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

2006·1.1 MB·English

by  Guy G. Musser

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3517, 41 pp., 14 figures, 4 tables May 17, 2006
Description of a New Genus and Species of Rodent
(Murinae, Muridae, Rodentia) from the Tower Karst
Region of Northeastern Vietnam
GUY G. MUSSER,1 DARRIN P. LUNDE,2 AND NGUYEN TRUONG SON3
ABSTRACT
Tonkinomysdaovantieni,anewgenusandspeciesofmuridrodentintheDacnomysDivision,is
described. It is represented by 14 adults collected from talus habitats in the forested tower karst
landscape of the Huu Lien Nature Reserve of northeastern Vietnam. The combination of
semispinous,dense,grayishblackfurcoveringupperparts;adarkgrayventer;grayears;athick,
bicolored tail considerably shorter than length of head and body; and large, extremely bulbous
footpads is unlike any other species of Indomalayan murid. Body size and build of the new rat,
alongwithsomecranialfeatures,aresimilartotheThaiLeopoldamysneilli,butothercranialtraits
coupled with molar occlusal patterns resemble morphology in species of the Indomalayan
Niviventer, Chiromyscus, and Saxatilomys. The new species is petricolous, includes insects in its
diet,andwasfoundonlyintaluscomposedoflargelimestoneblocks.Itsdistributioninthereserve
is likely patchy. Whether this limestone rat is restricted to the extensive karst regions of
northeastern Vietnam or also occurs in southern China and elsewhere in the northern karst
landscapesofIndochina,andVietnaminparticular,willbeknownonlybyconductingsurveysin
limestone regionsoutsideof northeastern Vietnam.
INTRODUCTION deformation and uplift, and spurred by sub-
sequent erosional processes, transformed
During Paleozoic times, a succession of those ancient tidal flows and marine land-
waterways covered what is now northern scapes into a spectacular terrestrial topogra-
Vietnam. Lithification, followed by tectonic phy of tower karst riddled by fissures and
1DivisionofVertebrateZoology(Mammalogy),AmericanMuseumofNaturalHistory.Currentaddress:1714Henley
Lane,Charleston,SC29412([email protected]).
2DivisionofVertebrateZoology(Mammalogy),AmericanMuseumofNaturalHistory ([email protected]).
3DepartmentofZoology,InstituteofEcologyandBiologicalResources,18HoangQuocVietRoad,CauGiay,Hanoi,
Vietnam([email protected]).
CopyrightEAmericanMuseumofNaturalHistory2006 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3517
Fig.1. TowerkarstlandscapewherewecapturedourseriesofTonkinomysdaovantieniwithintheHuu
LienNatureReserve.Tropicalmoistdeciduousforestcoversthesteepslopes,butthevalleybottomhasbeen
clearedfor agriculture. PhotographedbyD. P.Lunde, April2004.
honeycombed with caverns. Beautiful cycad inmindwemadespecialeffortstosetaportion
rosettessecuredhighon sheer limestone cliffs, of our traps on tree limbs, woody vines
and a forest cover in which many of the looping through the understory, and on high
components are adapted to karstic habitats, limestone ledges. At one place, chunks of
are the living botanical link to those ancient limestone had long ago fallen from two high
seas. A dark gray rat, its fur coloration forestedtowers,fillingthespacebetweenthem
indistinguishable from the limestone, its lair with huge blocks, their surfaces now partially
concealed deep within fissured cliffs and covered with tropical vegetation, and riddled
limestone talus, is the zoological connection. beneathwithtunnelsandfissuresdetectableat
We discovered this limestone rat during the surface only by small scattered openings
a survey (April, 2004) of small mammals in (fig. 2). We set traps on top of this block pile,
aforestedtowerkarstregionthatformsmuch and also tied traps to lengths of rope and
ofLangSonProvinceinnortheasternVietnam carefully lowered them through the openings
(Głazek,1966;Tuyet,1998)(fig. 1).Ourintent to the bottom, to depths of at least 8 m.
