During 2007 the Royal Australian Mint began using a new echidna reverse featuring a tiny version of the designer Stuart Devlin's initials with a slightly larger echidna. The difference is quite visible to the naked eye as can be seen on the 2008 dated pair below.

A closeup clearly shows the difference in the SD.

The tiny SD reverse is scarce on 2007 issues but both the old "small SD" and the new "tiny SD" reverse have been seen on all issues from 2007 to 2012.