A New Montane Species of Spiny Pocket Mouse (Rodentia: Heteromyidae: Heteromys) from Northwestern Costa Rica

2006·0.99 MB·English

by  Robert P. Anderson

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3509, 38 pp., 10 figures, 4 tables March 16, 2006
A New Montane Species of Spiny Pocket Mouse
(Rodentia: Heteromyidae: Heteromys) from
Northwestern Costa Rica
ROBERT P. ANDERSON,1,2 AND ROBERT M. TIMM3
ABSTRACT
Recent taxonomic works have recognized only two species of spiny pocket mice of the genus
Heteromys (Rodentia: Heteromyidae) from Costa Rica. Within Costa Rica, the widespread H.
desmarestianusisconsideredtooccurthroughoutthewetCaribbeanlowlands,aswellasatmiddle
andhighelevationsontheCaribbeanandPacificslopesofthecountry’smainmontanesystems.In
contrast,H.oresterusisknownfromonlyafewlocalitiesathighelevationsinthewesternportion
of the Cordillera de Talamanca in central Costa Rica. Our morphological and morphometric
analysesofspecimensfromnorthwesternCostaRicarevealthepresenceofanundescribedspecies
of the genus, which we describe as Heteromys nubicolens. This new species ranges from 750 to
1840m in elevation in the Cordillera de Tilara´n and Cordillera de Guanacaste. Heteromys
desmarestianusisfoundinthesurroundingmesiclowlandsandfoothills.Externally,bothspecies
possessdarkbrowndorsalpelage,butH.nubicolensdiffersbyoveralllargersizeandbydistinctive
cranialproportions.Inmostcranialmeasurements,H.nubicolensislargerthanH.desmarestianus;
however, H. desmarestianus has a wider interorbital region and a wider braincase. Known
populations of H. nubicolens occur in three highland areas (Monteverde, Volca´n Rinco´n de la
Vieja–Volca´n Santa Mar´ıa, and Cerro Cacao), but populations in these areas are probably
disjunct, being separated by intervening lowlands. Heteromys nubicolens is likely widespread
throughouttheCordilleradeTilara´nandCordilleradeGuanacaste,butitspresenceinotherareas
ofthecountryisunlikely.EvenafterrecognizingH.nubicolensasdistinctfromH.desmarestianus,
morphological,karyological,andgeneticdataindicatethatH.desmarestianusrepresentsaspecies
complex. Further research is therefore necessary to evaluate the taxonomic status of this species
complexinotherregionsofthecountryandotherpartsofitswidespreadgeographicdistribution.
RESUMEN
Recientestrabajostaxono´micoshanconsideradoqueso´lodosespeciesderatonesdeabazones
(5rato´nbolsero,ratonbolso´n,rato´nmochilero)delge´neroHeteromys(Rodentia:Heteromyidae)
1DivisionofVertebrateZoology(Mammalogy),AmericanMuseumofNaturalHistory([email protected]).
2DepartmentofBiology,CityCollegeoftheCityUniversityofNewYork,NewYork,NY10031([email protected].
cuny.edu).
3NaturalHistoryMuseumandDepartmentofEcology&EvolutionaryBiology,UniversityofKansas,Lawrence,KS
66045([email protected]).
CopyrightEAmericanMuseumofNaturalHistory2006 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3509
habitanenCostaRica.Heteromysdesmarestianus,conunaampliadistribucio´ngeneral,habitaen
esepa´ısenlastierrasbajashu´medasdelCaribe,as´ıcomotambie´nenlasestribacionescariben˜asy
pac´ıficasdelasprincipalescadenasmontan˜osas,enaltitudesmediasyelevadas.Porelcontrario,
H.oresterusseconoceso´lodeunaspocaslocalidadesdealtamontan˜aenlaparteoccidentaldela
Cordillera de Talamanca, en la regio´n central de Costa Rica. Nuestros ana´lisis morfolo´gicos y
morfome´tricos de ejemplares provenientes del noroccidente costarricense revelan la presencia de
unaespecienodescritadelge´nero,lacualdescribimosaca´ comoHeteromysnubicolens.Estanueva
especiehabitaentrelos750ylos1840mdealtitudenlaCordilleradeTilara´nylaCordillerade
Guanacaste. Heteromys desmarestianus se encuentra en el piedemonte y en las tierras bajas
hu´medasadyacentesaestascordilleras,rodeandoladistribucio´ndeH.nubicolens.Externamente
ambas especies poseen un pelaje dorsal de coloracio´n parda oscura, pero H. nubicolens se
caracterizaportenerengeneralunmayortaman˜ocorporalyproporcionescraneanasdistintivas.
