The Bramble Cay melomys, or Bramble Cay mosaic-tailed rat (Melomys rubicola), is a recently extinct species of rodent in the family Muridae and subfamily Murinae. It was an endemic species of the isolated Bramble Cay, a low-lying vegetated coral cay with a habitable area of approximately 5 acres located at the northern tip of the Great Barrier Reef in Australia. Described by researchers as having last been seen in 2009 and declared extinct by the Queensland Government and University of Queensland researchers in 2016, it was formally declared extinct by the International Union for Conservation of Nature (IUCN) in May 2015 and the Australian government in February 2019. Having been the only mammal endemic to the reef, its extinction was described as the first extinction of a mammal species due to anthropogenic climate change.
Taxonomy
The Bramble Cay melomys is an extinct member of the genus Melomys, which contains approximately 20 species of rodents living in the wet habitats of northern Australia (Far North Queensland), New Guinea, Torres Strait Islands and islands of the Indonesian archipelago. The genus is in the subfamily Murinae, and the family Muridae. The Bramble Cay melomys was first discovered in April 1845 by Charles Bampfield Yule, commander of the British ship HMS Bramble on Bramble Cay, a vegetated coral cay measuring located at the northern tip of the Great Barrier Reef. At that time, the animal was so plentiful that his crew shot them with bows and arrows for fun. In May 1845, while visiting Bramble Cay via HMS Fly, naturalist John MacGillivray and Joseph Jukes collected a holotype, stored today in the British Museum of Natural History. From the specimen, Oldfield Thomas formally described and named the species Melomys rubicola in 1924. DNA obtained from historic specimens indicates that its closest relative in Australia is the Cape York melomys (Melomys capensis), with the genetic divergence between the two species being so low that it was barely above what would be expected for diversity within species.
Description
Melomys rubicola was relatively large for a rodent, with a body-length ranging from and a tail-length between . Compared to other mice, it had a long tail, short ears, and large feet. Its weight was recorded as between . The tail was prehensile at the tip and covered with rough scales. The fur was reddish brown above and greyish brown below, with black guard hairs on its back. It was similar in appearance to the Cape York melomys, to which it was closely related. As with other species of melomys, it was described as having a Roman nose.
Distribution and ecology
Scientists are uncertain on how the animal reached Bramble Cay. Studies have theorized that it either reached Bramble Cay from the island of New Guinea by floating on driftwood, or that it reached the region when it was still above water at a time when Australia was connected to New Guinea by a land bridge, and then persisted into recent times.
The Bramble Cay melomys was described in 2002 as Australia's most isolated mammal. The cay is located in the northeastern portion of the Torres Strait, approximately from the mouth of the Fly River in Papua New Guinea. The cay is between , but the rodent only occupied the vegetated portion of the island, measuring approximately . The vegetation of the island comprises grasses and herbs, generally shorter than .
Although 11 species of plants have been recorded on the island in the past, only three to five species have been recorded as present at the same time. Common species include Portulaca oleracea, Boerhavia albiflora, Cenchrus echinatus, and Amaranthus viridis. Three species were observed in 1994: Amaranthus viridis, Boerhavia tetrandra (genus Boerhavia), a type of spinach eaten by humans; and Lepturus repens. A 1998 study showed significant loss of vegetation since 1924, mostly on the southern and northern shores of the island.
The island was also characterised by large populations of seabirds, as well as ecological disturbance caused by annual green turtle breeding. The Bramble Cay melomys preferred the more densely vegetated areas, and avoided those parts of the island that had high densities of seabirds. The species was observed to feed on P. oleracea as well as on turtle eggs. The breeding season of the species was lengthy, and the sex ratio was skewed towards females.