AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2730, pp. 1-23, figs. 1-1 3, tables 1, 2 June 7, 1982 Results of the Archbold Expeditions. No. 107. A New Genus of Arboreal Rat from Luzon Island in the Philippines GUY G. MUSSER' ABSTRACT The taxon latidens Sanborn, 1952 originally nar-like occlusal surfaces are not characteristic of named and described as a species ofRattus is taken Rattus. The species is known by two specimens out of that genus and placed in Abditomys, new from the island of Luzon in the Philippines. The genus. Some of its distinctive features, such as relationship oflatidens to other Murinae with nails nails instead of claws on the halluces, wide upper on the halluces is discussed. Aspects ofits natural incisors, and large molars with simple and lami- history are presented. INTRODUCTION I propose a new genus for a native Phil- the fauna will be analyzed in a separate re- ippine rat originally described as Rattus la- port. tidens (Sanborn, 1952), endemic to the island There is an impression among mammal- of Luzon in the Philippines. This report is ogists and biogeographers that the native one of several already published (Musser, Philippine rats are well known, especially 1977a, 1977b, 1979, 1981a; Musser and that spectacular segment of the fauna that Freeman, 1981; Musser and Gordon, 1981) lives on the western highlands in northern or in manuscript dealing with the taxonomy Luzon (Thomas, 1898). This is not so. We and geographic distribution of Philippine know less about the Philippine rats than most murids. With this and future papers, I intend other murid groups in the Far East. The nat- to document the morphological limits ofcer- ural history of nearly all the native species tain species and provide information about is either unknown or encapsulated in sketchy their insular distributions and natural his- descriptions made by collectors. Many of the tories. Possible phylogenetic relationships of native genera were thought to be restricted I Archbold Curator, Department of Mammalogy, American Museum of Natural History. Copyright ©) American Museum of Natural History 1982 ISSN 0003-0082 / Price $1.90 2 AMERICAN MUSEUM NOVITATES NO. 2730 for their work with the Scanning Electron 1 bis Microscope and the resulting micrographs. a-lab Mrs. Frances A. Hufty, of Archbold Expe- alc ditions, Inc., contributed part ofthe financial pd- support for my work. plc hd- ABBREVIATIONS AND METHODS a-lab- Specimens referred to here are in collec- pd- tions of the American Museum of Natu- plc- 7- al History, New York (AMNH); the Brit- hd- ish Museum (Natural History), London -lab- (BMNH); the Field Museum of Natural His- Pd- tory, Chicago (FMNH); the Rijksmuseum hd- van Natuurlijke Historie, Leiden (RMNH); and the National Museum ofNatural History FIG. 1. Nomenclature of dental structures us- of the Smithsonian Institution, Washington, ing right upper and lower molars of Lenothrix D.C. (USNM). canus. Upper molars: cusps are numbered accord- Values for lengths of head and body, tail, ing to Miller's (1912) scheme and are referred to hind foot, and ear are from the labels attached in the text with the prefix t; pc, posterior cingulum. to study skins. Cranial and dental measure- Lower molars: a-cen, anterocentral cusp; a-lab, ments were taken with dial calipers graduated anterolabial cusp; a-ling, anterolingual cusp; pd, to tenths of millimeters; limits ofthose mea- protoconid; hd, hypoconid; md, metaconid; ed, surements are explained in Musser (1970, entoconid; pc, posterior cingulum; alc, anterior 1979). The nomenclature I use for cusps and labial cusplet; plc, posterior labial cusplet. cusplets on the molars is diagrammed in fig- ure 1. DIAGNOSIS AND DESCRIPTION to Luzon or Mindanao but actually have more extensive distributions over the archi- Named and described by Sanborn (1952) pelago. The diversity ofthe fauna, at the level as a species of Rattus, the characteristics of ofgenera and species, is greater than generally latidens are known from an adult female (the realized. There are specimens hidden under holotype) and an adult male, both from the misidentifications in museum collections island of Luzon in the Philippines. Sanborn that represent new taxa, there are samples of (1952, p. 125) diagnosed latidens as "A large new species obtained from various islands dark species with tail slightly longer than during recent exploration, and there are head and body; skull short, with thick ros- many species now placed in Rattus that really trum, large bullae and short palate ending do not belong there. The species, latidens, is between last molars; molar pattern like that one of these. To separate it from Rattus, to of Rattus, but incisors nearly twice the width contrast it to other species that have nails found in most species of Rattus and wider instead ofclaws on their halluces, and to pro- than in the