En la mayor´ıa de las medidas craneanas, H. nubicolens posee un mayor taman˜o que H.
desmarestianus;sinembargo,H.desmarestianustieneunamayoranchuradelaregio´ninterorbitaly
delacajacraneana.LaspoblacionesconocidasdeH.nubicolensseencuentranentresa´reasdealta
montan˜a(Monteverde,elVolca´nRinco´ndelaVieja–Volca´nSantaMar´ıayelCerroCacao),pero
estaspoblacionesprobablementeposeendistribucionesdisyuntas,estandoseparadasporlastierras
bajasqueseinterponenentreellas.EsprobablequeH.nubicolenstengaunaampliadistribucio´nen
laCordilleradeTilara´nylaCordilleradeGuanacaste,perosupresenciaespocoprobableenotras
regionesdelpa´ıs.InclusoconelreconocimientodeH.nubicolenscomounaespeciediferenteaH.
desmarestianus, datos morfolo´gicos, cariolo´gicos y gene´ticos indican que H. desmarestianus
constituyeuncomplejodeespecies.Porlotanto,senecesitanestudiosadicionalesparaevaluarla
taxonom´ıa de este complejo de especies en otras partes del pa´ıs y en otras regiones de su amplia
distribucio´ngeogra´fica.
INTRODUCTION Talamanca.Nearlycontinuousatanelevation
of 1500 m, it contains several peaks higher
Although Costa Rica encompasses an area than 2500 m. A broad connection, the Valle
of only ca. 51,000 km2, the region’s complex
Central (or Meseta Central), joins the
geological history and highly variable topog-
Cordillera Central and the northwestern por-
raphy and climate have contributed to a di-
tion of the Cordillera de Talamanca at
verse fauna and flora (Janzen, 1983;
elevations of ca. 1000–1500 m. To the north-
McPherson 1985, 1986; Wilson et al., 2002).
west of the Cordillera Central, an older range
This portion of the Central American isthmus
of lower (,2000 m) Tertiary volcanic peaks
was formed by anextremely complexseries of
and ridges forms the Cordillera de Tilara´n,
events related to the subduction of the Cocos
which is continuous at an elevation of ca.
Plate under the Caribbean Plate (Coates and
1200 m.Finally,theCordilleradeGuanacaste
Obando, 1996; Denyer et al., 2000; Montero-
represents the northernmost mountain range
P.,2000).Today,fourmajormountainranges
in the country. Similar in origin to the
exist in Costa Rica, each oriented diagonally
Cordillera Central, it runs from the
from southeast to northwest (fig. 1); these
Cordillera de Tilara´n to near the Nicaraguan
rangesvarygreatlyinoriginandage(Castillo-
borderand iscomprisedofaseriesofisolated
M., 1984; Bergoeing, 1998; Alvarado et al.,
Quaternary volcanoes, most of which reach
2000; Kussmaul, 2000; Salazar-Mondrago´n,
1500–2000 m.Lowpassesbetweenmostofthe
2000). The Cordillera de Talamanca repre-
volcanoes of the Cordillera de Guanacaste
sents the highest and most massive montane
connecttheCaribbeanandPacificlowlandsat
system in southern Central America. Formed
elevations of 500–700 m. To the north of this
primarily during the Tertiary, this range of
range lie the expansive Nicaraguan lowlands.
mixed geological origin extends from western
Panama to central Costa Rica, with many
peaksreachingmorethan3000 minelevation. SPINY POCKET MICE
The Cordillera Central of Costa Rica is
a younger (Quaternary) volcanic range that The rodent family Heteromyidae is com-
lies to the north of the Cordillera de prised of three subfamilies: Heteromyinae
2006 ANDERSON AND TIMM:COSTA RICAN SPINYPOCKET MOUSE 3
Fig.1.MapofCostaRicaandadjacentregionsofNicaraguaandPanama,showingthepositionofmajor
mountainranges.Grayshadingdenotesregionshigherthan1000minelevation,andareasshowninblack
lieabove 2000m.
