NovltatesAMERICAN MUSEUM PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 3085, 39 pp., 17 figures, 6 tables December 27, 1993

A New Genus for Hesperomys molitor Winge and Holochilus magnus Hershkovitz (Mammalia, Muridae) with an Analysis of Its Phylogenetic Relationships

ROBERT S. VOSS1 AND MICHAEL D. CARLETON2 CONTENTS Abstract ...... 2 Resumen ...... 2 Resumo ...... 3 Introduction ...... 3 Acknowledgments ...... 4 Materials and Methods ...... 4 Lundomys, new genus ...... 5 Lundomys molitor (Winge, 1887) ...... 5 Comparisons With Holochilus ...... 11 External Morphology ...... 13 Cranium and Mandible ...... 15 Dentition ...... 19 Viscera ...... 20 Phylogenetic Relationships ...... 21 Character Definitions ...... 23 Results ...... 27 Phylogenetic Diagnosis and Contents of Oryzomyini ...... 31 Natural History and Zoogeography ...... 32 Natural History ...... 32 Zoogeography ...... 35 References ...... 35 Appendix: Reanalysis of Data from G-banded Chromosomes ...... 38

' Associate Curator, Department of Mammalogy, American Museum of Natural History. 2 Curator, National Museum of Natural History, Smithsonian Institution; Research Associate, Department of Mammalogy, American Museum of Natural History.

Copyright © American Museum of Natural History 1993 ISSN 0003-0082 / Price $4. 1 0 2 AMERICAN MUSEUM NOVITATES NO. 3085

ABSTRACT

The muroid fossils from Lagoa Santa, Brazil, suggested that Holochilus and Oryzomys are more that Winge described as Hesperomys molitor in closely related to each other than either is to Sig- 1887 are indistinguishable from Recent Uruguay- modon. Because most of the derived similarities an specimens described by Herskovitz as Holo- between Holochilus and Sigmodon are dental traits, chilus magnus in 1955. We synonymize these and because both genera are herbivorous, adaptive nominal taxa and diagnose Lundomys, new genus, convergence is a plausible ad hoc explanation of with molitor as its type and only valid species. We our phylogenetic results. We hypothesize that oth- summarize the morphological characters of Re- er derived traits from functionally diverse ana- cent and fossil specimens of Lundomys molitor tomical systems are synapomorphies of a mono- and provide comparisons with species of Holo- phyletic group that includes Holochilus, Lundomys, chilus. Pseudoryzomys, Zygodontomys, and oryzomyines The phylogenetic relationships ofLundomys and (sensu stricto). We diagnose the tribe Oryzomyini Holochilus (sensu stricto) are analyzed to test the accordingly and emphasize differences with pre- rival hypotheses that Holochilus (sensu lato) is more vious tribal concepts based on symplesiomorphy. closely related to Sigmodon than to Oryzomys, or Natural history information from Recent pop- vice versa. Also ofinterest is the phylogenetic sig- ulations suggests that Lundomys molitor is semi- nificance of numerous derived similarities among aquatic and occurs in sympatry with Holochilus Holochilus, Lundomys, and Pseudoryzomys. The brasiliensis in pampas habitats at temperate lati- uniquely most-parsimonious tree determined by tudes in Uruguay and southernmost Brazil (Rio 25 morphological characters of Holochilus, Lun- Grande do Sul). The Lagoa Santa fossils (from the domys, Oryzomys, Pseudoryzomys, and Sigmodon tropical Brazilian state of Minas Gerais) therefore suggests that Holochilus and Sigmodon form a document a considerable range extension north- monophyletic group with Pseudoryzomys and ward in the late Pleistocene, probably coincident Lundomys as successively more distant sister taxa: with global climatic cooling. The paleoecological ((((Holochilus, Sigmodon) Pseudoryzomys) Lun- significance ofother Lagoa Santa fossils have been domys) Oryzomys). Previous studies of male gen- similarly interpreted by previous investigators. italia and G-banded chromosomes, however, have

RESUMEN

Los muroideos f6siles de Lagoa Santa, Brazil, mas alejados: ((((Holochilus, Sigmodon) Pseu- que Winge describio como Hesperomys molitor en doryzomys) Lundomys) Oryzomys). No obstante, 1887 son indistinguibles de los especimenes Re- estudios anteriores de la morfologia peneal y de cientes del Uruguay descritos por Hershkovitz bandeo G cromos6mico han sugerido que Holo- como Holochilus magnus en 1955. Reconocemos chilus y Oryzomys estan filogeneticamente mas estos taxa nominales como sinonimos y descri- cerca que cualquier otro lo esta de Sigmodon. bimos Lundomys, genero nuevo, con molitor como Puesto que la mayoria de los caracteres derivados su especie tipica y 'unica. Resumimos los carlac- similares entre Holochilus y Sigmodon son den- teres morfologicos de los especimenes Recientes y tarios, y puesto que ambos generos son herbivoros, f6siles de Lundomys molitor y proporcionamos la convergencia adaptativa es una explicacion comparaciones con las especies de Holochilus. plausible de nuestros resultados filogeneticos. Pro- Las relaciones filogeneticas de Lundomys y Ho- ponemos la hipotesis de que otros caracteres de- lochilus (sensu stricto) son analizadas para probar rivados de sistemas anatomicos funcionalmente las hipoteses rivales de que Holochilus (sensu lato) diversos son sinapomorfias de un grupo monofi- esta filogeneticamente mlas cerca de Sigmodon que letico que incluye Holochilus, Lundomys, Pseu- de Oryzomys, o viceversa. Tambien es de interes doryzomys, Zygodontomys, y oryzominos (sensu el significado filogenetico de numerosos caracteres stricto). De acuerdo con esto, damos una diagnosis derivados similares entre Holochilus, Lundomys, de la tribu Oryzomyini y resaltamos las diferencias y Pseudoryzomys. El arbol mas parsimonioso de- entre nuestra clasificacion y otras basadas en sim- terminado por 25 caracteres morfologicos de Ho- plesiomorfias. lochilus, Lundomys, Oryzomys, Pseudoryzomys, y La informacion ecologica sobre poblaciones Re- Sigmodon sugiere que Holochilus y Sigmodon for- cientes sugiere que Lundomys molitor es semia- man un grupo monofiletico, con Pseudoryzomys y cuatica y vive en simpatria con Holochilus bras- Lundomys como taxa hermanos sucesivamente iliensis en los habitats subtropicales y templados 1 993 VOSS AND CARLETON: NEW MUROID GENUS 3 del Uruguay y del extremo sur de Brasil (Rio Gran- bablemente coincidiendo con una de las epocas de de do Sul). Los especimenes f6siles de Lagoa Santa enfriamiento climatico global. El significado pa- (desde el estado brasileiio tropical de Minas Ge- leoecologico de otros f6siles de Lagoa Santa ha rais) documentan, pues, una mayor extension geo- sido interpretado de manera semejante por inves- graifica hacia el norte en el Pleistoceno tardio, pro- tigadores anteriores.

RESUMO

Os muroideos f6sseis de Lagoa Santa, Brasil, proximamente aparentados entre si do que cada descritos por Winge em 1887 como Hesperomys um 6 com Sigmodon. Uma vez que a maior parte molitor, sao indistinguiveis dos especimes Recen- das semelhan,as derivadas entre Holochilus e Sig- tes procedentes do Uruguai, que foram descritos modon e baseada em caracteristicas dentarias, e por Hershkovitz em 1955 como Holochilus mag- devido ao fato de que ambos os generos sao her- nus. Consideramos ambos os tAxons nominais bivoros, a convergencia adaptativa 6 uma expli- como sinonimos e propomos um novo genero, cacao ad hoc plausivel de nossos resultados filo- Lundomys, tendo como unica especie valida a es- geneticos. Estabelecemos a hipotese de que outras pecie tipo, molitor. Apresentamos um resumo das caracteristicas derivadas de diferentes sistemas caracteristicas morfologicas de especimes Recen- funcionais anatromicos constituem sinapomorfias tes e f6sseis de Lundomys molitor e o comparamos de um grupo monofiletico que inclue Holochilus, com especies de Holochilus. Lundomys, Pseudoryzomys, Zygodontomys, e ori- As relac6es filogeneticas de Lundomys e Holo- zomiineos (sensu stricto). Assim, propomos uma chilus (sensu stricto) saio analisadas a fim de testar nova diagnose da tribo Oryzomyini e enfatizamos duas hipoteses concorrentes, que consideram Ho- as diferencas de conceitos tribais anteriores ba- lochilus (sensu lato) mais aparentado com Sig- seados em simplesiomorfias. modon do que com Oryzomys, e vice versa. Tam- Informag6es sobre a historia natural de popu- bem e de interesse o significado filogenetico de lag6es Recentes sugerem que Lundomys molitor 6 numerosas semelhan,as derivadas entre Holochi- uma forma semi-aquatica e ocorre simpatrica- lus, Lundomys, e Pseudoryzomys. A partir da ana- mente com Holochilus brasiliensis nos habitats de lise de 25 caracteristicas morfologicas de Holo- pampas em latitudes temperadas no Uruguai e na chilus, Lundomys, Oryzomys, Pseudoryzomys, e parte sul do Brasil (Rio Grande do Sul). Desta Sigmodon, a arvore filogenetica mais parsimonio- maneira, os f6sseis de Lagoa Santa (procedentes sa sugere que Holochilus e Sigmodon formam um do estado tropical brasileiro de Minas Gerais) do- grupo monofiletico, tendo como grupos irmaos cumentam uma consideravel ampliagfio da distri- sucessivamente mais distantes Pseudoryzomys e bui,cao para o norte durante o Pleistoceno tardio, Lundomys: ((((Holochilus, Sigmodon) Pseudory- possivelmente coincidente com o resfriamento cli- zomys) Lundomys) Oryzomys). No entanto, es- matico global. 0 significado paleoecologico de ou- tudos anteriores baseados na genitalia masculina tros f6sseis de Lagoa Santa foram interpretados de e nos cromossomos preparados para bandas "G" maneira similar por outros pesquisadores. sugeriram que Holochilus e Oryzomys seriam mais

INTRODUCTION Among the many specimens offossil mam- is not included in the synopses ofNeotropical mals excavated by Peter Wilhelm Lund from muroids prepared by Gyldenstolpe (1932) and caves near Lagoa Santa in central Brazil (Voss Tate (1932), nor does it appear in Moojen's and Myers, 1991) are several cranial frag- (1952) treatise on Brazilian rodents or Ca- ments ofa large rat that Winge (1887) named brera's (1961) monumental catalog of South Hesperomys molitor. Apparently unknown American mammals. Hershkovitz (1962) from living specimens, molitor was listed as listed molitor as a Pleistocene species of Cal- an extinct Pleistocene form of Oryzomys by omys, but no other 20th-century mention of Trouessart (1898) and the name subsequently the name preceded Massoia's (1980) sugges- vanished from the literature ofRecent mam- tion that molitor closely resembles Holochi- malogy for over half a century. The species lus magnus, a Recent but apparently uncom- 4 AMERICAN MUSEUM NOVITATES NO. 3085 mon semiaquatic species from Uruguay and terials and Methods) for their hospitality while southern Brazil. we visited their collections, and for their pa- Colin Campbell Sanborn collected the type tience and generosity in extending many loans series of Holochilus magnus in Uruguay in of scarce material. Tove Hatting, Hans Baa- 1926 but did not recognize that his specimens g0e, Frits Braestrup, and Mogens Andersen included two sympatric kinds of marsh- of the Universitets Zoologisk Museum en- dwelling rats; in a summary report (Sanborn, thusiastically supported our studies ofLund's 1929), all were identified as H. vulpinus. San- collections, and their careful stewardship of born's mistake was eventually discovered by this important research resource merits high Hershkovitz (1955) who described H. mag- praise. nus and illustrated many of its diagnostic All of the drawings in this report are the characters. For Hershkovitz (1955, 1962, work of Pat Wynne, whose graceful rendi- 1966), the genus Holochilus belonged to a tions ofteeth and skulls clarify many essential small assemblage ofherbivorous muroids, the details of our comparisons. Peter Goldberg "sigmodont" group (also including Neoto- photographed the skulls and toothrows, and mys, Reithrodon, and Sigmodon), distin- printed figure 17 from a negative in the guished from other Neotropical genera by AMNH Department of Mammalogy ar- their distinctively flat-crowned, lophodont chives. The portrait of Lund reproduced in molars. figure 1 was provided by Tove Hatting. To test Massoia's (1980) hypothesis, we Nancy Simmons ran the phylogenetic anal- borrowed the type material of Hesperomys yses of our data and generously consented to molitor from the Universitets Zoologisk Mu- read yet another long manuscript about rats. seum in Copenhagen and compared it with We also thank Phil Myers, Jim Patton, and all of the specimens of Holochilus magnus Scott Steppan for their critical comments, in- available in North American collections. Be- cluding those with which we did not agree. cause we were unable to detect any qualita- Any remaining errors or annoying idiosyn- tive or quantitative differences between fossil crasies are, of course, our own. and Recent material, we concluded that these taxa are conspecific. The species, for which molitor is apparently the oldest available MATERIALS AND METHODS name, shares some derived attributes with SPECIMENS: The specimens examined in the members of the genus Holochilus, but differs course of this study are deposited in the col- strikingly in other traits. lections ofthe American Museum ofNatural In this report we document our inference History, New York (AMNH); the Field Mu- that Hesperomys molitor and Holochilus seum of Natural History, Chicago (FMNH); magnus are conspecific, and we diagnose a the Museum ofComparative Zoology at Har- new genus to contain them. We describe com- vard University, Cambridge (MCZ); the Mu- parisons between the new genus and Holo- seum of Michigan State University (MSU); chilus (sensu stricto), provide phylogenetic the University of Michigan Museum of Zo- analyses of morphological and karyotypic ology (UMMZ); the National Museum of data, and evaluate the hypothesis that these Natural History, Washington, D.C. (USNM); taxa, together with Pseudoryzomys, Zygo- and the Universitets Zoologisk Museum, Co- dontomys, and the oryzomyine genera of penhagen (UZM). Hershkovitz (1944, 1960), form a monophy- MEASUREMENTS, AGE CRITERIA, AND letic group. Finally, we summarize available ANATOMY: Total length (TL), length of tail natural history information from Recent (LT), and length ofhindfoot (including claws, populations of molitor and discuss the paleo- HF) were recorded from specimen tags; un- ecological implications of the Lagoa Santa distorted hindfeet were also remeasured on fossils. dry study skins to check the accuracy of val- ACKNOWLEDGMENTS ues recorded by the collector. Length ofhead- and-body was obtained by subtracting LT We are grateful to the curators and tech- from TL. nicians of the museums listed below (in Ma- Cranial and dental dimensions were mea- 1993 VOSS AND CARLETON: NEW MUROID GENUS 5 sured with dial calipers and recorded to the nearest 0.05 mm, but values reported below are rounded to the nearest 0.1 mm. The fol- lowing measurements were defined and il- lustrated by Voss (1991): Condylo-incisive length (CIL), length of the diastema (LD), crown length ofthe upper molar series (LM), breadth of Ml (BM 1), length of the incisive foramina (LIF), breadth ofthe rostrum (BR), breadth of the palatal bridge (BPB), breadth of the zygomatic plate (BZP), least interor- bital breadth (LIB), depth ofthe incisors (DI), and length of the orbital fossa (LOF). Zygo- matic breadth (ZB) is measured across the squamosal zygomatic processes (Voss, 1988: fig. 1). Crown length ofthe lower molar series (Lm l-m3) only appears in the caption to fig- ure 6 of this report. The term "adult" here denotes animals with completely erupted dentitions regardless of apparent sexual maturity. "Older specimens" or "older adults" refer to animals with well- worn molars. Unless otherwise noted or explained, our anatomical terminology follows Reig (1977), Carleton (1980), Voss, (1988), and Carleton and Musser (1989). Fig. 1. Peter Wilhelm Lund (1801-1880), ARCHIVES: Fieldnotes quoted or cited in whose lonely dedication and prodigious labors to this report are conserved in the archives of document the prehistoric diversity of Brazilian the Department ofMammalogy ofthe Amer- mammals we acknowledge with a genus named in ican Museum of Natural History, as are the his honor. photographic records of the 1962-63 Uru- guayan expedition (from which fig. 17 is re- 1991). Lund's scientific career and the impact produced). of his research on the development of South American paleontology are described by Pau- la Couto (1950), Hatting (1980), and Simp- LUNDOMYS, NEW GENUS son (1984). TYPE SPECIES: Hesperomys molitor Winge, DIAGNOSIS AND DESCRIPTION: As for the 1887. single included species, below. ETYMOLOGY: For Peter Wilhelm Lund (fig. 1), whose excavations of caves near Lagoa molitor Santa provided the first detailed record of an Lundomys (Winge, 1887) extinct mammalian fauna from South Amer- Hesperomys molitor Winge, 1887: 14. ica. Unlike many professional fossil hunters Oryzomys molitor: Trouessart, 1898: 528. obsessed with large specimens for public dis- Holochilus magnus Hershkovitz, 1955: 657. play, Lund was an academically accom- Calomys molitor: Hershkovitz, 1962: 123. plished biologist who studied both fossil and Holochilus molitor: Massoia, 1980: 282. Recent species to test hypotheses about the TYPE MATERIAL: We designate as lectotype history oflife. As a consequence, Lund's col- the large cranial fragment (fig. 2) illustrated lections are extraordinarily diverse, especial- by Winge (1887) and labeled in his hand, ly in small mammals, and provide a unique consisting of the facial skeleton and anterior resource for understanding Quaternary ex- portion of the braincase of a young adult an- tinctions in South America (Voss and Myers, imal; the specimen is deposited in the pale- 6 AMERICAN MUSEUM NOVITATES NO. 3085

