Book excerpt: Introduction There are different levels on the endangered scale, including extinct, critically endangered, endangered, vulnerable, near threatened, and least concern. Extinct animals are no longer living on the Earth, like the dinosaurs. Critically endangered means that animal is at an extremely high risk for becoming extinct in the wild. Endangered just means that an animal is at a very high risk for becoming extinct in the wild. The biggest threat to most animals is humans; we are destroying and taking over their habitats. Humans are also over killing and illegally hunting several endangered animals.