PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3517, 41 pp., 14 figures, 4 tables May 17, 2006

Description of a New Genus and Species of (, , Rodentia) from the Tower Karst Region of Northeastern Vietnam

GUY G. MUSSER,1 DARRIN P. LUNDE,2 AND NGUYEN TRUONG SON3

ABSTRACT Tonkinomys daovantieni, a new genus and species of murid rodent in the Dacnomys Division, is described. It is represented by 14 adults collected from talus habitats in the forested tower karst landscape of the Huu Lien Nature Reserve of northeastern Vietnam. The combination of semispinous, dense, grayish black fur covering upperparts; a dark gray venter; gray ears; a thick, bicolored tail considerably shorter than length of head and body; and large, extremely bulbous footpads is unlike any other species of Indomalayan murid. Body size and build of the new rat, along with some cranial features, are similar to the Thai neilli, but other cranial traits coupled with molar occlusal patterns resemble morphology in species of the Indomalayan , Chiromyscus, and . The new species is petricolous, includes insects in its diet, and was found only in talus composed of large limestone blocks. Its distribution in the reserve is likely patchy. Whether this is restricted to the extensive karst regions of northeastern Vietnam or also occurs in southern China and elsewhere in the northern karst landscapes of Indochina, and Vietnam in particular, will be known only by conducting surveys in limestone regions outside of northeastern Vietnam.

INTRODUCTION deformation and uplift, and spurred by sub- sequent erosional processes, transformed During Paleozoic times, a succession of those ancient tidal flows and marine land- waterways covered what is now northern scapes into a spectacular terrestrial topogra- Vietnam. Lithification, followed by tectonic phy of tower karst riddled by fissures and

1 Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History. Current address: 1714 Henley Lane, Charleston, SC 29412 ([email protected]). 2 Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History ([email protected]). 3 Department of Zoology, Institute of Ecology and Biological Resources, 18 Hoang Quoc Viet Road, Cau Giay, Hanoi, Vietnam ([email protected]).

Copyright E American Museum of Natural History 2006 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3517

Fig. 1. Tower karst landscape where we captured our series of Tonkinomys daovantieni within the Huu Lien Nature Reserve. Tropical moist deciduous forest covers the steep slopes, but the valley bottom has been cleared for agriculture. Photographed by D. P. Lunde, April 2004. honeycombed with caverns. Beautiful cycad in mind we made special efforts to set a portion rosettes secured high on sheer limestone cliffs, of our traps on tree limbs, woody vines and a forest cover in which many of the looping through the understory, and on high components are adapted to karstic habitats, limestone ledges. At one place, chunks of are the living botanical link to those ancient limestone had long ago fallen from two high seas. A dark gray rat, its fur coloration forested towers, filling the space between them indistinguishable from the limestone, its lair with huge blocks, their surfaces now partially concealed deep within fissured cliffs and covered with tropical vegetation, and riddled limestone talus, is the zoological connection. beneath with tunnels and fissures detectable at We discovered this limestone rat during the surface only by small scattered openings a survey (April, 2004) of small in (fig. 2). We set traps on top of this block pile, a forested tower karst region that forms much and also tied traps to lengths of rope and of Lang Son Province in northeastern Vietnam carefully lowered them through the openings (Głazek, 1966; Tuyet, 1998) (fig. 1). Our intent to the bottom, to depths of at least 8 m. was to sample, using a variety of traps and Unsure if we would catch anything different other techniques, as many native species as from the common rats already encountered in possible. Our past field experience in nearby different habitats—Niviventer fulves- Indochina had taught us that setting traps cens, N. langbianis, and andamanen- on the ground in regular lines would quickly sis—we were very pleased, and somewhat sample the generalists of the more common surprised, to capture a dark gray rat on top terrestrial habitats but not those specialized of the rubble and two from deep within the for life on substrates above the forest floor or labyrinth. Additional individuals were cap- in unusual petricolic environments. With this tured during the days that followed. 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 3

Fig. 2. Habitat where we trapped 13 of the 14 examples of Tonkinomys daovantieni showing large blocks of limestone overgrown with creeping vines (left) and a portion of the steep slopes of an adjacent karst tower (right). Our trail to the site is visible between these two structures. Photographed by D. P. Lunde, April 2004.

We knew nothing like this had ever Srilankamys; and the recently described been caught in Vietnam or elsewhere in Laotian Saxatilomys (Musser et al., 2005). Southeast Asia. Except for their fur coloration We also contrast Tonkinomys with members of and short tails, the rats resembled species of the Dacnomys Division represented by fossils Leopoldamys, but no member of that genus recovered from Indochinese Plio-Pleistocene has dark gray fur and a tail shorter than head sediments: extinct species of Leopoldamys and body. Those two attributes also pointed and Niviventer, and the extinct genera to Berylmys, but none of them have dark gray Wushanomys and Qianomys. Of these, the underparts. We knew our sample of the new rat requires close and careful compari- limestone rat represented an undescribed sons only with Leopoldamys, Niviventer, species, but only after study in the museum Chiromyscus, Saxatilomys and the Plio- did we confirm our suspicion that it could not Pleistocene Wushanomys and Qianomys. be placed in any named genus. Descriptions of new taxa, and in particular Here we describe the limestone rat as a new those occurring in gradually diminishing genus and species, and summarize our limited tropical forest refuges, should be published observations about its natural history. We as soon as possible. Phylogenetic inquiries focus on describing the animal and comparing take time—incorporating the new rat into it to murines with which it is morphologically phylogenetic analyses employing samples of most similar, members of a cluster containing all native Indochinese murines will be the genera that Musser and Carleton (2005) refer subject of a future report. to as the Dacnomys Division: extant species of Our discovery joins those of several other the Indomalayan Chiromyscus, Dacnomys, small-bodied mammals living in Indochina Leopoldamys, and Niviventer; the Sri Lankan that have been discovered and described, with 4 AMERICAN MUSEUM NOVITATES NO. 3517 little fanfare, during the past five years: two under a second number in addition to its shrews, Chodsigoa caovansunga and Crocidura departmental catalog number. Some fluid-pre- kegoensis (Lunde et al., 2003, 2004); three served specimens and accompanying skulls will bats, Hipposideros scutinares (Robinson et al., be retained at AMNH; others will be returned 2003), Rhinolophus stheno microglobosus to the Department of Zoology at the Institute (Csorba and Jenkins, 1998) and Myotis of Ecology and Biological Resources in Hanoi. annamiticus (Kruskop and Tsytsulina, 2001); Comparative material we consulted, pri- and a rabbit, Nesolagus timminsi (Averianov et marily samples of Leopoldamys, Niviventer, al., 2000; Can et al., 2001). These can be added Chiromyscus, and Saxatilomys, are in collec- to an assemblage of large mammals occurring tions at AMNH; the Field Museum, Chicago; in Vietnam, and some in nearby Laos, named and the National Museum of Natural History, and described as new within the last decade or Washington, DC. so, but with attendant worldwide publicity: Values (in millimeters, mm) for total length, two primates, Trachypithecus ebenus and length of tail (LT), length of hind foot, Pygathrix cinerea (summarized in Groves, including claw (LHF), and length of ear from 2001); three muntjacs, Muntiacus truongsonen- intertragal notch to crown (LE) are those we sis, M. vuquangensis, and M. puhoatensis (see obtained in the field and recorded in our field reviews in Amato et al., 2000; Groves and journals. Values for length of head and body Schaller, 2000; Grubb, 2005); and the saola, (LHB) were determined by subtracting length Pseudoryx nghetinhensis (see review and refer- of tail from total length. Weights were obtained ences in Groves and Schaller, 2000).4 All are in the field with a Pesola spring scale (300-gram a testimony to the significant results derived capacity). The distal portion of the tail is white from past biodiversity surveys, discoveries (unpigmented) in all specimens of the limestone that provide compelling stimulus for zoolo- rat. We measured the length of this white tip on gists to continue detecting the real diversity of the dorsal surface of each tail and calculated it small mammals in Vietnam. as a percentage of total tail length. Values for cranial and dental measurements were obtained MATERIALS AND METHODS by Lunde using digital calipers accurate to the nearest 0.01 mm; however, values were round- All 14 examples of the new rat were fixed in ed to the nearest 0.1 mm. The following cranial 10% formalin in the field and subsequently and dental dimensions (listed in the sequence transferred to 70% ethanol for storage. Liver they appear in tables) were measured; their samples were collected prior to fixation and limits are illustrated in figure 3 and defined in placed in lysis buffer in the field, and later Musser and Newcomb (1983). stored in liquid nitrogen at the American ONL occipitonasal length (5 greatest Museum of Natural History (AMNH). Skulls length of skull) were subsequently removed from 10 of 13 ZB zygomatic breadth specimens (one of the 14 preserved is repre- IB interorbital breadth sented by only an ear with a bit of fur-covered LR length of rostrum skin attached, the only remnant left in the trap BR breadth of rostrum by a hungry predator) and cleaned by a der- BBC breadth of braincase mestid colony, American Museum. The ele- HBC height of braincase ments of each specimen are identified by BZP breadth of zygomatic plate a catalog number in the Department of LD length of diastema Mammalogy, AMNH. Each liver sample was LIF length of incisive foramina BIF breadth of incisive foramina transferred to the American Museum Cryo LBP length of bony palate (palatal bridge) Collection (AMCC), where it is registered BBP breadth across bony palate at first

4 molars Viverra tainguensis, another supposed newly discovered PPL postpalatal length species living in Vietnam, was described by Sokolov et al. (1997). Its specific integrity, however, was questioned by BMF breadth of mesopterygoid fossa Walston and Veron (2001), and the name is currently LB length of bulla included in the synonymy of the large Indian civet, Viverra CLM1-3 crown length of maxillary molar row zibetha (Wozencraft, 2005). BM1 breadth of first upper molar 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 5

Fig. 3. Views of cranium and molars of an adult Bunomys chrysocomus showing limits of cranial and dental measurements. See text for abbreviations and additional information. 6 AMERICAN MUSEUM NOVITATES NO. 3517

Old adults, adults, and young adults (as occiput; (8) squamosal root of each zygomatic defined by Musser and Heaney, 1992: 5) were arch situated high on side of cranium where its lumped as ‘‘adults’’ and measurements derived posterior ridge-like portion runs horizontally from them were used to calculate standard just below posteroventral margin of the descriptive statistics (mean, standard devia- parietal and projects ventrad to form dorso- tion, and observed range). Small sample size lateral side of cranium; (9) lateral cranial wall dictated that we combine sexes in the analyses. intact anterior to occiput, without large Anatomical terminology follows Brown (1971) subsquamosal foramen; (10) narrow alisphe- and Brown and Yalden (1973) for external noid struts in most specimens; (11) wide and features of the head and limbs; Bugge (1970) moderately long incisive foramina, their pos- for the cephalic arteries; Wahlert (1985) for terior borders located just before anterior the cranial foramina; and Carleton (1980), margins of molar rows, even with them, or Carleton and Musser (1984), Musser and penetrating slightly between; (12) posteriorly Durden (2002), Musser and Heaney (1992), divergent maxillary molar rows; (13) wide and Musser et al. (1998), and Voss (1988) for long bony palate projecting beyond molars cranial morphology. Names of cusps and to form a wide platform; (14) moderately cusplets of upper and lower molars are noted spacious sphenopalatine vacuities; (15) wide in figure 13; sources of this terminology are and shallowly excavated pterygoid fossae; explained by Musser and Newcomb (1983: (16) small ectotympanic bulla relative to skull 332). size, incompletely covering periotic so that dorsal and slanting posterodorsal wall of SYSTEMATIC DESCRIPTION OF THE carotid canal formed by periotic and not NEW GENUS AND SPECIES ectotympanic; (17) large foramen for stapedial artery, no sphenofrontal foramen or squamo- Tonkinomys, new genus soalisphenoid groove, indicating the widespread TYPE SPECIES: Tonkinomys daovantieni, the murine cephalic arterial pattern; (18) coronoid new species described below. process of dentary small, condyloid and angular DIAGNOSIS: A genus of Muridae in the processes joined by shallow concave posterior Dacnomys Division (Musser and Carleton, margin of dentary, and alveolar incisor 2005) of the subfamily Murinae (as delimited capsule only slightly evident on lateral surface by Carleton and Musser, 1984) that is set of dentary; (19) upper incisors opisthodont apart from all other described murid genera by relative to rostrum; (20) first upper molar with the following combination of morphological four large roots (anterior, two lingual, and traits: (1) fur covering head and body semi- posterior), second and third molars each with spinous and grayish black, spattered with three roots (anterior, lingual, and posterior); a white blaze on forehead in most individuals, (21) each lower molar with two roots; underparts dark gray with white patch on the (22) molars brachydont, with cusp rows form- chest, ears gray, rhinarium and lips and chin ing uncomplicated occlusal patterns resembling unpigmented; (2) mystacial and superciliary those in species of Niviventer, Chiromyscus,and vibrissae very long; (3) dorsal surfaces of front Saxatilomys. feet white, hind feet white with brown hairs on ETYMOLOGY:FromTonkin, used during metatarsal region; (4) tail much shorter than the French colonial period (1883–1954) for length of head and body, thick and round in the protectorate occupying the northern third cross-section and well-haired, the proximal of Vietnam, and the Greek mys, referring to one-half to three-fourths of its dorsal and mouse, or rat in this case. Although most lateral surfaces dark brown, the distal one- often negatively associated with Vietnam’s fourth to one-half white (unpigmented); dark French administration, the name (5) palmar and plantar pads large, swollen, Tonkin has an illustrious origin. It is derived and set close together; (6) four pairs of teats; from the Vietnamese Don Kinh, which means (7) robust skull with moderately long and wide ‘‘eastern capital’’, and was the name given to rostrum, prominent postorbital and temporal what is now Hanoi by Emperor Le Loi who, ridges, sturdy zygomatic arches, and deep in 1427, along with his band of Vietnamese 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 7

TABLE 1 Summary Statistics for Cranial and Dental Measurements (mm) and Weight (m) of Tonkinomys daovantieni from Vietnam (Mean, plus or minus one SD, observed range in parentheses, and number of specimens in each sample are listed for each measurement. Sample contains both sexes and a range in age from young to old adults. Individuals measured and weighed are identified in the footnote.)