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Fig. 2. The lectotype ofLundomys molitorwith its label (both about x 1.5, left), and Winge's (1887) illustration (right). ontological collections of the Universitets of this taxon with Recent material hitherto Zoologisk Museum but does not have a cat- identified as Holochilus magnus in qualita- alog number. The lectotype was collected from tive characters ofthe nasal bones, interorbital the cave chamber that Lund designated "Lapa region, zygomatic arch, zygomatic plate, in- da Escrivania Nr. 5," near Lagoa Santa, Mi- cisive foramina, palatal bridge, orbital and nas Gerais, Brazil. Two additional, uncata- alisphenoid foramina, and maxillary denti- loged specimens in the Universitets Zoologisk tion (compare fig. 2 with figs. 3A and 4A, and Museum (also labeled by Winge) are hereby fig. 5A with 5B). These qualitative likenesses, designated paralectotypes; these consist of together with completely overlapping mea- another large skull fragment and an isolated surement variation (table 1) compel us to maxillary toothrow, both from Lapa da Es- conclude that molitor and magnus are con- crivania Nr. 5. A complete mandible (fig. 2, specific. Characters determinable only from right) from another cave, Lapa da Serra das Recent material are therefore included in the Abelhas, was also part of Winge's hypodigm diagnosis, description, and comparisons that but does not represent the same species as follow. the cranial material from Lapa da Escrivania EMENDED DIAGNOSIS: Very large rodents of Nr. 5; its taxonomic allocation will be the the muroid subfamily Sigmodontinae (sensu topic of a future report. Carleton and Musser, 1984) with tail longer REMARKS: Comparisons between Recent than head-and-body; hindfeet large, conspic- specimens and fossils are inevitably limited uously webbed, with long fringes of silvery by the anatomical incompleteness of the lat- hairs along plantar margins, without ungual ter. The type series ofLundomys molitor con- tufts, and with only five small plantar pads; sists ofjust three fragmentary specimens, but skull with narrow interorbit and convergent these are sufficient to document the identity zygoma; broad zygomatic plate with spinous 1993 VOSS AND CARLETON: NEW MUROID GENUS 7 anterodorsal process; posterior wall of orbit TABLE 1 without prominent vertical ridge along fron- Sex and Craniodental Measurements (mm) ofAdult tal-squamosal suture; tegmen tympani not Lundomys molitor from Lagoa Santa (Brazil) and connected to posterior suspensory process of from Uruguay squamosal; subsquamosal fenestra patent and Lagoa Santa subequal to postglenoid foramen; incisive fo- The Another ramina long, extending posteriorly to or be- lecto- speci- tween molar alveoli; palate long and narrow type men Uruguaya with prominent posterolateral pits; alisphen- strut Sex 5 males, 5 females oid absent; carotid circulation without 2 sex unknown stapedial contribution to facial supply; molar CIL 40.8 ± 3.0 (35.2-45.0) 11 dentition bunodont; labial and lingual folds LD 10.6 11.7 11.7 ± 1.2 (9.7-13.5) 12 not interpenetrating; unworn M and M2 with LM 8.0 8.5 8.3 ± 0.1 (8.0-8.5) 12 small mesolophs; M3 shorter than M2; un- BM1 2.5 2.6 2.6 ± 0.1 (2.5-2.8) 12 worn ml and m2 usually with small meso- LIF 8.4 9.8 8.7 ± 0.6 (7.7-9.8) 12 lophids; superior and inferior masseteric BR 7.9 8.0 7.3 ± 0.6 (6.2-8.2) 12 ridges of mandible converging as open chev- BPB 3.3 3.5 3.2 ± 0.5 (2.4-4.0) 10 ron; capsular process of lower incisor alve- BZP 3.8 4.8 4.5 ± 0.4 (3.6-5.1) 12 olus inconspicuous; basihyal without ento- LIB 5.4 5.3 5.1 ± 0.3 (4.7-5.5) 10 ZB 24.3 ± 1.5 (21.5-26.1) 10 glossal process; first rib articulating with DI 2.8 2.5 ± 0.3 (2.1-2.8) 12 transverse processes of seventh cervical and LOF 14.2 15.5 ± 1.1 (13.5-17.2) 11 first thoracic vertebrae; 12 ribs; gall bladder absent. a The mean, standard deviation, observed range (in MORPHOLOGICAL DESCRIPrION: Very large parentheses), and sample size are provided for mea- surements of: AMNH 206363, 206364, 206366, 206368, rats with huge hindfeet and long tails (table 206380,206381, 206392,206393; FMNH 29255, 29257, 2). Body pelage long, dense, and soft; clear 29258 (the type of Holochilus magnus), 29260-29263; yellow-brown along sides, near Clay Color MCZ 26944; USNM 259641. (Smithe, 1975-1981: 123B), but darker dor- sally from concentration ofglossy, dark brown guard hairs; paler ventrally, near Warm Buff phalange 1 ofdigit II; claw ofdigit V extends (op. cit.: 124), but the bases of ventral hairs to end of phalange 1 of digit IV; interdigital gray. Ears small and well provided with short, webs present and well developed, extending brownish or yellowish fur, not contrasting beyond first phalanges among digits II, III, sharply with fur ofhead and nape. Mystacial, and IV. Tail unicolored (dark), sparsely haired superciliary, genal, submental, interramal, (the epidermal scales clearly visible), and and carpal vibrissae present; mystacial vi- without a tuft or pencil of longer hairs at tip. brissae short, not extending posteriorly be- Mammae eight in inguinal, abdominal, post- hind pinnae when laid back against head. axial, and pectoral pairs. Manus covered dorsally with short, pale hairs, Skull with blunt, massive rostrum flanked without tufts of long ungual hairs at bases of by deep zygomatic notches; interorbital re- claws (which therefore appear naked); plantar gion very narrow, with sharp but not beaded surface hairless and densely squamate, with supraorbital margins; braincase with low scar two large carpal pads and three very small oftemporalis origin on each side but without interdigital pads. Pes covered dorsally with well-developed temporal crests; posterior wall short, pale hairs; without ungual tufts of lon- of orbit without a prominent vertical ridge ger hairs (claws naked); dense fringes oflong, along frontal-squamosal suture; lambdoidal silvery hairs present along medial plantar and nuchal crests well developed in older margins ofmetatarsus and digits I and II, and adults. Zygomatic plate broad, with concave along lateral plantar margins ofdigits IV and anterior margin and spinous anterodorsal V; plantar surface hairless and densely squa- process; zygomatic arches strong and con- mate, with one metatarsal and four very small vergent anteriorly (widest across squamosal interdigital pads (hypothenar pad absent); roots); jugal present and always separating claw of digit I extends at least to middle of maxillary and squamosal zygomatic process- 8 AMERICAN MUSEUM NOVITATES NO. 3085

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A B C Fig. 3. Dorsal and ventral views of skulls (x 1.5) of Lundomys and Holochilus. A, young adult Lundomys molitor (AMNH 206364, about the same age as the lectotype); B, an older adult (AMNH 206393); C, Holochilus brasiliensis (AMNH 206369); D, Holochilus sciureus (AMNH 210263). es. Incisive foramina long, extending poste- sory oval foramina confluent). Carotid cir- riorly to or between molar alveloli; palatal culation with facial supply from internal bridge long and narrow, with prominent pos- anastomosis of internal carotid artery, not terolateral pits; parapterygoid fossae each from stapedial artery (pattern 3 of Voss, about as wide as mesopterygoid fossa, mod- 1988). Tegmen tympani not connected to erately recessed above level ofpalate; roof of posterior suspensory process of squamosal; mesopterygoid fossa apparently completely dorsolateral wall ofbraincase above auditory ossified or with very small sphenopalatine bulla perforated by subequal postglenoid fo- vacuities flanking basisphenoid-presphenoid ramen and subsquamosal fenestra. Auditory suture (but mesopterygoid region damaged in bullae globular (with short and narrow bony most available specimens). Alisphenoid strut eustacian tubes); periotic broadly exposed absent (buccinator-masticatory and acces- posteromedially between ectotympanic and 1993 VOSS AND CARLETON: NEW MUROID GENUS 9

basioccipital but not extending anteriorly to carotid canal. Coronoid process of mandible about level with condyle; angular process not produced posteriorly much beyond condyle; superior and inferior masseteric crests converging as .4 open chevron (not tightly compressed to form a single anterior ridge); capsular process of lower incisor alveolus an inconspicuous A NS.M swelling below base of coronoid process. Ba- sihyal without entoglossal process. Upper incisors opisthodont, with smooth- ly rounded (not faceted), bright yellow-or- ange enamel bands. Upper and lower molars bunodont; labial and lingual cusp margins rounded (not angular). Anterocone of un- worn MI weakly divided into subequal labial and lingual lobes by shallow anteromedian flexus; anteroloph present but small on un- worn MI, well developed on M2 and M3; shallow protoflexus present on unworn M2; small mesoloph always present on MI and M2 (but never fused with mesostyle on labial cingulum), usually absent from M3; minute posteroloph present on newly erupted upper molars but quickly obliterated by wear; all upper molars with three roots. Anteroconid of ml entire (not divided by anteromedian flexid), but enclosing large enamel pit; minute anterolophids present on all unworn lower molars; small mesolophids present on un- worn ml and m2, absent from m3; discrete posterolophids present and persistent on ml and m2, usually absent on m3; ml with three or four roots, m2 and m3 with two roots each. Tuberculum of first rib articulating with transverse processes of seventh cervical and -iik-. 1:,1. first thoracic vertebrae; second thoracic ver- tebra with greatly elongated neural spine; ax- ial skeletal counts (from nine specimens) in- cluding 12 ribs, 19 thoracicolumbar vertebrae, 4 sacrals, and 35 or 36 caudals; entepicon- dylar foramen of humerus absent. Stomach unilocular and strictly hemiglan- dular, with no leftward extension ofglandular epithelium into corpus; gall bladder absent (Voss, 1991: table 4); other visceral charac- ters undetermined.

D Fig. 4. Lateral views of skulls and mandibles (both x 1.5) of Lundomys and Holochilus. Speci- mens are the same as those in figure 3. to AMERICAN MUSEUM NOVITATES NO. 3085

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PET

Fig. 5. Right upper molars ofLundomys and Holochilus. A, the lectotype ofLundomys molitor (LM = 8.0 mm); B, a Recent specimen (AMNH 206388, LM = 8.3 mm); C, Holochilus brasiliensis (AMNH 206372, LM = 8.1 mm); D, Holochilus sciureus (AMNH 134703, LM = 7.3 mm).

KARYOTYPES: Five specimens (two males Hershkovitz (1955) suggested that a fluid- and three females) collected along the Ivai preserved specimen from Lagoa Santa iden- River near Tupancireta, Rio Grande do Sul, tified by Winge (1887) as Sigmodon vulpinus Brazil (28°56'S, 53°40'W) were karyotyped (= Holochilus brasiliensis) might actually be by Freitas et al. (1983), who reported a dip- an example of Holochilus magnus (= Lun- loid number of52 and a fundamental number domys molitor). We examined the specimen of58; the biarmed autosomes consist ofthree in question (UZM 399), which has since been pairs of large metacentrics and one small partially skeletonized, and determined that metacentric pair; the X is submetacentric, the the cranium and dentition are unambigu- Y is metacentric. ously those of H. brasiliensis. The type lo- DISTRIBUTION: All Recent specimens of cality of L. molitor is therefore considerably Lundomys molitor ofwhich we are aware have removed from the known geographic range been collected in Uruguay or in the adjacent of Recent populations (fig. 7). Brazilian state of Rio Grande do Sul (fig. 7). SPECIMENS EXAMINED: Brazil -Minas Ger- Redford and Eisenberg (1992) stated that the ais, near Lagoa Santa (the lectotype and two species occurs in Argentina and mapped a paralectotypes, in the Universitets Zoologisk locality in the delta of the Parana; we have Museum, Copenhagen). Uruguay - Cane- -seen no specimens or other published records lones, Bafiado de Tropa Vieja, 36 km E Mon- of Recent material from from that country, tevideo (AMNH 206363-206366); Lavalleja but Bond and Massoia (1981) and Lezcano (formerly Minas), Paso de Averias, Rio Ce- et al. (1992) reported late Pleistocene mate- bollati (FMNH 29255,29257,29258; USNM rial from the province of Buenos Aires. 259641); Soriano, 3 km E Cardona (AMNH 1993 VOSS AND CARLETON: NEW MUROID GENUS I1I

Fig. 6. Right lower molars of Lundomys and Holochilus. A, Lundomys molitor (AMNH 206388, Lml-m3 = 8.7 mm); B, Holochilus brasiliensis (AMNH 206372, Lml-m3 = 8.8 mm); C, Holochilus sciureus (AMNH 134703, Lml-m3 = 7.5 mm).

