He and his son Frederick Robert Zietz, also a zoologist, worked on preserving bones from a diprotodon skeleton. Along with E. C. Stirling, also at the South Australian museum, he undertook the direction of the first major palaeontology excavation at Lake Callabonna, where a large series of Diprotodont skeletal material was collected. Zietz was responsible for identifying a hitherto unknown species of shark from Investigator Strait, which became known as Asymbolus vincenti, or Gulf catshark.

He is buried in West Terrace Cemetery in Adelaide.