Apomys microdon Hollister 1913

Apomys microdon Hollister 1913, Proc. U. S. Natl. Mus ., 46: 327.

Type Locality: Philippines, Cataduanes Isl, Biga.

Vernacular Names: Small Luzon Apomys.

Synonyms: Apomys hollisteri (Ellerman 1949) .

Distribution: Endemic to the Greater Luzon Faunal Region and widespread on Luzon in secondary lowland forest and primary montane forest (Heaney et al., 1991; Heaney et al., 1998; Heaney et al., 1999; Musser and Heaney, 1992). Formerly thought to also occur on Leyte and Dinagat (Musser, 1982 b), but those samples have been referred to A. littoralis .

Conservation: IUCN – Lower Risk (lc).

Discussion: Included within Apomys abrae hylocetes Group by Musser (1982 b). Phylogenetic analyses of mtDNA cytochrome b sequences identifies M. musculus, an undescribed species from Sibuyan Isl and Negros Isl, and another undescribed species from Sibuyan Isl as the closest phylogenetic allies to A. microdon (Steppan et al., 2003) .

Ellerman (1949) provided hollisteri as a replacement name for Apomys microdon because it was preoccupied by Mus microdon Peters (1852), which is a form of Mastomys, and Ellerman had included both Apomys and Mastomys in Rattus . Corbet and Hill (1992:379) used hollisteri as the correct name stating that microdon was permanently invalid following Article 59(b) of the 3 rd edition of the International Code of Zoological Nomenclature (International Commission on Zoological Nomenclature, 1985 d), which states that a "junior secondary homonym replaced before 1961 is permanently invalid." But according to article 59.3 of the 4th edition of the Code (ICZN, 1999), a "junior secondary homonym replaced before 1961 is permanently invalid unless the substitute name is not in use and the relevant taxa are no longer considered congeneric, in which case the junior homonym is not to be rejected on grounds of that replacement." Except for Corbet and Hill’s account, microdon is the name that has been in use, especially for the last 20 years, in all the ecological, biological, biogeographical, and taxonomic literature covering Philippine mammals. Additionally, all modern practicing rodent systematists agree that Hollister’s microdon and Peters’s microdon refer to species in different genera ( Apomys and Mastomys, respectively) that are in unrelated (except as members of Murinae) phylogenetic clades. We continue to follow Musser (1982 b) in using microdon . Corbet and Hill (1992:379) correctly noted that A. microdon is closely related to A. insignis (an alliance documented by Musser, 1982 b) and also stated that A. microdon "could conceivably be considered conspecific with A. insignis " but morphological evidence does not support this supposition (Musser, 1982 b).