was to sample, using a variety of traps and Unsure if we would catch anything different
other techniques, as many native species as from the common rats already encountered in
possible. Our past field experience in nearby different habitats—Niviventer fulves-
Indochina had taught us that setting traps cens, N. langbianis, and Rattus andamanen-
on the ground in regular lines would quickly sis—we were very pleased, and somewhat
sample the generalists of the more common surprised, to capture a dark gray rat on top
terrestrial habitats but not those specialized of the rubble and two from deep within the
for life on substrates above the forest floor or labyrinth. Additional individuals were cap-
in unusual petricolic environments. With this tured during the days that followed.
2006 MUSSERETAL.: NEW RODENTFROM VIETNAM 3
Fig.2. Habitatwherewetrapped13ofthe14examplesofTonkinomysdaovantienishowinglargeblocks
oflimestoneovergrownwithcreepingvines(left)andaportionofthesteepslopesofanadjacentkarsttower
(right).Ourtrailtothesiteisvisiblebetweenthesetwostructures.PhotographedbyD.P.Lunde,April2004.
We knew nothing like this animal had ever Srilankamys; and the recently described
been caught in Vietnam or elsewhere in Laotian Saxatilomys (Musser et al., 2005).
SoutheastAsia.Exceptfortheirfurcoloration WealsocontrastTonkinomyswithmembersof
and short tails, the rats resembled species of the Dacnomys Division represented by fossils
Leopoldamys, but no member of that genus recovered from Indochinese Plio-Pleistocene
hasdark gray furand a tailshorter thanhead sediments: extinct species of Leopoldamys
and body. Those two attributes also pointed and Niviventer, and the extinct genera
toBerylmys,butnoneofthemhavedarkgray Wushanomys and Qianomys. Of these, the
underparts. We knew our sample of the new rat requires close and careful compari-
limestone rat represented an undescribed sons only with Leopoldamys, Niviventer,
species, but only after study in the museum Chiromyscus, Saxatilomys and the Plio-
didweconfirmoursuspicionthatitcouldnot Pleistocene Wushanomys and Qianomys.
be placed in any named genus. Descriptions of new taxa, and in particular
Herewe describethelimestonerat asanew those occurring in gradually diminishing
genus and species, and summarize our limited tropical forest refuges, should be published
observations about its natural history. We as soon as possible. Phylogenetic inquiries
focusondescribingtheanimalandcomparing take time—incorporating the new rat into
it to murines with which it is morphologically phylogenetic analyses employing samples of
most similar, members of a cluster containing all native Indochinese murines will be the
genera that Musser and Carleton (2005) refer subject of a future report.
toastheDacnomysDivision:extantspeciesof Our discovery joins those of several other
the Indomalayan Chiromyscus, Dacnomys, small-bodied mammals living in Indochina
Leopoldamys, and Niviventer; the Sri Lankan that have been discovered and described, with
4 AMERICAN MUSEUMNOVITATES NO. 3517
little fanfare, during the past five years: two under a second number in addition to its
shrews, Chodsigoa caovansungaandCrocidura departmentalcatalog number.Somefluid-pre-
kegoensis (Lunde et al., 2003, 2004); three servedspecimensandaccompanyingskullswill
bats, Hipposideros scutinares (Robinson et al., be retained at AMNH; otherswillbe returned
2003), Rhinolophus stheno microglobosus to the Department of Zoology at the Institute
(Csorba and Jenkins, 1998) and Myotis ofEcologyandBiologicalResourcesinHanoi.
annamiticus (Kruskop and Tsytsulina, 2001); Comparative material we consulted, pri-
andarabbit,Nesolagustimminsi(Averianovet marily samples of Leopoldamys, Niviventer,
al.,2000;Canetal.,2001).Thesecanbeadded Chiromyscus, and Saxatilomys, are in collec-
to an assemblage of large mammals occurring tions at AMNH; the Field Museum, Chicago;
in Vietnam, and some in nearby Laos, named andtheNationalMuseumofNaturalHistory,
anddescribedasnewwithinthelastdecadeor Washington, DC.