(spiny pocket mice), Dipodomyinae (kanga- semiarid tropical and subtropical habitats
roo rats and kangaroo mice), and Pero- from northern Mexico and southern Texas to
gnathinae (silky pocket mice). Heteromyines Panama (Genoways, 1973; Morales and
represent a well-defined monophyletic group Engstrom, 1989; Rogers and Engstrom,
distinct from either of the two other living 1992; Williams et al., 1993). In contrast,
subfamilies (Hafner, 1981; Hafner and species of Heteromys inhabit wetter (typically
Hafner, 1983; Wahlert, 1991; see also Ryan, evergreen) forests from southern Mexico to
1989: 94–98; Brylski, 1990). Two extant western Ecuador (Williams et al., 1993;
genera,HeteromysandLiomys,arerecognized Anderson, 1999; Anderson and Jarr´ın-V.,
in the Heteromyinae and can be distinguished 2002; Anderson, 2003b).
from each other by a number of morpholog- Present taxonomy recognizes eight species
ical characters (Anderson, 2003b). Species of of Heteromys, including two recently de-
Liomys inhabit deciduous forests and other scribed from northern South America
4 AMERICAN MUSEUMNOVITATES NO. 3509
(Williams et al., 1993; Anderson and Jarr´ın- MATERIALS AND METHODS
V., 2002; Anderson, 2003b; but see Patton,
MUSEUM SPECIMENS
1993). Of these, only three species are known
from southern Central America (Nicaragua, We examined 401 specimens of Heteromys
Costa Rica, and Panama): H. desmarestianus, from the principal study area of northwestern
H. oresterus, and H. australis (Patton, 1993; CostaRica,representingallknowntousfrom
Williamsetal.,1993;Reid,1997;Wilsonetal., that region (appendix 1). For the purposes of
2002; see also Goodwin, 1946; Wainwright, thispaper,wedefinenorthwesternCostaRica
2002). As currently conceived, the widespread as those areas of the country northwest of the
H. desmarestianus ranges from southern depression that separates the Cordillera de
Mexico (Estado de Veracruz) to northwestern Tilara´n from the Cordillera Central,4 and
Colombia in a wide variety of both lowland north of the crest of the Cordillera Central
and montane habitats. In contrast, H. ores- (fig. 1). This study region includes the totality
terus is endemic to the Cordillera de oftheProvinciadeGuanacaste,largeportions
Talamanca in central Costa Rica. Finally, of the Provincia de Alajuela and Provincia de
the primarily South American species H. Heredia, andtheextremenorthernpart ofthe
australis shows a marginal distribution in Provincia de Puntarenas. Although our main
extreme eastern Panama (Anderson, 1999). interest was in comparing the distinctive
Although Heteromys desmarestianus is populations of Heteromys found at upper
often an abundant member of small mam- elevations of the Cordillera de Tilara´n and
mal communities in Mexico and Central Cordillera de Guanacaste with populations
Americaand hasbeenwell studiedecological- of H. desmarestianus present in the immedi-
ly at a few classical localities (e.g., Fleming, ately adjacent foothills and lowlands, delimi-
1983; Timm et al., 1989; Sa´nchez-Cordero, tation of the present principal study area
1993), several studies have indicated that it also allowed us to make comparisons with
represents a complex of externally similar specimens from highland regions in the
species. Across the range of the species Cordillera Central and with a much larger
sample of H. desmarestianus from the
complex, considerable variation exists in
Caribbean lowlands.