largest species." Those wide in- vide notes and speculations about its natural cisors should have prompted Sanbom to look history are my intentions here. closer at the holotype. The configuration of I am grateful to the curators who allowed the cranium and the occlusal patterns of the me access to collections under their care; to molars are unlike species of Rattus; further- Ms. Fran Stiles, Ms. Marjorie Shepatin, and more, each hallux has a nail instead ofa claw, Mr. Helmut Sommer for the artwork; to a specialization not found in any Rattus. The Messrs. Arthur Singer, Peter Goldberg, and two specimens of latidens represent a species Jim Coxe for the photographs; and to Mr. outside of the morphological radiation char- Robert J. Koestler and Mr. Richard Sheryll acterizing not only Rattus but all other known 1982 MUSSER: LUZON ISLAND RAT 3 genera of murids and requires its own genus, first lower molars four-rooted; each third up- which is named and diagnosed below. per molar squarish in occlusal outline, only a little smaller than the second; upper molars with simple occlusal surfaces, no cusps t7, no ABDITOMYS, NEW GENUS posterior cingula, no cusps t3 on second and TYPE SPECIES: Rattus latidens Sanbom third molars; cusp t9 broadly merged with (1952, p. 125); based on the holotype, an cusp t8 on first and second molars; front two adult female (FMNH 62347), collected April rows of cusps form thin and gently arcuate 29, 1946, from Mount Data, 7500 feet, laminae on each first upper molar and on the Mountain Province, Luzon, the Philippines. front row of each second and third upper An adult male (USNM 357244) obtained on molar; last row ofcusps on each upper molar March 14, 1967 from Los Baflos, Laguna laminar, nearly transverse; occlusal surfaces Province, Luzon (Barbehenn, Sumangil, and of lower molars consisting of transverse Libay, 1972-1973) is the only other known laminae formed from two elongate cusps; specimen of the species. posterior cingulum a wide flat-topped cone KNowN DISTRIBUTION: The island of Lu- in center ofposterior margin on first and sec- zon in the Philippine Islands (fig. 2). ond lower molars; small anterolabial cusps ETYMOLOGY: Abditomys is formed by com- on second and third molars; no anterocentral bining the Latin, abditus, meaning hidden or cusp at front of first lower molar; no labial concealed, with the Greek, mys, for mouse cusplets on any lower molars. or rat. I allude to the past concealment of DESCRIPTION: Abditomys latidens is a large- latidens-so distinctive in features of skin, bodied rat with a tail longer than the com- skull, and teeth-within the morphological bined lengths of head and body (table 1, fig. confines of the genus Rattus, to which it is 3). The upperparts of the head and body are not closely related. brown with tawny highlights. The underparts DIAGNOSIS: A genus ofarboreal murid dis- are buffy yellow with gray suffused through tinguished from all other species by the fol- the base of the coat. Color of the venter is lowing combination of features: large body indistinctly demarcated from that ofthe dor- size, long, monocolored tail; four pairs of sum. The pelage covering the head and body mammae; a large nail instead of a claw on is long (30-35 mm. over the back) and coarse, each hallux; squamosal roots of the zygo- but not spinous. Long (up to 50 mm.) and matic arches situated high on sides of the conspicuous guard hairs emerge from the braincase; squarish interparietal, its anterior coat everywhere over the top and sick.s Z-f the one-third between the parietals, the posterior body, and are especially prominent over the two-thirds roofing the occipital bulge; no rump. The ears are large and brown. The tail strut ofalisphenoid bone covering lateral part is brown everywhere, appears naked, but is of the alisphenoid canal; masticatory-bucci- covered with short, stiff, inconspicuous hairs. nator foramina merged with foramen ovale The feet are dark or pale brown over the en- accessorius; incisive foramina long and thin; tire dorsal surfaces down to the base of the palatal bridge short, ending well before backs claws. The claws on the front feet are sharp of third molars; deep mesopterygoid and and small, especially relative to the large dig- pterygoid fossae; sphenopalatine and sphe- ital pads all textured with transverse and nopterygoid vacuities large; bullae large and semicircular striations. There is a prominent inflated; upper incisors very wide, absolutely pointed nail on each hallux; the other digits and relative to breadth of rostrum; molars in claws long and wide, gleaming white, the uppers terminate large, elongate, sharp (fig. large relative to area of palatal bridge; high 4). The female has four pairs of mammae: a cusps that slant back with appreciable over- pectoral pair, postaxillary pair, and two in- lap between first and second molars, and be- guinal pairs.