206368, 206373, 206380, 206381, 206388); and exploratory nature of these exercises. Trienta y Tres, 8 mi E Trienta y Tres (FMNH Specimens of Lundomys molitor are not 29260, 29261, 29263; MCZ 26944), and Rio abundant, and with only the small samples Olimar Chico, 25 km WSW Trienta y Tres at hand it is possible that we have underes- (AMNH 206392, 206393). Total = 22. timated the variability of this taxon. Addi- tional complexity is introduced by character variation within Holochilus that clearly mer- COMPARISONS WITH HOLOCHILUS its recognition at the species level. Whereas Lundomys molitor resembles species of Hershkovitz (1955) referred all ofthe named Holochilus in numerous characters, including forms ofHolochilus (in the strict sense ofthis derived aspects ofexternal, craniodental, and report) to H. brasiliensis, we provisionally visceral morphology. Differences in other an- accept Massoia's (1981) argument that bras- atomical traits are substantial, however, and iliensis (including darwini and vulpinus) suggest that each genus represents an evolu- should be restricted to populations of large tionarily distinct lineage with a unique com- rats with unexpanded paracones and vestigial bination of adaptations for diet and loco- mesolophs on Ml and M2. This distinctive motion. In these comparative accounts we species ranges from northeastern Argentina describe morphological similarities and dif- (cf. Massoia, 1974: fig. 1) throughout Uru- ferences that provide data for subsequent guay to the southeastern states of Brazil (in- analyses ofphylogenetic relationships-and/or cluding parts of Minas Gerais and Bahia; evidence of ecological specializations. Massoia, 1981). The remaining geographic We emphasize at the outset the preliminary populations ofHolochilus, for which the old- 12 AMERICAN MUSEUM NOVITATES NO. 3085

Fig. 7. Geographic distribution of Recent and fossil samples of Lundomys molitor. Recent collection localities with unpunctuated geographic coordinates (degrees and minutes S latitude / W longitude, if known) are numbered as follow: 1, BRAZIL, Rio Grande do Sul, Tupancireta (2856/5340) (reported by Freitas et al., 1983; specimens not examined by us); 2, URUGUAY, Canelones, Bafiado de Tropa Vieja (3447/5552); 3, URUGUAY, Lavalleja, Paso de Averias (3336/5419); 4, URUGUAY, Soriano, 3 km E Cardona; 5, URUGUAY, Trienta v Tres, 8 km E Trienta y Tres (3314/5423) and 6, 25 km WSW Trienta y Tres. est unambiguously available name appears to brasiliensis are explained in greater detail be- be sciureus Wagner 1842, comprise a mor- low.) We acknowledge that karyotypic com- phologically cohesive assemblage of smaller parisons have revealed substantial diver- animals with expanded paracones but no me- gence among some geographic samples of solophs on Ml and M2. (These and other sciureus-like rats (e.g., those currently re- characters distinguishing H. sciureus from H. ferred to chacarius and venezuelae; see Vidal 1993 VOSS AND CARLETON: NEW MUROID GENUS 13

TABLE 2 Summary Statisticsa for External Measurements (mm) of Adult Specimens of Lundomys molitor and Species of Holochilus Species Length of head-and-body Length of tail Length of hindfoot Lundomys molitorb 193 ± 22 (160-230) 10 235 ± 19 (195-255) 10 62 ± 3 (58-68) 12 Holochilus brasiliensisc 193 ± 14 (167-211) 10 198 ± 10 (183-214) 10 54 ± 2 (51-56) 10 Holochilussciureusd 164 ± 18 (123-193) 33 150 ± 16 (115-178) 33 39 ± 3 (35-46) 33 a The sample mean plus or minus one standard deviation, the observed range (in parentheses), and the sample size. b The sample identified in the footnote to table 1. c Specimens from Uruguay, Depto. Soriano: AMNH 206369, 206372, 206374-206379, 206382, 206383. dSpecimens from Paraguay, Depto. Presidente Hayes: UMMZ 125997-126004, 126074-126078, 133971-133974, 133976, 133977, 133979, 133980, 166197-166206, 166208, 166209. et al., 1976; and Aguilera and Perez-Zapata, tive to the combined length ofhead and body, 1989), but the morphological data at hand the appendages ofLundomys molitorare larg- do not yet suggest clearcut subdivisions of er than those of Holochilus species (table 2). this complex. The tail provides a particularly conspicuous Skins and skulls of Holochilus brasiliensis morphometric contast, averaging much lon- and of the H. sciureus complex (for brevity, ger than head-and-body in Lundomys, about hereafter referred to simply as H. sciureus) as long as head-and-body in H. brasiliensis, that we examined for these comparisons in- and consistently shorter than head-and-body clude large series from the AMNH, FMNH, in H. sciureus. Comparisons ofrelative length and USNM collections. Fluid-preserved of the hindfoot yield the same taxonomic specimens (which are much less numerous) ranking, but qualitative aspects of this organ are cited by museum catalog number in the are more informative. descriptive accounts below. In both Lundomys and Holochilus, the three middle digits ofthe hindfoot (II, III, and IV) are much longer than the outer digits (I and EXTERNAL MORPHOLOGY V); the claw of digit I does not extend more Size and general aspect: That a systematic than half the length of the first phalange of mammalogist as astute as Sanborn (1929) did II, while the claw of V does not extend be- not recognize another taxon within the series yond the first interphalangeal joint of IV. ofUruguayan specimens he identified as Hol- These unremarkable digital proportions are ochilus vulpinus (= H. brasiliensis) is elo- widespread among other Neotropical mu- quent testimony to the close external resem- roids, including such strictly terrestrial (non- blance between Holochilus and Lundomys. arboreal and nonaquatic) species as Zygo- Species ofHolochilus and Lundomys molitor dontomys brevicauda (Voss, 1988). are all large rats (table 2) whose tawny or The dorsal pelage of the hindfoot in both brownish dorsal pelage is grizzled or streaked genera is close and sparse, and the claws ap- with darker guard hairs. Populations of H. pear naked because they are not concealed sciureus from tropical lowland habitats have by ungual tufts of longer hairs. (Most other short, close fur, but at temperate latitudes (as Neotropical muroids have well-defined tufts in Uruguay) both H. brasiliensis and L. mol- of long, curved hairs rooted at the bases of itor have dense, soft, luxurious pelts. The ears the claws; when present, these ungual tufts are small and well furred in each genus, the are as long as or longer than the claws they mystacial vibrissae are short (not extending wholly or partially conceal.) Another note- behind the pinnae when folded back along worthy aspect of the pelage of the hindfoot the cheeks), and tails are sparsely haired with is the development of what may be termed conspicuous annuli of coarse scales. Other "natatory fringes" along some of the plantar external traits merit closer attention. margins. These are formed by longer hairs External proportions and hindfeet: Rela- with a silvery cast, although tinged with the 14 AMERICAN MUSEUM NOVITATES NO. 3085

predominant pigment (usually yellowish or brownish) of the dorsal pelage ofthe foot. In Lundomys molitor, stiff, dense natatory fring- es are present along the medial plantar mar- gins ofthe metatarsus and digits I and II, and along the lateral plantar margins of digits IV and V; the lateral metatarsus and other digital plantar margins are unfringed. Natatory fringes are present but only weakly developed in Holochilus brasiliensis and H. sciureus. In both Lundomys and Holochilus, the plantar epithelium is smooth over the heel, but the remainder (from about the level of the thenar pad nearly to the ends ofthe digits, and including the webs) is densely covered with small tubercles that have the appearance of scales; this uniformly squamate surface is interrupted only by five or six small plantar pads (Sierra de Soriano, 1965: lamina III). The thenar (medial metatarsal) pad and four interdigital pads are invariably present; a very small hypothenar pad is occasionally present in specimens of H. sciureus (often unilater- ally), but not in any examples of H. bras- iliensis or Lundomys molitor that we exam- ined. The hindfeet are webbed in both Holochi- lus and Lundomys. Although present be- tween all adjacent digits, webs are best de- veloped between II and III and between III and IV. Webs between these middle digits extend only to the ends of the first phalanges in both species of Holochilus, but in Lun- domys the webs extend well beyond the first interphalangeal joint (especially between digits III and IV; Sierra de Soriano, 1965: Ilamina III). Mammae: Two skins of adult female Lun- domys molitor (AMNH 206380, 206392) have eight mammae in four pairs, one in- guinal, one abdominal, one postaxial, and one pectoral (see fig. 8 for a diagram ofmammary loci). Hershkovitz (1955) reported ten mam- mae for Holochilus, but mammae number is variable in that genus. All of the lactating female specimens of H. brasiliensis that we examined (e.g., AMNH 206369, 206372, 206379; MSU 17892, 17893) have eight mammae in the same anatomical pattern as described for L. molitor, but geographic sam- ples of H. sciureus have either eight or ten Fig. 8. Anatomical loci ofmammary pairs dis- teats (table 3). Populations ofH. sciureus with cussed in the text. ten mammae have paired thoracic teats in 1993 VOSS AND CARLETON: NEW MUROID GENUS 15 addition to the usual complement ofinguinal, TABLE 3 abdominal, postaxial, and pectoral pairs. Mammae Counts from Geographic Samples of the Holochilus sciureus Complex CRANIUM AND MANDIBLE Samplesa Mammae Zygomatic and orbital morphology: In both Bolivia, Depto. Beni Lundomys and Holochilus the zygomatic plate AMNH 210274 ten is very broad and a blunt spinous process 210275 ten extends its free dorsal edge to define a deep 210303 ten zygomatic notch on each side ofthe rostrum. 210305 ten The stout zygomatic arches are widest across Brazil, Edo. Amazonas their squamosal roots and converge anteri- AMNH 37083 eight orly. In specimens of Lundomys, the jugal is 92280 eight small but consistently present and separates 92730 eight the zygomatic processes ofthe maxillary and 93539 eight squamosal bones. In both Holochilus bras- Brazil, Edo. Goias iliensis and H. sciureus, however, the jugal is AMNH 134693 eight smaller and irregularly formed, such that the 134699 eightb maxillary and squamosal are often in contact Colombia, Depto. Meta along the midportion of the zygomatic arch. AMNH 136322 tenc The anterior interorbital region in both 142121 ten Lundomys and Holochilus is very narrow and 142122 ten basically hourglass-shaped with sharp dor- solateral margins, but the posterior frontals Paraguay, Depto. Pres. Hayes UMMZ 126001 ten of Holochilus are usually produced as raised 166197 ten supraorbital beads (especially prominent in 166201 ten older specimens). The dorsolateral margins 166205 ten ofthe posterior frontals sometimes form small shelves in Lundomys but raised beads are Peru, Depto. Loreto absent even in the oldest specimens we ex- AMNH 76278 eight 76281 eight amined. 76283 eight A vertical bony ridge is developed on the 76288 eight posterior wall of the orbit in Holochilus, ex- 76289 eight tending approximately from the supraorbital 76290 eight bead previously described to a point just above the zygomatic root of the squamosal; Venezuela, Edo. Trujillo the USNM 372662 ten ridge usually overlaps the line of frontal- 372663 ten squamosal contact, and obscures the suture 372664 ten from lateral view (fig. 9B). As with other os- seous features associated with muscular ori- a Only adult specimens with large mammae surround- gins, the development ofthe postorbital ridge ed by well-defined areolae are listed for each sample. b Collector's label notes only six mammae. appears to vary with age and size. It is better c defined in mature specimens than in younger Collector's label notes only eight mammae. animals, and is better expressed in larger- bodied populations (e.g., of H. brasiliensis) Palate and palatal foramina: The incisive than in smaller-bodied ones (e.g., some geo- foramina ofthe diastemal palate consistently graphic samples ofthe H. sciureus complex). extend posteriorly to or between the molar A distinct postorbital ridge is never present alveoli in Lundomys (figs. 3A, 3B), but in in Lundomys although a low scar posterior Holochilus these openings are less extensive. to the frontal-squamosal suture ofsome spec- In young adult Holochilus (with fully erupted imens may be homologous; accordingly, the but unworn maxillary dentitions), the foram- suture is plainly visible in lateral view (fig. ina sometimes extend posteriorly between the 9A). molar alveoli but in older specimens the fo- AMERICAN MUSEUM NOVITATES NO. 3085

Fig. 9. Postorbital morphology. A, Lundomys molitor (AMNH 206393); B, Holochilus brasiliensis (AMNH 206369). The suture between the frontal (fr) and squamosal (sq) bones is not marked by any conspicuous relief in Lundomys, but a prominent bony fold (the postorbital ridge, pr) partially conceals this suture in mature specimens of Holochilus. ramina always stop well short of the molar Carotid circulation: The occurrence and rows (figs. 3C, 3D). conformation of certain foramina and other The palatal bridge of Lundomys is unam- osteological features suggest that the facial biguously "long" in the sense defined by (ophthalmic and internal maxillary) circula- Hershkovitz (1962: 54) because it is pro- tion is supplied by the internal carotid, not duced posteriorly beyond the molar rows. by the stapedial artery, in both Lundomys Mature adult specimens of Holochilus bras- and Holochilus: (1) the stapedial foramen is iliensis also have long palates, but in some absent or persists only as a tiny perforation samples of H. sciureus the mesopterygoid in the petrotympanic fissure on the postero- fossa often extends to or slightly between the medial surface ofeach auditory bulla; (2) the third molars. In both genera, paired posterior interior surfaces of the squamosal and ali- palatal foramina perforate the maxillary-pal- sphenoid are not marked by a vascular groove, atine suture between the second molars, and and the sphenofrontal foramen is absent; (3) prominent posterolateral palatal pits are the posterior opening ofthe alisphenoid canal present between the third molars and the is absent or small and irregularly formed; and mesopterygoid fossa. Small foramina of in- (4) the carotid canal (between the bulla and constant number and morphology are usually the basioccipital) is large, and an oblique in- present in the shallow grooves that connect ternal groove crosses the roofofthe parapter- the posterior palatal foramina with the pos- ygoid fossa to join with the anterior opening terolateral palatal pits. ofa short alisphenoid canal. The relationship Alisphenoid strut: In all specimens ofHol- of these skeletal traits to alternative patterns ochilus examined, a stout strut ofthe alisphe- of cephalic arterial circulation is explained noid separates the buccinator-masticatory fo- and illustrated by Voss (1988: fig. 18) and by ramen from the foramen ovale accessorius Carleton and Musser (1989: figs. 20, 21). (fig. 1 OA). The alisphenoid strut is absent from Ear region and temporal foramina: The ec- all available specimens ofLundomys in which totympanic bullae of both Lundomys and a single alisphenoid perforation represents the Holochilus are globular capsules that appear confluent buccinator-masticatory and oval neither very small nor grossly enlarged in foramina (fig. 1OB). comparisons with those ofother Neotropical 1993 VOSS AND CARLETON: NEW MUROID GENUS 17