karyotypes and allozymes (Mascarello and
We also examined critical specimens from
Rogers, 1988; Rogers, 1989, 1990) and in
other regions (appendix 2). These included all
cranial morphology (Rogers, 1986). Recent
Costa Rican and Panamanian voucher speci-
fieldwork by several researchers in the
mens from karyological and genetic studies
Cordillera de Tilara´n and Cordillera de
(Mascarello and Rogers 1988; Rogers 1989,
Guanacaste in northwestern Costa Rica has
1990). Furthermore, we examined representa-
led to new collections of a distinctive species
tivesamplesofallcurrentlyrecognizedspecies
of Heteromys. We herein undertake a revision
of Heteromys, including almost all holotypes
of Heteromys in northwestern Costa Rica,
and lectotypes representing nominal taxa
describe a species new to science, provide
currently referred to the genus. The only
detailed morphological comparisons between
holotype or lectotype in the genus that we
it and adjacent populations of H. desmares-
did not examine is that of H. desmarestianus
tianus, and summarize the natural history
psakastus;inlieuoftheholotype,weexamined
and biogeographic information available
eight paratypes. Apparently, no holotype
for the new species. This work represents
exists for H. thompsonii, a name that Lesson
a step toward characterizing the morpholo-
(1827)clearlyusedtorefertothespinypocket
gy and distributions of H. desmarestianus
mouse from Trinidad named by Thompson
and the species currently confused with it.
We hope that it will facilitate future studies 4The southern slope of the division between the
by other researchers, leading to a more CordilleradeTilara´nandtheCordilleraCentralismarked
complete taxonomic understanding of approximately by the course of the R´ıo Barranca,
these common rodents so characteristic of although the hills of the Montes del Aguacate to the
southeastofthatriver(nearSanRamo´n)aresimilartothe
rainforest habitats in the northern
Cordillera de Tilara´n in geological origin (Bergoeing,
Neotropics. 1998;Kussmaul,2000).
2006 ANDERSON AND TIMM:COSTA RICAN SPINYPOCKET MOUSE 5
(1815)asMusanomalus,nowreferredtoasH. UMMZ*University of Michigan Museum of
anomalus. In considerations of species bound- Zoology,AnnArbor
aries, we apply morphological and (when USNM United States National Museum of
available) karyotypic and/or genetic data to NaturalHistory,Washington,DC
allow evaluation under the evolutionary spe-
cies concept (Wiley, 1978). We examined external and cranial morpho-
Localities and specimens examined from logical characters, making comparisons
northwestern Costa Rica are detailed in the among specimens of approximately the same
Gazetteer (appendix 1), and other specimens age. Cranial nomenclature follows Wahlert
examined are listed separately (appendix 2). (1985), Anderson (1999, 2003b), and
Locality information not provided by the Anderson and Jarr´ın-V. (2002). Specimens
collector appears in brackets and, where appli- were assigned to the age classes of Rogers
cable, is followed by the source. Where the and Schmidly (1982) based on patterns of
original elevation was reported in feet, we tooth eruption, toothwear, and molt. Age
provide that datum as well as the metric classes 1–3 represent juveniles and subadults;
equivalent to the nearest whole number. classes 4–6 are progressively older adults.
Specimensexaminedarehousedinthefollowing Age classes do not constitute a continuous
museumcollections(whereapplicable,abbrevia- variable (such as absolute age), but rather are
tions follow Hafner et al., 1997—except for categories roughly corresponding to relative
UCR, see Savage, 2002). An asterisk denotes age within population samples (Voss et al.,
museums with material from northwestern 1990).
CostaRica.
MEASUREMENTS
AMNH American Museum of Natural
History,NewYork Standard cranial measurements for
ANSP Academy of Natural Sciences of Heteromys (fig. 2) follow Anderson and
Philadelphia,Philadelphia Jarr´ın-V.(2002)andweretakentothenearest
BM(NH)Natural History Museum, London 0.01 mm with digital calipers. We measured
[formerly British Museum (Natural alladultspecimensofHeteromysinageclass4
History)] with intact skulls from northwestern Costa
EBRG Museo de la Estacio´n Biolo´gica de Rica, as well as from all available samples of
RanchoGrande,Maracay,Aragua H.oresterus.Externalmeasurementsandmass
FMNH* Field Museum, Chicago [formerly were copied from specimen tags and, when
FieldMuseumofNaturalHistory] necessary, from primary field notes.
