Archboldomys Musser, 1982

Balete, Danilo S., Rickart, Eric A., Heaney, Lawrence R., Alviola, Phillip A., Duya, Melizar V., Duya, Mariano Roy M., Sosa, Timothy & Jansa, Sharon A., 2012, Archboldomys (Muridae: Murinae) Reconsidered: A New Genus and Three New Species of Shrew Mice from Luzon Island, Philippines, American Museum Novitates 2012 (3754), pp. 1-60 : 23-32

Archboldomys Musser, 1982

TYPE SPECIES: Archboldomys luzonensis Musser, 1982a: 30 .

INCLUDED SPECIES: Only the type species and A. maximus , n. sp .

DISTRIBUTION: Known only from two mountains on Luzon Island: Mt. Isarog in southeastern Luzon and Mt. Amuyao in the Central Cordillera of northern Luzon (fig. 1).

Taxon DNA No. 1 Museum No. cytochrome b IRBP source 2 source 2

Archboldomys maximus EAR 6356 FMNH 193526 this study this study

Archboldomys maximus LRH 7572 FMNH 193522 this study this study Archboldomys maximus DSB 4436 FMNH 193528 this study

Archboldomys maximus DSB 4577 FMNH 193944 this study

Archboldomys luzonensis LRH 4098 USNM 573834 AY 6878583 DQ 1914954

Archboldomys luzonensis EAR 1982 USNM 573839 this study

Archboldomys luzonensis RBU 285 USNM 573836 this study

Archboldomys luzonensis EAR 1826 USNM 573835 AY 6878573 EU 3498375 Rhynchomys soricoides EAR 4978 FMNH 175618 this study

Rhynchomys soricoides LRH 6366 FMNH 169170 this study

Rhynchomys soricoides LRH 5959 FMNH 167320 this study

Rhynchomys tapulao DSB 3505 FMNH 183555 this study

Rhynchomys tapulao DSB 3480 FMNH 183554 this study

Rhynchomys isarogensis LRH 4157 USNM 573577 this study

Rhynchomys isarogensis EAR 1833 USNM 573900 DQ 1914894 AY 3261084

Rhynchomys banahao LRH 7020 FMNH 178429 this study

Chrotomys gonzalesi EAR 1850 USNM 458953 DQ 1915034

Chrotomys gonzalesi LRH 4176 USNM 458952 AY 3244616

Chrotomys sibuyanensis SMG 5150 FMNH 145701 AY 6878623 DQ 1915044

Chrotomys whiteheadi LRH 7523 FMNH 193960 this study

Chrotomys whiteheadi LRH 7515 FMNH 193737 this study

Chrotomys whiteheadi LRH 7533 FMNH 193962 this study this study

Chrotomys whiteheadi LRH 7424 FMNH 188360 this study

Chrotomys whiteheadi DSB 4499 FMNH 193748 this study

Chrotomys whiteheadi LRH 6841 FMNH 175575 this study

Chrotomys whiteheadi LRH 7406 FMNH 188458 this study

Chrotomys mindorensis DSB 3558 FMNH 183551 this study

Chrotomys mindorensis DSB 3520 FMNH 183549 this study

Chrotomys mindorensis JAE 543 KU 164432 this study this study

Chrotomys mindorensis JAE 526 KU 164431 this study

Chrotomys mindorensis JAE 520 KU 164430 this study

Chrotomys silaceus EAR 6365 FMNH 193714 this study

Chrotomys silaceus DSB 4587 FMNH 193734 this study

Chrotomys silaceus LRH 6784 FMNH 175723 this study this study Chrotomys silaceus EAR 4614 FMNH 169132 this study

Soricomys montanus DSB 4570 FMNH 193521 this study this study

EMENDED DIAGNOSIS: The genus Archboldomys is defined phylogenetically as the most recent common ancestor of A. luzonensis and A. maximus and all of its descendants (figs. 7, 8). They are small-bodied shrew mice most similar superficially to Soricomys , new genus, but differ from it and other known murids in the combination of the following cranial and dental features (table 11): (1) uniformly dark and unpatterned pelage; (2) tail substantially or slightly shorter than the length of head and body; (3) moderately long, tapered rostrum; (4) upturned nasal tips projecting slightly beyond the anterior margins of the premaxillae; (5) slanting anterior edge of zygomatic plate relative to horizontal molar row; (6) long and slender tympanic hook; (7) spacious squa-

moso-mastoid vacuity; (8) mastoid entire or without fenestra in adults; (9) ophistodont upper incisor procumbency; (10) upper incisors forming an acute triangle at their posterior margin in ventral view (fig. 9); (11) broad molariform tooth row with prominent cusps

(figs. 10, 11); (12) squarish first upper molars

(figs. 10, 11); and (13) small but conspicuous interpremaxillary foramen present (fig. 9).