Holotypea Sample (with holotype)b

Length of head and body 213 204.6 6 10.34 (184–217) 13 Length of tail 177 169 6 7.0 (156–183) 13 Length of hind foot 40 39.0 6 1.1 (37–41) 13 Length of ear 30 30.0 6 0.8 (29–31) 14 Weight 160 171 6 22.8 (140–205) 13 Occipitonasal length 51.2 50.0 6 1.6 (47.1–52.4) 7 Zygomatic breadth 21.6 21.3 6 0.2 (20.9–21.6) 7 Interorbital breadth 6.7 6.9 6 0.2 (6.6–7.3) 7 Length of rostrum 17.7 17.1 6 0.6 (15.9–17.7) 7 Breadth of rostrum 7.7 7.8 6 0.4 (7.1–8.5) 7 Breadth of braincase 17.7 17.7 6 0.2 (17.4–18.1) 7 Height of braincase 11.7 11.8 6 0.2 (11.4–12.0) 7 Breadth of zygomatic plate 4.9 4.8 6 0.1 (4.7–5.0) 7 Length of diastema 13.3 13.6 6 0.5 (12.9–14.6) 7 Length of incisive foramina 9.1 9.5 6 0.5 (8.9–10.2) 7 Breadth of incisive foramina 3.4 3.5 6 0.2 (3.4–3.9) 7 Length of bony palate 10.7 10.5 6 0.3 (10.0–10.7) 7 Breadth across bony palate at M1 9.6 9.6 6 0.1 (9.5–9.8) 7 Postpalatal length 16.2 15.7 6 0.6 (14.6–16.4) 7 Breadth of mesopterygoid fossa 3.9 3.8 6 0.2 (3.5–3.9) 7 Length of bulla 6.2 6.3 6 0.1 (6.2–6.5) 7 Crown length of M1-3 8.3 8.3 6 0.2 (8.0–8.8) 7 Breadth of first upper molar 2.1 2.1 6 0.1 (2.0–2.2) 7 a AMNH 275618. b AMNH 275575-275577, 275586, 275593, 275602, 275618, 275627, 275644, 275688, 275692, 275711, and 275712. rebels, expelled from Vietnam the repressive American Museum Cryo Collection (AMCC Ming occupiers. By the early 1800s, the capital 125060). The skull (figs. 10, 11) was later was moved to Hue, and the Emperor Minh extracted and cleaned by dermestids in a colony Mang renamed the ‘‘eastern capital’’ Hanoi, at the American Museum. meaning ‘‘this side of the river’’. REFERRED MATERIAL:Inadditiontothe holotype, 13 additional adults of T. daovantieni were collected from the vicinity of Laˆn Ða˘t Tonkinomys daovantieni, new species Village during April, 2004, on the days in- HOLOTYPE: AMNH 275618, an adult fe- dicated (AMCC catalog numbers tied to liver male collected by the authors (DPL 1706) on 17 samples are in brackets). April 13:AMNH April, 2004, in the vicinity of Laˆn Ða˘t Village 275575 [125016], male; 275576 [125017], male; , (21u409520W/106u209280E), 150 m, Huu˜ Lieˆn 275577 [125018], male. April 14:275586 Nature Reserve, Hu,u˜ Lieˆn Commune, Hu,u˜ [125027], female; 275593 [125034], male. April Lun˜g District, Lang So,n Province, Vietnam. 16: 275602 [125044], male. April 19:275627 The specimen was fixed in 10% formalin for [125069], male; 275644 [125086], male. April 23: several days before being transferred to 70% 275688 [125130], male. April 24:275692 ethanol for storage. A liver sample was [125134], male; 275693 [125135], ear with collected prior to fixation and placed in lysis attached bit of furry skin only. April 25: buffer before its ultimate transfer to the 275711 [125153], male; 275712 [125154], female. 8 AMERICAN MUSEUM NOVITATES NO. 3517

Fig. 4. A live Tonkinomys daovantieni (AMNH 275593). Note the unpigmented distal portion of the tail and the blaze of white on the forehead. Other external traits are described in the text. Photographed by D. P. Lunde, April 2004.

GEOGRAPHIC DISTRIBUTION: Tonkinomys Professor Tien was educated in Hanoi under the French daovantieni is currently known only from the colonial Administration. He taught several generations of Vietnamese scientists and carried his Biology Faculty type locality, but the species probably occurs through the difficult years after his country gained its in suitable forested habitats throughout the freedom. Though Professor Tien’s principal works and karst landscapes of northern Vietnam (identi- many of his papers were in mammalian zoology, his advice, fied as the ‘‘Vietbac Karst Zone’’ by Tuyet, his academic research, and most importantly his student 1998: 187; or the Caobang and Bacson regions support was never limited to this. Certainly, all senior biologists in northern Vietnam today gladly call Professor by Głazek, 1966), and possibly in southern Tien their teacher. It is hard to calculate the importance of China (see the distributions of karst outcrops this gentle and thoughtful man in the history of Vietnam’s mapped in Tuyet, 1998, and Zhang, 1989). science. He was the father of his field in Vietnam. His loss was a great blow for us, though he left for the world an DIAGNOSIS: Because daovantieni is the only incalculable legacy of studies of the rich biology of Vietnam, known species of Tonkinomys, generic and and a scholarly tradition for those who will follow in his specific diagnoses are the same. footsteps. ETYMOLOGY: We are honored to name this distinctive gray-furred and short-tailed lime- The biodiversity surveys undertaken in stone endemic after the late Ða`o Va˘n Tieˆ´n, northern Vietnam during the past decade that who when he died on May 3, 1995, at the age have contributed so significantly to knowledge of 78, was emeritus professor of biology at the of mammalian diversity in that country can be National University of Hanoi. Our esteem for viewed as extensions of earlier vertebrate this Vietnamese scholar is reflected in the surveys in northern Vietnam from 1957 to obituary prepared by Groves and Weitzel 1971 initiated and managed by Professor Tieˆ´n. (1995: 15216): His results generated large and important 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 9

terize live Tonkinomys daovantieni (figs. 4, 5; table 1). Detailed descriptions of its external features, skull, and dentition are provided below. External traits: The dense fur covering upperparts of head and body is grayish black with burnished highlights, and consists of three types of hairs. The soft underhairs (up to 12 mm long) are gray for their entire length. The overfur layer (up to 15 mm thick) is formed by wide, flexible, and grooved spines, each pale gray for most of its length and tipped with brown or black. Scattered guard hairs project 5210 mm beyond the overhairs, the basal half of each is gray, the distal half black. The combination of hair types and their pigmented banding patterns imparts a thick and semispinous texture, and a burnished, grayish black tone to the upperparts. The dorsal pelage is less spiny along the sides of the body, appears especially soft and gray over the shoulders and hips, and gradually blends into the softer and shorter (up to 8 mm thick) dark gray fur covering the underparts. That coat is formed by soft underhairs mixed with soft, wide, and grooved spines; both kinds of hairs are gray for their entire lengths. Although paler than the dorsal coat because Fig. 5. Underparts of Tonkinomys daovantieni it has no dark brown guard hairs, no sharp (AMNH 275593). The dark grayish black dorsal demarcation exists between dorsal and ventral coat merges gradually into the dark gray venter, fur. A white patch (size ranges from 10 mm which is broken by a white pectoral patch (found long and 5 mm wide to 30 mm by 12 mm) in ten other specimens of the sample of 13). Photographed by D. P. Lunde, April 2004. interrupts the dark gray fur over the chest in 11 of the 13 specimens; the other two lack this chest mark. On the forehead a blaze of white collections of voucher specimens (currently hairs (expression ranges from a few hairs to housed at the University of Hanoi), and were a patch 15 mm long and 5 mm wide) con- summarized by him in 1985 (Ða`o, 1985). That trasting with surrounding dark fur is present body of field data and museum specimens, and in nine specimens; four, including the holo- the scientific results derived from them formed type, lack the blaze. Sides of the face and the foundation of ‘‘Checklist of Mammals in throat are dark gray; the lips, chin, and Vietnam’’ published nine years later (Ða˘ng et rhinarium are unpigmented. Fur covering the al., 1994), which at the time stood as the finest lower limbs is dark gray everywhere, but and most comprehensive annotated list of shorter than that on the torso. Vietnam mammals, and today remains not Eyes, relative to head area, are large, only an important reference, but a tribute to proportionally similar to species of Rattus.A Professor Tieˆ´n, his students, and his collea- wide unpigmented ring surrounds each narrow gues. and circular, dark brown eyelid. Beyond the MORPHOLOGICAL DESCRIPTION: Large head eyes, the fur is dark gray covering this part of and eyes, a stocky body, dark gray ears, short the head, and although somewhat more and bicolored tail, grayish black (gunmetal) suffused with black, this darker tone does upperparts, and dark gray underparts charac- not define a facial mask. 10 AMERICAN MUSEUM NOVITATES NO. 3517

The pinnae (external ears) are moderately large, but not disproportionately expansive relative to body size. They are dark gray, somewhat oval in outline, and rubbery in texture. Short brown hairs (visible only under magnification) are sparsely scattered over both outer and inner surfaces, but do not tint the gray background. The mystacial vibrissae are either dark brown or unpigmented, fine, and very long (up to 75 mm); when laid against the head the longest projects up to 20 mm beyond the distal margin of each pinna. The longest in each pair of superciliary (or supraorbital) vibrissae (up to 60 mm long) also extend well past the pinna when appressed against the head. The short submental and interramal vibrissae are unpigmented. The few short (up to 25 mm) genal vibrissae are inconspicuous and unpigmented for most of their lengths. The base of the wrist supports four moderate- ly long (up to 10 mm) unpigmented ulnar carpal vibrissae, and from the inside of each heel springs a longer (up to 15 mm) unpig- mented tarsal vibrissa. The tail is appreciably shorter than the length of head and body (LT/LHB 5 83%, average of 13 individuals) and it is thick (range in 13 specimens is 5.7 mm to 6.3 mm, mea- sured laterally at midpoint of tail length) and round in cross section (table 1; fig. 6). The proximal one-half to three-fourths is dark brown on dorsal and lateral surfaces (pro- duced by the brown pigment in scales and scale hairs). The ventral surface is white, as are all surfaces of the distal one-fourth to one-half (25%–44% of total tail length among the 13 specimens). In a few specimens, scattered scales in the unpigmented regions retain very pale brown pigment, which provides a slight speckling to the white portion, usually over the ventral surface. Scales in the overlapping annuli are moderately large (10 annuli of Fig. 6. Holotype of Tonkinomys daovantieni. scales per centimeter, counted along basal Dorsal (left) and ventral (right) views of the tail. one-third of the tail), and beneath each scale Note increasing length of scale hairs from base to emerge three hairs. These are bristle-like and tail tip. Basal two-thirds of dorsal and lateral about as long as two scale annuli (1.0 mm) surfaces of tail is dark brown, produced by brown near the base of the tail, but those at the tail pigment in both scales and scale hairs (a); scales and scale hairs (c) on underside and distal one-third of tip are softer and longer (526 mm); there is the tail are unpigmented. See text for discussion of a gradual increase in hair length and texture pattern variation within the complete sample. Tail from base to tail tip. Because the hairs are is round in cross-section (b). mostly longer than the scale annuli, the tail 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 11

Fig. 7. Holotype of Tonkinomys daovantieni. Top: Lateral view of left hind foot. Bottom: Lateral view of left front foot. The bulbous palmar and planter pads are clearly evident. appears somewhat hairy, especially the distal surface is formed by six very large and half (fig. 6). swollen pads (tubercles) in a tight cluster: Claws are unpigmented, as are their thin two inner interdigitals (2 and 3), two outer covering of hairs (ungual tufts) and the interdigitals nearly opposite each other (1 digits of the front and hind feet. So too is and 4), a large hypothenar (nearly as large the dorsal metacarpal and metatarsal integu- as an interdigital) just behind and slightly ment, but an overlying covering of brown overlapping the lateral interdigital, and an hairs imparts a diluted brown wash to these even larger thenar (fig. 8). Size and protuber- surfaces. Both front and hind claws are not ance of the pads relative to plantar surface, unusually long, and are gently curved (fig. 7). and their contiguous positions resemble the Their covering ungual tufts either do not or conformation seen in arboreal murines like the only slightly project beyond the claw tips Sulawesian species of Margaretamys (Musser, (fig. 8). Each palmar surface is naked and 1981: 279). They contrast with such terrestrial mostly unpigmented. Its topography is dom- examples as Sundanese Sundamys muelleri and inated by five huge and swollen pads: three Berlymys bowersii (Musser and Newcomb, interdigital, thenar, and hypothenar (fig. 8). 1983: 357), Rattus argentiventer (Musser, Gray patches mark some of the pads, and 1973: 7), or Sulawesian (Musser the ventral surfaces of all are nearly smooth, 1991: 27) whose pads are smaller relative to exhibiting only traces of semicircular and area of the plantar surface with the two outer transverse lamellae. The hind foot is moder- interdigital mounds set well apart from the ately long and wide (table 1). Its naked inner pair, and the hypothenar and thenar plantar surface and some of the pads are widely spaced from each other and the dark gray. The anterior half of the plantar interdigitals. 12 AMERICAN MUSEUM NOVITATES NO. 3517

Fig. 8. Holotype of Tonkinomys daovantieni. Left: Palmar view of left front foot. Right: Plantar view of left hind foot (compare with the plantar views of Chiromyscus, Niviventer, and Saxatilomys in fig. 9). Abbreviations: hy, hypothenar pad; po, pollex; th, thenar pad; 1—4, first through fourth interdigital pads. 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 13

Fig. 9. Plantar views of left hind feet of adults of Indomalayan murines in the Dacnomys division. A, Chiromyscus chiropus (AMNH 268333, southern Vietnam). B, Niviventer langbianis (AMNH 272251, northern Vietnam). C, N. fulvescens (AMNH 272376, northern Vietnam). D, Saxatilomys paulinae (BMNH 2000.292, Lao PDR). The feet of the arboreal C. chiropus and N. langbianis are short and adorned with large and bulbous plantar pads compared with the longer foot and relatively smaller pads in the terrestrial/ scansorial N. fulvescens. The four interdigital pads (at the bases of the digits), thenar (t), and hypothenar (h) of S. paulinae are set appreciably closer than in any of the other species, are more swollen, and larger, not only absolutely but relative to plantar surface, an overall plantar adornment resembling that exhibited by Tonkinomys daovantieni (fig. 8).