Fig. 10. Foramina and associated features of the alisphenoid bone. A, Holochilus sciureus (AMNH 210263); B, Lundomys molitor (AMNH 206393). A prominent strut of the alisphenoid (als) separates the buccinator-masticatory foramen (bmf) from the foramen ovale accessorius (foa) in Holochilus, but in Lundomys the strut is absent and the two foramina are confluent; a prominent groove or trough (bmt) marks the dorsal passage of the buccinator and masticatory nerves along the outer surface of the alis- phenoid in both taxa. muroids. The bullae are slightly more inflated these openings are noteworthy. The post- in Holochilus than in Lundomys, however, glenoid foramen and subsquamosal fenestra as can bejudged by the extent ofperiotic bone (separated by a slender hamular process of exposed between the ectotympanic and the the squamosal) are of approximately equal basioccipital: only a narrow sliver ofthe per- size in Lundomys and the central lumen of iotic is visible on the ventromedial aspect of the braincase is visible through each. In both the bulla in Holochilus, but a broad wedge of species of Holochilus, however, the post- the periotic is exposed in Lundomys. In nei- glenoid foramen is at least twice as large as ther genus does the periotic extend forward the subsquamosal fenestra. In H. brasiliensis to reach the carotid canal, which is instead the subsquamosal fenestra is always distinct enclosed completely between the ectotym- and patent, but in H. sciureus this opening is panic and basioccipital. often occluded by an expanded hamular pro- The anterior suspension of the auditory cess or by an internal crest or septum of the complex in both genera resembles that de- periotic. scribed for Oryzomyspalustrisby Voss (1993): Mandible: The mandibular conformation the tegmen tympani projects anterodorsally of the two genera differs in numerous details from the bulla but is not connected to a pos- (fig. 1 1). The coronoid process is small and terior suspensory process of the squamosal. angled posterodorsally in Lundomys, its tip In lateral view, the tegmen tympani of Lun- slightly below or about level with the con- domys often appears to touch or overlap the dyloid process, and the sigmoid notch is posterior margin of the squamosal, but no therefore narrow and elliptical. The coronoid posterior suspensory process is present and process ofHolochilus is much larger, oriented the bones are not pressed closely together in more nearly vertically, and projects well above any specimens we examined. In most speci- the condyle, and the sigmoid notch is cor- mens of Holochilus the tegmen tympani is respondingly broad and oval. The angular separated from the squamosal by an obvious process of Lundomys does not extend pos- (though sometimes narrow) gap. teriorly behind the condyle and the angular The postglenoid foramen and the subsqua- notch is a shallow concavity. By contrast, the mosal fenestra perforate the lateral wall of angular process ofHolochilus is produced well the braincase above the auditory bulla in both behind the condyle and the angular notch is genera, but differences in the relative sizes of much deeper. 18 AMERICAN MUSEUM NOVITATES NO. 3085

Fig. 11. Lateral views of right mandibles. A, Lundomys molitor (AMNH 206363); B, Holochilus brasiliensis (AMNH 206383); C, H. sciureus (AMNH 210259). Labeled structures include the angular notch (an), the angular process (ap), the capsular process ofthe lower incisor alveolus (cap), the condylar process (con), the coronoid process (cor), the inferior masseteric crest (inf), the mental foramen (mf), the sigmoid notch (sn), and the superior masseteric crest (sup).

In Lundomys, the alveolus ofthe lower in- sigmoid notch (in brasiliensis and other sci- cisor is short and terminates in a small cap- ureus). sular process directly beneath the coronoid The superior and inferior masseteric crests process or its leading edge. The lower incisor ofLundomys converge as a more-or-less open alveolus ofHolochilus is substantially longer chevron that ends below the middle of ml and terminates in a much larger capsular pro- or its anterior root. In Holochilus, the mas- cess below the trailing edge of the coronoid seteric crests are closely approximated an- (in some samples of sciureus) or below the teriorly, often forming a single crest that ex- 1993 VOSS AND CARLETON: NEW MUROID GENUS 19

B

ant

lab

Fig. 12. Oblique views and cross sections of left upper incisors. A, Lundomys molitor (AMNH 206368); B, Holochilus sciureus (AMNH 210255). ant, anterior; lab labial. tends beyond the anterior root of ml and Molar crown morphology: The molars of approaches the mental foramen. The degree both Lundomys and Holochilus are moder- ofconjunction ofthe masseteric crests is vari- ately high-crowned by comparison with those able within Holochilus: consistently long in ofsome pentalophodont muroids, but the two H. brasiliensis and many populations of H. genera diverge conspicuously in other aspects sciureus, but shorter in other geographic sam- of their occlusal design. The molars of Lun- ples ofthe latter (whose converging crests re- domys retain a bunodont or cuspidate topog- semble the open chevron of Lundomys but raphy, with the principal lingual and labial extend further forward, nearly to the mental cusps elevated above a central longitudinal foramen). trough; these dental surfaces appear crested Collectively, these anatomical differences in younger specimens, but develop a terraced impart a deeper, stocky appearance to the configuration with wear (descriptive termi- mandible of Holochilus that contrasts with nology after Hershkovitz, 1955, 1962, 1967). the slender, elongate conformation ofthis el- In contrast, the molars ofboth young and old ement in Lundomys. specimens ofHolochilus are flat-crowned with cusps and connecting lophs deployed in a sin- gle occlusal plane (Hershkovitz, 1955: fig. DENTITION 142). Upper incisors: The upper incisors ofboth In Lundomys, the principal cusps are ar- Lundomys and Holochilus are large, strong, ranged in essentially opposite pairs with their opisthodont teeth with yellow-orange enamel lingual and labial margins bluntly rounded bands, but closer inspection reveals consis- (figs. 5A, 5B, 6A). The principal cusps ofHo- tent differences. The enamel bands that form lochilus sciureus (figs. SD, 6C), however, are the anterior surfaces of these teeth are arranged in an alternating pattern-especially smoothly rounded in Lundomys (fig. 12A), as observed in the relative displacements whereas the enameled surface of each upper of the protocone/paracone, hypocone/- incisor in Holochilus is distinctly angular be- metacone, and hypoconid/entoconid pairs- cause a flattened medial facet is more-or-less and their labial and lingual margins are acute- sharply demarcated from a well-defined lat- ly angled (prismatic). Specimens of H. bras- eral bevel (fig. 1 2B). iliensis are intermediate to Lundomys and H. 20 AMERICAN MUSEUM NOVITATES NO. 3085 sciureus with regard to cusp arrangement and deep enameled pit that persists until ad- prismatic definition. vanced stages of wear. A small anteroloph is The labial and lingual folds (flexi/flexids) present on the unworn Ml ofLundomys but of Lundomys extend only to the midline of appears to be consistently absent from that the molars and do not interpenetrate. By con- tooth in Holochilus. A shallow indentation trast, certain labial and lingual folds ofHolo- (the protoflexus) consistently demarcates the chilus extend far beyond the midline, but the procingulum from the protocone on the M2 pattern of interpenetration differs apprecia- of Lundomys; this fold is absent in Holochi- bly between H. brasiliensis and H. sciureus. lus and the anteroloph and protocone are The principal lingual fold (hypoflexus) ofMI therefore merged to form a single broad loph and M2 is considerably deeper in H. bras- across the front of that tooth. iliensis than in H. sciureus, a difference cor- Molar roots: The upper molars of Lun- related with the presence of a vestigial me- domys each have three large, externally vis- soloph in the former (see below) and the ible roots (anterior, posterior, and lingual); expanded paracone of the latter.3 Analogous although small accessory rootlets may be species differences in the lower dentition are present internally, they are invisible when the also evident. teeth are still in place (figs. 13A, 13C). In Mesoloph(id) development provides other contrast, the first upper molar of Holochilus important distinctions between Lundomys has a prominent fourth root that is clearly and Holochilus. A small but distinct meso- visible on the labial side of the tooth (figs. loph (which never reaches the buccal margin) 13B, 13D). In both genera, the first lower occurs on Ml and M2 but is usually absent molar has two large roots (anterior and pos- from M3 in Lundomys; small mesolophids terior) and two accessory rootlets (labial and are likewise usually present on ml and m2 lingual) that are visible externally in older but not on m3. In Holochilus brasiliensis, a specimens; m2 and m3 are always two-root- vestigial mesoloph is sometimes present on ed. Ml and M2, but usually the median mure of those teeth retains only a small deflection that VISCERA marks the location ofthe absent structure; in contrast, a well-developed mesoloph is al- Stomach: The gastric morphology of Lun- ways present on M3. Mesolophids are usually domys molitor closely resembles that illus- absent in the mandibular dentition of H. trated by Carleton and Musser (1989: fig. 28) brasiliensis. No trace of a mesoloph(id) is for Oryzomys palustris, and conforms to the present on Ml, M2, and in the lower denti- unilocular-hemiglandular condition de- tion of H. sciureus (except as rare individual scribed by Carleton (1973). The gastric lumen variants), whereas a distinct mesoloph is usu- is undivided by septa or infolding of the ally present on M3 (not, however, on the stomach walls, and glandular tissue is re- specimen illustrated in fig. 5D). Correlated stricted to the antrum (right half); the corpus with the usual presence of a mesoloph on M3 (left half) is entirely lined with cornified ep- in Holochilus species, the length ofthat tooth ithelium (note that muroid stomachs are con- is equal to or exceeds the length of M2; in ventionally illustrated in ventral view). Some Lundomys, the third molar is always smaller stomachs of L. molitor exhibit a slight left- than the second. ward deflection of the bordering fold from The two genera contrast in other occlusal the incisura angularis, but glandular epithe- features. The anterocone ofLundomys is nar- lium does not extend beyond the esophagus row and weakly divided by a shallow anter- in any ofthe specimens we examined (AMNH omedian flexus when unworn, but the broad- 206373, 206388, 206392, 206393). er anterocone ofHolochilus is undivided. The Stomachs of Holochilus (Carleton, 1973: anteroconid ofHolochilus is likewise broader fig. 3C) differ consistently from the condition than its homolog in Lundomys, but in both observed in Lundomys: the organ is uniloc- genera this cusp is undivided and encloses a ular, but the bordering fold bends abruptly leftward from the incisura angularis and loops 3Species differences first noted by Massoia (1981). far into the corpus before curving back again 1993 VOSS AND CARLETON: NEW MUROID GENUS 21

P; ,W7. , 1. .Mw, A ;4 ..I B C i i..t:. T A. #".'7.1- ..,.4 I V*

Fig. 13. Upper molar alveoli and molar roots of Lundomys molitor and Holochilus brasiliensis. A, left upper molar alveoli ofL. molitor (AMNH 286380); B, the same ofH. brasiliensis (AMNH 206378); C, labial view ofleft upper molars ofL. molitor (AMNH 206393); D, the same ofH. brasiliensis (AMNH 206362). The arrow in B indicates the alveolus of the labial molar root of Ml in H. brasiliensis; the arrow in D indicates the root itself, which is exposed in older specimens. Both structures are absent in L. molitor. to cross the greater curvature at a point about and in additional examples of H. sciureus opposite the esophagus. This morphology oc- from Paraguay (UMMZ 124225, 124226, curs without appreciable differences in spec- 125484, 133970) and Bolivia (AMNH imens ofH. brasiliensis from Argentina (MSU 210286). 17892, 18692, 18797, 19355) and of H. sci- ureus from Bolivia (AMNH 210286), Para- RELATIONSHIPS guay (UMMZ 124225, 124226, 125484, PHYLOGENETIC 133970), and Venezuela (AMNH 257335, Current knowledge of higher-order rela- 257336, 266925). tionships among muroid rodents provides an Gall bladder: The absence of gall bladders insecure foundation for phylogenetic studies in Lundomys and Holochilus was reported by at lower taxonomic levels. Ideally, we would Voss (1991: table 4, Appendix 2) from dis- like to accept a well-corroborated hypothesis sections oftwo specimens ofL. molitor (iden- of monophyly for some group that includes tified as H. magnus therein) and two of H. Lundomys, Holochilus, and other Neotrop- "brasiliensis" (sensu Hershkovitz, 1955); the ical genera, and identify outgroups in order latter (AMNH 257335 and 257336, from to polarize the character transformations of Venezuela) are referable to H. sciureus in the interest. Unfortunately, compelling evidence sense ofthis report. We have since confirmed of monophyly for the subfamily Sigmodon- the absence ofgall bladders in H. brasiliensis tinae (sensu Carleton and Musser, 1984) is (sensu stricto: MSU 17892, 18692, 18797) lacking and the current tribal-level classifi- 22 AMERICAN MUSEUM NOVITATES NO. 3085

TABLE 4 for discussions of the polarity of these char- Outgroup Exemplars Surveyed acter states, and Voss, 1988: 437, for com- (See accompanying text for explanation) ments about their distribution among Neo- tropical muroids). This group apparently Tylomyinesa "South American Crice- Nyctomys sumichrasti coincides with the Otonyctomys hatti tines" of Hooper and Musser (1964) minus Ototylomys phyllotis Nyctomys (a Central American tylomyine), Tylomys mirae and with Reig's (1980) concept of Sigmo- dontinae. Neotominesa In order to polarize character transfor- Hodomys alleni Nelsonia neotomodon mations in the Neotropical muroid fauna, we Neotoma (N.) floridana assume that reasonable outgroup compari- Neotoma (Teanopus) phenax sons can be made to North and Central Neotoma (Teonoma) cinerea American tylomyines, neotomines, pero- Xenomys nelsoni myscines, and other genera with simple phalli Peromyscinesb (Carleton, 1980, 1989). As noted by Voss Habromys lepturus (1993), this assumption is supported princi- Isthmomys pirrensis pally by geographic propinquity and bio- Megadontomys thomasi chemical results because morphological evi- Neotomodon alstoni dence that these northern taxa are closely Onychomys leucogaster related to Neotropical muroids is currently Osgoodomys banderanus unavailable. Carleton (1980: table 7) provid- Peromyscus leucopus ed much useful outgroup data for the present Podomysfloridanus study, but we examined outgroup exemplars Incertae sedis (table 4) for new and hitherto unpolarized Baiomys musculus characters. Ochrotomys nuttalli We focus on two rival hypotheses about Reithrodontomys (Aporodon) creper the relationships of Holochilus (sensu lato). Reithrodontomys (R.) sumichrasti Derived resemblances in craniodental mor- Scotinomys xerampelinus phology noted by Wagner (1842), Winge a After Carleton (1980). (1887, 1941), Thomas (1928), Ellerman b After Carleton (1989). (1941), and Hershkovitz (1955) suggest that Holochilus and Sigmodon are closely related, cation of South American muroids (e.g., as an hypothesis that appeared compelling to summarized by Reig, 1984: table 16-1) is Reig (1984) whose tribe Sigmodontini con- thoroughly unsatisfactory from a phyloge- tained only these two genera. Hooper and netic perspective (see Carleton and Musser, Musser (1964), however, reported similari- 1989: 53-55; and Voss, 1991: 33-37). Nev- ties in phallic characters between Holochilus ertheless, some provisional hypothesis of and certain species of Oryzomys and sug- monophyly must be adopted for any progress gested that the former might be an oryzo- to be made in understanding the phylogenetic myine rather than a member of Hershko- significance of character distributions in the vitz's (1955) sigmodont group. Additional Neotropical fauna. evidence that Holochilus and oryzomyines For the purpose ofthe analyses that follow, (sensu Hershkovitz, 1944, 1960) may be we assume the monophyly of a predomi- closely related was discussed by Baker et al. nantly Neotropical group of sigmodontine (1983) and Voss (1991). genera in which (1) the entepicondylar fora- The taxonomic units of our analysis in- men of the humerus is absent, (2) the ento- clude Sigmodon hispidus, S. peruanus, Lun- glossal process of the basihyal is absent, (3) domys molitor, Holochilus brasiliensis, H. the tuberculum ofthe first rib articulates with sciureus, Oryzomys subflavus, and Pseudo- the transverse processes of the seventh cer- ryzomys simplex. The two species of Sig- vical and first thoracic vertebrae, and (4) the modon were chosen to represent substantially glans penis is complex (see Carleton, 1980, divergent morphologies within the genus; ex- 1993 VOSS AND CARLETON: NEW MUROID GENUS 23