COMMENTS: Archboldomys and Crunomys :

Musser (1982a) noted the similarity of Archboldomys to Crunomys , specifically C. melanius and C. celebensis , and hinted at a possibly close phylogenetic relationship, based in particular on the shape, simplified cuspidation, and FIG. 11. Upper molar rows of A, Archboldomys occlusal patterns of their molars. He proposed luzonensis (FMNH 95122, holotype); B, Soricomys mussseri (FMNH 147176, holotype); and C, S. the hypothesis that “the old native rodents of kalinga (FMNH 175555, holotype). Modified from the Philippine Islands may represent an adap- Balete et al. (2006).

tive radiation in which all members are more closely related to each other than to rats and mice on the Asian mainland to the west, Sulawesi and the Lesser Sundas to the south, or to Australia and New Guinea area to the east.” In spite of including one species from Sulawesi ( C. celebensis ), Crunomys was grouped with Archboldomys , Chrotomys , Celaenomys (now part of Chrotomys ; Rickart et al., 2005), and Rhynchomys . This was further reinforced in the first assessment of phylogenetic alliances of the native Philippine murid fauna ( Musser and Heaney, 1992), in which the Crunomys Group was erected within the Old Endemic Division (Division I), consisting of A. luzonensis , Crunomys fallax , C. melanius , and C. rabori (now part of C. melanius ; see Rickart et al., 1998).

Genus

Feature Apomys Archboldomys Chrotomys Rhynchomys Soricomys

Color pattern absent (except absent mid-dorsal stripe (only fore- absent (except dorsal- absent (except dorsal-ventral dorsal-ventral head blaze or shoulder ventral countershading) countershading) countershading) stripe in some C. silaceus )

Tail length relative to slightly shorter to shorter to slightly shorter shorter shorter to slightly longer head and body longer longer length

Nasal tip extension along edge beyond edge behind edge beyond edge along edge relative to anterior margin of premaxil-

lary

Incisive foramina long and broad long and narrow short and broad long and narrow short and broad

Interpremaxillary minute short and narrow long and wide long and narrow minute foramen

Orientation of zygo- slanting slanting vertical slanting vertical matic plate

M1 relative to ven- overlap up to first overlap up to 2nd no overlap complete overlap overlap up to first row tral maxillary root of row row zygomatic plate

Maxillary molar complete complete complete (M3 absent in M3 absent complete tooth row composi- C. silaceus )

tion

Maxillary molar long and narrow long and broad short and narrow short and narrow long and narrow tooth row shape

M1 and M2 shape long and narrow short and broad short and narrow short and narrow long and narrow

The discovery of Crunomys suncoides on Mt. Kitanglad (central Mindanao) and Soricomys musseri (as Archboldomys musseri ) on Mt. Cetaceo (NE Luzon) enabled further assessment of the hypothesized Archboldomys - Crunomys phylogenetic alliance and redefinition of both genera ( Rickart et al., 1998). However, no shared derived morphological traits were found that unite Archboldomy and Crunomys as a distinct clade; the presumed synapomorphies in the shape, size, and simplified cuspidation patterns of molars of the two genera were inferred to have resulted from convergence on shrewlike feeding habits ( Rickart et al., 1998). The karyotypic differences between Archboldomys and Crunomys (table 7; Rickart and Heaney, 2002), as well as additional cranial, dental, and external morphological differences, reinforced the hypothesized close phylogenetic link among Archboldomys , Chrotomys , and Rhynchomys , but were unsupportive of their sister-taxon relationship with Crunomys ( Rickart and Musser, 1993; Rickart et al., 1998). The split between Archboldomys and Crunomys was later strongly supported by molecular data, indicating that A. luzonensis is closest to the members of the Chrotomys Division that includes Rhynchomys , Chrotomys , and Apomys ( Jansa et al., 2006) . Crunomys (represented by C. melanius ), on the other hand, was recovered as sister taxon to Maxomys , within the clade that includes the Philippine native murid rodents belonging to the New Endemic Division, along with allied species from the Sunda Shelf ( Musser and Heaney, 1992; Jansa et al., 2006). FIG. 12. A, Archboldomys maximus (FMNH 193525), Comparison of Archboldomys and Soricoadult female. Photographed by L.R. Heaney, 1 March 2007. B, Soricomys montanus (FMNH 193514), adult mys, new genus: Aside from A. luzonensis , male. Photographed by J.F. Barcelona, 28 February shrew mice previously attributed to Archbold- 2007. C, Soricomys leonardocoi (FMNH 190962), omys included S. musseri (as A. musseri ) and adult male. Photographed by M.R.M. Duya, 29 May S. kalinga (as A. kalinga ), from Mt. Cetaceo in 2006. the Sierra Madre, and the vicinity of Mt. Bali-

