Batomys sp.

Ochoa, Janine, Mijares, Armand S. B., Piper, Philip J., Reyes, Marian C. & Heaney, Lawrence R., 2021, Three new extinct species from the endemic Philippine cloud rat radiation (Rodentia, Muridae, Phloeomyini), Journal of Mammalogy 102 (2), pp. 1-22 : 15-17

Batomys sp. Heaney et al. 2011:236

Figs. 5G , 9A, 9B , and 11 ; Tables 1 and 3

Holotype.— PNM II-1977-J3-7554 , a partial right dentary with m1–3 present ( Figs. 11A and 11B ); the incisor and most surrounding bone, and all portions posterior to m3, are absent. m1–3 ( Fig. 5G ) are moderately worn, indicating that the animal was an adult at the time of death.

Type locality.— Callao Cave , Peñablanca Municipality, Cagayan Province, Luzon Island, Philippines ( Fig. 1 ), 17°42 ′ 11.7 ″ N, 121°49 ′ 25.5 ″ E, Square 2, Layer 14 (2.45 m below surface).

Paratype.— PNM II-1977-J3-7573 , a partial left dentary with m1–2 and incisor. The entire anterior portion of the dentary is present except for a thin layer of bone that lies anterior to the base of the incisor (figure 1A in Heaney et al. 2011). The dentary is broken diagonally from the area lateral to the missing m3 to the anterior base of the angular process; the posterior portion of the dentary is absent. m1 and m2 are present and in good condition; they are lightly worn, indicating that the animal was an adult at the time of death. m3 is absent, but its alveoli are present .

Age of specimens.— Specimens 7554 and 7573 derive from the Late Pleistocene levels of Callao Cave dated at least ca. 66,700 BP ( Table 1 ).

Distribution.— Known only from the two specimens from Callao Cave ( Fig. 1 ).

Etymology.— The new species is named for the Cagayan River Valley, in which lies the cave complex that has produced the known specimens, combined with the Latin “- ensis,” meaning “from.”

Diagnosis.— A member of the genus Batomys as diagnosed and defined by Musser and Heaney (1992) and Musser et al. (1998). Largest species of Batomys , with robust dentary. Lower incisor broad, 1.5 mm at midpoint. Lower toothrow length is 10.22 mm. m1 length ranges from 4.05 to 4.3 mm; m1 width ranges from 2.27 to 2.88 mm ( Table 3 ). Metaconid–protoconid laminae in m1–3 are less strongly arched than hypoconid– entoconid laminae. Posterior cingula on m1 and m2 are large, cordate, and somewhat elongate ( Fig. 5G ).

Description and comparisons.— The largest known member of the genus Batomys ; overall dental terminology follows that shown in Figs. 2C and 2D . Measurements of individual teeth are provided in Table 3 . Molar and dentary depth measurements of B. cagayanensis are greater than those of the three species from Luzon ( B. dentatus , B. granti , and B. uragon ), including comparisons for individuals with heavily worn teeth ( Fig. 9 ). The dentary is robust, with a large mental foramen and deep masseteric fossa ( Fig. 11A ); within the Philippines, only Phloeomyini have equally robust dentaries. In B. granti , the anteroconid is nearly connected by a structure with the anterior side of the protoconid; this structure is present in one of our two B. cagayanensis but is less elongate than in B. granti . In comparison with B. dentatus , posterior cingula on m1 and m2 are larger and more cordate (compare Fig. 5G with figure 21 in Musser et al. 1998). The lower incisor of B. cagayanensis (figure 1 in Heaney et al. 2011) is broad, with width at the midpoint of 1.5 mm, and from the tip to the anteriormost projection of bone along the medial edge at the alveolus is 4.7 mm. The dorsal wear surface of the incisor extends nearly to the base of the dentary bone, with the tip ending well above the occlusal plane of the lower molars. The lower incisor of B. granti is narrower and longer, with width at the midpoint of 1.2 mm, and from the tip to the anteriormost projection of bone along the medial edge is 5.9 mm (n = 8 adults). The dorsal wear surface of the incisor extends about 1.5 mm above the base of the dentary bone, with the tip ending at or near the occlusal plane of the lower molars. Batomys uragon has lower incisors that are very similar, 1.2 mm in width and 4.8 mm in length along the medial edge (n = 2). Batomys dentatus also have narrower incisors than B. cagayanensis , only slightly wider than those of B. granti ( Heaney et al. 2011) .