TABLE 5 Morphological Characters of Seven Neotropical Muroids and a Hypothetical Ancestor Charactersa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 2122 23 24 25 Ancestor a a a a a a a a ? a a a a a a a a a a ? a a a a a Holochilus brasiliensis b b b c a b b b a a b b b b b b a c b b c b b b b Holochilus sciureus b b b c a/b b b b a a b b b b c c a c b b c b b b b Lundomys molitor b b b c a b a a b b b b a a a b b b a b b a b a b Oryzomys subflavus a a a a a a b a b b b b a a a a a a a b a b b a b Pseudoryzomys simplex a a b b a b b a b b b b a a a b b c a b c b b b b Sigmodon hispidus a a a a b b b a b a b a a b b c b c b a c b b b a Sigmodon peruanus a a a a b b b a a a a a a b c c b c b a c b a ? ? a Numbered and described in the text. cept as noted below, character information cluded autapomorphies and uninformative for both was extracted from Voss (1992). characters (e.g., unordered multistate char- Holochilus brasiliensis and H. sciureus are acters with only a single state expressed by included separately to test generic monophy- more than one taxon). Some characters that ly and to distinguish interspecific character afford clear distinctions between Lundomys differences from character variation of un- and Holochilus (e.g., size ofthe ectotympanic known significance within the latter taxon. bullae, relative size ofthe preglenoid foramen Oryzomys subflavus4 is a South American and subsquamosal fenestra, mandibular congener ofthe North American type species morphology) proved intractable when we (0. palustris) which it closely resembles in tried to define states for other taxa, and these many characters; our character data for this were also omitted from our analysis. Where taxon were obtained from Bolivian and Par- we recorded only the modal character state, aguayan series in the AMNH and UMMZ this fact is noted in the character-state de- collections. Pseudoryzomys is an enigmatic, scription (e.g., "usually present") or we de- monotypic South American genus that may scribe the variation explicitly in the remarks be closely related to oryzomyines (Voss and that follow. Multistate morphological char- Myers, 1991; Voss, 1991); in the course of acters are ordered as specified in the state preparing this report, we observed many descriptions. Our final data set (table 5) in- striking similarities between Pseudoryzomys cludes a hypothetical ancestor, reconstructed and Lundomys that clearly merit evaluation by outgroup analysis, as the designated root in a phylogenetic context. Except as noted for our trees. below, character information for P. simplex We analyzed phylogenetic relationships was extracted from Voss and Myers (1991). using the exhaustive search option of PAUP Many characters are known to vary among Version 3.1 (Swofford, 1993) to find trees of these seven taxa, but not all are useful for minimal length by the criterion of unweight- analyzing phylogenetic relationships. We ex- ed Wagner parsimony (forward and reversed transformations of all characters counted 4We provisionally use Oryzomys subflavus (Wagner) equally). Descriptive statistics for trees for Brazilian, Paraguayan, and Bolivian populations with (length, L; and consistency index, CI) were the anatomical traits described and tabulated herein. We defined by Kluge and Farris (1969). Our tree follow Cabrera (1961) by regarding Mus vulpinus Lund diagrams were drawn by MacClade (Mad- and Calomys laticeps Winge as synonyms. Oryzomys dison and Maddison, 1992). buccinatus (Olfers), based on Azara's (1801) ambiguous description of the "Rat troisieme ou rat angouya," is sometimes used in reference to Bolivian and Paraguayan CHARACTER DEFINITIONS specimens (Musser and Carleton, 1993). The convoluted taxonomy ofthis morphologically distinctive species will 1. Ungual tufts on hindfoot: (a) present; (b) be discussed elsewhere (R. S. Voss and P. Myers, in absent. prep.). Remarks.-As noted by Voss (1993), tufts 24 AMERICAN MUSEUM NOVITATES NO. 3085 of long ungual hairs are uniformly present in zomyines, we observed no interdigital web- tylomyines, neotomines, peromyscines, and bing on the hindfeet of Oryzomys subflavus.5 other North and Central American out- The highly developed webs ofLundomys are groups. Voss (1992) described the manus and autapomorphic and therefore are not distin- pes of Sigmodon as "without conspicuous guished from the less extensive webs ofHol- tufts of longer hairs at the bases of claws," ochilus in our character-state coding. but that description was intended to distin- 5. Mammary counts: (a) eight (thoracic teats guish the long but sparse ungual hairs ofSig- absent); (b) ten (thoracic teats present). modon from the thick and very obvious tufts Remarks.-All tylomyines, neotomines, present in certain other Neotropical muroids; peromyscines, and other North and Central the claws of Sigmodon are not naked like American outgroup taxa have either four or those of Lundomys and Holochilus. Ungual six teats in inguinal, abdominal, and (in taxa tufts are coded as "present" ifthe hairs rooted with six) postaxial pairs (Carleton, 1980; but at the bases of the claws equal or exceed the note that an alternative nomenclature for claws in length, and as "absent" if the hairs mammary loci is used therein). Derived are always much shorter than the claws. mammary counts of eight or more in many 2. Natatory fringe on hindfoot: (a) absent; Neotropical muroids always include a pec- (b) present. toral pair (Voss, 1988), and counts of ten Remarks.-Natatory fringes are not pres- include thoracic teats as well. We coded ent in any outgroup taxa. The highly devel- mammary variation within the H. sciureus oped natatory fringes of Lundomys are au- complex as taxonomic (rather than popula- tapomorphic and simple presence is therefore tion) polymorphism because it apparently oc- coded for both that genus and Holochilus. curs only among geographic samples (table 3. Plantar pads on hindfoot: (a) thenar, hy- 3) that may prove to represent distinct spe- pothenar, and four interdigital pads present cies. and well developed; (b) all pads very small, 6. Anterodorsal margin of zygomatic plate: hypothenar usually absent. (a) smoothly rounded, without a sharp corner Remarks. -All tylomyines, neotomines, or spinous process; (b) produced as a sharp and most peromyscines have six well-devel- corner or spinous process. oped plantar pads. Among the outgroups, only Remarks. -A sharp anterior corner or spi- Onychomys and Podomys (both peromys- nous process extending the free dorsal margin cines) lack one or both ofthe metatarsal pads, of the zygomatic plate is absent in all out- losses that Carleton (1980) interpreted as au- group taxa, many of which lack well-defined tapomorphies as we do also. The hypothenar zygomatic notches (Carleton, 1980). of Oryzomys subflavus is very small but ap- 7. Supraorbital margins: (a) without raised pears to be present in all of the specimens at beads; (b) with raised beads, at least in older hand. specimens. 4. Interdigital webbing on hindfoot: (a) ab- Remarks.-Beaded and unbeaded supra- sent; (b) present but small, not extending to orbital margins both occur among the out- first interphalangeal joint of any digits; (c) groups, but we concur with Hershkovitz present, extending to or beyond first inter- (1962) and Carleton (1980) that the beadless phalangeal joints of digits II, III, and IV (de- morphology is plesiomorphic. The supraor- rived from state b). bital margins are unambiguously beaded or Remarks.-Interdigital webbing is another not in most of the taxa included in our anal- trait that is not developed in any ofthe North ysis, but many specimens of Pseudoryzomys and Central American outgroups. The or- simplex have indistinct supraorbital beads. dering ofthe states recognized above is linear, 8. Postorbital ridge: (a) absent, posterior following our perception of a graded series of successively more derived morphologies I The bases of the digits are, of course, connected by among the taxa of our study. Although the integument, so pulling adjacent toes in opposite di- Hershkovitz (1944: 12) claimed that the three rections will always raise a small bridge of skin between middle digits ofthe hindfoot are "partly, but them. Interdigital webs are to be distinguished from such not always conspicuously webbed" in all ory- anatomically trivial effects. 1993 VOSS AND CARLETON: NEW MUROID GENUS 25 orbital wall without conspicuous relief, fron- by regarding a complete stapedial contribu- tal-squamosal suture exposed; (b) present and tion as primitive. Intermediate states for this concealing frontal-squamosal suture in most character are not exhibited by any ofthe taxa older specimens. included in our analysis. Remarks.-A thick postorbital ridge that 12. Bullar suspension: (a) posterior suspen- obscures the frontal-squamosal suture is uni- sory process of squamosal present and con- formly absent among the outgroup taxa we nected to the tegmen tympani; (b) posterior surveyed. suspensory process absent, tegmen tympani 9. Incisive foramina: (a) short, not extend- not touching or barely in contact with squa- ing posteriorly to or between molar alveoli mosal. except in juveniles and some young adult Remarks. -The polarity of this character specimens; (b) long, extending to or between was discussed by Voss (1993) who reported molar alveoli in all or most adult specimens. that in all outgroup taxa the tegmen tympani Remarks. -Long and short incisive foram- is tightly connected to the squamosal. Our ina are both represented among the outgroup character-state coding emphasizes presence exemplars we surveyed (table 4) with no com- or absence of the posterior suspensory pro- pelling taxonomic pattern to suggest which is cess, not contact between the tegmen tym- primitive for Neotropical muroids. We there- pani and the squamosal per se. fore coded the ancestral state for this char- 13. Enamel band of upper incisors: (a) acter as unknown. smoothly rounded or flattened, but without 10. Alisphenoid strut: (a) present, buccin- labial bevel; (b) flattened medially, with dis- ator-masticatory and accessory oval foram- tinct labial bevel. ina separate; (b) absent, buccinator-masti- Remarks.-Although a few outgroup taxa catory and foramen ovale confluent. have flattened enamel bands (e.g., Onycho- Remarks. -An alisphenoid strut separates mys species), none exhibits the prominent the buccinator-masticatory and accessory oval labial bevel characteristic of Holochilus spe- foramina in all of the outgroup samples ex- cies. amined by Carleton (1 980),6 and we therefore 14. Molar occlusal topography: (a) buno- interpret the strut as primitively present dont; (b) flat-crowned. among Neotropical muroids. The alisphe- Remarks.-Among the outgroups, only noid strut was reported as present or absent neotomines and Neotomodon alstoni (a per- in Pseudoryzomys simplex by Voss and My- omyscine) have flat-crowned molars. Hinton ers (1991), but it is usually absent (in ten (1926), Hershkovitz (1967), Vorontsov specimens with undamaged alisphenoids, the (1979), and Carleton (1980) are among the strut is completely absent in six, present uni- many students ofmuroid dental morphology laterally in three, and present on both sides who have interpreted bunodont dentitions as in only one). plesiomorphic, and we see no reason to con- 11. Carotid circulation: (a) with complete tradict this broad consensus in the present stapedial contribution to the facial (internal analysis. maxillary and ophthalmic) supply; (b) with- 15. Molar occlusal design: (a) cusps essen- out any stapedial contribution to the facial tially opposite with rounded outer margins supply. (not prismatic), lingual and labial folds not Remarks.-We follow the now-standard interpenetrating; (b) cusps slightly alternating phylogenetic interpretation of muroid carot- with more acute outer margins, some lingual id arterial variation (Bugge, 1970; Carleton, and labial folds deeply interpenetrating; (c) 1980; Voss, 1988; Carleton and Musser, 1989) cusps conspicuously alternating with acute outer margins (prismatic), some lingual and 6 Absence of an alisphenoid strut in the sense of this labial folds deeply interpenetrating (derived report is equivalent to absence of a foramen ovale in from state b). Carleton (1980). In the course of checking outgroup ex- Remarks.-Our description of states for emplars (table 4), however, we noted some polymor- this character reflects the obvious interrela- phism for this character within and among samples of tionship of cusp position, cusp shape, and Onychomys leucogaster. fold morphology in molar occlusal pattern 26 AMERICAN MUSEUM NOVITATES NO. 3085 definition. Our scoring of taxa emphasizes many outgroup taxa with divided anterocon- the upper dentition, in which differences are ids, however, the internal sulcus of the an- most apparent. Carleton (1980) and Voss teromedian flexid is deeper than the crevice (1993) provided our rationale for supposing that communicates with the anterior margin that the ancestral Neotropical muroid molar of the tooth and is often isolated by wear as had opposite, rounded cusps and folds that a small enamel island. The large pit in the did not interpenetrate. ml procingulum of Holochilus, Lundomys, 16. Mesolophs on Ml and M2: (a) meso- Oryzomys subflavus, and Pseudoryzomys may lophs large, extending from median mure to be a phylogenetic remnant of an ancestral labial cingulum (fused with mesostyle); (b) anteromedian flexid; certainly, it appears to mesolophs small, not or seldom extending to be a derived trait. The undivided, unpitted labial cingulum (not fused with mesostyle), anteroconid of Sigmodon may be ancestral sometimes absent from worn teeth, or re- to the divided morphology (Carleton, 1980: duced to a slight but perceptible labial de- character 2), or may have evolved from the flection of median mure; (c) mesolophs ab- pitted condition by loss ofthe pit. We regard sent (derived from state b). the ancestral state for this character as un- Remarks.-Although mesoloph(id)s are known. present or absent in various outgroup taxa, 21. Mesolophids in lower dentition: (a) we follow the orthodox interpretation (e.g., present and well developed, extending to lin- Stehlin and Schaub, 1951; Hershkovitz, 1962, gual cingulum; (b) present in unworn denti- 1967; Carleton, 1980) ofmuroid dental evo- tions but small, not extending to lingual cin- lution by assuming that pentalophodont mo- gulum; (c) absent (derived from state b). lars (with well-developed accessory crests) are Remarks.-We follow the standard inter- primitive. pretation of muroid molar evolution for this 17. Mesoloph on M3: (a) usually present character (see analysis for character 16). and well developed; (b) absent or vestigial. 22. Labial root of Ml: (a) absent; (b) pres- Remarks. -Our ancestral character-state ent. assignment for this character follows the pre- vailing consensus (see the analysis for char- Remarks. -An externally visible labial root acter 16). The taxonomic distribution of the is absent from Ml in all of our outgroup ex- mesoloph on M3 vs. MI-2 (table 4) clearly emplars. Carleton (1980: table 7) recorded an indicates that this serially homologous crest internal "labial" root for Reithrodontomys has undergone independent evolutionary sumichrasti and Megadontomys thomasi transformations on different teeth. (outgroup species that we also examined: ta- 18. Anteroloph on Ml: (a) present and well ble 4), but as internal roots and labial roots developed, extending to labial cingulum; (b) sometimes occur on the same tooth (fig. 1 3B) small, not extending to cingulum; (c) absent they should be distinguished in phylogenetic (derived from state b). analyses. Externally visible labial roots are Remarks. -A well-developed anteroloph present in Reithrodontomys megalotis and R. is part ofthe plesiomorphic, pentalophodont montanus (Carleton, 1980: table 7), but the bauplan (see the analysis for character 16). plesiomorphic state for Neotropical muroids 19. Protoflexus of M2: (a) present as a shal- is probably absence. low indentation, at least in unworn denti- 23. Accessory roots of ml: (a) only labial tions; (b) absent. accessory root usually present (three roots to- Remarks.-The protoflexus separates the tal); (b) labial and lingual accessory roots usu- procingulum from the protocone in primi- ally present (four roots total). tive, pentalophodont dentitions (see Reig, Remarks.-Lingual rootlets appear to be 1977: fig. 3). uniformly absent from the first lower molars 20. Internal enameled pit of ml procingul- of tylomyines, neotomines, peromyscines, um: (a) absent; (b) present. and other North and Central American out- Remarks.-None of the outgroup exem- group taxa (Carleton, 1980). plars that we examined (table 4) have a large 24. Gastric glandular epithelium: (a) re- enameled pit in the procingulum of ml. In stricted to antrum (stomach strictly hemi- 1993 VOSS AND CARLETON: NEW MUROID GENUS 27 glandular); (b) extends beyond esophagus, into zomys to the planar, tetralophodont config- corpus. uration of Sigmodon and Holochilus. Remarks.-Although both ofthe states that The monophyletic group that includes we recognize for this character were sub- Lundomys, Pseudoryzomys, Sigmodon, and sumed in the unilocular-hemiglandular mor- Holochilus in this phylogenetic reconstruc- photype that Carleton (1973, 1980) hypoth- tion (fig. 14A) is supported by four unique esized to be primitive for muroids, the and unreversed character transformations pronounced leftward extension of glandular (apomorphic states in parentheses): acquisi- tissue into the corpus ofHolochilus and Sig- tion ofa sharp anterodorsal corner or spinous modon hispidus (both described in Carleton, process on the zygomatic plate (6b), reduc- 1973) differs conspicuously from the strictly tion of mesolophs on M1-2 (16b), reduction hemiglandular condition defined herein. Be- ofthe anteroloph ofM1 (1 8b), and reduction cause several outgroup taxa have strictly of mesolophids (21b). The next node from hemiglandular stomachs (species of Tylomys, the root is diagnosed by three uniquely de- Ototylomys, Scotinomys, and Baiomys; rived and unreversed transformations that Carleton, 1973) whereas none have glandular Pseudoryzomys shares with Sigmodon and epithelium in the corpus, we assume that the Holochilus: loss ofthe anteroloph ofM I (1 8c), former condition is primitive for Neotropical loss of mesolophids (21c), and extension of muroids. The two available stomachs of glandular epithelium into the gastric corpus Pseudoryzomys simplex (UMMZ 133912, (24b). Finally, a sister-group relationship be- 134387) were originally described by Voss tween Sigmodon and Holochilus is supported and Myers (1991) as hemiglandular (sensu by three uniquely shared and unreversed Carleton, 1973, 1980) but each has a well- character states: flat-crowned molars (14b), defined extension ofglandular epithelium into the alternating arrangement of molar cusps the corpus. The gastric morphology of Sig- separated by interpenetrating folds (1 5b), and modon peruanus is unknown. absence of the protoflexus of M2 (19b). The 25. Gall bladder: (a) present; (b) absent. two species of Holochilus uniquely share de- Remarks.-We follow Vorontsov (1979), rived states of posterior orbital morphology Carleton (1980), and Voss (1991) in assuming (8b) and incisor shape (13b). No unique apo- that absence of the gall bladder is derived. morphies are shared by the two species of Although Voss (1992) included presence ofa Sigmodon, whose close relationship is in- gall bladder in his diagnosis of Sigmodon, stead supported by homoplastic character this character state has yet to be confirmed transformations. for S. peruanus because fluid-preserved spec- The next-most-parsimonious phylogeny imens are not available. (fig. 14B) depicts alternative groupings de- termined by a set ofmutually compatible ex- ternal characters: Pseudoryzomys uniquely shares derived transformations of plantar RESULTS pads (3b) and interdigital webs (4b) with Lun- The shortest tree for our character data (fig. domys and Holochilus; and Lundomys and 14A) supports Hershkovitz's (1955: 653) sug- Holochilus share uniquely transformed un- gestion that ".... Sigmodon is most nearly gual tufts (lb), natatory fringes (2b), and in- related to Holochilus and, in most respects, terdigital webs (4c). Obviously, many of the nearer H. brasiliensis than the latter is to its dental traits interpreted as synapomorphies larger congener H. magnus," but the illus- ofmonophyletic groups in figure 14A are less trated cladistic position ofPseudoryzomys was parsimoniously explained in this reconstruc- not predicted by any prior systematic study tion as independently derived traits of Sig- ofNeotropical muroids. This topology is pri- modon, Pseudoryzomys, and Holochilus. marily determined by a set ofmutually com- Phylogenetic hypotheses that recognize patible dental characters and illustrates a se- Holochilus, Lundomys, and Pseudoryzomys quence of taxa with molars progressively as oryzomyines (i.e., as members of a mono- simplified and transformed from the buno- phyletic group that includes Oryzomys but dont, pentalophodont morphology of Ory- not Sigmodon) are much less parsimonious 28 AMERICAN MUSEUM NOVITATES NO. 3085