Each female in our sample has four pairs of bone (in the anterolateral pocket of the mammae: one pectoral, one postaxillary, and orbit) is small, rectangular, and fused with two inguinal. the dorsal maxillary zygomatic root (no Skull: Tonkinomys daovantieni has an elon- shared suture with the frontal). Dorsolateral gate skull, sturdy in appearance, the visual margins of the interorbit, which is about as impression reflecting a long rostrum, narrow wide as the rostrum, are defined by high cranium, and robust zygoma. In dorsal view ridges that are prominent as they sweep (fig. 10), the rostrum is moderately long and back along the dorsolateral postorbital mar- wide, its parallel sides dimpled by a small gins of the frontals; these ridges become nasolacrimal capsule (just anterior to the weaker in expression and less pronounced anterior spine of each zygomatic plate). The where they extend (as temporal ridges) onto distal portion of the rostrum is slightly the parietal margins (accentuating dorsolater- tapered, the anterior margin of the nasals is al rims of the cranium) to about the level of triangular, and the adjacent premaxillaries the posterior edge of the squamosal zygomatic project well beyond the posterior nasal-frontal root. Here the temporal ridge is barely suture. A moderately deep zygomatic notch is discernable, and the parietal extends ventrally evident between the rostral wall and the to form the dorsolateral cranial wall between projecting anterior spine of the zygomatic the posterior margin of the zygomatic root plate. The dorsal portion of each lacrimal and the lamboidal ridge; a bony swelling 14 AMERICAN MUSEUM NOVITATES NO. 3517

Fig. 10. Holotype of Tonkinomys daovantieni. Dorsal (left) and ventral (right) views of cranium. Measurements are listed in table 1. outlines the parietal-squamosal connection all another; neither zygoma bows out far from the way to the lamboidal ridge. The interpar- the skull. ietal is long (in anterior-posterior plane) and The skull appears long, low, and without moderately wide (its lateral margins are within significant basicranial flexion when viewed the parietal and supraoccipital sutures, not from lateral perspective (fig. 11). The rostrum extending to the parietal-squamosal suture) is rectangular in side view, and extends slightly and its posterior two-thirds roofs a deep beyond the incisor faces to enclose the nasal occiput with a slightly convex or chevron- aperature in a short tube in which nasals shaped posterior margin. Zygomatic arches provide the roof and premaxillaries the sides. are robust and arranged nearly parallel to one Much of the ventral maxillary root of each 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 15

Fig. 11. Holotype of Tonkinomys daovantieni. Top: Lateral view of cranium. Middle: Lateral view of left dentary with incisor and molars. Bottom: Medial view of same dentary. zygomatic arch lies anterior to the molar row, does not project far enough forward to with the posterior margin of the zygomatic conceal the nasolacrimal capsule, which is plate extending behind the front margin of the small and only slightly inflated. Maxillary and toothrow (0.521.0 mm is the range in our squamosal zygomatic processes are joined by sample of skulls). The zygomatic plate is wide, a long jugal to form a thick and robust its convex anterior margin projecting beyond zygomatic arch. The squamosal root of each the dorsal maxillary zygomatic root to form arch is situated high on the side of the cranium a moderately deep zygomatic notch (best seen where its posterior ridge2like portion extends in dorsal view). This anterior spine of the plate horizontally just below the posteroventral 16 AMERICAN MUSEUM NOVITATES NO. 3517

margin of the parietal, which projects ventrad to form the dorsolateral side of the cranium. The low ridge of the squamosal zygomatic root disappears 10–15 mm anterior to the vertical ridge formed by the squamosal-exoc- cipital suture. The configuration is similar to, but not identical with, that documented for species of Leopoldamys (see Musser, 1981:fig. 18) and Niviventer (Musser et al., 2005: figs. 7 and 8). Dorsal to the auditory (ectotympanic) bulla and posterior to the squamosal zygo- matic root, the squamosal forming the side of the cranium is intact except for a minute subsquamosal foramen at the prominent ridge formed by the squamosal-exoccipital suture. This foramen is the only landmark identifying where the squamosal and a wide hamular process of the squamosal have completely fused to form the solid cranial wall. A spacious postglenoid foramen that is confluent in some specimens with a wide postalar fissure (ventral to the postglenoid foramen) separates the squamosal margin from the periotic flange and dorsoanterior surface of the ectotympanic (auditory) bulla. That capsule is attached to the squamosal dorsally by the posteroventral portion of that bone, which represents the cranial wall fused with a wide hamular process. There is no anterior attachment, which is the usual pattern among most murines. An anterior flange of the periotic, the tegmen tympani, is present (and partly separates the dorsal postglenoid foramen from the ventral postalar fissure), but is separated by a narrow or moderately wide gap from the posterior margin of the squa- mosal in most specimens; there is no posterior suspensory process of the squamosal to which the tegmen tympani could attach (in some cricetid , the tegmen tympani Fig. 12. Holotype of Tonkinomys daovantieni overlaps a posterior projection of the squa- illustrating details in enlarged view of left basicra- mosal to form one of the suspensory attach- nial region. Abbreviations: ab, auditory bulla; al, ments between ectotympanic capsule and alisphenoid; bo, basioccipital; bp, bony palate; cc, squamosal; see the diagrams in Voss, 1993: carotid canal; fo, foramen ovale; hp, hamular 19). The moderately inflated mastoid is tightly process; iog, groove for the infraorbital artery; sutured to squamosal and exoccipital. It is mlf, middle lacerate foramen; pp, pterygoid plate (its ventral surface is the pterygoid fossa); ppm, completely ossified, without the moderate or posterolateral palatal margin; pt, periotic; spv, large fenestrae found in some murines sphenopalatine vacuity; sq, squamosal; stf, ( celebensis, for example; Musser, stapedial foramen. 1982: 38) and sigmodontines (see Carleton and Musser, 1989: 34); only a very small opening penetrates the dorsal mastoid-exocci- 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 17 pital suture. The foramen magnum is directed margin (up to 20% of the palate extends past caudad (which reflects the horizontal rather the third molars) unmarked by any bony ridge than arched axis of the skull—no significant in most specimens, slightly thickened in basicranial flexion), and the deep occiput others. Each posterolateral margin of this projects slightly beyond posterior surfaces of shelf extends as a flat, bony surface onto the the occipital condyles. The ethmoid foramen anterior portion of each pterygoid plate where within the orbit is tiny, and the optic its sharp diagonal border marks the antero- foramen moderately large. The dorsal palatine medial margin of each pterygoid fossa. The foramen is separate from the sphenopalatine ventral surface of the bony palate is smooth foramen, a configuration usual among except for a pair of oblong posterior palatine Asian murines, with a few exceptions where foramina (in the maxillary-palatine suture the two foramina are coalesced (Musser, 1982: opposite the middle or posterior half of each 22). Eight specimens have a bony alisphenoid second molar), a pair of shallow grooves, and strut (ranging from moderately wide to small or minute nutrient foramina scattered slender in the sample) on each side of the over the palatal shelf. The mesopterygoid skull posterior to the orbit and dorsad to the fossa is wide, and dorsolateral margins of its pterygoid ridge (the lateral edge of the roof are perforated by long and moderately pterygoid plate). The strut separates wide sphenopalatine vacuities. On each side of the foramen ovale accessorius from the the pterygoid fossa, a robust hamular process combined buccinator-masticatory foramen of the pterygoid marks the boundary between on the side of the cranium, and obscures the the mesopterygoid fossa and each adjacent anterior opening of the alisphenoid canal. One pterygoid plate, its ventral surface sculptured specimen exhibits a strong strut on the left by a shallow pterygoid fossa. The bony side, but only a bony thread on the right. Only pterygoid plate is breached by the large one individual in our sample of skulls lacks ventral opening of the foramen ovale in its struts (which are represented by only a dorsal posterior half; its anteromedial portion along nubbin on each side). In this specimen, the the rim of the bony palatal extension is slightly opening to the alisphenoid canal is evident, the fenestrated (irregular traces of the sphenopter- foramen ovale accessorius and buccinator- ygoid vacuity). A shallow trough (in which the masticatory foramina coalesce (basically dis- infraorbital artery passes) scores the ventral appear), and the course of the buccinator and margin of the pterygoid plate between the masticatory nerves is marked by a shallow ventral opening of the foramen ovale and the groove extending from the foramen ovale onto middle lacerate foramen. Small relative to the side of the alisphenoid. overall size of the skull, the globular and only The short rostral tube anterior to faces of slightly inflated ectotympanic (auditory) bulla the incisors, wide rostrum, long incisive does not conceal nearly all of the periotic as it foramina and bony palate, diverging molar does in some other murine groups, species of rows, moderately wide mesopterygoid fossa Rattus, for example. In Tonkinomys daovan- and pterygoid plates, and small bullae are the tieni, a wide, wedge-shaped segment of the topographic highlights when the skull is periotic is exposed between the dorsal capsular studied from ventral perspective (figs. 10, margin and basioccipital, and this wedge of 12). Just behind the incisors is a tiny inter- periotic extends anteriorly to form the dorsal premaxillary foramen, and beyond it the and slanting posterodorsal wall of the carotid rostrum is perforated by long and spacious canal. The conformation resembles that illus- incisive foramina, their posterior rims situated trated by Carleton and Musser (1989: 33) for slightly before (0.5 mm) anterior margins of the sigmodontine, Oligoryzomys, and is unlike the first molars, even with those molar many other muroid rodents in which a more surfaces, or projecting slightly (not more than inflated ectotympanic capsule covers most of 0.5 mm) between them. The bony palate is the periotic and the anteromedial margin of wide and long, extending 1.5–2.0 mm beyond this capsule meets the basioccipital, so the the molar rows to form a broad platform with opening to the carotid canal is bounded by the a slightly concave and smooth posterior ectotympanic capsule and adjacent basiocci- 18 AMERICAN MUSEUM NOVITATES NO. 3517 pital (the condition in Oryzomys palustris deep sigmoid notch between coronoid and depicted by Carleton and Musser, 1989: 33; prominent condyloid processes, and a shallow- and species of Rattus and its allies illustrated ly concave posterior margin connecting con- in Musser and Heaney, 1992: 99). Tapering dyloid and angular processes (fig. 11). In rostrally from the ectotympanic capsule is contrast with the wide and conspicuous a moderately short and wide bony eustachian ventral masseteric ridge, the dorsal ridge is tube. A spacious middle lacerate foramen either undetectable or indicated by a shallow, separates the anterior slope of the ectotympa- elongate depression. Besides the ventral mas- nic capsule from posterior margin of the seteric ridge, the only other significant struc- pterygoid plate. ture that marks an otherwise smooth lateral The cephalic arterial pattern possessed by dentary surface is a slight bulge below the Tonkinomys daovantieni is not unique among anterior root of the coronoid process that in members of Murinae (as that subfamily is turn marks termination of the incisor alveolus delineated by Carleton and Musser, 1984; within the bone. In no specimen did the incisor Musser and Carleton, 2005). As in all de- capsule extend farther caudad to project into scribed species of Niviventer, Chiromyscus, the condyloid process (checked by shining Saxatilomys, and Leopoldamys, T. daovantieni a high-intensity light through the dentary) as it lacks a sphenofrontal foramen and related does in some other murines (Musser and squamosoalisphenoid groove, the petrotym- Heaney, 1992: 84). Topography of the lingual panic fissure between bullar capsule and dentary surface resembles that characteristic periotic is perforated by a spacious stapedial of most other murines, the primary landmarks foramen continuous laterally with a deep being a prominent lingual ridge above which groove on dorsal surface of the periotic, and is the large mandibular foramen (as in there is a shallow but wide groove on the Papagomys armandvillei, for example; see posterior ventral surface of the pterygoid plate Musser et al., 1986: 5). The body of the (fig. 12). This set of osteological landmarks dentary projects anteriorly beyond the molar signals a cephalic arterial pattern in which the row as a moderately short and stocky tube supraorbital branch of the stapedial artery is containing the incisor. Just in front of the absent and the orbital circulation derives from molar row on the dorsolateral labial surface is the distal portion of the infraorbital branch. a small mental foramen. The infraorbital is a continuation of the Dentition: Enamel faces of upper and lower stapedial artery, which passes over the dorsal incisors are pale orange and smooth, without groove in the periotic, through the middle grooves or shallow sulci. Thickness of the lacerate foramen, continues in the shallow enamel relative to the dentine is similar to that groove ventral to the posterior margin of the in species of Rattus and many other murines pterygoid plate to course through the ali- (Musser and Heaney, 1992: 79). The upper sphenoid canal, and emerges onto the orbital incisors curve caudad after emerging from floor through the anterior alar fissure. the rostrum (opisthodont conformation; see Common to most murines (Carleton and Thomas, 1919; Hershkovitz, 1962: 103). Musser, 1984; Musser and Newcomb, 1983; Gnawing edges of the uppers are at right Musser and Heaney, 1992), this pattern of angles to the long axis of the skull, so their vessels and associated osteological landmarks combined tips form a straight cutting edge (as is also characteristic of some sigmodontine in species of Rattus; see Musser and Heaney, rodents (described and diagramed for 1992: 79), not curved or V-shaped (as in some Oligoryzomys by Carleton and Musser, 1989; Philippine and endemics; see Musser pattern 2 in Voss, 1988), and is derived and Heaney, 1992; Musser and Durden, 2002). compared with the cephalic arterial pattern The lower incisors are moderately long and hypothesized to be primitive for muroid curved, their cutting tips either straight or rodents (Bugge, 1985; Carleton, 1980). arcuate. Mandible: The sturdy dentary supports Alveolar patterns for roots of upper molars a delicate coronoid process, relative to extent are distinctive. A large anterior root, two of the deep ascending ramus, a moderately robust lingual roots, and a large posterior 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 19 holdfast anchor each first upper molar. No cusp t3 (seen in young rats but unidentifiable labial root is present between the large in older with more worn chewing anterior and posterior anchors. Three roots surfaces); a complete arcuate lamina derived hold the second and third molars in place: from the total coalesence of cusps t4, t5, and a large anterior and posterior, and small t6; and small posterior chunk either diamond- lingual. Two large roots anchor each lower shaped or oblong in outline (formed primarily molar. Except for the first upper molars, the of cusp t8; cusp t9 is either absent or pattern of roots in all our examples of unidentifiable due to its total incorporation Tonkinomys daovantieni is primitive for mur- into cusp t8). We could not detect a cusp t7 ines (Musser and Newcomb, 1983; Musser and (on the lingual cingulum between cusps t4 Heaney, 1992). and t8 when present; see Musser and Upper molar rows are moderately long Newcomb, 1983: 333), posterior cingulum (about 17% of occipitonasal length) and (pressed against the posterior margin of cusp strongly diverge posteriorly (width of bony t8, if present; see Musser and Newcomb, 1983: palate is considerably greater between third 333), accessory cusplets, or longitudinal crests molars than between the first; see fig. 10). connecting the cusps to form a garland Occlusal surfaces of the brachydont (low- configuration (‘‘stephanodonty’’; see Schaub, crowned) molars are simple in topography, 1938, and Misonne, 1969) on any of the upper consisting of tightly pressed rows exposing molars. When present these structures provide chunky chewing surfaces in the shapes of complexity to the occlusal planes and in some narrow chevrons and diamonds (fig. 14). murines significantly increase chewing sur- Occlusal surface of each first upper molar faces. consists of two anterior rows of cusps, each in Occlusal planes of the lower molars are also the form of a tight chevron, and a large comprised of uncomplicated patterns (fig. 14). roughly diamond-shaped posterior surface. An anterolingual cusp coalesced with a smaller The most anterior chevron is comprised of anterolabial forms the anteroconid, the most cusps t1, t2, and t3; cusps t2 and t3 are so anterior cusp row, which is narrower than the coalesced that their limits are obliterated, at lamina behind it. The second and third are in least in adults. The blended cusps t4, t5, and t6 the shape of narrow chevrons and represent form the second chevron, although the labial unions of protoconid-metaconid and hypoco- and lingual cusps retain some definition. The nid-entoconid, respectively. A roughly trian- large, chunky posterior third of the molar gular posterior cingulum forms the entire consists primarily of cusp t8 merged with posterior fourth of the molar. Except for a smaller, indistinct cusp t9 to form a roughly lacking an anteroconid, occlusal cusp patterns diamond-shaped chewing surface. On the of the second molar resemble patterns seen in occlusal surface of each second upper molar, the first. The anterior half of each third molar the anterior chevron is represented by only consists of a front chevron formed by union of a large cusp t1 forming the anterolingual protoconid and metaconid and behind that portion of the tooth. In seven out of 10 a large oblong structure likely representing the specimens, a small cusp t3 sits on the complete fusion of hypoconid and entoconid. anterolabial margin; in two others, the cusp Anterolabial cusps are absent from second is missing and the anterolabial border is and third molars in most specimens, but we marked by only an inconspicuous cingulum; are not certain about others in the sample and presence or absence of cusp t3 in the tenth because their molars are worn to a level such specimen cannot be determined because the that, if present, these cusps are now indistinct molars are too worn. The complete chevron because they have completely coalesced with and chunky posterior portion of the second the adjacent lamina; we did find evidence of molar, in size and shape, resembles compara- a small anterolabial cusp on the third molar of ble rows in the first molar. Each third molar the holotype (fig. 14). We had the same has an occlusal pattern that is basically frustration determining the frequency of pos- a compacted form of that characterizing the terior labial cusplets on some specimens. This second molar: a conspicuous cusp t1; minute small cone is prominent and forms the 20 AMERICAN MUSEUM NOVITATES NO. 3517

