50 Dollars - Elizabeth II Heaviside's Dolphins

Oliver Heaviside's dolphin — Cephalorhynchus heavisidii — was named not for the Victorian mathematician Oliver Heaviside, as is commonly assumed, but for a Captain Haviside (note the spelling discrepancy) who reportedly brought a specimen to the Natural History Museum in the early 19th century. The attribution to the wrong Heaviside has never been formally corrected.

Cook Islands issued dozens of wildlife-themed silver commemoratives in this period under licensing arrangements that had little to do with local fauna or commerce — these coins were designed entirely for the collector market and saw no domestic circulation.