HadromysDivision. Usually considered closely allied to Arvicanthis and its relatives, especially Golunda (Misonne, 1969), but a combination of primitive and derived cranial and dental traits divorces Hadromys from that group: best hypothesis now available on phylogenetic affinities would be to derive the species of Hadromys from some late Miocene Asian ancestor, possibly a species of Karnimata (= Progonomys, according to Mein et al., 1993), and to consider any resemblance to the Arvicanthis cluster a reflection of convergent evolution (Musser, 1987b). No fossils have been described that suggest phylogenetic links between Hadromys and either Asian Golunda or extinct Asian genera such as Saidomys, Parapelomys, and Dilatomys (see descriptions of those genera in Brandy, 1981; Gupta and Prasad, 2001; Jacobs, 1978; Ôen, 1983) that have been labeled "Asian arvicanthines" (e.g., Cheema et al., 2003)

Hadromys loujacobsi, known by fossil fragments from Late Pliocene and early Pleistocene sediments in Punjab region of N Pakistan, is a more derived (dentally) relative of living H. humei (Cheema et al., 2003; Musser, 1987b). Prohadromys varavudhi, described from isolated molars found in Thailand (late Pliocene to early Pleistocene) is dentally closely related to the species of Hadromys, but has less specialized molars reflected by their lower coronal heights and more arcuate cusp rows (Chaimanee, 1998). Something with that kind of molar configuration could be a direct potential ancestor of Hadromys. An earlier dental fragment from middle Pliocene of Pakistan was identified as Hadromys sp. and is also less derived than H. loujacobsi (Cheema et al., 1997). Available data indicate that H. humei and its extant and extinct relatives once occurred over a wide area of the Indomalayan region and may have originated and evolved in what is now Indochina (Chaimanee and Jaeger, 2000b).