Fig. 13. Diagram of maxillary (left) and mandibular (right) molar rows from right side of Bunomys chrysocomus illustrating structural terms. Maxillary molars: cusps are numbered according to Miller’s (1912) scheme and referred to in the text with the prefix ‘‘t’’. Mandibular molars: a-lab, anterolabial cusp; a-ling, anterolingual cusp; alc, anterior labial cusplet; ed, entoconid; hd, hypoconid; md, metaconid; pc, posterior cingulum; pd, protoconid; plc, posterior labial cusplet. anterolabial margins of the posterior laminae described Lao PDR Saxatilomys (one species). of first and second molars in the holotype Musser (1981), Musser and Newcomb (1983), (fig. 14). The cusplets are present but in- Musser and Heaney (1992), Musser and conspicuous on first and second molars in Carleton (2005), and Musser et al. (2005) have three other specimens (the laminar outline chronicled the geographic distributions of reflects the blending of a cusplet with the these genera, along with their taxonomies, anterolabial laminar margin), and are either descriptions of morphologies, and postulated absent or undetectable in seven rats (because phylogenetic relationships. In conformation of the cusplet has completely coalesced with the body and limb proportions, and in character- adjacent cusp). A posterolabial cusplet clearly istics of skull and teeth, T. daovantieni most does not occur on any third molar in any of closely resembles species of Leopoldamys, the specimens at hand. Niviventer, Chiromyscus, and Saxatilomys. Our comparisons contrast Tonkinomys first COMPARISONS with extant examples of Leopoldamys, then with Niviventer and Chiromyscus, and finally The morphological attributes of Ton- with Saxatilomys. kinomys daovantieni place it in the Dac- A large body of literature has accumulated nomys Division of Musser and Carleton over the past two decades reporting fossil (2005), which contains the Indomalayan murines, mostly isolated molars and incisors, Chiromyscus (one species), Dacnomys (one), which have been recovered from Pliocene, Leopoldamys (six), and Niviventer (17); Sri Pleistocene, and Holocene sediments in the Lankan Srilankamys (one); and the recently Indomalayan region. Some material has been 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 21

Fig. 14. Occlusal views of maxillary (left) and mandibular (right) molar rows from right side of the holotype of Tonkinomys daovantieni (CLM1-3 5 8.3 mm, CLm1-3 5 8.3 mm). See figure 13 for terminology of cusps and cusplets. described as new taxa whose diagnostic traits weight, and posture of the live animal closely identify them as members of the Dacnomys resemble Tonkinomys daovantieni (Marshall, Division, and other samples have been re- 1988: 485, provided a photograph of a live garded as examples of extant members of that Leopoldamys). Although the two species are group. We examined pertinent publications to similar in body size (table 2), they are strik- determine whether any of the new taxa that ingly dissimilar in other particulars of external are based on fossils represent examples of morphology. Leopoldamys neilli has: (1) short, Tonkinomys. The significance for nomencla- sleek brown fur over upperparts of head and ture is obvious. Equally important is the body that is sharply demarcated from white zoogeographic context. If some samples of underparts (long, semispinous, grayish black fossils that have been identified as either fur over the dorsum and dark gray venter in T. extinct or extant species are actually examples daovantieni); (2) slightly smaller external pin- of Tonkinomys, or close phylogenetic relatives, nae, both absolutely and relative to head and they would provide a window through which body length; (3) a long, slender, tapered tail could be glimpsed the past distribution of this that is much longer than length of head and unique limestone rat, and the geologic depth body, LT/LHB 5 124% on average, and of its evolutionary history. similar to an inverted U in cross-section—flat Leopoldamys: The smallest extant member ventral surface and arched across sides and of the six currently recognized species of top (less tapered in T. daovantieni, chunky and Leopoldamys (Musser and Carleton, 2005) is much shorter than head and body, LT/LHB 5 the Thai L. neilli (only the extinct L. minutus is 83%, and round in cross-section); (4) a very smaller, described from samples recovered slender, pointed tail tip that is covered with from late Pliocene–early Pleistocene fissure short scale hairs no longer than 122 mm (tip and cave sediments; Chaimanee, 1998), and of tail is stubby in T. daovantieni, covered by the head and body proportions, body size, much longer hairs, 527 mm, and brush-like in 22 AMERICAN MUSEUM NOVITATES NO. 3517

TABLE 2 Summary Statistics for Cranial and Dental Measurements (mm), and Tail-to-Body Ratio of Tonkinomys, Leopoldamys, and Niviventer Selected to Demonstrate Contrasts in Relative Tail Length, and Size of Body, Skull, and Maxillary Molar Rowa (Mean, observed range in parentheses, and number of specimens are listed for each measurement; values for L. neilliare means derived from a sample of 12. LT/LHB expressed as %.)

T. daovantieni L. neillib N. andersoni c N. confucianusc (Vietnam) (Thailand) (Sichuan, Yunnan) (Sichuan)

LHB 204.6 (184–217) 13 217 171.6 (150–198) 46 143.2 (125–170) 24 LT 168.9 (156–183) 13 270 229.7 (194–269) 44 182.7 (160–204) 23 LT/LHB 83 124 134 128 LHF 39.0 (37–41) 13 42 35.1 (31–40) 47 29.8 (28–32) 20 LE 30.0 (29–31) 13 27 26.4 (22–28) 19 21.0 (20–23) 24 ONL 50.0 (47.1–52.4) 7 51.9 41.7 (38.7–45.7) 37 36.9 (33.9–40.5) 25 CLM 8.33 (8.0–8.8) 7 8.3 7.3 (6.9–7.5) 18 5.8 (5.3–6.3) 59 a Leopoldamys neilli is the smallest in body size of any extant Leopoldamys, N. andersoni is among the largest within Niviventer, and N. confucianus represents most species in the genus in body size, along with body and tail proportions. b Values are from Marshall (1988: 485), and are means derived from 12 adults. c Lengths of head and body, tail, hind foot, ear, and ONL are from Musser and Chiu (1979: 584); lengths of maxillary molar rows are unpublished summaries by Musser and Lunde (ms.) derived from AMNH samples collected in China. appearance); and (5) swollen plantar tubercles incisive foramina, their posterior margins well situated in distal two-thirds of plantar surface, anterior to faces of first upper molars (longer as seen in Tonkinomys (figs. 9, 10), but slightly in T. daovantieni, the posterior edges located smaller relative to plantar area—the thenar just before anterior margins of first molars, pad, for example, forms about 17% of planter even with them, or slightly projecting between surface (T. daovantieni has relatively more the first molars); (2) a much shorter bony expansive plantar pads—the thenar constitu- palate, its posterior margin aligned somewhere tes about 20% of plantar surface). Short, sleek between the middle or end of each third upper fur with the coat that covers upperparts of the molar, depending upon the species and vari- head and body strikingly contrasting with the ation within each sample (longer in T. ventral covering is characteristic of all extant daovantieni, extending beyond the molar rows species of Leopoldamys. Also common to all to form a wide platform); (3) longer postpalatal extant species in that genus is a very long and length, which reflects the shorter bony palate tapered tail, with its cross section resembling (much shorter in T. daovantieni); (4) wider, an inverted U, and its tip covered by very chunky molars relative to size of skull, which short bristles. Elongate hind feet are common is correlated with an absolutely narrower bony to all Leopoldamys, as are the number of palate (smaller, gracile molars relative to size plantar tubercles, their size relative to plantar of skull, and an attendant absolutely wider surface, and distribution in the distal two- bony palate in T. daovantieni); (5) molar rows thirds of the plantar surface. that barely diverge posteriorly (molar rows The skull of L. neilli is similar to that of T. diverge appreciably along anterior-posterior daovantieni in overall size (table 2), and the axis in T. daovantieni); (6) a small, moderately two are remarkably alike when viewed from inflated ectotympanic bulla relative to size of a dorsal perspective (compare the cranial the skull (more inflated capsule in T. daovan- photographs of Leopoldamys in Musser, tieni, and absolutely larger in most examples); 1981: 259, and the drawing on p. 264, with and (7) a very long, bony eustachian tube, the renditions in fig. 10). In ventral view, especially contrasted with the small bulla however, the two species are strikingly dissim- (much shorter eustachian tube in T. daovan- ilar. Compared with the Vietnam species, L. tieni). These differences also separate T. neilli (and all other extant species of daovantieni from specimens we examined Leopoldamys) has: (1) significantly shorter representing the other five species of 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 23

Leopoldamys. Our study of those compara- cusps t2 and t3, and a discrete cusp t1 on its tive samples also reveals that L. neilli and the posterolingual margin. The second lamina is other species of Leopoldamys have wider and not as straight but gently arcuate. These are sturdier alisphenoid struts relative to skull diagnostic molar traits for Leopoldamys.In size, and these struts are present in every contrast, the two comparable laminae in individual of each species (relatively weaker Tonkinomys are tight chevrons—cusps t1 and struts in T. daovantieni, and absent from t3 are opposite each other in the first lamina, some specimens). as are cusps t4 and t6 in the second. Patterns of roots beneath certain molars Furthermore, cusps t4 and t6 in T. daovantie- that are characteristic of T. daovantieni are ni, although coalesced with the central cusp t5, dissimilar to those exhibited by species of are large relative to overall dimensions of the Leopoldamys. Both extant samples (material in lamina, and retain part of their identity as AMNH and USNM; also see Musser, 1981: cusps. Comparable cusps in the second lamina 260) of Leopoldamys and those represented by in Leopoldamys are relatively smaller and so fossils (Chaimanee, 1998; Zheng, 1993) have broadly merged with cusp t5 that their four-rooted upper molars: large posterior, boundaries are not determinable. The large single large lingual (we have never encoun- chunky posterior lamina in Leopoldamys is tered a specimen with two lingual roots), large wider than long, but roughly diamond-shaped anterior, and a small labial, which is some- in Tonkinomys. Contrasts in second upper times divided (also four roots in T. daovantie- molars are similar to those seen in the first. ni, but there are two large lingual holdfasts The third upper molars in Leopoldamys have instead of one, and no labial root). All a stretched, ridge-like cusp t4 compared with Leopoldamys have a second upper molar that the shorter version in Tonkinomys; otherwise, is anchored by either three or four roots (only the occlusal patterns in the two genera are three roots in all our T. daovantieni). Both similar. Leopoldamys and Tonkinomys have three- Cusps form either nearly straight or gently rooted third upper molars. All species of arcuate lamina in the lower (mandibular) Leopoldamys have four-rooted first lower molars of Leopoldamys. The posterior cingula molars: two large anterior and posterior are wide and elliptical in cross-section in all anchors, and smaller labial and lingual hold- members of that genus, prominent posterior fasts (all examples of T. daovantieni have only cusplets adorn the labial margin of the first two roots, an anterior and posterior coequal and second molars, and two nearly straight in size). Second and third lower molars in laminae form the occlusal surface of each third Leopoldamys have two roots (large anterior molar (see the illustrations in Musser, 1981: and posterior), which is also the pattern in T. 260). In parallel with the upper molars of daovantieni. Tonkinomys, the two cusps forming the In addition to the marked contrasts in laminae of its lower molars are diagonally robustness and width of molars between oriented so that after wear they form chevrons Leopoldamys and Tonkinomys, occlusal pat- in which the arms are very close, the posterior terns of molars are different (compare illustra- cingula are roughly triangular, labial cusplets tions of molar rows for Leopoldamys in are indistinct or not present on most speci- Musser, 1981: 262, with those of Tonkinomys mens (prominent only in the holotype), and in fig. 14). Coronal surfaces of maxillary the occlusal surface of the third molar is molars are characterized by simple patterns formed by a distinct anterior chevron-shaped in both genera (no cusp t7 or posterior lamina and a posterior oblong chunk. cingulum on any molar, no accessory cusplets, Niviventer and Chiromyscus: We examined no longitudinal crests connecting the primary samples of all 17 of the currently recognized cusps), but the conformations of laminae species of Niviventer and the single species of forming the occlusal surfaces are dissimilar. Chiromyscus ( and geographic dis- The anterior lamina of the first molar in tributions for both genera are summarized in Leopoldamys consists of a nearly horizontal Musser and Carleton, 2005; specimens form- segment, formed by the complete fusion of ing the comparative samples we utilized are 24 AMERICAN MUSEUM NOVITATES NO. 3517 listed in the Appendix by Musser et al., 2005). We accept the current, although provision- We preface our comparisons by explaining al, contents of Niviventer for our compara- that the present contents of Chiromyscus and tive context. We will also refer only to Niviventer will likely be altered after careful ‘‘Niviventer’’, understanding that the contrasts systematic revision of these genera. Musser between species in that genus and Tonkinomys (1981) characterized them, provided provi- are much the same as between the latter and sional diagnoses and contents, but his exposi- C. chiropus. tion was more of a taxonomic summary and While the body conformation of Ton- meant to be a working hypothesis, not a sys- kinomys daovantieni recalls small-bodied tematic revision. That kind of study has yet to Leopoldamys, no such resemblance exists be realized. Most species will remain in between the Vietnamese animal and any Niviventer, but two sets may eventually be species of Niviventer. Among the largest differently allocated. Except for its nail-like species of Niviventer in body size is N. claw on the hallux, shelf-like ridges bordering andersoni, which is still appreciably smaller dorsolateral margins of the postorbital region than T. daovantieni (table 2). In all species of and braincase, pattern of roots beneath the first Niviventer, dorsal head and body fur ranges upper molar (table 3), color pattern of the from buffy or brownish gray through brown dorsal pelage, and large and very bulbous to reddish brown (Musser, 1981). Niviventer plantar pads set close together, other external brahma and N. eha have grayish white under- and most cranial and dental characteristics of parts (Musser, 1970), N. hinpoon has a buffy the arboreal C. chiropus are similar to those pale gray venter (Marshall, 1988), but all other features in the species of Niviventer, particular- species have white venters. No example of ly N. langbianis (Musser, 1981; Musser and Niviventer has Tonkinomys’s unique dorsal Lunde, ms.). The latter is also arboreal and ventral pelage coloration. Some species (observations by Lunde and Musser derived of Niviventer, however, do have semispinous from trapping surveys in Vietnam), and shares pelage similar in texture to that possessed by with C. chiropus comparable prominent post- T. daovantieni (N. fulvescens and N. tenaster orbital and temporal ridges, the number of are good examples). The conformation of roots anchoring each first upper molar, a nail- tail and proportional relationship between like claw on the hallux, a pelage color pattern lengths of tail and body in Tonkinomys that does not match in details but is similar, (stocky, with a stubby tip, and significantly and equal expression of plantar pads. A shorter than combined head and body revisionary inquiry may either move N. lang- length) does not occur in any species of bianis to Chiromyscus,orC. chiropus will be Niviventer. The tail is tapered to a pointed subsumed within Niviventer (that name would tip and gracile in appearance in all species of then be a synonym of the older Chiromyscus). Niviventer, and much longer than length of Niviventer andersoni and N. excelsior form head and body in all species except N. hinpoon, another set now allocated to Niviventer that in which the tail is equal to or slightly longer will probably be removed. Musser (1981) than head and body length (table 2; Marshall, described a suite of cranial and dental traits 1988; Musser, 1970, 1973, 1981; Musser and held by these two species that contrast with Chiu, 1979; Lunde and Son, 2001). The the characters common to the other species in plantar pads of Tonkinomys are larger, Niviventer. Should information from other closer together, and more swollen relative to anatomical systems, and that derived from plantar surface than in any terrestrial or chromosomal and biochemical surveys, sup- scansorial species of Niviventer, including N. port the cranial and dental distinctions, he hinpoon, which is thought to be closely (p 328) noted ‘‘… that the phylogenetic re- associated with limestone cliff habitats lationship between Niviventer and the N. (Marshall, 1988), or even the arboreal N. andersoni division [would be] better expressed langbianis and Chiromyscus chiropus (fig. 9); by excluding the latter from Niviventer and N. fulvescens (fig. 9) exhibits the configuration placing N. andersoni and N. excelsior in of plantar pads that is common to most a genus of their own.’’ species of Niviventer. 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 25

