It was 10 percent larger than its closest living relative, the Australian musk duck Biziura lobata,[2] with which it has sometimes been combined.

The first discovery of the fossil remains of the duck, a single tarsometatarsus associated with large numbers of moa bones, was made at Enfield, near Oamaru in the South Island of New Zealand.

Subsequently, additional material was obtained from Marfells Beach, adjacent to Lake Grassmere at the north-eastern end of the South Island, and described in 1969 by Ron Scarlett, who considered the bird to be referable to B.

Allowing for the larger size, the measurements indicate that the New Zealand bird also had relatively bigger legs and shorter wings than the Australian, suggesting that it was becoming more sedentary, although still fully capable of flight.

[5] The combination of differences in size, shapes, and the relative proportions of the bones confirm that the New Zealand musk duck was a distinct species.