Detailed Findings & Methodology

The IUCN places animals in the following categories: data deficient, least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct. Animals designated vulnerable, endangered, or critically endangered are those most at risk of extinction.

Animals face various threats, including climate change, overfishing, poaching, disease, pollution, habitat loss, illegal hunting, invasive species, overdevelopment, and desertification. Mammals such as elephants and primates are under threat as their low reproductive rates limit their ability to adapt to changing environments.

Protecting animals from extinction is a daunting task, and requires determining which species are most endangered. All animals are not equal; listing a species as critically endangered doesn’t mean its scarcity or chances of extinction are the same as other animals sharing that status. Other variables include protection measures, the particular kinds of threats faced by the animal, and genetic diversity.

Scientists are also reluctant to declare a species extinct because there is always the possibility an animal might exist in the wild and has not been seen for years. Rare animals might be so elusive that scientists are unable to track them. Funding and protection efforts for at-risk animals depend on their presence in a given area.

Animals such as polar bears, penguins, and sea lions are considered at least vulnerable because of climate change, which is robbing them of their habitat. But because their populations have not fallen to very few in number, they are not on our list.

Mammals, reptiles, birds, amphibians, and fish — all the major invertebrates — populate the list, among them: the Imperial Woodpecker, the Chinese Paddlefish, the Green-flecked Salamander, the San Quintin Kangaroo Rat, the Aru Flying Fox, the Fernandina Giant Tortoise, and the Rio Pescado Stubfoot Toad.

24/7 Wall St. based its list of the world’s rarest and possibly extinct animals on data provided by the International Union for Conservation of Nature. All of the animals on the list are assessed as critically endangered, one level below extinction. Most of the creatures on the list are estimated to number fewer than 250 mature individuals. Many have rates of decline of more than 80% over the last 10 years or three generations, whichever is longer, and the reduction may not be reversible. We also considered how geographically limited the animal is.