so, but with attendant worldwide publicity: Values(inmillimeters,mm)fortotallength,
two primates, Trachypithecus ebenus and length of tail (LT), length of hind foot,
Pygathrix cinerea (summarized in Groves, including claw (LHF), and length of ear from
2001);threemuntjacs,Muntiacustruongsonen- intertragal notch to crown (LE) are those we
sis, M. vuquangensis, and M. puhoatensis (see obtained in the field and recorded in our field
reviews in Amato et al., 2000; Groves and journals. Values for length of head and body
Schaller, 2000; Grubb, 2005); and the saola, (LHB) were determined by subtracting length
Pseudoryx nghetinhensis (see review and refer- oftailfromtotallength.Weightswereobtained
ences in Groves and Schaller, 2000).4 All are inthefieldwithaPesolaspringscale(300-gram
a testimony to the significant results derived capacity).Thedistalportionofthetailiswhite
from past biodiversity surveys, discoveries (unpigmented)inallspecimensofthelimestone
that provide compelling stimulus for zoolo- rat.Wemeasuredthelengthofthiswhitetipon
giststocontinuedetectingtherealdiversityof thedorsalsurfaceofeachtailandcalculatedit
small mammals in Vietnam. as a percentage of total tail length. Values for
cranialanddentalmeasurementswereobtained
byLunde using digital calipers accurate tothe
MATERIALS AND METHODS
nearest0.01 mm;however,valueswereround-
All14examplesofthenewratwerefixedin edtothenearest0.1 mm.Thefollowingcranial
10% formalin in the field and subsequently and dental dimensions (listed in the sequence
transferred to 70% ethanol for storage. Liver they appear in tables) were measured; their
samples were collected prior to fixation and limits are illustrated in figure 3 and defined in
placed in lysis buffer in the field, and later MusserandNewcomb(1983).
stored in liquid nitrogen at the American
ONL occipitonasal length (5 greatest
Museum of Natural History (AMNH). Skulls
lengthofskull)
were subsequently removed from 10 of 13 ZB zygomaticbreadth
specimens (one of the 14 preserved is repre- IB interorbitalbreadth
sentedbyonlyanearwithabitoffur-covered LR lengthofrostrum
skinattached,theonlyremnantleftinthetrap BR breadthof rostrum
by a hungry predator) and cleaned by a der- BBC breadthof braincase
mestid colony, American Museum. The ele- HBC heightofbraincase
ments of each specimen are identified by BZP breadthof zygomaticplate
a catalog number in the Department of LD lengthofdiastema
LIF lengthofincisive foramina
Mammalogy, AMNH. Each liver sample was
BIF breadthof incisive foramina
transferred to the American Museum Cryo
LBP lengthofbonypalate(palatalbridge)
Collection (AMCC), where it is registered
BBP breadth across bony palate at first
molars
4Viverratainguensis,anothersupposednewlydiscovered
PPL postpalatallength
specieslivinginVietnam,wasdescribedbySokolovetal.
BMF breadthof mesopterygoid fossa
(1997).Its specific integrity,however,wasquestionedby
LB lengthofbulla
Walston and Veron (2001), and the name is currently
includedinthesynonymyofthelargeIndiancivet,Viverra CLM1-3 crownlengthofmaxillarymolarrow
zibetha(Wozencraft,2005). BM1 breadthof first uppermolar
2006 MUSSERETAL.: NEW RODENTFROM VIETNAM 5
Fig. 3. Views of cranium and molars of an adult Bunomys chrysocomus showing limits of cranial and
dentalmeasurements.See textfor abbreviationsandadditional information.