The skull of Tonkinomys is appreciably Shapes of the upper and lower incisors in larger (as indexed by occipitonasal length) Tonkinomys, their enamel color and thickness, and more robust than all species of Niviventer, and the opisthodont conformation of the even N. andersoni, which has the largest skull uppers resemble the incisors in all species of among the species in the genus (table 2). Niviventer. The larger size of these structures The skull of Tonkinomys, however, is not in Tonkinomys provides the obvious contrast. a giant version of Niviventer; compared with Reflecting the much greater skull dimensions Niviventer, Tonkinomys has: (1) insignificant of Tonkinomys when compared with species of basicranial flexion (most species of Niviventer Niviventer are the elongate molar rows of the display marked basicranial flexion); (2) max- former, which are much longer than even the illary molar rows that are situated farther largest-bodied species of Niviventer (table 2). forward relative to posterior margin of the Occlusal patterns of the upper molars fit zygomatic plate (front of molar row either within the range of variation we observed even with back of zygomatic plate or well among most species of Niviventer, except that behind it in most specimens of Niviventer); cusps t4 and t6 on the second lamina of the (3) the squamosal root of the zygoma origi- first molar in Tonkinomys tend to retain more nating higher on side of the braincase (set of their identity, and cusp t9 is smaller and lower in Niviventer, particularly N. andersoni indistinct relative to the huge central cusp t8. and N. excelsior); (4) more slender alisphenoid The anterior lamina on the first upper molar struts relative to size of skull, with some in N. andersoni and N. excelsior resembles specimens lacking struts (relative to skull size, the shape in Leopoldamys, and contrasts with alisphenoid struts are more substantial in all the comparable chevron-shaped lamina in species of Niviventer, and present in all speci- Tonkinomys, but those two species also differ mens we examined); (5) strongly posteriorly from most other species of Niviventer in this diverging molar rows (parallel or only slightly trait. Coronal patterns of lower molars in diverging in Niviventer); (6) a bony palate Tonkinomys are also closely similar to those in projecting appreciably beyond posterior mar- the species of Niviventer. gins of third molars to form a wide platform While occlusal patterns on upper and lower (posterior margin of bony palate ends molars in our sample of Tonkinomys fall about 0.5 mm anterior to posterior surfaces within the range of variation of the patterns of upper third molars, even with them, or we observed among the species of Niviventer, no more than about 0.5 mm beyond in all the number of roots anchoring most of those species of Niviventer); (7) a posterior margin molars do not—this set of structures by of the bony palate that is smooth or only themselves identifies Tonkinomys as the rep- slightly thickened (the palatal border is de- resentative of a monophyletic group separate fined by a prominent and thick bony ridge from Niviventer, a position only strengthened in Niviventer); and (8) a thick, bony, and by the external and cranial contrasts between flat posterolateral projection of the bony the two genera already described. Except for palate covering the anteromedial portion of the first upper molar, which has four roots, each pterygoid plate, its sharp diagonal Tonkinomys exhibits the primitive number of border (ppm in fig. 12) defining the anterio- roots anchoring upper (three per tooth) and medial edge of the pterygoid fossa (no such lower (two per tooth) molars. All species of conformation in any species of Niviventer). Niviventer, in contrast, have multi-rooted Other than the larger size of each dentary molars (table 3; also see Chaimanee, 1998, in Tonkinomys, we did not detect any signif- and Zheng, 1993). First upper and lower icant differences with those of Niviventer in molars can be used as examples. Most species overall shape; positions of foramina; ex- of Niviventer have five-rooted first upper panse of coronoid, condyloid, and angular molars: large anterior, two smaller lingual, processes relative to body of the dentary; large posterior, and small labial (some speci- expression of masseteric and lingual ridging; mens have one or more labial rootlets in or position of the posterior terminus of the addition to the primary labial anchor). In N. incisor capsule. langbianis, and also in Chiromyscus chiropus, 26 AMERICAN MUSEUM NOVITATES NO. 3517

TABLE 3 of Tonkinomys has a labial anchor, and the Number of Roots on M1 and m1 in Selected Species four-rooted pattern is formed by large anterior of Niviventer, and the Species of Chiromyscus and and posterior roots along with two prominent Saxatilomys lingual roots. A small labial root, not a divided (Number opposite species indicates specimens examined. Symbol key: 4/4, M1 with large lingual, forms the fourth root in N. langbianis anterior, single lingual, and posterior roots, and and Chiromyscus. Although our survey results a small labial root; m1 with large anterior and for second and third upper molars are not posterior roots, and small labial and lingual roots. summarized in table 3, we also determined 5/4, M1 with large anterior and posterior roots, two that second upper molars in Niviventer have lingual, and a small labial root; m1 with large four roots (three in Tonkinomys), and third anterior and posterior roots, and small labial and upper molars have three (as in Tonkinomys, lingual anchors. 5/2, M1 with large anterior and which is the usual number for the third molar posterior roots, two lingual, and a small labial root; m1 with a large anterior root and large posterior in most murines, even when the first and root. Specimens surveyed are in AMNH, BMNH, second molars have more than three roots). FMNH, and USNM.)a Four roots (large anterior and posterior, smaller labial and lingual) anchor each first Roots (M1/m1) lower molar in all species of Niviventer (and Chiromyscus), but only two are present in the Species 4/4 5/4 5/2 Vietnamese limestone rat. Two to four is the N. andersoni (China: Sichuan, Yunnan) — 46 — range in number of roots anchoring each N. excelsior (China: Sichuan) — 12 — second lower molar among species of N. brahma (northern Myanmar) — 7 — Niviventer, and each third lower molar has N. eha (northern Myanmar) — 17 — either two or three roots (two roots beneath N. langbianis (Vietnam) 40 — — second and third molars of Tonkinomys). N. cremoriventer (Sunda Shelf) — 53 — Saxatilomys: Described from two whole N. hinpoon (Thailand) — 15 — N. confucianus (China, northern —53— animals along with 14 individuals represented Myanmar) by cranial, mandibular, and dental fragments N. tenaster (China: Hainan, Vietnam) — 55 — recovered from owl pellets, S. paulinae has N. conninga (Taiwan) — 53 — been recorded only from the Khammouan N. rapit (northern Borneo) — 6 — Limestone National Biodiversity Conser- N. fraternus (Sumatra) — 20 — vation Area in Lao PDR (Musser et al., 2005). N. lepturus (Java) — 21 — Body size, build, and proportions of limbs, N. cameroni (Malay Peninsula) — 42 — pinnae, and tail that are characteristic of S. C. chiropus (Vietnam) 2 — — S. paulinae (Lao PDF) — — 11 paulinae resemble most species of Niviventer; ‘‘S. paulinae simply looks like a Niviventer and a Labial roots are divided into two or more rootlets on not like any other species in any other genus’’ some upper and lower molars, but we did not count these (Musser et al., 2005: 20). That Lao species projections as independent roots. In some specimens, the strikingly contrasts with the large-bodied and posterior root on the lower molar is furrowed down the middle suggesting separate posterolingual and poster- short-tailed Vietnamese animal. Tonkinomys olabial anchors, but we scored this configuration as one daovantieni is more robust in build and much large root. The sample of S. paulinae consists of two whole larger in body size than S. paulinae (range in animals and fragments recovered from owl pellets, so the length of head and body is 184–217 mm for count is derived from 3 first upper molars and 8 first lower 13 examples of T. daovantieni versus 144– molars. Sample sizes for all the other species are based on 150 mm for two S. paulinae). Its thick, stubby complete specimens. tail is shorter than head and body length (LT/LHB 5 83%, average of 13 specimens) four roots anchor each molar: large single compared with the slim, tapered, and gracile lingual, large anterior and posterior roots, and tail of S. paulinae that is appreciably longer small labial. Tonkinomys also possesses four than body length (LT/LHB 5 112%–116% for roots beneath each first upper molar, but the two individuals). The tail of both species is pattern is different from that in N. langbianis bicolored, but the dark brown and white and Chiromyscus. No specimen in our sample pattern is different in each. In T. daovantieni, 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 27 the tail is dark brown except for the ventral matic arch is situated high on the side of the surface, which is white, and the distal one- cranium where its ridge-like portion runs fourth to one-half, which is white on all horizontally just below the posteroventral surfaces; the tail of S. paulinae is dark brown margin of the parietal, which projects ventrad on dorsal and lateral surfaces from base to tip, to form the dorsolateral side of the braincase; and white (with slight speckling) over only its the low ridge of the squamosal root disappears ventral surface. Both species have dense and 10–15 mm anterior to the vertical ridge dark gray fur covering upperparts and under- formed by the squamosal-exocciptal suture parts of the head and body. Saxatilomys (fig. 11). The configuration is similar to that paulinae, however, lacks a white forehead characteristic of Leopoldamys and Niviventer. blaze and white pectoral patch, a pattern The squamosal root of each arch in exhibited by most examples of T. daovantieni, Saxatilomys also originates high on the side and its venter is lightly frosted in contrast to of the cranium, but is oriented diagonally so the total gray of the Vietnamese animal. that its posterior ridge-like portion extends Tonkinomys and Saxatilomys do share bul- diagonally to merge with the squamosal- bous plantar pads that are very large relative parietal suture (which forms the temporal to plantar surface and arranged in a tight ridge) well anterior to the vertical ridge cluster (compare the plantar surface of T. created by the squamosal-exoccipital suture daovantieni in fig. 8 with that of S. paulinae in (see figs. 6 and 8 in Musser et al., 2005). The fig. 9). parietal does not drop below the temporal Tonkinomys and Saxatilomys possess an ridge, and the upper portion of the braincase elongate skull, wide zygomatic plate relative consists only of the squamosal. to cranial size, narrow alisphenoid struts Tonkinomys daovantieni and S. paulinae present in most specimens, bony palate have a wide and long bony palate that projects projecting past the third molars to form beyond the molar rows to form a broad a broad shelf with either a smooth or slightly platform. In Tonkinomys, the posterolateral thickened (not ridged) posterior margin, edges of this shelf extends as a flat, bony strongly divergent maxillary molar rows, and surface onto the anterior portion of each a similar mandibular conformation (compare pterygoid plate where its sharp diagonal figs. 10 and 11 with the views of Saxatilomys border (ppm in fig. 12) marks the anterome- in Musser et al., 2005: fig. 6). dial margin of each pterygoid fossa. No such The two species differ in size and some conformation exists in S. paulinae (or in any qualitative traits. Tonkinomys has a more species of Niviventer). robust and larger skull (occipitonasal length, The globular and only slightly inflated for example, ranges from 47.1 to 52.4 mm in ectotympanic (auditory) bulla of Tonkinomys seven T. daovantieni, and 40.3 to 40.5 mm for does not conceal all of the periotic. A wide, the two intact skulls of S. paulinae). Size of the wedge-shaped segment of that bone is exposed gracile skull in the Lao genus resembles the between the dorsal capsular margin and larger-bodied species of Niviventer (the basioccipital, and this wedge of periotic Indochinese N. tenaster, for example; compare extends anteriorly to form the dorsal and the values listed in tables 1 and 4 of Musser et slanting posterodorsal wall of the carotid al., 2005, with those presented in table 1). canal (fig. 12). The conformation is primitive Tonkinomys further contrasts with Saxa- among murines and closely resembles the tilomys by having a less tapered rostrum morphology depicted by Carleton and (when viewed from dorsal or ventral aspect), Musser (1989: 33) for the sigmodontine, significantly less basicranial flexion (marked Oligoryzomys, and by Musser and Heaney flexion in Saxatilomys; see fig. 6 in Musser (1992: 99) for some of the Philippine Old et al., 2005), and spacious incisive foramina Endemic murines. By contrast, the globular (not the narrow slits of Saxatilomys. ectotympanic capsule exhibited by Saxa- Three other qualitative features provide tilomys covers all but a narrow wedge of the marked contrasts between the two genera. In periotic, and the anteromedial margin of the Tonkinomys, the squamosal root of the zygo- capsule meets the basioccipital, so that it is the 28 AMERICAN MUSEUM NOVITATES NO. 3517 ectotympanic (or auditory capsule) that forms Tonkinomys and Saxatilomys (along with the posterior wall of the opening into the most species of Niviventer) share similar carotid canal. This structural relationship maxillary and mandibular molar occlusal between ectotympanic and periotic is special- patterns. Distinctions between the Viet- ized, and is particularly well illustrated in namese and Lao limestone rats are present Carleton and Musser (1989: 33) for the but not spectacular (contrast fig. 14 with the sigmodontine Oryzomys palustris. Species of occlusal views of Saxatilomys in Musser et al., Rattus and its allies have a comparable pattern 2005: fig. 10): compared with Saxatilomys, (Musser and Heaney, 1992: 99). cusps t4 and t6 on the second lamina of the Primary dental differences between Ton- first maxillary molar in Tonkinomys tend to kinomys and Saxatilomys involve size, one retain more of their identity (less distinct in proportional feature, and pattern of molar Saxatilomys and in most species of roots. Tonkinomys has larger upper and lower Niviventer), second and third mandibular incisors than does Saxatilomys, but otherwise molars lack anterolabial cusps in most speci- pigmentation and thickness of enamel, their mens (most species of Niviventer also lack shapes, and opisthodont configuration of the these cusps, but they are present in uppers relative to the rostrum are similar. Saxatilomys), and the cusps on upper and Tonkinomys also has longer molar rows (as lower molars form more distinct and tighter indexed by lengths of maxillary rows: 8.0– chevrons (cusp rows more arcuate, with 8.8 mm in 7 specimens of Tonkinomys, 7.2– greater space between arms of each chevron 7.3 mm for three Saxatilomys); length of in Saxatilomys). maxillary row relative to occipitonasal length Other genera: We also compared examples for the two genera, however, is, on average, of Dacnomys and Srilankamys, other not significantly different (the ratio, CLM1-3/ Indomalayan members of the Dacnomys ONL, using mean values from each generic Division, with our sample of Tonkinomys. sample, is 17% for Tonkinomys and for Dacnomys is a giant version of Niviventer, Saxatilomys). In contrast to molar length, especially N. andersoni, in its external and the individual molars in Tonkinomys are not cranial traits, as well as root patterns of the significantly wider than are the molars of molars (see description and illustrations in Saxatilomys (using breadth of the first upper Musser, 1981). Those molars, however, are molar as a guide, the mean is 2.1 mm for 7 large, chunky, and hypsodont, with compli- examples of Tonkinomys and for 3 specimens cated cuspidate occlusal patterns, and strik- of Saxatilomys; contrast the values listed ingly contrast with the brachydont and gracile in table 1 with those figs. in table 4 in molars with their simple occlusal patterns Musser et al., 2005: 21), indicating significant- possessed by all species of Niviventer. ly narrower molars relative to length of the Tonkinomys bears no close resemblance to maxillary row (the ratio, BM1/CLM1-3, using Dacnomys in external, cranial, or dental traits. mean values from each generic sample, is 25% A combination of traits, some of which for Tonkinomys and 29% for Saxatilomys). recall features in Niviventer, others that re- Two roots (large anterior and posterior) semble Maxomys, and some that are unique, anchor each lower molar in all specimens characterizes the morphological definition of examined of Tonkinomys and Saxatilomys, Srilankamys (see the description and illustra- but the root patterns for the first and tions in Musser, 1981). Its membership in the second maxillary molars are dissimilar in Dacnomys Division is provisional, pending the two genera. In Tonkinomys, the first reassessment of its phylogenetic relationships maxillary molar has four roots (anterior, by additional morphological characters in posterior, and divided lingual), the second combination with molecular data (Musser has three. Saxatilomys has five-rooted first and Carleton, 2005). Srilankamys shares the molars (table 3) and four-rooted second mo- same pattern of molar roots with Tonkinomys, lars; in samples of both Tonkinomys and but otherwise its diagnostic external and Saxatilomys, three roots anchor each third cranial traits, along with molar occlusal molar. patterns, are unlike those of Tonkinomys. 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 29

