Apomys (Megapomys) crinitus, Heaney & Balete & Duya & Duya & Kyriazis & Rickart & Steppan & Rowsey, 2025

Heaney, Lawrence R., Balete, Danilo S., Duya, Mariano Roy M., Duya, Melizar V., Kyriazis, Christopher C., Rickart, Eric A., Steppan, Scott J. & Rowsey, Dakota M., 2025, Three new species of Philippine forest mice (Apomys, Muridae, Mammalia), members of a clade endemic to Mindoro Island, Zootaxa 5647 (1), pp. 1-26 : 19-20

Apomys (Megapomys) crinitus , new species lsid:zoobank.org:act: C7D99D2B-5CBB-487A-984B-401C2913EC95

Figs. 2C and 6A ; Tables 1 and 4

Holotype. Originally cataloged as FMNH 222954 ; to be transferred to PNM where it has been assigned catalog number PNM 9666 . Adult male captured on 3 March 2014, field number D. S. Balete 10324. Fresh tissue removed from thigh and placed in 95% ethanol. The rest of the specimen was preserved in formalin, then transferred to 75% ethanol; skull ( Fig. 6A ) removed and cleaned using dermestid beetles and a weak ammonia solution. All parts in good condition.

Type Locality. Philippines: Mindoro Island: Occidental Mindoro Province: Sablayan Municipality: Mt. Iglit-Baco National Park : 2.6 km S, 3.4 km E Mt. Mangibok peak, elevation 700 m; 12.69909 o N, 121.0608 o E ( Fig. 1 ) .

Measurements. Tables 1 and 4.

Specimens examined (7). Sablayan Municipality : Mt. Iglit-Baco National Park: 2.6 km S, 3.4 km E Mt. Mangibok peak, elevation 700 m: 12.69909 o N, 121.0608 o E ( FMNH 222953 , 222954 , 222955 ) ; 4.5 km S, 5.4 km W Mt. Talullah peak, elevation 140 m: 12.83108 o N, 121.93764 o E ( FMNH 228507 , 228508 , 228799 ) ; 2.5 km S, 4.0 km E Mt. Mangibok peak, elev. 880 m: 12.70077 o N, 121.06602 o E ( FMNH 241729 ) ; 4.0 km S, 5.0 km W Mt. Talullah peak, elevation 140 m: 12.82673 o N, 121.94192 o E ( FMNH 228509 , 228510 ) .

Etymology. From the Latin crinitus , an adjective meaning long-haired or fringed, in reference to the fringe of white hair behind each ear.

Diagnosis and Description. A member of the genus Apomys , with diagnostic features as listed above. A small mouse (HB x̄ = 128 mm, BOL x̄ = 31.56 mm). The dorsal pelage of A. crinitus is a rich orange-brown with ochraceous highlights extending to top of head, darkening slightly but noticeably along the midline and between the eye and area supporting vibrissae, and paler orange-brown cheeks, producing a dark partial mask ( Fig. 2C ). Scattered long dark guard hairs barely project above dorsal pelage; underfur slate gray. Vibrissae up to 50 mm long. Small tuft of nearly white to slightly pale sandy-orange hair behind ear, longer than adjacent fur. Dorsal pelage becoming paler and brighter laterally before an abrupt transition to ventral pelage. Ventral fur is pale cream-colored with slight ochraceous wash, becoming nearly pure white on throat and under rostrum with pale gray underfur. Ears long and conspicuous, LE/HB x̄ = 0.16 ( Table 1); skin on ears medium brown, paler toward base and at rim of ears, with microscopic hairs on both surfaces. Tail medium brown dorsally, white ventrally (when clean); a tiny white tip is sometimes present at tip of tail. Tail is bare, relatively long (TV/HB x̄ = 1.19; Table 1), with no hairs readily visible except for having short, inconspicuous hairs toward tip. Forefeet with pale cream fur dorsally that extends from lower forearm to base of digits; ventral side is unpigmented. Hind feet similarly furred and colored, relatively long and narrow (HF/HB x̄ = 0.28). Digits and claws on fore and hind feet curved, moderate in length. The skull of A. crinitus shares the diagnostic features of the genus Apomys as listed above, but is one of the smaller species of the subgenus Megapomys (BOL = 31.56 mm), with relatively broad zygomatic arches, narrow palate, high braincase, and broad zygomatic plate ( Table 4).

