With more than 41,000 species currently under threat of extinction worldwide, it might not be long before endangered loggerhead turtles, red wolves and manatees disappear from the US for good. We have lost incredible creatures before, from the hordes of prehistoric megafauna (giant mammals) that met their maker some 10,000 years ago to more recent losses brought about by humans. Here, we take a look at the animals that once lived on the land and in the waters of the modern United States of America, now gone forever...