The head and body length was about 25 to 27 centimetres (9.8 to 10.6 in), considerably larger than black rats, and their backs were covered in a two-centimetre thick layer of fat.

Their hair was described as being thick, coarse and dark reddish-brown in colour, with a slightly lighter underside.

[3] The rats lived on the higher hills and denser forests of the island.

They lived in small colonies, in burrows among the roots of trees or under hollow logs of sago palms in primary forest.

They are suggested to have succumbed to a disease brought by black rats that had been inadvertently introduced by sailors, as mass die-offs are noted around 1902–1903, after which they were never seen again.