Murinae

The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. This subfamily is larger than all mammal families except the Cricetidae and Muridae, and is larger than all mammal orders except the bats and the remainder of the rodents. The Murinae are native to Africa, Europe, Asia, and Australia. They are the only terrestrial placental mammals native to Australia. They have also been introduced to all continents except Antarctica, and are serious pest animals. This is particularly true in island communities where they have contributed to the endangerment and extinction of many native animals. Two prominent murine human commensals have become vital laboratory animals. The brown rat and house mouse are both used as medical subjects. The murines have a distinctive molar pattern that involves three rows of cusps instead of two, the primitive pattern seen most frequently in muroid rodents. The first known appearance of the Murinae in the fossil record is about 14 million years ago with the fossil genus Antemus. Antemus is thought to derive directly from Potwarmus, which has a more primitive tooth pattern. Likewise, two genera, Progonomys and Karnimata, are thought to derive directly from Antemus. Progonomys is thought to be the ancestor of Mus and relatives, while Karnimata is thought to lead to Rattus and relatives. All of these fossils are found in the well-preserved and easily dated Siwalik fossil beds of Pakistan. The transition from Potwarmus to Antemus to Progonomys and Karnimata is considered an excellent example of anagenic evolution. Most of the Murinae have been poorly studied. Some genera have been grouped, such as the hydromyine water rats, conilurine or pseudomyine Australian mice, or the phloeomyine Southeast Asian forms. No tribal level taxonomy has been attempted for the complete subfamily. It appears as if genera from Southeast Asian islands and Australia may be early offshoots compared to mainland forms. The vlei rats in the genera Otomys and Parotomys are often placed in a separate subfamily, Otomyinae, but have been shown to be closely related to African murines in spite of their uniqueness. Three genera, Uranomys, Lophuromys, and Acomys, were once considered to be murines, but were found to be more closely related to gerbils through molecular phylogenetics. They have been assigned a new subfamily status, Deomyinae. Molecular phylogenetic studies of Murinae include Lecompte, et al. (2008), which analyzes African murine species based on the mitochondrial cytochrome b gene and two nuclear gene fragments. Lecompte, et al. (2008) estimates that African murines colonized Africa from Asia approximately 11 million years ago during the Miocene.