B

Fig. 14. Two hypotheses of phylogeny for our character data (table 5). A, the most-parsimonious tree (L = 46, CI = 0.65); B, the next-most-parsimonious alternative (L = 48, CI = 0.62). than the preceding examples (fig. 15). Nev- ofthe characters in our data represent dental ertheless, such trees are supported by three comparisons. Including so many characters uniquely derived and unreversed attributes: from a single anatomical system has the ob- absence of a posterior suspensory process of vious risk that convergent adaptations rather the squamosal (1 2b), a large enamel pit in the than shared ancestry could determine the to- procingulum of ml (20b), and absence of a pology of phylogenetic reconstructions. Sig- gall bladder (25b). If these derived traits are modon and Holochilus are both herbivores homologous, then the numerous apomorphic that principally subsist on the green, vege- dental resemblances between Sigmodon and tative tissues ofgrasses and forbs (references Holochilus are perforce convergent. cited in Voss, 1992). The flat-crowned, lo- Although parsimony clearly favors the hy- phodont molar architecture that constitutes pothesis that Holochilus and Sigmodon are the principal evidence of close relationship sister taxa, it is noteworthy that almost half between these genera conforms to the general 1993 VOSS AND CARLETON: NEW MUROID GENUS 29

A

B

Fig. 15. The two most parsimonious phylogenies for our character data (table 5) under the constraint that Holochilus, Lundomys, and Pseudoryzomys are oryzomyines. The statistics for both trees are iden- tical (L = 53, CI = 0.57). occlusal design common to many mammals 1962) are strikingly divergent. Unfortunate- that eat plant vegetative tissues (Rensberger, ly, primitive and derived character states of 1973; Janis and Fortelius, 1988), so an ad the glans penis were not distinguished, and hoc hypothesis of functional convergence is no tabular summary of character data was not implausible. provided for analysis. Hooper and Musser's Evidence that Holochilus is more closely (1964: 45) cautious suggestion that "the po- related to oryzomyines than to Sigmodon has sition of Holochilus be reexamined with the been cited in surveys of genitalic and chro- thought in mind that it may be a well differ- mosomal characters. Hooper and Musser entiated oryzomyine rather than a sigmo- (1964) reported detailed similarities between dont" provoked Hershkovitz (1966: 130) to the glandes penes of Holochilus and Oryzo- argue that "a combination of fundamental mys, and emphasized that the phallic char- cranial, dental, and external characters ... acters of Sigmodon (described by Hooper, unite Sigmodon, Reithrodon, Neotomys, and 30 AMERICAN MUSEUM NOVITATES NO. 3085

Fig. 16. The strict consensus of 10,000 equally parsimonious phylogenies (each with L = 46 and CI = 0.98) for 16 muroid species with G-banded karyotypes. The data ofBaker et al. (1983) were reanalyzed as unordered characters, and trees were rooted with Neotoma micropus as the designated outgroup (see Appendix). The generic taxonomy has been updated to reflect current usage (Musser and Carleton, 1993) but specific epithets follow Baker et al.'s (1983) identifications.

Holochilus into a closely knit group," yet only cluding Sigmodon, is unambiguously sup- their "sigmodont" molar morphology ported by the karyotypic data they published. uniquely distinguishes these genera as a group Voss (1991) suggested that absence ofa gall apart from other Neotropical muroids. Sub- bladder supports the monophyly of a group sequent suggestions that Neotomys and comprising Holochilus (sensu lato), Pseudo- Reithrodon are phyllotines (Pearson and Pat- ryzomys, Zygodontomys, and the oryzo- ton, 1976; Olds and Anderson, 1989; Braun, myine genera of Hershkovitz (1944, 1960). 1993) imply that sigmodont dentitions have The present report summarizes additional arisen at least twice in Neotropical muroid evidence that we believe justifies formal rec- evolution. ognition of the tribe Oryzomyini with essen- Comparisons of G-banded chromosomes tially the same membership (see below). Al- among Holochilus, Sigmodon, and 13 species though this taxonomic action is not consistent of ory-zomyines were interpreted by Baker et with the most parsimonious interpretation of al. (1983) as corroborating Hooper and Mus- our own data, the phylogenetic congruence ser's (1964) hypothesis that Holochilus might ofcertain cranial and visceral characters with be an oryzomyine. We agree. Although our the results of prior genitalic and karyotypic reanalysis (see Appendix) produced a much studies appears persuasive despite our in- less resolved phylogeny (fig. 16) than that ability to include the total evidence in a single originally proposed by Baker et al. (1983: fig. analysis. 4), their conclusion that Holochilus belongs Within the Oryzomyini, Lundomys ap- in a monophyletic group with Nectomys pears most closely related to Holochilus and squamipes and other oryzomyines, but ex- Pseudoryzomys, but two different hypotheses 1993 VOSS AND CARLETON: NEW MUROID GENUS 31 ofphylogeny for these genera provide equally netic diagnosis is an hypothesis concerning parsimonious explanations of our character derived character states of the most recent data. A sister-group relationship between common ancestor of a monophyletic group Holochilus and Pseudoryzomys (fig. 15A) is and differs in important respects from diag- supported by apomorphic states ofdental and noses in nonphylogenetic classifications gastric characters (1 8c, 21c, 24b), whereas ex- (Rowe, 1987). Most significantly, apomor- ternal apomorphies (lb, 2b, 4c) suggest that phic traits ofan ancestor may be transformed Lundomys and Holochilus are more closely in descendant taxa, so that a phylogenetically related (fig. 1 5B). Although we are impressed diagnostic character state is not necessarily by the close overall resemblance in size and shared by all members of the group in ques- external appearance between Lundomys mol- tion. itor and Holochilus brasiliensis, we acknowl- edge the genuine ambiguity of the character data analyzed herein and decline to advocate TRIBE ORYZOMYINI VORONTSOV, 1959 either of these phylogenetic alternatives. PHYLOGENETIC DIAGNOSIS: Members ofthe Chromosomal, molecular, and genitalic char- Neotropical muroid complex (previously di- acters will perhaps prove useful in future ef- agnosed in this report) descended from a forts to resolve this trichotomy. common ancestor with the following traits: (1) a pectoral pair of mammae (mammary counts of eight or more in all known descen- PHYLOGENETIC DIAGNOSIS dant taxa); (2) a long palate with prominent AND CONTENTS OF ORYZOMYINI posterolateral pits (reversed in Holochilus As explained by Carleton and Musser sciureus which has a markedly shorter pal- (1989) and Voss (1991, 1993), the concept of ate); (3) no alisphenoid strut separating the an oryzomyine group emerged gradually in buccinator-masticatory and accessory oval the taxonomic literature on Neotropical mu- foramina (reversed in Holochilus and some roids. Common to all concepts ofthis group, species of Oligoryzomys); (4) no posterior as explicitly stated in diagnoses (e.g., Tho- suspensory process of the squamosal at- mas, 1917; and Hershkovitz, 1944, 1960) or tached to the tegmen tympani (secondary implied by lists ofincluded genera (e.g., Tate, overlap between tegmen tympani and squa- 1932; Reig, 1984, 1986), is the shared pos- mosal occurs in Lundomys and some species session of pentalophodont molars with well- of Oecomys, but the contact neve-r involves developed mesolophs and mesolophids. Thus, a distinct suspensory process of the latter whether oryzomyines were construed nar- bone); and (5) no gall bladder. rowly (as by Hershkovitz, 1944, 1960) or in CONTENTS: Holochilus, Lundomys, tMe- a broader sense (Vorontsov, 1959; Reig, 1980, galomys, Melanomys, Microryzomys, Nea- 1984, 1986), the group was perceived in con- comys, Nectomys, Nesoryzomys, Oecomys, tradistinction to tetralophodont genera (e.g., Oligoryzomys, Oryzomys, Pseudoryzomys, akodonts, phyllotines, and sigmodonts) that Scolomys, Sigmodontomys, Zygodontomys. lack well-developed mesolophs and meso- REMARKS: The phylogenetic classification lophids. Unfortunately, pentalophodonty is of tylomyines and "thomasomyines," pre- a primitive trait for muroids (Stehlin and viously included in the Oryzomyini by Vo- Schaub, 1951; Hershkovitz, 1962, 1967; Reig, rontsov (1-959) and Reig (1980, 1984, 1986), 1977), so the traditional "evidence" for group is discussed by Carleton (1980) and Voss recognition is based on symplesiomorphy (1993), respectively. Except by including four (Voss, 1991). tetralophodont genera, our tribal concept co- Our concept of Oryzomyini differs from incides with the narrow-sense oryzomyine the aforementioned classifications by includ- group of Hershkovitz (1944, 1960). The im- ing several tetralophodont genera: Holochi- plied reduction and loss of the mesoloph(id) lus, Lundomys, Pseudoryzomys, and Zygo- in one or more clades descended from a pen- dontomys. Justification for this revision of talophodont oryzomyine ancestor were dis- tribal contents is summarized in the phylo- cussed by Voss (1991), and we note that ei- genetic diagnosis given below. A phyloge- ther ofthe phylogenetic topologies illustrated 32 AMERICAN MUSEUM NOVITATES NO. 3085 in figure 15 could provide the outline for an 19 April 1963 near the Rio Olimar Chico, appropriate evolutionary scenario. about 25 km WSW Trienta y Tres, Depar- Some of the derived character states at- tamento Trienta y Tres. The local vegetation tributed to the oryzomyine ancestor in our (fig. 17) consisted ofa low riparian woodland phylogenetic diagnosis have not been sur- surrounded by rolling, grassy plains heavily veyed in all hypothesized members of the grazed by cattle and sheep. Thermometer re- tribe because only anatomically incomplete cordings (in S. Anderson's fieldnotes) docu- specimens are available for many species. We mented an average 24-hour minimum tem- predict that future morphological research will perature of 48°F and an average 24-hour require emendments to our phylogenetic di- maximum of72°F at this camp. Tuttle's trap- agnosis: additional homoplastic character line was set along a small stream about one- transformations will doubtless be discovered, half mile from the river: but more tribal synapomorphies may also be found, and new member genera remain to be At about 4:30 pm I began setting 50 rat traps along the stream near where I caught the [Oligoryzomys] described. delticola last night. I set the traps from 15 to 25 feet apart on both sides of the stream. I waded down the stream and set the traps along the banks. Most of the NATURAL HISTORY AND portion of the stream where my traps are set is well ZOOGEOGRAPHY shaded by trees [and] there are many large ferns over- hanging the stream. The stream banks are about 6 NATURAL HISTORY feet high, and the ferns and moss grow on these banks. Above, on the level, are ... sagebrush-like plants up Lundomys molitor is not a common rat in to 5 feet tall and spaced about 8 feet apart. Beneath zoological collections, and ecological infor- these bushes is ... grass about a foot tall. [Tuttle's mation is correspondingly scant. The first notes for 10 April] known Recent specimens, collected by C. C. The following day, 11 April, this trapline Sanborn in 1926, were not recognized as dis- caught nothing, but on the morning of 12 tinct from sympatric Holochilus brasiliensis April the first oftwo specimens ofLundomys until Hershkovitz (1955) described them as molitor taken at this locality (AMNH 206392) H. magnus. Sanborn (1929) remarked that H. "vulpinus" (comprising his series of H. was found in a trap brasiliensis and L. molitor) ". . . was rather ... about 2 feet from the edge of the stream, which is about 4 feet wide at that point. The water was only common along the Rio Cebollati and in some 6 inches deep, but about 30 feet downstream there marshes in Trienta y Tres [Uruguay]. One are several places where it is up to 2 feet deep. The was shot at night by shining its eyes with a trap was placed in an indistinct runway in grass about jacklight." 9 inches tall. For about 250 feet up- and downstream Natural history data reported by Barlow the banks are about 6 feet high and covered with ferns whose fronds are up to 4 feet long and overhang the (1969) were derived from 11 specimens of water. The trees, mostly less than 25 feet tall, are dense Lundomys molitor obtained by the American enough that very little direct sunlight reaches the Museum of Natural History expedition to stream. The [specimen] had 3 embryos, 1 in the right Uruguay in 1962-63. Seven of these were [uterine] horn and 2 in the left, each about 12 mm trapped by M. D. Tuttle (at two localities long, crown-rump. [Ibid., 12 April] described below), and four were purchased On 14 April another specimen (AMNH from Sr. Marcellino Sanchez (who caught 206393), an adult male, was trapped them in the Ba-nado de Tropa Vieja); the lat- ter were subsequently prepared by Barlow and ... about 400 feet from where the last was taken. It R. G. Van in was caught in a trap placed beneath a large fern at the Gelder Montevideo. Barlow entrance to a runway coming from the stream, which (1969) abstracted habitat descriptions for L. was about 3 feet below the trap and over about a foot. molitor from Tuttle's fieldnotes, but omitted The stream [here] is about 1.5 feet deep and 3.5 feet many details and did not acknowledge his wide ... [and] about half-shaded by trees ... The source; rather than paraphrasing Tuttle again, upper portions of [the] stream bank are covered with a thin-bladed grass about 10 inches tall. Just above we quote his field observations verbatim be- the water level, the banks are nearly entirely covered low. by liverworts and a little moss. There are runways The AMNH expedition camped from 7- about 2.5 inches in diameter [through] the grass, and 1993 VOSS AND CARLETON: NEW MUROID GENUS 33