ICN Instituto de Ciencias Naturales, Occipitonasal length (ONL): greatest dis-
Universidad Nacional de Colombia, tance from anteriormost projection of nasal
Bogota´ bones to posteriormost portion of occipital
KU* UniversityofKansasNaturalHistory bone.
Museum,Lawrence Zygomatic breadth (ZB): greatest width
LACM* Natural History Museum of Los across zygomatic arches at right angle to
AngelesCounty,LosAngeles longitudinal axis of cranium.
LSUMZ*Louisiana State University Museum Rostral length (RL): greatest distance
ofNaturalScience,BatonRouge from notch lateral to lacrimal bone to ante-
MCZ Museum of Comparative Zoology, riormostprojectionofnasalboneonsameside
HarvardUniversity,Cambridge of cranium.
MNCR* Museo Nacional de Costa Rica, San Nasal length (NL): greatest distance from
Jose´ anteriormost projection of one nasal bone to
MVZ* Museum of Vertebrate Zoology, itsposteriormostprojection(notnecessarilyat
UniversityofCalifornia,Berkeley medial suture between nasals).
ROM* RoyalOntarioMuseum,Toronto Least interorbital constriction (IOC): least
UCR* Museo de Zoolog´ıa, Universidad de width across interorbital constriction at right
CostaRica,SanJose´ angle to longitudinal axis of cranium.
6 AMERICAN MUSEUMNOVITATES NO. 3509
Fig. 2. Dorsal, ventral, and lateral views of a cranium of Heteromys showing the methods for taking
measurements.Abbreviations andmeasurements are definedin Materials andMethods.
Squamosal breadth (SB): width across ietal bone, always taken along medial line of
squamosals anterior to external auditory cranium even when notch present in posterior
meatus at right angle to longitudinal axis of border.
cranium. Parietal breadth (PB): greatest width
Maxillary toothrow length (MTR): dis- across parietal crests at right angle to longi-
tancefromanteriorlipofalveolusofpremolar tudinal axis of cranium.
to posterior lip of alveolus of third molar. Skull depth (SD): greatest distance from
Interparietal width (IW): greatest trans- dorsalmost point of braincase to horizontal
verse width measured from lateralmost pro- plane passing through ventral borders of
jections of interparietal bone at right angle to maxillary cheek teeth and ventral borders of
longitudinal axis of cranium. occipital condyles (taken by placing skull on
Interparietal length (IL): greatest dis- glass microscope slide with upper incisors
tancefromanteriormostprojectionofinterpar- rested overedgeofslide,andthen subtracting
ietal bone toposteriormost borderof interpar- thickness of slide).
2006 ANDERSON AND TIMM:COSTA RICAN SPINYPOCKET MOUSE 7
STATISTICS of H. oresterus with those of the montane
species from northwestern Costa Rica.
Specimens in age class 4 (the most abun-
Finally, we conducted a principal compo-
dant adult age class) were used for all
nents analysis (PCA) of specimens from
quantitative comparisons. Statistical analyses
northwestern Costa Rica, based on the vari-
were performed in Minitab (1998; release
ance-covariance matrix of log -transformed
e
12.1), and probabilities were compared to
cranial measurements. We interpreted the
a 5 0.05 for hypothesis testing. Material
multivariate axes by examination of loadings
from northwestern Costa Rica was used
and of coefficients (elements) of the unit
for the primary analyses detailed here. Using
eigenvector. Loadings are Pearson product-
species assignments based on our qualitative
moment correlationcoefficientsbetweenspec-
morphological examinations, we calculated
imen scores on each axis and the log -
descriptive statistics for standard external e
transformed variables.
