Carpomys dakal Ochoa & Mijares & Piper & Reyes & Heaney 2021, new species
Creators: name: Ochoa, Janine
name: Mijares, Armand S. B.
name: Piper, Philip J.
name: Reyes, Marian C.
name: Heaney, Lawrence R.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Muridae
Carpomys
Carpomys dakal

description: Carpomys dakal, new species
Figs. 3A, 3B, 4A, and 5A; Tables 1 and 2;
Supplementary Data SD1
Holotype.— PNM II-1977-J11A-16301, left dentary with incisor and m1–3; only a small portion of the dentary posterior to m3 is present (Figs. 3A and 3B). The m1–3 are lightly worn (Fig. 5A), indicating that the animal was a young adult at the time of death.
Type locality.— Minori Cave, Barangay Quibal, Peñablanca Municipality, Cagayan Province, Luzon Island, Philippines (Fig. 1), 200 m elevation, 17°43 ′ 17 ″ N, 121°49 ′ 42 ″ E, Chamber Dof Minori Cave, Square 27; derives from Holocene aceramic level 40–50 cm below cave surface.
Paratypes.— (n = 10; Supplementary Data SD1). Callao Cave: partial right dentary with m2 (PNM II-1977-J3-10196); partial left dentary with m1 (PNM II-1977-J3-10544); partial right maxillary with M2 (PNM II-1977-J3-11075/3); Minori Cave Chamber A: partial leftdentary with m1–2 (PNM II-1977- J11B-2986); Minori Cave Chamber D: partial left maxilla with M1–3 (PNM II-1977-J11A-15997); partial right maxilla with M1–2 (PNM II-1977-J11A-16447); partial left maxilla with M1–2 (PNM II-1977-J11A-16481); partial left maxilla with M1–2 (PNM II-1977-J11A-16825); partial right dentary with m2–3 (PNM II-1977-J11A-16951); Musang Cave: partial left dentary with m1–3 (PNM II-1976-M-101).
Age of specimens.— Callao Cave specimens 10544 and 10196 originated in a layer dated at least ca. 67,000 BP; specimen 11075 is from Layer 11 of Callao Cave, which is older than ca. 30,000 cal BP but younger than 52,000 BP; seven specimens from Minori Cave, including the holotype, are from aceramic Holocene levels (prior to the introduction of pottery on Luzon at 4,500 –4,000 cal BP); Musang Cave specimen 101 derives from aceramic-bearing level (Level I 3; Table 1).
Etymology.— The new species name comes from the languages of the Dupaningan Agta, Itawes, and Ibanag of NE Luzon, an adjective meaning “large” in all three languages (see Tharp and Natividad 1976; Greenhill et al. 2008; Robinson 2011); we use it as an adjective in the nominative singular neuter.
Distribution.— Known from three cave sites in the Callao Cave complex, Peñablanca Municipality, Cagayan Province (Fig. 1).
Diagnosis.— A member of the genus Carpomys as diagnosed by Musser and Heaney (1992) and as emended above (see Emended Diagnosis and Description and Comparisons); a giant species much larger than the two living species, Ca. melanurus and Ca. phaeurus (Table 2). The dentary is robust both absolutely and proportionately, with strongly marked inferior and superior masseteric ridges. Lower incisor is unusually wide, 2.3 mm at its midpoint. Upper toothrow length is 13.58 mm; lower toothrow length ranges from 13.25 to 13.46 mm. M1 length ranges from 4.49 to 5.49 mm; M1 width ranges from 3.42 to 4.41 mm. m1 length ranges from 5.93 to 6.57 mm; m1 width ranges from 3.37 to 4.53 mm (Table 2).
Description and comparisons.— A giant cloud rat, largest known member of Carpomys (Table 2; Fig. 6), easily distinguished from the two extant species by its much greater size. The dentary is both larger and proportionately more robust than in extant species, with strongly marked inferior and superior masseteric ridges. The mental foramen is moderately high relative to the apex of the masseteric ridges, situated close to the dorsal surface of the mandible and anterior to m1. The lower incisor, as represented on the holotype, is robust, orange-yellow on the anterior surface, 2.3 mm wide at its midpoint and 8.5 mm long from its tip to the point it meets the dentary bone along its medial edge. The dorsal wear surface extends fully to the beginning of the dentary bone slightly below the anteriormost projection of bone along the medial edge, and the tip lies slightly below the occlusal plane of the mandibular molars. The lower incisor of Ca. phaeurus also is orange-yellow on the anterior surface, but is both shorter and more slender, 1.0 mm wide at its midpoint and 5.0 mm (n = 2) from its tip to the anteriormost projection of bone along the medial edge. In this species, the dorsal wear surface extends from the tip about 90% of the way to the highest point of the dentary bone; the tip lies slightly below the occlusal plane of the mandibular molars, equivalent to Ca. dakal. The lower incisor of Ca. melanurus (n = 1) is 1.3 mm wide at the midpoint, and about 6.0 mm from its tip to the anteriormost projection of bone along the medial edge. Thus, the lower incisor of Ca. dakal is nearly twice the width of those of the two extant species.
Overall molar morphology follows that shown in Figs. 2A and 2B. Measurements of individual teeth are provided in Table 3. Molar dimensions of the two living Carpomys species comprise only 40–80% of corresponding measurements in Ca. dakal. Molar dimensions of Musseromys species are only 20–30% of the corresponding measurements in Ca. dakal. The variation in molar characters observed in Ca. dakal also is seen in Ca. melanurus and Ca. phaeurus; size is the main distinguishing character that differentiates the dental morphology of fossil species from the living species. Additional cusplets are often present in M1 and M2 of Carpomys (Fig. 4A; Supplementary Data SD1B and C): a labial cusplet between t3 and t6 of M1 and a smaller cusplet between t5 and t8 of M2, which are absent in other phloeomyine genera. The M1 cusplet is found in three out of five Ca. dakal specimens, compared to two out of five Ca. phaeurus specimens and none in three Ca. melanurus specimens. The M2 cusplet is present in one of five specimens of Ca. dakal and is absent in specimens of the two extant species.
Molar tooth dimensions of Ca. dakal are within the size range of the giant cloud rats Cr. schadenbergi and Cr. heaneyi, but compared to them, Ca. dakal has a more slender dentary (Fig. 3). The maxillary region is robust (Fig. 7); our fragmentary material implies that the palate is rather smooth with a raised ridge supporting the molar teeth, and a large posterior palatal foramen (ppf) adjacent to M2 (Fig. 7A), as seen in the two extant Carpomys species. No trace of the deep palatal grooves of Crateromys spp. is evident. It appears that the bony palate terminates about one-third of the way posterior to the anterior edge of M3, as in Ca. melanurus, rather than at the anterior edge of M3, as in Ca. phaeurus. The anterior root of the zygomatic arch appears to originate labial to M1 (Fig. 7B), similar to the extant species of Carpomys, and perhaps a bit further posterior than that of Cr. schadenbergi and Cr. ballik n. sp.
description: Published as part of 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), pp. 1-22 in Journal of Mammalogy 102 (2) on pages 10-12, DOI: 10.1093/jmammal/gyab023, http://zenodo.org/record/5613298