The bulldog rat (Rattus nativitatis) was a species of rat endemic to Christmas Island in the Indian Ocean. The rats lived on the higher hills and denser forests of the island. They had short tails and their backs were covered in a two centimetre thick layer of fat. They lived in small colonies, in burrows among the roots of trees or under hollow logs in primary forest. They were sluggish and never climbed and may have seemed half-dazed in daylight. The last record dates from 1903. They may have succumbed to a disease brought by black rats that had been inadvertently introduced by sailors.