Apomys sacobianus Johnson 1962

Apomys sacobianus Johnson 1962, Proc. Biol. Soc. Wash., 75: 318.

Type Locality: Philippines, Luzon Isl, Pampanga Province, Sacobia River, Clark Air Base.

Vernacular Names: Long-nosed Luzon Apomys.

Distribution: Greater Luzon Faunal Region. Endemic to Luzon and recorded only from primary forest at the type locality; limits unresolved.

Conservation: IUCN – Vulnerable.

Discussion: Included within the Apomys abrae hylocetes Group by Musser (1982 b), but allied to the Apomys datae Group by Ruedas (1995) because he thought the holotype (USNM 304352) and another specimen he identified as A. sacobianus (USNM 557717) exhibited the primitive murine cephalic arterial pattern typical of A. datae . Musser (1982 b), however, described a derived pattern for A. sacobianus, which is typical for species in the A. abrae-hylocetes Group, and our restudy of the holotype reaffirms those observations. Apomys sacobianus is morphologically closely related to the N Luzon A. abrae, being a slightly larger-bodied, grayer version occurring in the S lowlands (Musser, 1982 b); whether it represents a larger-bodied geographic variant of A. abrae or a separate species will have to be determined by study of specimens from intermediate localities and altitudes.

Heaney et al. (1998) recorded A. sacobianus from Isabela, Mountain, and Zambales provinces on Luzon, each represented by a single specimen. He (L. Heaney, in litt., 2002) tentatively determined the Isabela and Zambales examples to be A. sacobianus, but acknowledged that the specimens require restudy to verify the identifications. USNM 557717 is from Mountain Province (Kiangan, Duwit, 4000 ft [1219 m]), has the derived carotid circulatory pattern typical of A. abrae-A. hylocetes (scheme B in Musser, 1982 b:6), but is much larger than A. sacobianus in skull length (40.0 mm versus 38 mm for A. sacobianus) and length of M1-3 (8.0 mm versus 7.1 mm), and likely represents a separate undescribed species; no example of A. abrae, which also occurs in Mountain Province, or any other species of Apomys comes close to it in size (Musser, 1982 b:table 4). Until identity of the other two specimens from Isabela and Zambales provinces are re-evaluated, we consider A. sacobianus to be represented only by the holotype.