Comparisons. Comparison with A. gracilirostris and A. veluzi as above. Relative to A. crinitus , A. minor sp. nov. is smaller, HB x̄ = 127 vs. 122 mm, tail both absolutely (x̄ = 151 vs. 140 mm) and relatively shorter (HB/TV x̄ = 1.19 vs. 1.15; Table 1). The dorsal fur of A. minor sp. nov. is darker brown with less evident ochraceous highlights; fur behind the ear similar to adjacent fur (nearly white tuft absent); darkened “mask” on muzzle largely absent; ventral pelage pale brown rather than cream, often with white blaze on lower abdomen that rarely extends to below jaw; ears dark brown; tail dark brown dorsally, rather than medium brown ( Fig. 2D ). Skull of A. minor sp. nov. differs from A. crinitus in being smaller overall (e.g., BOL = 30.79 mm vs. 31.56 mm, HB = 122 mm vs. 128 mm), but with nearly equal orbito-temporal length, upper molar toothrow length, and M1 breadth, and greater labial breadth at M3 ( Table 4).

Distribution. Currently known from two localities at 140 m elevation on the lower slopes of Mt. Tallulah (survey area 4 in Fig. 1 ), and 700 m and 880 m on Mt. Mangibok (survey area 5 in Fig. 1 ; see Specimens Examined for details).

Ecology. We captured A. crinitus in seasonally deciduous forest over limestone at two localities, both at 140 m, that were nearby each other (see Specimens Examined); the number captured per 100 trap-nights at both localities was 0.51. All were captured at night, on the ground. The tallest trees reached 25–35 m, including Shorea , Ficus , Elaeocarpus , Artocarpus , Sterculia , and Mangifera ; wild bananas ( Musa ) and palms and other understory and ground plants were common. Thin (1–2 cm) layers of leaf litter and humus were present. The most abundant native small mammal was Chrotomys mindorensis ; Anonymomys mindorensis , Apomys microdon , and Rattus everetti gala were also present, and non-native Rattus tanezumi was common. Extensive sampling at 160 m and 180 m captured no A. crinitus .

At 700 m on Mt. Mangibok (survey area 5 in Fig. 1 ), we captured three A. crinitus in disturbed lowland forest over limestone, along the steep banks of a shallow river, surrounded by agricultural fields that were burned frequently. Trees reached 12–20 m in height, with genera typical of lowland forest over limestone. Understory and ground-cover plants were abundant. Leaf litter and humus layers were each 3–5 cm thick. Other native small mammals at this locality included Apomys musculus , Rattus everetti gala , and Rattus mindorensis , but the exotic pest rats Rattus exulans and R. tanezumi predominated. At 880 m, in twelve trap-nights, we captured one A. crinitus , along with one Apomys musculus and one Rattus tanezumi . We captured none in our nearby 930 m locality in 603 trap-nights, where non-native rats predominated (eight Rattus exulans , and seven R. tanezumi , plus four arboreal Apomys musculus ); the dominance of the non-native pest rats was associated with the heavily disturbed habitat.

Six male A. crinitus weighing 54–80 g had testes measuring from 5 x 4 to 8 x 5 mm. An adult female that weighed 60 g had two pairs of pigmented inguinal mammae.

Figures

FIGURE 1. A, Map of Mindoro Island showing topographic features and the locations of areas intensively surveyed by the authors. 1 = Mt. Calavite; 2 = Mt.Abra de Ilog; 3 = Mt. Halcon; 4 = Mt. Tallulah; 5 = Mt. Mangibok; 6 = Mt.Wood; 7 = Barangay Morente; 8 = Mt. Masulong; 9 = Sta. Teresa Hill and Mt.Alibug; 10 = Ilin Island. Apomys gracilirostris were captured in area 3; A. veluzi sp. nov. in area 2; A. crinitus sp. nov. in areas 4 and 5; and A. minor sp. nov. in areas 6 and 9. Members of the subgenus Megapomys were not detected in areas 1, 7, 8, and 10. B, Elevational ranges of the four species of Megapomys on Mindoro based on specimens reported here. For each species, black circles indicate elevations at which the given species was documented; open circles are elevations along the same transects where the relevant species was not documented; short horizontal lines indicate the maximum elevation along the given transect. For A. gracilirostris, open triangles indicate elevations at which Ruedas (1995) reported that species. Dark vertical lines connect localities along a single transect where the given species was documented.

FIGURE 2. Drawings of four species of Apomys (Megapomys) from Mindoro. A = A. gracilirostris (from study area 3 in Fig. 1), B = A. veluzi sp. nov. (from study area 2 in Fig. 1), C = A. crinitus sp. nov. (from study areas 4 and 5 in Fig. 1), D = A. minor sp. nov. (from study areas 6 and 9 in Fig. 1).

FIGURE 6. Photographs of the skulls of A Apomys crinitus sp. nov. (holotype, FMNH 222954) and B Apomys minor sp. nov. (holotype, FMNH 228798).