6 AMERICAN MUSEUMNOVITATES NO. 3517
Old adults, adults, and young adults (as occiput;(8)squamosalrootofeachzygomatic
defined by Musser and Heaney, 1992: 5) were archsituatedhighonsideofcraniumwhereits
lumpedas‘‘adults’’andmeasurementsderived posterior ridge-like portion runs horizontally
from them were used to calculate standard just below posteroventral margin of the
descriptive statistics (mean, standard devia- parietal and projects ventrad to form dorso-
tion, and observed range). Small sample size lateral side of cranium; (9) lateral cranial wall
dictatedthatwecombinesexesintheanalyses. intact anterior to occiput, without large
AnatomicalterminologyfollowsBrown(1971) subsquamosal foramen; (10) narrow alisphe-
and Brown and Yalden (1973) for external noid struts in most specimens; (11) wide and
features of the head and limbs; Bugge (1970) moderately long incisive foramina, their pos-
for the cephalic arteries; Wahlert (1985) for terior borders located just before anterior
the cranial foramina; and Carleton (1980), margins of molar rows, even with them, or
Carleton and Musser (1984), Musser and penetrating slightly between; (12) posteriorly
Durden (2002), Musser and Heaney (1992), divergentmaxillarymolarrows;(13)wideand
Musser et al. (1998), and Voss (1988) for long bony palate projecting beyond molars
cranial morphology. Names of cusps and to form a wide platform; (14) moderately
cusplets of upper and lower molars are noted spacious sphenopalatine vacuities; (15) wide
in figure 13; sources of this terminology are and shallowly excavated pterygoid fossae;
explained by Musser and Newcomb (1983: (16) small ectotympanic bulla relative to skull
332). size, incompletely covering periotic so that
dorsal and slanting posterodorsal wall of
carotid canal formed by periotic and not
SYSTEMATIC DESCRIPTION OF THE
ectotympanic; (17) large foramen for stapedial
NEW GENUS AND SPECIES
artery, no sphenofrontal foramen or squamo-
Tonkinomys, new genus
soalisphenoidgroove,indicatingthewidespread
TYPESPECIES: Tonkinomysdaovantieni,the murine cephalic arterial pattern; (18) coronoid
new species described below. processofdentarysmall,condyloidandangular
DIAGNOSIS: A genus of Muridae in the processes joined by shallow concave posterior
Dacnomys Division (Musser and Carleton, margin of dentary, and alveolar incisor
2005) of the subfamily Murinae (as delimited capsule only slightly evident on lateral surface
by Carleton and Musser, 1984) that is set of dentary; (19) upper incisors opisthodont
apartfromallotherdescribedmuridgeneraby relativetorostrum; (20)first upper molar with
the following combination of morphological four large roots (anterior, two lingual, and
traits: (1) fur covering head and body semi- posterior), second and third molars each with
spinous and grayish black, spattered with three roots (anterior, lingual, and posterior);
awhiteblazeonforeheadinmostindividuals, (21) each lower molar with two roots;
underparts dark gray with white patch on the (22) molars brachydont, with cusp rows form-
chest, ears gray, rhinarium and lips and chin inguncomplicatedocclusalpatternsresembling
unpigmented; (2) mystacial and superciliary thoseinspeciesofNiviventer,Chiromyscus,and
vibrissaeverylong;(3)dorsalsurfacesoffront Saxatilomys.