measurements, mass, cranial measurements,
and three derived ratios (tail length/head-and-
body length; least interorbital constriction/
occipitonasal length; and parietal breadth/ SYSTEMATICS
occipitonasal length). For these analyses, all
localities for each species were pooled A NEW SPECIES OF HETEROMYS FROM
because sample sizes were too small at most NORTHWESTERN COSTA RICA
individual sites. Additionally, we conducted
Our analyses indicate that two species of
a series of two-tailed t-tests comparing means
Heteromys are present in northwestern Costa
of the two species for each measurement or
Rica.Inthisregion,Heteromysdesmarestianus
ratio.
is widely distributed in mesic areas from low
We then conducted analyses of three geo-
elevations to ca. 1000 m in the Cordillera de
graphic samples in northwestern Costa Rica
Tilara´n and Cordillera de Guanacaste, but it
withrelativelylargesamplesizes.Intwocases,
ascendstomorethan2000 mintheCordillera
nearby localities were pooled to create the
Central. The other species is restricted to
samples. La Selva (localities 18, 19; appendix
middle and high elevations of the Cordillera
1),CerroCacao(locality28),andMonteverde
de Tilara´n and Cordillera de Guanacaste
(localities 30–32; all on the Pacific slope or
(750–1840 m). It displays cranial proportions
crest of the Cordillera de Tilara´n) constituted
and measurements distinct from those of H.
these samples. First, we calculated the same
desmarestianus, as well as differences from all
descriptive statistics mentioned above. Then,
other recognized species of the genus. As no
to test for morphological differentiation be-
available name exists for this species, we
tweenhighlandsamplesfromtheCordillerade
describe it as:
Tilara´n and the Cordillera de Guanacaste, we
conducted a series of two-tailed t-tests com-
paring means of the samples from Cerro
Heteromys nubicolens, new species
Cacao and Monteverde for those measure-
Cloud-dwelling Spiny Pocket Mouse
ments and ratios.
We also compared the highland species Figures 3, 5, 6, 7
from northwestern Costa Rica with
Heteromys oresterus (known only from the HOLOTYPE: KU 159025, nulliparous adult
Cordillera de Talamanca) using the measure- female; skin, skull, and postcranial skeleton in
ments and ratios mentioned above. To do so, excellent condition; plus frozen tissues origi-
we first calculated standard descriptive statis- nally preserved in 95% ethanol (fig. 3).
tics for specimens from the type locality of H. Collected on 16 October 2000 from COSTA
oresterus (El Copey de Dota). Next, we RICA:PUNTARENAS:Monteverde,Monteverde
calculated descriptive statistics for all individ- Cloud Forest Reserve, Investigator’s Trail,
uals (of age class 4) that we consider to be H. 10u189N, 84u489W, at 1550 m elevation by
oresterus (appendix 2). We then conducted Robert M. Timm and Christy M. McCain;
a series of two-tailed t-tests comparing means originalnumberRMT4468.
8 AMERICAN MUSEUMNOVITATES NO. 3509
Fig. 3. Dorsal, ventral, and lateral views of the cranium of the holotype of Heteromys nubicolens (KU
159025), anadult femalein ageclass 4.See appendix1 forfull provenience.
2006 ANDERSON AND TIMM:COSTA RICAN SPINYPOCKET MOUSE 9
PARATYPES: We designate as paratypes the suture dipping well ventral to parietal crest
following 24 specimens (adults in age classes posterior to its widest point; braincase not
4–6; skins and skulls in good condition) from inflated; interorbit narrow; rostrum long and
the Pacific slope or crest of the Cordillera de cylindrical; skull large (ONL 35.72–41.02 mm
Tilara´nintheMonteverderegion,andhoused in adult specimens of age class 4; tables 1, 2),
in a variety of museum collections (appendix elongated and relatively narrow; body size
1): COSTA RICA: PUNTARENAS: Monteverde, average to large for genus; dorsal pelage soft
1450 m, ROM 97307; Monteverde, Arthur to moderately spiny; dorsal coloration dark
Rockwell’scafetales,1400 m,UMMZ115419, brown and only faintly grizzled with thin
115420; Monteverde, Cerro Amigos, 1790 m, ochraceoushairsintermixedamongspines;no
KU 142057; Monteverde, Hoge woods, lateral ochraceous band present on flanks;
1420 m, LACM 64867; Monteverde, John plantar surface of hind feet naked.
