Bramble Cay is a small vegetated sand cay in the northern Torres Strait, with a highest point around three metres above sea level. The melomys was endemic to it and to nothing else, one of the most restricted mammal ranges ever documented. Surveys in the late 1970s estimated several hundred animals.
Monitoring recorded a steep loss of vegetation cover on the cay, from roughly two hectares in 2004 to about one tenth of that by 2014, attributed to inundation by seawater during storm surges on a rising baseline sea level. The rodent depended on that vegetation for food and shelter. The last confirmed sighting was by a fisherman in 2009, and intensive trapping surveys in 2011 and 2014 found nothing.
The Australian government formally declared the species extinct in February 2019. It is widely reported as the first mammal extinction attributed principally to anthropogenic sea level rise. A closely related melomys survives in New Guinea, so the genus continues, but this island population is gone.