it in Kalinga Province, in the northern Central Cordillera , respectively (fig. 1; Musser,

1982a; Rickart et al., 1998; Balete et al., 2006).

Some additional specimens from the southern Central Cordillera were referred to “ A. ”

kalinga ( Heaney et al., 2010; Rickart et al.,

2011b). They were discussed within the context of broadening morphological and geo-

graphical ranges of the genus Archboldomys ,

but a suite of diagnostic features that set apart the two species groups (i.e., A. luzonensis vs.

the other two) was highlighted in the description of the latter two species (see the diagnosis of Soricomys ; Rickart et al., 1998; Balete et al., 2006). We confirmed the consistency of the differences with the collection of a large,

short-tailed species in the Central Cordillera

( A. maximus , n. sp.) that occurred sympatrically with the small, relatively long-tailed S.

montanus, n. sp., on Mt. Amuyao (fig. 1).

These discoveries clearly indicated the presence of two species groups of shrew mice on

Luzon, consisting of a relatively larger-bod-

ied, short-tailed group composed of A. luzonensis and A. maximus , n. sp., from Mt.

Amuyao, and a smaller-bodied, relatively longer-tailed group composed of S. kalinga , S.

FIG. 13. Cranium and mandible of Archboldomys musseri , S. leonardocoi , n. sp., and S. monta- maximus , adult male (FMNH 193531, holotype) in nus, n. sp. (fig. 12). The two groups are sepa- dorsal, ventral, and lateral views.

rated by distinct and consistent differences in external, cranial, and dental features; among the most prominent differences (for Archboldomys vs. Soricomys ) are longer incisive foramina (vs. shorter); small but apparent interpremaxillary foramena (vs. absent, with only tiny nutrient foramina present); zygomatic plate slanting (vs. nearly perpendicular to molar row); M1 and M2 short and broad (vs. long and narrow); upper incisors slightly [ A. luzonensis ] to strongly [ A. maximus , n. sp.] ophistodont (vs. orthodont); upper incisors forming an acute angle at posterior tips in ventral view (vs. broadly rounded; fig. 9); and tympanic hook long and narrow (vs. short and broad; figs. 3, 10, 13; tables 1–5, 11). Both Archboldomys and Soricomys , n. gen., have the carotid arterial pattern in which a large stapedial artery branches off from the common carotid artery and enters the otic capsule through the stapedial foramen, passes through the bulla, and then passes through a groove in the pterygoid plate into the foramen ovale (see Musser, 1982a: figs. 30, 31).

This distinction between Archboldomys and Soricomys is also supported by the karyotypic data showing substantial differentiation between Archboldomys and Soricomys , new genus, especially in diploid number and X-chromosome morphology (table 7; fig. 5; Rickart and Heaney, 2002). Our phylogenetic analyses of molecular data from representatives of these species and other members of the Chrotomys Division ( Apomys , Chrotomys , and Rhynchomys ) not only supported the above morphological and karyological differentiation between the two groups, it also failed to recover the monophyly of Archboldomys . Instead, it showed that the small-bodied members ( Soricomys , n. gen.) are the sister taxon to Chrotomys , and the largebodied members ( Archboldomys sensu stricto) are sister to the clade that includes Soricomys , Chrotomys , and Rhynchomys (figs. 7, 8). This evidence clearly supports the establishment of a new genus, Soricomys , that accommodates two shrew mice formerly attributed to Archboldomys ( S. kalinga and S. musseri ), and two additional new species, as described below.