Like Crateromys and other species of Batomys , B. cagayanensis has mandibular molars in which there is a large anteroconid comprising an anterocentral cusp fused with anterolabial and anterolingual cusps, which forms the anterior third of the tooth ( Fig. 5G ). On m3, the metaconid–protoconid lamina is strongly arched with a deep cleft posterior to the central connection between the metaconid and protoconid centers, similar to the morphology of Crateromys ( Figs. 5D–F ) but differing from Carpomys in which this lamina is gently and smoothly arched and the cleft is shallower ( Figs. 5A and 5B ). The lower molars of B. cagayanensis are high-crowned, but less so than in Crateromys , and they lack the small but distinct m3 posterior cingulum that is present on some specimens of Crateromys . The m3 hypoconid and entoconid are fused into a round loph ( Fig. 5G ), whereas this loph is chevronate in the Luzon Crateromys ( Figs. 5A and 5B ). Although the dentary of B. cagayanensis is robust relative to most murids, it is less robust as well as smaller than in all Crateromys , including even the smallest known species of the genus, Cr. paulus ( Figs. 9A and 9B ; Musser and Heaney 1992; Heaney et al. 2011; Reyes et al. 2017).

Luzon members of Rattini ( Abditomys , Bullimus , Rattus everetti , and Tryphomys —Musser and Heaney 1992) have dentaries somewhat less robust. Tryphomys is smaller overall, but Abditomys is larger. In Batomys , the anterolingual cusp is large, the laminae that comprise the molars are distinct and more strongly inclined than in Luzon Rattini , and the posterior cingulum of m1 and m2 is large ( Fig. 5G ); those of Abditomys and Tryphomys are, respectively, smaller, less distinct and less slanted anteriorly. Bullimus and R. everetti have lower-crowned mandibular molars than Batomys , with laminae that are gently arched and composed of more extensively fused cusps; they have a well-defined labial cusplet on m1 and m2, and their molars are smaller (Musser and Heaney 1992; Heaney et al. 2011).

Figures

Fig. 5.—Occlusal view of mandibular molars of (A) Carpomys dakal n. sp. (PNM II-1977-J11A-16301, holotype), leftside; (B) Carpomys phaeurus (FMNH62291),leftside;(C) Musseromysinopinatus (FMNH 193840), left side; (D) Crateromys ballik n. sp. (PNM II-1977-I8-402, holotype), right side (mirrored); (E) Crateromys schadenbergi (FMNH 62291), left side; (F) Crateromys heaneyi (CMC M626), left side; (G) Batomys cagayanensis n. sp. (PNM II-1977-J3-7554, holotype), right side (mirrored); (H) Batomys granti (FMNH 214412), left side.

Fig. 9.—Bivariate plots of Crateromys and Batomys dental and mandibular measurements (in mm). Data are in Table 3.

Fig. 11.—Holotype of Batomys cagayanensis n. sp. (PNM II-1977-J3-7554), right dentary: (A) labial view of mandible (mirrored); (B) lingual view of mandible.

Fig. 1.—Map of the Callao Cave Complex, showing location of cave sites: Callao (1), Eme (2), Dalan Serkot (3), Minori (4), and Musang (5). Inset shows the location within Luzon Island.

Fig. 2.—Maxillary and mandibular left molar toothrows of Carpomys dakal n. sp. (A and B, respectively; PNM II-1977-J11A-15997 and PNM II-1976-M-101) and Crateromys schadenbergi (C and D, respectively; FMNH 62295), showing the location of cusps and conids referred to in the text. pc = posterior cingulum.