Musser and Carleton (2005) included the sabanus) and Niviventer (N. fulvescens)and Philippine Mindoran endmic Anonymomys new species in those genera that are extinct mindorensis in the Dacnomys Division. Its and represented only by fossils (L. minutus placement there, however, is very provisional. and N. gracilis). Judged from her descriptions, Some morphological traits of Anonymomys measurements, and illustrations, all these recall those of genera in the Dacnomys samples are correctly allocated to genus; none Division, particularly Niviventer, but others represents Tonkinomys. suggest a closer affinity to Bornean and Pleistocene samples from Guangxi Province Sulawesian Haeromys, a member of the in southern China were determined by Chen et Micromys Division of Musser and Carleton al. (2002) to contain examples of Niviventer (2005). Tonkinomys is morphologically distant and Leopoldamys, but no identifications to from Anonymomys and requires no compar- species were provided. Zheng et al. (1997) isons with it. reported the extant Niviventer confucianus and Our comparative study also included the extinct N. preconfucianus from Plio-Pleistocene Indomalayan Maxomys, although that genus fissure fillings in Shandong Province. Mea- is not contained within the Dacnomys Group surements and drawings of molar occlusal (Musser and Carleton, 2005). Species of patterns presented in these reports convince Maxomys are prominent members of the us their generic attributions are correct. Indochinese murine fauna (Corbet and Hill, Zheng (1993) has provided perhaps the 1992), and some share with Tonkinomys the most comprehensive and thorough survey of same number of roots anchoring each molar fossil murines recovered from late Pliocene (Musser et al., 1979). Any close similarity ends and Pleistocene cave and fissure fillings. All with that character complex. No species of come from the northern margin of the Maxomys has the pelage coloration possessed Yunnan-Guizhou Plateau within an area by Tonkinomys, or the thick, short tail, or the bounded by 104u to 110uE and 26u to 31uN crowded, fleshy palmar and plantar pads. in the provinces of Sichuan and Guizhou. By Additionally, all Maxomys have short, wide clear descriptions and a wealth of measure- incisive foramina that have the outline of an ments, Zheng meticulously documented those inverted heart, a bony palate ending well parts of the samples representing extant anterior to posterior margins of the molar Leopoldamys edwardsi and extinct L. edward- rows, a very long postpalatal region, and other sioides; extant Niviventer fulvescens, N. con- cranial attributes, as well as molar occlusal fucianus, N. andersoni, and possibly N. excel- patterns (see descriptions and illustrations in sior; and the extinct N. preconfucianus. His Musser, 1991) that are not shared with descriptive and quantitative data, along with Tonkinomys. We found no derived characters clear illustrations, provide unquestionable that identified Tonkinomys as either a member support for his identifications. or close relative of Maxomys. Zheng (1993) also described three new Fossils: Reports covering murines recovered species in two new genera that seem morpho- from late Pliocene to Pleistocene sediments in logically similar to Niviventer and other caves and limestone fissures in Thailand members of the Dacnomys Division. Wusha- and China contain descriptions of samples nomys brachyodus is represented by a large identified as species of Leopoldamys, Nivi- cranial fragment containing intact molar rows, venter, and related extinct genera. The bulk dentary fragments with complete or partial of the material is comprised of isolated molar rows, and numerous isolated upper and molars; a few samples contain cranial and lower molars. The fossils come from sediments mandibular fragments. Only some of the thought to be no older than 2.5 million years publications contain information pertinent to ago, and no younger than 1.0 million years our inquiry. ago. Judged by length of upper (9.30 mm, 1 In her detailed and comprehensive treatise specimen) and lower (8.80–9.20 mm, 5 speci- on the Plio-Pleistocene rodents of Thailand, mens) molar rows, this extinct species is much Chaimanee (1998) described samples repre- larger than Tonkinomys daovantieni (uppers, senting extant species of Leopoldamys (L. 8.03–8.78 mm, 7 specimens; lowers, 7.64– 30 AMERICAN MUSEUM NOVITATES NO. 3517

