Definition: Nyctotherus is a genus of mammals in the family Cervidae, commonly known as ground sloths or tree-sloths. They belong to the order Apalaeontid (also known as "earless" or "no-tail" animals), and are found on both land and sea. Nyctotherus has a long history of being associated with ancient forests and is believed to have played an important role in shaping these ecosystems.