-2007 07:03:09.151,8
2549,529,62,10-12-2007 07:03:09.151,2
2549,529,62,10-02-2007 07:03:10.151,2
2549,529,62,10-12-2007 07:13:09.151,2
2549,529,62,10-12-2007 07:03:09.151,2
2549,529,62,10-12-2007 17:03:09.151,1