8.52 mm, 10 specimens). Range in measure- configuration recalls that typical of the long- ments of first upper (4.00–4.90 mm by 2.14– nosed Sulawesian murines, Bunomys prolatus 2.66 mm, 85 examples) and lower (3.40– and B. chrysocomus (Musser, 1991: 12–13). In 3.95 mm by 1.90–2.20 mm, 97 specimens) Tonkinomys, posterior margins of the incisive molars of W. brachyodus overlaps with those foramina end just in front of anterior faces of of T. daovantieni (table 4), but average longer the first molars, even with them, or extend and wider (see Zheng, 1993: 190). Most of the only slightly beyond (no more than 0.5 mm); first upper molars in W. brachyodus have three the bony palate extends 1.5–2.0 mm beyond roots, but Zheng noted that some molars have the molar rows forming a much more expan- a divided lingual (see Zheng, 2004: 175), which sive platform, and the interorbit is wide (6.6– is the pattern in T. daovantieni. First lower 7.3 mm; table 1), which is the usual pro- molars have two roots, the primitive pattern portion in skulls the size of Tonkinomys (and that is also typical of the Vietnamese limestone other murines, Leopoldamys neilli, for exam- rat. ple). The bony projection containing the lower Molar occlusal patterns of Wushanomys are incisor in the dentary of Tonkinomys is shorter unlike those of Tonkinomys. The anterior and thicker, and the dorsal outline from molar lamina on the first upper molar in row to incisor tip is more deeply concave, Wushanomys consists of a straight segment a shape common to species of Niviventer, formed by the complete fusion of cusps t2 and Leopoldamys, and other murines with less t3, and a posteriorly offset cusp t1; the second specialized dentaries (Musser, 1981: 272; lamina is arcuate in outline; and cusp t9 is Zheng, 1993: 204). distinct in the posterior part of the tooth (see Zheng’s description of the cranial traits in the illustration in Zheng, 1993: 192). These Wushanomys brachyodus tantalizingly resem- occlusal outlines are strongly dissimilar to bles the conformation in other extinct mur- the strong, tight chevrons formed by the two ines, such as the Canary Islands Malpaisomys front laminae on the first upper molar in insularis, which was likely adapted to living Tonkinomys (fig. 14) and its cusp t9, so and climbing about in the creviscular system coalesced with the large central cusp t8 that of lava fields (Boye et al., 1992; Hutterer et al., it resembles a low ridge. Laminar outlines on 1988). Perhaps W. brachyodus lived and lower molars of Wushanomys are also nearly climbed about in karstic fissures, had a long straight or form wider-armed chevrons, a con- rostrum, and included invertebrates in its diet. trast with the tight chevrons in Tonkinomys. Whatever its habitat and habits, the summa- The cranial and mandibular fragments of tion of morphological traits characterizing the W. brachyodus provide additional compara- complement of fossil remains identifies, in tive information. Zheng did not illustrate the our view, a monophyletic group (at the level specimen, but described it as having very long of genus) separate from that represented incisive foramina that terminate 1.7 mm pos- by Tonkinomys daovantieni; other than terior to anterior faces of first molars, a bony Wushanomys likely being a member of the palate extending about 0.7 mm beyond the Dacnomys Group, there seems no closer molar rows to form a short platform, a very phylogenetic link between Wushanomys and narrow interorbit (6 mm), especially for what Tonkinomys. seems to be a large skull judging from lengths Zheng (1993) described a second species of of molar rows, and a flat, wide zygomatic Wushanomys, W. hypsodontus, based on a few plate (no measurement listed). Zheng did isolated molars that are high-crowned, have include a drawing of a partial dentary (the slightly more complex occlusal surfaces, and body of the ramus behind the molar row is greater dimensions than found in W. brachyo- gone, p. 204). The portion anterior to the dus. The time span in which the fossils lie is 2.0 molar row, along with the incisor, is long and to 1.8 million years ago. slender, and the dorsal outline from anterior Zheng’s other new genus and species, margin of the molar to incisor tip is gently Qianomys wui, is based on a small series of concave. This conformation usually accom- dentary fragments containing full or partial panies a long rostrum, and the mandibular molar rows, an isolated first lower molar, and 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 31 two upper molars. These were recovered from Tonkinomys, Niviventer, Leopoldamys, and sediments thought to be late Pleistocene, Saxatilomys. 400,000 to about 200,000 years ago. The two Qianomys wui is certainly a different species upper molars (4.40 mm and 4.60 mm long) than Tonkinomys daovantieni. Whether the fall within the high end and slightly beyond gross similarities between the two in molar the range of variation in molar length we occlusal patterns signal close phylogenetic recorded for Tonkinomys daovantieni, but they relationship or convergence cannot be de- are much wider (2.35 mm and 2.40 mm) than termined until we can compare the fossils the molars of T. daovantieni (table 4). The directly with our extant samples, and until occlusal pattern does not match that of cranial material representing Qianomys is Tonkinomys, and five roots are present. The recovered and described. Resolving the am- uppers are not examples of the Vietnamese biguous association between the present sam- limestone rat. Even Zheng noted their close ple of upper molars and lowers allocated to similarity to Niviventer in crown outline and Qianomys is also critical. That genus would number of roots, and suggested they may not resemble only Saxatilomys among members of be correctly associated with the lower molars, the Dacnomys Division if the five-rooted first to which the generic and specific name is upper molars with their Niviventer-like occlu- nomenclaturally attached. We agree. For us, sal patterns actually belong to Qianomys with Zheng’s diagram (p. 199) of a first upper its two-rooted lower molars. molar closely resembles N. andersoni in A recent report by Zheng (2004) documents occlusal pattern; however, the size is slightly identities of rodents, represented mostly by outside the range of variation we obtained isolated molars, collected from sedimentary from our sample of that species (table 4) and layers in Longgudong Cave (30u39914.90N/ that which Zheng derived from his material of 110u04929.10E), the ‘‘Jianshi Homind Site’’ in N. andersoni (p. 181). western Hubei Province of central China. The three intact lower molar rows of Geological age was given as Early Pleisto- Qianomys for which measurements are pro- cene, but correlation between the 11 sedimen- vided (8.60, 9.40, and 9.43 mm) are apprecia- tary layers sampled and the geomagnetic bly longer than those in Tonkinomys (7.64– polarity timescale indicated a range extending 8.52 mm, 10 specimens) as are length and from the Olduvai Event of the Matuyama width dimensions of the first lower molars Chron (the Pleistocene/Pliocene boundary) (3.66–4.20 mm by 2.10–2.34 mm, 8 specimens back to earlier than 2.15 million years before of Qianomys; 3.40–3.50 mm by 1.90–2.00 mm the present, reflecting initial deposition during in Tonkinomys, table 4). If molar dimensions the Late Pliocene (see Flynn et al., 1997, and are any indication of skull and body size, Q. Qiu, 1989, for illuminating expositions of wui was a much larger rat than T. daovantieni. Chinese geochronology at the end of the Qianomys and Tonkinomys share the same Neogene). Among the murines recovered were primitive root pattern, two beneath each lower three species in the Dacnomys Division. One is molar. Occlusal patterns formed by the rows the extinct Niviventer preconfucianus, which of laminae fall within the range of patterns Zheng himself had named and described in exhibited by Tonkinomys as well as species of 1993, and another is represented by isolated Niviventer. Zheng, however, claimed that none molars identified only as an undetermined of the molars he assigned to Qianomys have species of Leopoldamys. The third is a new anterolabial cusps on the second and third species of the extinct Wushanomys, W. ultimus, molars or posterolabial cusplets on any molar, described from molars recovered from all but features, in addition to number of roots, which the top two layers of the cave sediments, most he used to distinguish Qianomys from from layers dated between 1.95 to earlier than Niviventer. Comparable cusps do occur on 2.15 million years before the present (Late the lower molars of T. daovantieni.An Pliocene). Molars from W. ultimus are in- illustration of a partial dentary (Zheng, 1993: termediate in size between the earlier described 204) indicates the portion anterior to the W. brachyodus and W. hypsodontus (Zheng, molar row to be similar in shape to that of 1993), express greater hypsodonty, and differ 32 AMERICAN MUSEUM NOVITATES NO. 3517 slightly in coronal patterns. Ranges in length drawings of molar occlusal cusp patterns, or and breadth values for first upper (3.90– to measurement values for the sample of N. 4.92 mm by 2.20–2.65 mm, 22 examples) and fulvescens. lower (2.90–4.30 mm by 1.98–2.30 mm, 18 We cannot verify the identification of N. specimens) molars of W. ultimus (see Zheng, fulvescens. That species is common in northern 2004: 173) overlap with those of Tonkinomys Vietnam and in many places occurs together daovantieni (table 4), but average slightly with N. tenaster (results of our trapping longer and wider. Each first lower molar of surveys in several different regions of northern W. ultimus has two roots, the pattern common Vietnam), which is somewhat larger in dimen- to the other two species of Wushanomys, but sions of body and skull, as well as length of first upper molars have either four (anterior, molar row and breadths of molars (Musser divided lingual, posterior) or five roots (a and Lunde, ms.). Niviventer tenaster also small labial holdfast or nubbin in addition to occurs in northern Thailand (Musser and the four primary roots). The pattern of the Carleton, 2005), but Chaimanee (1998) did four primary roots beneath the first upper not include it in her report. The material molars and two anchoring first lower molars reported by Bacon et al. (2004) should be also characterizes Tonkinomys daovantieni, but reexamined to determine whether it is really N. molars of that Vietnamese rat are not hypso- fulvescens or possibly N. tenaster. dont, and although the extinct and extant Measurements listed by Bacon et al. (2004) species share molars similar in size, their for two first lower molars of Leopoldamys (4.0 occlusal patterns are dissimilar. The occlusal by 2.6 mm and 4.7 by 2.8 mm) fall within the cusp patterns characteristic of W. ultimus range of variation for the larger species of resemble, except for minor details, those in that genus (Chaimanee, 1998; Zheng, 1993), W. brachyodus and differ from T. daovantieni and well outside the range for our sample in the configurations we previously described of Tonkinomys (table 4). The lower second contrasting W. brachyodus and the Vietnamese and third molars that were identified as Leo- species. poldamys are also large and likely represent These new samples of the Dacnomys that genus. But these fossil molars may not Division recovered from the Jianshi Homind belong to L. sabanus. Leopoldamys requires Site provide additional information on Late taxonomic revision because more species exist Pliocene geographic distributions of Niviventer than are usually recognized (four were listed and Leopoldamys. The geographic range of by Musser and Carleton, 1993, and six by Wushanomys is also expanded as is the Musser and Carleton, 2005, which still under- diversity of species in that genus. Judged estimates the number of species), and the from Zheng’s (2004) descriptions, measure- situation in northern Vietnam is especially ments, and illustrations, none of the identified complex. At least two species occur there. One fossil molars represent the Vietnamese may be L. edwardsi, the other is usually Tonkinomys. identified as L. sabanus, but is actually Our final survey of fossils assesses the a different species (Gorog et al., 2004; identification of murines recovered from Musser and Carleton, 2005). Pleistocene sediments in Ma U’Oi cave in An upper first molar and lower first molar northern Vietnam, south of Hanoi (Bacon et were identified as Niviventer andersoni in al., 2004). One mandible containing a complete Bacon et al. (2004). Ma U’Oi cave is far south molar row was identified as Niviventer fulves- of the present geographic distribution of N. cens; an upper first molar and a lower first andersoni, which extends from eastern Xizang molar were attributed to N. andersoni; and (Tibet) through northern Yunnan, western a dentary containing all molars, and isolated Sichuan, and northern Ghizhou to southern first and second molars, were determined as Shaanxi, and over an altitudinal range from Leopoldamys sabanus. The molars were iden- 6000 to 10,000 ft (Musser and Chiu, 1979; tified by comparing them with Chaimanee’s Musser and Carleton, 1993, 2005). We sought (1998) treatise on fossil Plio-Pleistocene Thai to determine whether these two fossil molars rodents. Unfortunately, we are not treated to belong to Tonkinomys. Dimensions of the first 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 33

TABLE 4 Summary Statistics for Lengths and Breadths (mm) of First Upper and Lower Molars of Niviventer andersoni (China, Yunnan and Sichuan), N. excelsior (China, Sichuan), N. tenaster (Vietnam), Pleistocene First Molars Identified as N. andersoni by Bacon et al. (2004), and Tonkinomys daovantieni (Vietnam) (Mean, plus or minus one SD, and observed range in parentheses are listed for each measurement. Samples consist entirely of AMNH specimens except those reported by Bacon et al., 2004.)

N. andersoni N. excelsior N. tenaster Bacon et al. T. daovantieni

(N 5 45) (N 5 13) (N 5 16) (N 5 1) (N 5 7)

Length of M1 3.7 6 0.1 3.3 6 0.1 3.2 6 0.1 3.7 4.2 6 0.1 (3.5–4.0) (3.1–3.6) (3.0–3.6) (4.1–4.5) Breadth of M1 2.1 6 0.1 1.9 6 0.1 1.7 6 0.1 2.0 2.1 6 0.1 (2.0–2.2) (1.8–2.0) (1.6–1.8) (2.0–2.2) Length of m1 3.3 6 0.1 3.0 6 0.1 2.8 6 0.1 4.1 3.5 6 0.1 (3.1–3.5) (2.8–3.2) (2.7–3.1) (3.4–3.5) Breadth of m1 1.8 6 0.1 1.7 6 0.1 1.6 6 0.1 2.5 2.0 6 0.1 (1.7–1.9) (1.6–1.9) (1.5–1.7) (1.9–2.0)

upper molar (3.7 by 2.0 mm) do fall within the consists of a nearly straight segment, formed range of variation of our values (table 4) and by the coalesence of cusps t2 and t3, and those tabulated by Zheng (1993: 181) for large a posteriorly displaced lingual cusp t1 (see figs. sample sizes of N. andersoni. Breadth of the in Musser, 1981, and Zheng, 1993). The fossil molar fits within our observed range for comparable lamina has an arcuate outline on first upper molars of Tonkinomys, but the the upper molar in N. tenaster, similar to that length is much too short—based on these found in N. confucianus (Musser, 1981). The data, the molar did not come from the fossil molar needs to be reexamined; it is not Vietnamese limestone rat. However, it may an example of Tonkinomys, and we question not represent N. andersoni. The width, for its identity as N. andersoni. example, matches our range of values for N. The first lower molar determined to be N. excelsior, and the length is only 0.1 mm andersoni in Bacon et al. (2004) is large (4.1 by shorter (table 4). Niviventer excelsior is a close 2.5 mm), and its dimensions fall far outside relative of N. andersoni that presently occurs the range of variation in our samples of only in high mountains north of the Yangtze Tonkinomys, Niviventer andersoni, N. excelsi- River (Musser and Chiu, 1979). For N. or, and N. tenaster (table 4). The tooth is excelsior to have once occurred in northern actually about the same size as the two first Vietnam, however, seems as implausible to us lower molars (4.0 by 2.6 mm, 4.7 by 2.8 mm) as the presence of N. andersoni there, espe- they identified as Leopoldamys. The values cially because all the fossils of other mammals are either misprints, or the molar does found in situ in the Ma U’Oi cave define ‘‘… belong to Leopoldamys; it, and the first upper a relatively modern fauna …’’ (Bacon et al., molar assigned to N. andersoni, warrants 2004: 312). Niviventer tenaster currently lives restudy. in northern Vietnam in forest habitats. Summary: There would have been an Lengths and breadths of first upper molars elegant symmetry in discovering ancient, from this species in our sample from that fossilized remnants hidden in limestone fis- country nearly embrace dimensions of the sures that represented the same murine species fossil molar (table 4), and that tooth just living today in creviscular habitats within the might be from a large individual of N. tower karst landscape forming northern tenaster. Both N. andersoni and N. excelsior Vietnam. Unfortunately, we cannot unambig- can easily be distinguished from N. tenaster by uously tie any published identifications of occlusal patterns. In the former pair, the fossilized fragments representing Indochinese anterior lamina on the first upper molar murines to the extant Tonkinomys daovantieni. 34 AMERICAN MUSEUM NOVITATES NO. 3517

Its past distribution and phylogenetic alliance to form a shelf with a smooth posterior to extinct taxa, as might have been illuminated margin; strongly diverging (along the ante- by fossils, remain a mystery. roposterior axis) maxillary molar rows; de- Unresolved also is the phylogenetic position rived root pattern for the first upper molar of Tonkinomys with respect to Leopoldamys, coupled with the primitive root patterns Niviventer, and Saxatilomys, the three extant underlying the other uppers and all the lower genera with morphologies most like that of molars. Tonkinomys. The differences enumerated Both Tonkinomys daovantieni and Saxa- above between Tonkinomys daovantieni on tilomys paulinae are associated with forested one hand and species of Leopoldamys and karstic habitats. Both genera display dark Niviventer on the other reflect a combination gray pelage, large and swollen plantar tuber- of primitive and derived features. Relative to cles, a bony palate that projects beyond the the pelage coloration, shape of tail, and its molar rows to form a broad platform, length relative to length of head and body in maxillary molar rows that appreciably diverge Leopoldamys and Niviventer, the contrasting posteriorly (along the anterior-posterior axis) condition in Tonkinomys is derived. Also and are long relative to length of skull, and representing specializations in Tonkinomys two-rooted mandibular molars. All but the are the position of the squamosal zygomatic root pattern are specialized traits. This com- roots high on the sides of the braincase, bination of attributes is not combined in any slender or no alisphenoid struts, its long species of either Leopoldamys or Niviventer (or incisive foramina, a very long bony palate Chiromyscus). We do not know whether the that projects beyond the molar rows to form morphological specializations shared by T. a broad shelf, posteriorly diverging maxillary daovantieni and S. paulinae phylogenetically molar rows, simple molar occlusal patterns, link these species closer to each other than to and a divided lingual root beneath the first species of Leopoldamys and Niviventer,or upper molar. Presence of three roots beneath rather reflect independent evolutionary adap- each second and third molar, and two roots tations to forested karstic environments in the anchoring each lower molar represent the Indochinese tropics. In opposition to the primitive condition in Tonkinomys compared shared specializations, external morphology with the derived state in Leopoldamys and of Tonkinomys (except for relative length of Niviventer. Tonkinomys daovantieni resembles tail) recalls a small-bodied Leopoldamys, while the Indochinese Leopoldamys neilli in body that of Saxatilomys resembles most species size, and it along with the other Indomalayan of Niviventer. Overall cranial form in species of Leopoldamys in general cranial Tonkinomys also resembles Leopoldamys, and conformation and a few cranial particulars except for those cranial traits that distinguish (position of the squamosal zygomatic roots, S. paulinae from species of Niviventer (com- for example); with Niviventer, Tonkinomys parisons are enumerated by Musser et al., shares long incisive foramina, comparable 2005), the general cranial conformation of inflation of the auditory bulla relative to the Saxatilomys is not unlike most species of underlying periotic bone, and similar molar Niviventer. Inferring the phylogenetic relation- occlusal patterns. Other traits exclude T. ship of Tonkinomys among species now allo- daovantieni from each of those genera as cated to the Dacnomys Division in general, and they are currently diagnosed (Musser, 1981). especially to species of Leopldamys, Niviventer No species of Leopoldamys or Niviventer (or (including Chiromyscus), and Saxatilomys will Chiromyscus), whether occurring in Indochina rest on results derived from future phylogenetic or on the islands on the Sunda Shelf, has analyses of information derived from both Tonkinomys’s combination of dark grayish morphological and molecular sources. black upperparts and dark gray underparts; thick tail with a stubby tip that is much HABITAT AND HABITS shorter than length of head and body; large, bulbous, and contiguous plantar pads; bony The Dao village of Lan Dat lies within palate projecting well beyond the third molars a spectacular tower karst landscape, its houses 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 35 and adjoining agricultural clearings scattered close to houses and fields, and scrub habitats over flat depressions nestled among high dominate clearings not utilized for crops limestone hills with steep sides and sheer, (fig. 1). Forest once growing on the few flat expansive cliffs. The area epitomizes the or gently sloping places above the valley and classic description of karst landforms: between limestone towers has been either ‘‘Karstic terrain is commonly characterized removed or thinned. The primary forest cover by closed depressions, subterranean drainage is also not undisturbed by human activity. and caves’’ (Gillieson, 1996: 59). The climate is Trails cut through the understory usually lead monsoonal, with most of the year’s rain to remnants of a huge emergent tree felled and concentrated from April to October. Average processed for lumber. Natural disturbance in annual rainfall (measured at Lang Son over the form of treefalls and landslips is eventually 50 years) is 1395 mm, and even though cold covered by shrubs and then taller second- temperatures dominate from November growth. through March, humidity remains high, the The day we broke camp and climbed out of annual relative humidity averaging 81% (Ðieˆ´u, the valley our usual trail chatter was silenced 1995). by a loud rumble, which had been generated Most of the flat areas, once supporting by a massive rockslide. This is a periodic, tropical moist deciduous forest, have been unpredictable event, according to the villagers, cleared by the Dao for rice cultivation and and potentially dangerous. Weathering of shifting agriculture. Forest remains at the the high cliff faces through the combined base of the cliffs, in ravines between the high forces of water dissolving the limestone, towers, and on the steep slopes, and it is not differences in temperature, and pressure from unlike Whitmore’s (1984: 174) description: large tree roots eventually dislodge chunks ‘‘… limestone slopes have a dense, irregular of cliff wall, some small, others huge. Such forest with trees clinging precariously, their an event formed the habitat in which we roots penetrating to great depths in crevices trapped most of the limestone rats. Above …’’ The forest consists of a low canopy (up the valley floor, a wide ravine between two to 15 m high) with taller (up to 25 m or contiguous limestone towers had been filled more) emergents scattered over the steep by a chunk of cliff wall the size of a small slopes. Most trees are small (1–3 ft in di- house along with smaller pieces—basically ameter near the base), except in places a talus of large blocks between the towers. allowing accumulation of sufficient soil The openings among the pieces were eventu- where huge emergents are able to grow. ally enlarged, mostly by water flowing into Here and there a grove of emergent species the rubble pile from the top, and under- forms a small area of high canopy. Palms neath it along the bottom of the old ravine. and bamboo clumps are scattered through The result is a honeycomb of passageways, the understory, strangler figs are uncommon, some extending vertically to small openings and woody vines drape over high limestone on top of the rubble, others opening to an ledges and form tangles beneath the forest uncovered section of the ravine. Walls of canopy. The limestone towers are densely the labyrinth are wet and the air is cool. forested except for the sheer cliffs. Clumps of Shrubs, vines, and moss cover the surface of Pandanus are common at the base of these the rubble, hill forest persists at the cliff walls, and sometimes grow higher where they bases of each tower, and small trees are can obtain purchase in joints and fissures. scattered over the talus (fig. 2). The surface Wedidnotencountercycadsintheforest, of the rubble is difficult to negotiate. Rain and saw them only high on the vertical cliffs. has sculpted the limestone into small depres- Isolated clumps of bamboo remain in some sions surrounded by knife-sharp edges; small of the clearings, and dense bamboo forest to large openings are everywhere, some as covers the steep slopes and tops of some deep as 8 meters that expand into large limestone towers. cavities; and some openings are concealed Most of the hillsides support primary forest, by loose limestone fragments that shift un- old and tall secondary growth covers hillsides derfoot. 36 AMERICAN MUSEUM NOVITATES NO. 3517