Fig. 17. The Rio Olimar Chico, about 25 km WSW Trienta y Tres, in Departamento Trienta y Tres, Uruguay. M. D. Tuttle's two specimens of Lundomys molitor from this locality were trapped beside a small stream about one-half mile from the river. The landscape of open, rolling plains broken by gallery forests along shallow watercourses is characteristic ofmuch ofthe country. Photographed by A. Ximenez in April 1963.

the liverworts have been worn away in a few areas the estancia of Sr. Julio Gerber, 3 km E Car- just above water level. [Ibid., 14 April] dona in Departamento Soriano. On his first Tuttle tried to trap more Lundomys molitor, day there he set 49 rat traps along a stream with additional rat traps, small Conibear ... only about 6 inches deep and 4 or 5 feet wide traps, and small leghold traps, on the evening which forms ponds as much as 100 feet long and 50 of 14 April. These were set where the stream feet wide . . . In some areas there are water hyacinths was deeper (to 3 ft) and unshaded by trees; in the stream, and cattails, rushes, and reeds, as well as a little Eryngium [Umbelliferae], grow at the ferns, liverworts, and moss were almost com- stream's edge. Grass is about 3 feet tall for about 700 pletely absent from the streambank along this ft by about 150 ft along the stream [and] between it extended portion of the trapline. The traps and a fence... There is a nearly continuous layer of were set within 10 in. of the water, and the fine, light green grass and clover beneath the taller to grass. I placed the 49 rat traps along the stream's edge Conibears were placed in the entrances and ... 48 Museum Specials beneath the 3-foot grass burrows that Tuttle thought might belong to on the higher but quite damp part ofthe area. [Tuttle's L. molitor. Neither these nor other traps set notes for 21 May] for L. molitor along unshaded streamsides were successful here. The only other muroid On the following morning these traplines species collected beside streams at this lo- yielded a real bonanza. cality was Oligoryzomys delticola, but two of were In the 25 rat traps which I set beneath bunches of specimens Reithrodon physodes grass with blades about . . . three feet tall right at the trapped on adjacent hillsides. water's edge ..., I caught 2 Scapteromys [tumidus] From 21-25 May 1963, Tuttle worked on and 3 Holochilus brasiliensis. In the 24 rat traps set 34 AMERICAN MUSEUM NOVITATES NO. 3085

... at the stream's edge on the other side of the fence might be the mollusc-eating rodent described where the grass with blades ... up to 4 feet tall, a by Burmeister (1879), but Barlow (1969: 41) little Eryngium, and many rushes, reeds, and cattails grow, I caught 13 Scapteromys [tumidus] and 1 [Lun- found primarily ". . . macerated greenish plant domys molitor; AMNH 206368]. In the 48 Museum material" in three stomachs (presumably from Specials set beneath grass about 3 feet tall in a wet the specimens collected by Sr. Sanchez in the area with a fine light green grass and clover growing Bafnado de Tropa Vieja). Our examination of beneath..., I caught 3 Akodon [azarae], 1 Oxymyc- the contents of two stomachs (AMNH terus nasutus, and 11 Scapteromys [tumidus]. [Ibid., 22 May] 206373,206388) from Tuttle's Soriano series of L. molitor revealed only crushed and Tuttle rebaited his traps on the afternoon of chopped fibrous tissue; we did not attempt the 22nd, but caught only 3 Scapteromys any histological analysis to determine wheth- tumidus (all in rat traps) on the 23rd. All the er this was of animal or vegetable origin, but traps were rebaited again and 15 rat traps we saw no identifiable animal parts in either were moved to a new area along the stream. stomach. On the next morning, the streamside rat traps Tuttle's efforts to collect Lundomys molitor produced 11 S. tumidus, one Holochilus near the Rio Olimar Chico by placing Con- brasiliensis, and one Lundomys molitor ibear traps at burrow entrances were proba- (AMNH 206373). The latter bly unsuccessful because L. molitor builds nests that are supported above the water in ... was caught beneath a dense growth ofrushes about 9 feet tall at the edge of a relatively open area. In reeds (Sierra de Soriano, 1969: 483-484): general, I believe that [Lundomys molitor] is most [Lundomys molitor] construye sus nidos sobre el agua, often found in protected areas where there is more con profundidades que en nuestros registros alcanzan cover, and that [Holochilus] brasiliensis is most com- hasta 1,50 m; los mismos presentan forma esferica y mon in the open areas. [Ibid., 24 May] se encuentran entre juncales, de los que la rata extrae los materiales que utiliza en la construcci6n. Los nidos This is the last entry in Tuttle's notes that propiamente dichos estan apoyados en los mismos provides ecological observations unambigu- juncos cortados a una altura de aproximadamente 80 with of Lundo- cm sobre el nivel del agua, en un area modificada por ously associated specimens el animal, que abarca alrededor de 60 cm2; los refugios mys molitor, but on the night of 25 May he estan normalmente a unos 20 cm de la superficie del shot 11 rats that were found swimming in the agua, con diimetros maximos y minimos de 30 y 25 same stream; nine were Holochilus bras- cm y altura de 9 a 11 cm; las paredes que lo forman iliensis, and two were L. molitor (AMNH presentan tres capas con diferentes grados de elabor- aci6n: la extema con un espesor de entre 4,5 y 5,0 cm 206380, 206381), but Tuttle assumed that all esta formada por trozos de juncos quebrados por in- were H. brasiliensis when he wrote up his cisi6n pero unidos por la corteza; dichos sectores apa- notes that evening. The last specimen of L. recen entretejidos; en la capa media, los juncos estan molitor collected at this locality (AMNH totalmente seccionados, tienen menor longitud (10- on the but no as- 15 cm), y corresponden en general a los extremos 206388) was taken 27th, apicales, apareciendo inflorescencias secas tambien sociated habitat information was recorded in quebradas por los incisivos de las ratas; en la pared Tuttle's journal or field catalog. interna, con un espesor de 4 a 5 cm, los trozos de Tuttle's fieldnotes provide unambiguous juncos son cortos (de 2 a 5 cm) y se encuentran roidos evidence that Lundomys molitor is nocturnal, y demenuzados, formando una cobertura intema del nido, que aparece entonces totalmente tapizado in- semiaquatic, and occurs sympatrically with cluso en el techo. Holochilus brasiliensis at some localities. The El refugio presenta ademas un vestibulo con una numbers of animals collected both by trap- rampa inclinada que conecta al nido con el agua y ping and by night hunting from 22-27 May viceversa, formada tambien por trozos de juncos que further suggest that L. molitor is less abun- se encuentran cortados totalmente y entretejidos, con dant than sympatric H. brasiliensis, but the longitudes de 25 a 30 cm aproximadamente. available data are inadequate to infer possible It is noteworthy that Holochilus bras- ecological differences between these rats. The iliensis and H. sciureus also build elevated predominantly herbivorous habits of Holo- nests (Barlow, 1969; Twigg, 1962, 1965). chilus are well documented (Martino and Nests made by Guyanese H. sciureus in sug- Aguilera, 1989; Twigg, 1962, 1965), but t-he arcane fields (Twigg, 1965) correspond in diet of Lundomys is essentially unkriown. several details ofconstruction with those de- Hershkovitz (1955) thought that L. molitor scribed above for Lundomys molitor. 1993 VOSS AND CARLETON: NEW MUROID GENUS 35

ZOOGEOGRAPHY range extensions suggest that prehistoric cli- Recent populations of Lundomys molitor mates in Minas Gerais were at least period- are known to occur between about 29 and 350 ically cooler than today's. Palynological data S in Uruguay and Rio Grande do Sul (fig. 7) from a peat core collected at 19°S in Minas where grasslands, marshes, gallery forests, and Gerais (Ledru, 1993) provide corroborating open woodlands form a complex mosaic of evidence of marked environmental changes subtropical pampas habitats (Barlow, 1969; over the last 30,000 years including cold-dry Belton, 1984). The Lagoa Santa fossils (col- and cold-moist climatic episodes. Additional lected in the tropics near 19°38'S) therefore examples of species currently living else- document a considerable northward exten- where but locally extinct may be discovered sion of the species at some time in the Pleis- among the fossils that Winge (1887) named tocene or early Holocene. Myocastor coypus, Habrothrix clivigensis, Habrothrix angusti- another rodent currently restricted to sub- dens, Oxymycterus talpinus, 0. cosmodus, tropical and temperate latitudes (Redford and Calomys anoblepas, and C. coronatus (Voss Eisenberg, 1992: map 11.112), is also rep- and Myers, 1991). Much yet remains to be resented by fossils from Lagoa Santa.7 As not- learned from Lund's paleontological legacy.- ed by Cerqueira (1982), such paleontological REFERENCES Aguilera, M., and A. Perez-Zapata Bugge, J. 1989. Cariologia de Holochilus venezuelae 1970. The contribution ofthe stapedial artery (Rodentia, Cricetidae). Acta Cient. Ve- to the cephalic stapedial supply in mu- nezolana 40: 198-207. roid rodents. Acta Anat. 76: 313-336. Azara, F. de Burmeister, H. 1801. Essais sur l'histoire naturelle des quad- 1879. Description physique de la Republique rupedes de la Province du Paraguay, vol. Argentine, tome III. Animaux ver- 2. Paris: Charles Pougens. tebres, pt. 1. Mammiferes vivants et Baker, R. J., B. F. Koop, and M. W. Haiduk eteints. Buenos Aires: Paul-Emile Coni 1983. Resolving systematic relationships with (Paris: F. Savy). G-bands: A study offive genera ofSouth 1961. Catalogo de los mamiferos de America American cricetine rodents. Syst. Zool. del Sur. Rev. Mus. Argentina Cienc. Nat. 32: 403-416. "Bernardino Rivadavia" 4(2): 309-732. Barlow, J. C. Carleton, M. D. 1969. Observations on the biology of rodents 1973-. A survey of gross stomach morphology in Uruguay. Life Sci. Contr. R. Ontario in New World Cricetinae (Rodentia, Mus. 75: 59 pp. Muroidea), with comments on func- Belton, W. tional interpretations. Misc. Publ. Mus. 1984. Birds ofRio Grande do Sul, Brazil. Part Zool. Univ. Michigan 146: 43 pp. 1. Reheidae through Furnariidae. Bull. 1980. Phylogenetic relationships in neotom- Am. Mus. Nat. Hist. 178: 369-636. ine-peromyscine rodents (Muroidea) Bond, M., and E. Massoia and a reappraisal of the dichotomy 1981. La presencia de Holochilus magnus within New World Cricetinae. Misc. (Rodentia, Cricetidae) en el Pleistoceno Publ. Mus. Zool. Univ. Michigan 157: superior de la provincia de Buenos Ai- 146 pp. res. Circ. Inform. Assoc. Paleontol. Ar- 1989. Systematics and Evolution. In G. L. gentina 8: 11. Kirkland Jr. and J. N. Layne (eds.), Ad- Braun, J. K. vances in the study ofPeromyscus (Ro- 1993. Systematic relationships of the tribe dentia), pp. 7-141. Lubbock: Texas Tech Phyllotini (Muridae: Sigmodontinae) of Univ. Press. South America. Oklahoma Mus. Nat. Carleton, M. D., and G. G. Musser Hist. Spec. Publ.: 50 pp. 1984. Muroid rodents. In S. Anderson and J.

