This is a puffball - Pisolithus arhizus. At this age, it is quite a neat little puffball, but will split and deform and become a gross, slimy, cracked mess as it matures. The black mess can be used as a natural textile dye.
In New Zealand it is restricted to growing in areas of high geothermal activity - this one was photographed in Tokaanu by Lake Taupo. But in Australia it is more widespread and is called the horse dung puffball.
|Horse dung puffball - Pisolithus arhizus|