Thirteen of the T. daovantieni were caught and on the forest floor, we did not encounter in this talus. Two were trapped on the surface, any T. daovantieni. A large cave was accessi- one beneath a shrub, the other one at the ble, but it was being used as a corral for cattle; margin of the rubble beneath a rotting trunk. the interior was dry, and mostly scrub and Five were taken in traps set at the bottom of young secondary forest persisted near the the ravine beneath the main overhanging entrance. Traps placed on ledges inside the limestone chunk (the configuration resembled cave and outside near the entrance yielded a small cave, but was really only a low passage nothing. We also set traps in a small, wet cave beneath the straddling rock). Another was used as a roosting site by bats. No limestone captured on a moss-covered ledge just outside rats were caught. Caves occur throughout the of this cave-like passage. Five others were area, but the openings to most are high in the caught in traps lowered by ropes through cliffs and inaccessible to us. small and large holes in the talus surface to the Certainly more field study is required to bottom of the labyrinth, which ranged from 4 assess the habitat requirements of T. daovan- to 8 m, depending on how close the vertical tieni, but our trapping experience suggests this passages were to sides of the ravine. In these forest species to be petricolous. It seems to situations, most live and snap-traps were require large areas of rock debris or talus that placed directly on the passageway floors. provides sufficient passageways and chambers Traps placed on limestone ledges above this for protected den sites, and a cool, damp rubble near bases of the towers, or in the dense environment. Long vibrissae; large, bulbous forest covering steep slopes away from the palmar and plantar pads; and a tail that is talus, yielded only Niviventer fulvescens and N. considerably shorter than head and body, that langbianis. is thick and stubby-tipped, and that has a well- Tonkinomys daovantieni was not the only haired distal half and tip are adaptations inhabitant of this talus. We captured a Rattus important in a creviscular environment. The andamanensis and a Niviventer fulvescens at vibrissae monitor the cracks and walls for the mouth of the cave-like passage, an N. prey, surface information, and passage width; fulvescens on the surface, and one at the the fleshy pads provide purchase on rock bottom of the deepest chamber. surfaces; and the tail is used for balance as The only limestone rat not trapped in or on the rat scurries up and over the rocks and the talus was taken in mature second growth through the crevices and passageways, or as hillside forest behind camp, which is at the other a fifth appendage when pressed against the end of the valley from the rubble where all the limestone (the hairs would aid in purchase by others were caught. Here between the massive pressing against the rough surface). We see cliffs and valley floor is a steep middle region of similar adaptations in other petricolous mur- limestone talus, formed of small to massive oid rodents. The bushy-tailed woodrat, chunks that broke away from the cliff above. Neotoma cinerea, for example, is a North This is the only talus-like structure we encoun- American cricetid analog to the Vietnamese tered here. While soil has filled in most of the murid, T. daovantieni. This species of Neotoma spaces among the blocks, apparently enough dens in caves, fissures in high cliffs, and deep interstices and underground extensions exist to in talus slopes (Finley, 1958; Grayson, 1999; provide the proper habitat for T. daovantieni. Musser’s trapping experience). Size and flesh- Either that or the animal wandered from places iness of its footpads relative to foot size, on the tower we did not survey. The forest length of tail relative to head and body covering the talus is dense and festooned with length, and even overall body size is closely woody vines. Niviventer fulvescens and the similar to these qualities in the limestone rat arboreal N. langbianis were common. (see measurements provided by Finley, 1958: Populations of T. daovantieni apparently 322–325). have a patchy distributional pattern. Despite A cool and damp environment of crevices our sampling efforts on other hillsides, where and larger passageways may be important to traps were placed beneath rocky outcrops, on the diet of T. daovantieni because the diversity ledges, at the bottom of deep fissures in cliffs, and numbers of arthropods is probably higher 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 37 there than in dry situations. Of two limestone 49), however, captured three individuals in rats kept captive, one devoured two kinds of lowland bamboo forest in a different part of cockroaches: a large-bodied species caught at Kanchanaburi Province. The trap sites aver- the talus, and a smaller species collected in aged 115 m from the base of the nearest village houses and at camp. This rat refused limestone mountain, and L. neilli was not offers of corn, manioc, snails, earthworms, encountered in the other habitat types Wiles grasshoppers, beetles, and small frogs. Our surveyed, indicating the species to prefer other captive rejected cockroaches offered lowland bamboo forest, which ‘‘… challenges during daytime, but headless bodies we piled the belief that L. neilli is strictly a cliff- in its cage were gone by morning. We are not dwelling rat.’’ sure whether they were dragged away by Niviventer hinpoon is apparently endemic to insects or eaten by the rat. We extracted the Korat Plateau in Saraburi Province of stomach contents from two rats. In one, the southern Thailand (Marshall, 1988; specimens stomach was distended with bait (mixture of in AMNH and USNM). One sample, which peanut butter, bacon pieces, oatmeal, and includes the holotype, was collected halfway raisins) in which were scattered pieces of very up the face of a forested limestone cliff outside small beetles, which were likely on the bait and the entrance to a cave. Another series came inadvertently ingested by the rat. The stomach from ‘‘… high above the valley floor, in of the other was partly full, containing scrubby vegetation at the base of vertical fragments of sclerites intermingled with soft limestone cliffs … ,’’ (Marshall, 1988: 459). unidentifiable animal tissue. Tonkinomys dao- Other species of murids were captured in the vantieni includes insects in its diet, but other forested stream valley below the cliffs, but not components remain to be discovered. N. hinpoon. Marshall (1988) also noted that The limestone rat is probably nocturnal, but one individual had been taken inside a lime- may also be active at times during the day. We stone cave at a different locality. Whether N. were drawn to the talus because during one hinpoon dens in clefts in cliffs or in talus is not late morning Lunde had glimpsed a large, recorded. Except for its tail, which is equal to dark gray rodent scurrying across the lime- or slightly longer than length of head and stone and disappearing into the rubble. body, its buffy gray underparts, and its Results from the first night’s traps revealed smaller body size (Marshall, 1988), the mor- the rodent to be the limestone rat. We kept phological traits of N. hinpoon are similar to our traps in place during day and night, and those of N. fulvescens; our multivariate anal- often checked them in the evening, but never yses of morphometric cranial and dental data caught any rats during the day. place it closer to N. fulvescens than to any other species (Musser and Lunde, ms.). CLOSING OBSERVATIONS Relative to palmar and plantar areas, the pads are no larger or set no closer together Other species of Indochinese murids live in than in N. fulvescens (see fig. 9) or any of the the tropical forests of karst regions but, except other species of Niviventer. Nothing in the for Saxatilomys paulinae, none have any of morphology of N. hinpoon points to an the diagnostic morphological attributes of obligate limestone cliff-dweller. We need to Tonkinomys daovantieni and none are so learn details of its actual microhabitat and ecologically tied to the kind of creviscular other aspects of its life history. habitat in which we discovered the Vietnamese Nothing comparable to the Vietnamese species. Two Thai murids are generally con- Tonkinomys, or to the Lao Saxatilomys,in sidered closely associated with limestone. morphology or habits has so far been found in Leopoldamys neilli is documented by a few the karst landscapes of Thailand. specimens captured on the upper sections of Whitmore (1984: 148) noted that karst forested limestone cliffs in Saraburi Province landscapes covered only a small part of and adjacent Kanchanaburi Province in tropical Asia. In Indochina they occur in southwestern Thailand (Marshall, 1988; speci- southern China, north and central Vietnam, mens in AMNH and USNM). Wiles (1981: central Lao PDR, southern Cambodia, 38 AMERICAN MUSEUM NOVITATES NO. 3517

Thailand, and northeastern Burma (Mid- ed karstic environments, or if other karstic dleton and Waltham, 1986; Zhang, 1989; islands in Indochina support different and Tuyet, 1998; also see the references cited in unique murine endemics. Surveys for small Whitmore, 1984). Except for the large lime- mammals, such as ours that yielded stone plateau in southern China, karst land- Tonkinomys, would uncover the mammalian scapes in Indochina are small in area, scat- diversity in these extraordinary isolated land- tered over the region, and constitute isolated scapes and provide an answer to our question. geological islands (see the informative distri- bution maps in Middleton and Waltham, ACKNOWLEDGMENTS 1986). They are difficult places in which to work, and most Indochinese karst habitats Our work in Vietnam has its origins in have been inadequately sampled for murid a National Science Foundation Grant rodents. (No. 9870232) to the Center for Biodiversity Saxatilomys paulinae and Tonkinomys dao- and Conservation at the American Museum of vantieni are the only petricolous Indochinese Natural History. Funds for the survey during murines that to date have been found to be April of 2004 were provided by the Division of endemic to tropical karstic environments. The Vertebrate Zoology (Mammalogy) at the Khammouan Limestone in central Lao PDR American Museum, and we are especially defines the known distribution of S. paulinae. grateful to Nancy Simmons for her help in That tower karst landscape is part of the Quy securing that money. Dr. Nguyen Xuan Dang, Dat massif (or Kebang karst block; Tuyet, Head of the Department of Zoology at the 1998: 189), which extends eastward at the Institute of Ecology and Biological Resources same latitude into Bienh Tri Thien Province of in Hanoi, allowed us to use the department as north-central Vietnam. In the Lao segment, S. a home base and offered the assistance of paulinae, the gymnure, Hylomys megalotis, members of the scientific staff: Nguyen Xuan and the hystricomorph rodent, Laonastes Nghia (mammalogist) and Doan Van Kien aenigmamus form a small community that (herpetologist). Mr. Le Dinh Thanh served as may be restricted to forested, rocky habitats camp cook and agreeable companion. Many within the extensive and massive karst land- residents of Lang Son Province supported our scape; this same mammalian assemblage may endeavors in the field, including Mr. Tran also occur in the Vietnamese segment of the Van Chuyen, our local forest guide, and Trieu Quy Dat massif (Musser et al., 2005). The Quy Sinh Duong, the head of the Dao village Dat outcrop forms a karstic island approxi- where we worked. Neil Duncan prepared the mately 475 km south of the expansive Vietbac skulls at the American Museum. The brilliant tower karst region in northern Vietnam where talent and competence of Patricia J. Wynne Tonkinomys daovantieni occurs. That lime- are reflected in her line drawings. The stone rat, isolated on a geological island morphological comparisons described in our separate from the one on which S. paulinae report are built on results of biological was found, has been recorded only from the surveys in the field, and the innumerable days type locality in northeastern Vietnam but may (over a span of three decades for Musser) have a wider geographic distribution in working in collections of museums in the forested habitats throughout the karst land- United States, Europe, and Asia. Custodians scapes of northern Vietnam and adjacent of those collections, some now deceased, southern China. Unlike the Khammouan allowed us to study specimens, and never Limestone region, no other petricolous mam- hesitated to loan material whenever we re- malian limestone endemics have been discov- quested it. This report, those already pub- ered in the same landscape occupied by T. lished under our names, and future contribu- daovantieni. tions now in manuscript, reflect in part the We have asked ourselves if the Vietnamese results of original research, but also the and Lao limestone rats are the only murine unselfish contributions of those persons who components of a pattern reflecting evolution- are responsible for maintaining research col- ary adaptation of ancestral murines to forest- lections—we thank you. 2006 MUSSER ET AL.: NEW RODENT FROM VIETNAM 39

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