I wrote a blog a while back about the depictions of animals on gold coins. That was prompted by the rise in gold prices and the rush to buy gold bars. In fact here is a photo of one of those coins:
Although gold coins are often the coins that animals are depicted on, other metals such as copper and silver are known. Animal depiction on a country's coins are more well known outside of the USA. Australia has most of their native species of wildlife are on their coins. New Zealand also has many of their birds on their coins.