7Reported as Myopotamus castoroides by Winge (1887) from the caves that Lund called Lapa do Bahu, Lapa da Cerca Grande, Lapa da Escrivania Nr. 1 and Nr. 1 1, Lapa da Serra das Abelhas, Lapa da Serra da Anta, and Lapa dos Tatus. It should be noted that although remains ofMyocastor coypus and Lundomys molitor were both excavated from Lapa da Escrivania, they occurred in separate chambers of the cave. 36 AMERICAN MUSEUM NOVITATES NO. 3085

K. Jones (eds.), Orders and families of Hinton, M. A. C. Recent mammals ofthe world, pp. 289- 1926. Monograph of the voles and lemmings 379. New York: Wiley. (Microtinae) living and extinct, vol. 1. 1989. Systematic studies of oryzomyine ro- London: British Museum (Natural His- dents (Muridae, Sigmodontinae): a syn- tory). opsis ofMicroryzomys. Bull. Am. Mus. Hooper, E. T. Nat. Hist. 191: 83 pp. 1962. The glans penis in Sigmodon, Sigmo- Cerqueira, R. mys, and Reithrodon (Rodentia, Crice- 1982. South American landscapes and their tinae). Occas. Pap. Mus. Zool. Univ. mammals. In M. A. Mares and H. H. Michigan 625: 11 pp. Genoways (eds.), Mammalian biology Hooper, E. T., and G. G. Musser in South America. Pymatuning Lab. 1964. The glans penis in Neotropical crice- Ecol., Spec. Publ. Ser. 6: 53-75. tines (Muridae) with comments on clas- Ellerman, J. R. sification ofmuroid rodents. Misc. Publ. 1941. The families and genera of living ro- Mus. Zool. Univ. Michigan 123: 57 pp. dents, vol. 2. Muridae. London: British Janis, C. M., and M. Fortelius Museum (Natural History). 1988. On the means whereby mammals Freitas, T. R. O., M. S. Mattevi, L. F. B. Oliveira, achieve increased functional durability et al. of their dentitions, with special refer- 1983. Chromosome relationships in three rep- ence to limiting factors. Biol. Rev. Cam- resentatives of the genus Holochilus bridge Philos. Soc. 63: 197-230. (Rodentia, Cricetidae) from Brazil. Ge- Kluge, A. G., and J. S. Farris netica 61: 13-20. 1969. Quantitative phyletics and the evolu- Gyldenstolpe, N. C. G. tion of anurans. Syst. Zool. 18: 1-32. 1932. A manual ofNeotropical sigmodont ro- Ledru, M.-P. dents. Kungl. Svenska Vetenskapsakad. 1993. Late Quaternary environmental and cli- Handl. Ser. 3, 11(3): 164 pp. + 18 pls. matic changes in central Brazil. Qua- Hatting, T. ternary Res. 39: 90-98. 1980. Den danske Zoolog P. W. Lund og hans Lezcano, M. J., C. Reboledo, and C. E. Schreiber udforskning af Brasiliens knoglehuler. 1992. Bioestratigrafia de los sedimentos de la Copenhagen: Zoologisk Museum. cuenca alta del rio de La Reconquista Hershkovitz, P. (Pleistoceno tardio, noreste del la prov- 1944. A systematic review of the Neotropical incia de Buenos Aires, Argentina). water rats of the genus Nectomys (Cri- Ameghiniana 29: 387. cetinae). Misc. Publ. Mus. Zool. Univ. Maddison, W. P., and D. R. Maddison Michigan 58: 101 pp. + folding map. 1992. MacClade, version 3: Analysis of phy- 1955. South American marsh rats, genus Ho- logeny and character evolution [com- lochilus, with a summary of sigmodont puter program and user's manual]. Sun- rodents. Fieldiana: Zoology 37: 639-673 derland, MA: Sinauer. + pls. 17-29. 1960. Mammals of northern Colombia, pre- Martino, A. M. G., and M. Aguilera M. liminary report No. 8: Arboreal rice rats, 1989. Food habits ofHolochilus venezuelae in a systematic revision of the subgenus rice fields. Mammalia 53: 545-561. Oecomys, genus Oryzomys. Proc. U.S. Massoia, E. Nat. Mus. 110: 513-568. 1974. Ataques graves de Holochilus y otros 1962. Evolution of Neotropical cricetine ro- roedores a cultivos de cafia de aziucar. dents (Muridae) with special reference Inst. Nac. Tec. Agrop., Idia 321/24: 1- to the phyllotine group. Fieldiana: Zo- 12. ology 46: 524 pp. 1980. El estado sistematico de cuatro especies 1966. South American swamp and fossorial de cricetidos sudamericanos y comen- rats of the scapteromyine group (Cri- tarios sobre otras especies congenrencas cetinae, Muridae) with comments on the (Mammalia-Rodentia). Ameghiniana glans penis in muroid taxonomy. Z. 17: 280-287. Siiugetierkd. 31: 81-149. 1981. El estado sistematico y zoogeografia de 1967. Dynamics of rodent molar evolution: a Mus brasiliensis Desmarest y Holochi- study based on New World Cricetinae, lus sciureus Wagner (Mammalia, Ro- family Muridae. J. Dent. Res. 46(5, dentia, Cricetidae). Physis, Secc. C, suppl.): 829-842. 39(97): 31-34. 1993 VOSS AND CARLETON: NEW MUROID GENUS 37

Moojen, J. Mus. Nat. Hist. (Zool. Ser.) 17: 147- 1952. Os roedores do Brasil. Rio de Janeiro: 165. Instituto Nacional do Livro. Sierra de Soriano, B. Musser, G. G., and M. D. Carleton 1965. Algunas estructuras externas relacion- 1993. Family Muridae. In D. E. Wilson and adas con la vida anfibia en dos especies D. M. Reeder (eds.), Mammal species del genero Holochilus Brandt, 1835 of the World: A taxonomic and geo- (Muridae, Cricetinae). Rev. Fac. Hum. graphic reference, 2nd ed., pp. 501-755. Cienc. 22: 209-220. Washington, D.C.: Smithsonian Insti- 1969. Algunos caracteres externos de criceti- tution Press. nos y su relacion con el grado de adap- Olds, N., and S. Anderson tacion a la vida acu'atica (Rodentia). 1989. A diagnosis of the tribe Phyllotini (Ro- Physis 28: 471-486. dentia, Muridae). In K. H. Redford and Simpson, G. G. J. F. Eisenberg (eds.), Advances in Neo- 1984. Discoverers of the lost world. An ac- tropical mammalogy, pp. 55-74. count of those who brought back to life Gainesville: Sandhill Crane Press. South American mammals long buried Paula Couto, C. de in the abyss of time. New Haven: Yale 1950. Lund e suas obras no Brasil. In P. W. Univ. Press. Lund, Memorias sobre a paleontologia Smithe, F. B. brasileira [translated works ofLund ed- 1975-1981. Naturalist's color guide. New York: ited by C. de Paulo Couto], pp. 27-66. Am. Mus. Nat. Hist. Rio de Janeiro: Instituto Nacional do Stehlin, H. G., and S. Schaub Livro. 1951. Die Trigonodontie der simplicidentaten Pearson, 0. P., and J. L. Patton Nager. Schweitzer. Paleontol. Abhl. 67: 1976. Relationships among South American 385 pp. phyllotine rodents based on chromo- Swofford, D. L. some analysis. J. Mammal. 57: 339-350. 1993. PAUP: Phylogenetic analysis using par- Redford, K. H., and J. F. Eisenberg simony, Version 3.1 (computer pro- 1992. Mammals ofthe Neotropics, vol. 2: The gram distributed by the Illinois Natural Southern Cone. Chicago: Univ. Chicago History Survey, Champaign, IL). Press. Swofford, D. L., and D. P. Begle Reig, 0. 1993. User's manual, PAUP Version 3.1 (dis- 1977. A proposed unified nomenclature for the tributed with computer program by the enamelled components of the molar Illinois Biological Survey, Champaign, teeth of the Cricetidae (Rodentia). J. IL). Zool. London 181: 227-241. Tate, G. H. H. 1980. A new fossil genus of South American 1932. [Taxonomic histories ofSouth and Cen- cricetid rodent allied to Weidomys, with tral American cricetid rodent genera]. an assessment of the Sigmodontinae. J. Am. Mus. Novitates 529,541,562,579, Zool. London 192: 257-281. 580, 581, 582, and 583. 1984. Distribuiqio geografica e historia evo- Thomas, 0. lutiva dos roedores muroides sulamer- 1917. On the arrangement ofthe South Amer- icanos (Cricetidae: Sigmodontinae). ican rats allied to Oryzomys and Rhipi- Rev. Brasil. Genet. 7: 333-365. domys. Ann. Mag. Nat. Hist. 8(20): 192- 1986. Diversity patterns and differentiation in 198. high Andean rodents. In F. Vuilleumier 1928. The Godman-Thomas expedition to and M Monasterio (eds.), High altitude Peru.-VII. The mammals of the Rio tropical biogeography, pp. 404-439. Ucayali. Ann. Mag. Nat. Hist. 10(2): New York: Oxford Univ. Press. 247-265. Rensberger, J. M. Trouessart, E.-L. 1973. An occlusion model for mastication and 1898. Catalogus mammalium tam viventium dental wear in herbivorous mammals. quam fossilium, nova editio, tomus 1. J. Paleontol. 47: 515-528. Berlin: R. Freiliinder & Sohn. Rowe, T. Twigg, G. I. 1987. Definition and diagnosis in the phylo- 1962. Notes on Holochilus sciureus in British genetic system. Syst. Zool. 36: 208-211. Guiana. J. Mammal. 43: 369-374. Sanborn, C. C. 1965. Studies on Holochilus sciureus berbicen- 1929. The land mammals of Uruguay. Field sis, a cricetine rodent from the coastal 38 AMERICAN MUSEUM NOVITATES NO. 3085

region ofBritish Guiana. Proc. Zool. Soc. 1992. A revision of the South American spe- London 145: 263-283. cies ofSigmodon (Mammalia: Muridae) Vidal, 0. R., R. Riva, and N. I. Baro with notes on their natural history and 1976. Los cromosomas del genero Holochilus biogeography. Am. Mus. Novitates I. Polimorfismo en H. chacarius Tho- 3050: 56 pp. mas (1906). Physis, Secc. B, 35(90): 75- 1993. A revision of the Brazilian muroid ro- 85. dent genus Delomys with remarks on Vorontsov, N. N. "thomasomyine" characters. Am. Mus. 1959. The system of hamster (Cricetinae) in Novitates 3073: 44 pp. the sphere of the world fauna and their Voss, R. S., and P. Myers phylogenetic relations [in Russian]. Biul. 1991. Pseudoryzomys simplex (Rodentia: Mosk. Obsh. Isp. Prir. Otd. Biol. 64: Muridae) and the significance ofLund's 134-137. collections from the caves of Lagoa 1979. Evolution of the alimentary system in Santa, Brazil. Bull. Am. Mus. Nat. Hist. myomorph rodents. New Delhi: Indian 206: 414-432. National Science Documentation Cen- Wagner, A. tre [published for the Smithsonian In- 1842. Beschreibung einiger neuer oder minder stitution]. bekannter Nager. Archiv Naturg. 8(1): Voss, R. S. 1-33. 1988. Systematics and ecology of ichthy- Winge, H. omyine rodents (Muroidea): patterns of 1887. Jordfundne og nulevende Gnavere (Ro- morphological evolution in a small dentia) fra Lagoa Santa, Minas Geraes, adaptive radiation. Bull. Am. Mus. Nat. Brasilien. E Museo Lundii 1(3): 200 pp. Hist. 188: 259-493. + 8 pls. 1991. An introduction to the Neotropical mu- 1941. The interrelationships of the mamma- roid rodent genus Zygodontomys. Bull. lian genera, vol. 2. Copenhagen: C. A. Am. Mus. Nat. Hist. 210: 113 pp. Reitzels Forlag.

APPENDIX comys, Nectomys, and Holochilus as outgroups to Reanalysis of Data from G-banded infer polarities and order character states within Chromosomes the genus. We doubt that Oryzomys, whether construed Baker et al. (1983) reported data from G-banded sensu lato (as by Baker et al., 1983) or in the more chromosomes of 16 New World muroids and at- restricted sense of Musser and Carleton (1993), is tempted to infer phylogenetic relationships from monophyletic. The genus (in all past or current patterns of shared and apparently derived rear- usages) is unrevised and no diagnostic synapo- rangements. The species represented in their study morphies are known. Membership in Oryzomys (table 6) included one neotomine (Neotoma mi- is therefore not an appropriate criterion for po- cropus) together with Sigmodon hispidus, Holo- larity estimation or character-state ordering, and chilus "brasiliensis" (= H. sciureus in the sense of phylogenetic analyses should not be constrained this report), and 13 oryzomyines (sensu Hersh- by assumptions of generic monophyly. kovitz, 1944, 1960). Baker et al. (1983) found suf- Because we could not evaluate the empirical ficient resolution in G-band patterns to suggest basis for Baker et al.'s (1983) hypotheses of char- homologies for the 12 largest autosomal pairs in acter-state ordering, we entered their data as each karyotype and recorded banding similarities unordered characters in an unweighted Wagner and differences among putative homologs. Band- parsimony analysis implemented by the branch- ing patterns observed in Neotoma micropus and and-bound algorithm ofPAUP Version 3.1 (Swof- in one or more Neotropical taxa were presumed ford, 1993). Our matrix (table 6) is condensed from to be primitive, a procedure consistent with our their table 1 by excluding uninformative or un- own assumptions of ingroup monophyly and out- interpretable chromosomes (i.e., 7, 9, 10, 13, 14, group comparison. Unfortunately, Baker and his and "A"). Tree topologies were rooted by desig- colleagues also assumed the monophyly of Ory- nating Neotoma micropus as the outgroup. We up- zomys (sensu lato, including Melanomys, Oeco- dated the generic taxonomy to reflect current usage mys, and Oligoryzomys) and used Sigmodon, Nea- but made no attempt to verify the accuracy of 1 993 VOSS AND CARLETON: NEW MUROID GENUS 39 specific identifications (except as noted above for Holochilus "brasiliensis"). A very large number ofalternative phylogenetic topologies provide maximally parsimonious in- terpretations ofthese data. The strict consensus of 10,000 such equally shortest trees (each requiring 46 steps; fig. 16), however, supports Baker et al.'s (1983) conclusion that Holochilus is more closely related to oryzomyines than to Sigmodon. By comparison, trees in which Sigmodon and Holo- chilus are constrained to be sister taxa require at least three additional character state changes (49 total) to fit the karyotypic evidence.

TABLE 6 Character Data from G-banded Chromosomes (See text for explanation) Chromosomesb C- C- Speciesa Cl C2 C3C4C5C6C8 11 12 Neotoma micropus 0 0 0 0 0 0 0 0 0 Sigmodon hispidus 2 10 ? 0 0 0 0 ? 4 Neacomys guianae 1 2 1 1 0 1 0 1 0 Nectomys squamipes 0 1 2 1 0 2 0 5 1 Holochilus "brasiliensis" 1 2 0 1 0 1 1 1 2 Oryzomys capito 1 2 0 2 1 3 1 3 0 Oryzomys sp. 1 3 0 2 1 3 1 3 0 Oryzomys palustris 1 4 3 1 0 1 ? 1 3 Melanomys caliginosus 1 5 3 1 0 1 ? 1 3 Oryzomys couesi 1 4 3 1 0 1 ? 1 3 Oryzomys caudatus 1 6 4 2 0 1 ? 3 0 Oecomys concolor 3 3 0 ? ? ? ? 3 0 Oligoryzomys delicatus 1 7 7 3 2 ? 1 4 ? Oecomys bicolor 4 8 5 4 3 ? 1 2 0 Oryzomys melanotis 1 3 0 2 0 1 1 3 0 Oryzomys alfaroi 1 9 6 5 4 4 1 6 ? a Generic taxonomy updated to reflect current usage, but sequence of taxa and species names follow Baker et al. (1983: table 1). b Chromosomal character states in Baker et al. (1983: table 1) recoded for PAUP analysis as follows: ? = un- identified segments; 0 = identical to Neotoma micropus; I = Mi (an alternative modification, arbitrarily num- bered); 2 = Mii; 3 = Miii; etc. Recent issues of the Novitates may be purchased from the Museum. Lists of back issues of the Novitates, Bulletin, and Anthropological Papers published during the last five years are available free of charge. Address orders to: American Museum of Natural History Library, Department D, Central Park West at 79th St., New York, N.Y. 10024.

0 This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).