Noronhomys

A member of the family Cricetidae and subfamily Sigmodontinae, it shares several distinctive characters with Holochilus and related genera within the tribe Oryzomyini, including high-crowned molars with simplified crown features and the presence of several ridges on the skull which help anchor the chewing muscles.[6] The biological details given in the Lettera's account of Fernando de Noronha agree with what is known of the natural history of the island, lending weight to the view that it derives from a visit, whether by Vespucci himself or by another explorer.The generic name, Noronhomys, combines the name of the island of Fernando de Noronha with the Ancient Greek μῦς mys "mouse"[8] and the specific name, vespuccii, honors Amerigo Vespucci.Sigmodontinae itself is the largest subfamily of the family Cricetidae, other members of which include voles, lemmings, hamsters, and deermice, all mainly from Eurasia and North America.[11] Carleton and Olson performed a detailed comparison of Noronhomys to members of the mainland genera Holochilus and Lundomys on the basis of both general morphology and morphometrical data, concluding that the Fernando de Noronha rat is distinct from both other animals.[17] This material documents that, with a skull of about 4 cm (1.5 in) (occipitonasal length), Noronhomys was a moderately large oryzomyine, smaller than Lundomys but well within the range of Holochilus.[23] Skull shape is strikingly different from both Holochilus and Lundomys, resulting in a clear separation from both of these taxa in statistical analyses of measurement data.The two masseteric ridges, which anchor some of the chewing muscles, are joined together as a single crest for a portion of their length and extend forward to a point below the first molar.[36] The molars are high-crowned (hypsodont) and planar, with the main cusps as high as the crests connecting them,[15] a configuration shared only with Holochilus and Carletonomys among oryzomyines.[3] The ancestor of Noronhomys may have been a semiaquatic animal, similar to living Holochilus or Lundomys, that arrived on Fernando de Noronha by chance on a floating log.[45] The morphology of the limb bones in Noronhomys suggests that the animal was not semiaquatic like its relatives, but terrestrial, consistent with its occurrence on a small island, where streams and pools are rare or absent.The introduced black rat and house mouse (Mus musculus), which became very common on the island, may have driven it to extinction by directly competing for food, preying on young Noronhomys, or transmitting diseases.