They are thought to be relatively early offshoots from the Murinae, with only
Rattini and
Phloeomyini being more
basal than them. They likely colonized
New Guinea (then a part of
Sahul) from either the
Sunda Shelf or the
Philippines during the late
Miocene or early
Pliocene, about 5 million years ago, and diversified extremely rapidly. From here, they colonized Australia about 2-3 million years ago, undergoing major
adaptive radiation. Earlier taxonomists formerly split this group into three subfamilies (Hydromyinae, Pseudomyinae, and an unnamed "Old Papuan group"). Although all were later merged into the
Murinae, they were still retained as multiple tribes (Anisomyini, Hydromyini, Uromyini, and Conilurini), with other taxonomists splitting them even further. However, a 2008 study found them to comprise a single group that had undergone a rapid diversification after colonizing Sahul, and thus placed them all into a single tribe, Hydromyini. Although the name "Hydromyini" derives from the
semiaquatic type genus Hydromys, which translates directly to "water mouse", only a few members of the tribe such as
Hydromys and
Xeromys are semiaquatic; the majority are terrestrial, and some such as
Notomys are even specifically adapted to arid environments. == Distribution ==