Campbell’s woods, 1520–1580 m, FMNH DESCRIPTION: Dorsal pelage (fig. 5) soft to
128417, 128419, 128420, 128423, 128425; KU moderately spiny and dark brown (sharply
142791; LACM 64863, 64865; MVZ 161224, contrasting with soft, pure white pelage of
161225; Monteverde, Monteverde Cloud venter), onlyfaintlygrizzled with thin ochrac-
Forest Reserve, Investigator’s Trail, 1550 m, eous hairs intermixed among spines (grizzling
KU 159022–159024, 159026, 159027, 159029; generally less pronounced along midline, pro-
MNCR1336;Monteverde,QuebradaQuecha, ducing slight dorsal stripe); ears dark brown
KU 143337; Monteverde, Stella Wallace’s to dark gray and small to medium in size; tail
house, KU 143339. strongly bicolored for most of its length (then
ETYMOLOGY: The adjective nubicolens, or unicolored dark distally), generally longer
‘‘cloud-dwelling,’’ derives from the Latin thanhead-and-bodylength(tables1,2);patch
nubes (cloud) and colo (dwell, inhabit) and is of dark coloration present on dorsal and
applied here in reference to the species’ externalsurfacesofforearms,continuouswith
distributionincloudforestspresentonmoun- darkcolorationofflanks;ventralandinternal
tainsthatriseabovethesurroundinglowlands surfaces of forearms white; hind feet large
of northwestern Costa Rica (Brown, 1956: (35 mm or greater in adults; tables 1, 2), with
213, 478). naked plantar surface; skull (figs. 3, 6, 7)
DISTRIBUTION: Known only from the moderately large for genus (tables 1, 2);
Cordillera de Tilara´n and Cordillera de anteriorhalfofpremaxillaryconvex(inflated),
formingasmooth(notstepped)lateralborder
Guanacaste of northwestern Costa Rica
of rostrum (in dorsal view); rostrum long and
(fig. 4). In the Monteverde region of the
cylindrical (not tapered anteriorly or with
Cordillera de Tilara´n, it is found from 750 to
dorsal flare anteriorly); nasals inflated anteri-
1840 montheCaribbeanslopeandfrom1350
orly; interorbital constriction narrow; brain-
to 1840 m on the Pacific slope. In the
case narrow,not inflated; parietaland tempo-
Cordillera de Guanacaste, the species has
ral crests weakly to moderately developed;
been collected at 1100–1500 m on Cerro
interparietal moderately wide, often with
Cacao and from 800 to 1200 m on Volca´n
slight anterior point; incisive foramina gener-
Rinco´n de la Vieja–Volca´n Santa Mar´ıa. See
ally thin and slightly tapering anteriorly; no
also Sympatry and Zones of Contact with
swellingatposteroventralborderofinfraorbi-
Heteromys desmarestianus, below.
tal foramen5; mesopterygoid fossa V-shaped,
DIAGNOSIS: A species of spiny pocket
with long, thin hamular processes of ptery-
mouse with adults showing the following
goids; shallow parapterygoid fossa; postalar
combination of characters (figs. 3, 5, 6, 7):
p4 (lower permanent premolar) with 3 lophs;
5Erroneously listed as ‘‘anterodorsal border of infra-
P4 (permanent upper premolar) with long,
orbitalforamen’’inAnderson(2003b).Inmostspeciesof
curved fold in anterior border of posterior Liomys,adistinctswellingispresentattheposteroventral
loph; mesopterygoid fossa V-shaped, with borderoftheinfraorbitalforamen(generallyanterodorsal
long, thin hamular processes of pterygoids; totheincisiveforamina).Suchaswellingisneverpresent
in species of Heteromys. Other, more salient and
optic foramen small, with exterior margin
consistent differences between the two genera are listed
formed bystrong barofbone;parietomastoid inAnderson(2003b:11).
10 AMERICAN MUSEUMNOVITATES NO. 3509
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Fig.4.Matrianglesdenregionshighe