feetwhite,hindfeetwhitewithbrownhairson ETYMOLOGY: From Tonkin, used during
metatarsal region; (4) tail much shorter than the French colonial period (1883–1954) for
length of head and body, thick and round in the protectorate occupying the northern third
cross-section and well-haired, the proximal of Vietnam, and the Greek mys, referring to
one-half to three-fourths of its dorsal and mouse, or rat in this case. Although most
lateral surfaces dark brown, the distal one- often negatively associated with Vietnam’s
fourth to one-half white (unpigmented); dark French administration, the name
(5) palmar and plantar pads large, swollen, Tonkin has an illustrious origin. It is derived
and set close together; (6) four pairs of teats; from the Vietnamese Don Kinh, which means
(7)robustskullwithmoderatelylongandwide ‘‘eastern capital’’, and was the name given to
rostrum, prominent postorbital and temporal what is now Hanoi by Emperor Le Loi who,
ridges, sturdy zygomatic arches, and deep in 1427, along with his band of Vietnamese
2006 MUSSERETAL.: NEW RODENTFROM VIETNAM 7
TABLE1
SummaryStatistics for CranialandDentalMeasurements(mm) andWeight (m)of Tonkinomysdaovantieni
from Vietnam
(Mean,plusorminusone SD, observed rangein parentheses,and numberof specimens in eachsample
are listedfor each measurement.Sample containsbothsexesand arange in agefromyoung to old
adults. Individualsmeasured andweighed areidentified in the footnote.)
Holotypea Sample(withholotype)b
Lengthofheadandbody 213 204.6610.34(184–217)13
Lengthoftail 177 16967.0(156–183)13
Lengthofhindfoot 40 39.061.1(37–41)13
Lengthofear 30 30.060.8(29–31)14
Weight 160 171622.8(140–205)13
Occipitonasallength 51.2 50.061.6(47.1–52.4)7
Zygomaticbreadth 21.6 21.360.2(20.9–21.6)7
Interorbitalbreadth 6.7 6.960.2(6.6–7.3)7
Lengthofrostrum 17.7 17.160.6(15.9–17.7)7
Breadthofrostrum 7.7 7.860.4(7.1–8.5)7
Breadthofbraincase 17.7 17.760.2(17.4–18.1)7
Heightofbraincase 11.7 11.860.2(11.4–12.0)7
Breadthofzygomaticplate 4.9 4.860.1(4.7–5.0)7
Lengthofdiastema 13.3 13.660.5(12.9–14.6)7
Lengthofincisiveforamina 9.1 9.560.5(8.9–10.2)7
Breadthofincisiveforamina 3.4 3.560.2(3.4–3.9)7
Lengthofbonypalate 10.7 10.560.3(10.0–10.7)7
BreadthacrossbonypalateatM1 9.6 9.660.1(9.5–9.8)7
Postpalatallength 16.2 15.760.6(14.6–16.4)7
Breadthofmesopterygoidfossa 3.9 3.860.2(3.5–3.9)7
Lengthofbulla 6.2 6.360.1(6.2–6.5)7
CrownlengthofM1-3 8.3 8.360.2(8.0–8.8)7
Breadthoffirstuppermolar 2.1 2.160.1(2.0–2.2)7
aAMNH275618.
bAMNH275575-275577,275586,275593,275602,275618,275627,275644,275688,275692,275711,and275712.
rebels, expelled from Vietnam the repressive American Museum Cryo Collection (AMCC
Mingoccupiers.Bytheearly1800s,thecapital 125060). The skull (figs. 10, 11) was later
was moved to Hue, and the Emperor Minh extractedandcleanedbydermestidsinacolony
Mang renamed the ‘‘eastern capital’’ Hanoi, attheAmericanMuseum.
meaning ‘‘this side of the river’’. REFERRED MATERIAL: In addition to the
holotype,13additionaladultsofT.daovantieni
were collected from the vicinity of Laˆn Ða˘t
Tonkinomys daovantieni, new species
Village during April, 2004, on the days in-
HOLOTYPE: AMNH 275618, an adult fe- dicated (AMCC catalog numbers tied to liver
malecollectedbytheauthors(DPL1706)on17 samples are in brackets). April 13: AMNH
April, 2004, in the vicinity of Laˆn Ða˘t Village 275575 [125016], male; 275576 [125017], male;
,
(21u409520W/106u209280E), 150 m, Huu˜ Lieˆn 275577 [125018], male. April 14: 275586
, ,
Nature Reserve, Huu˜ Lieˆn Commune, Huu˜ [125027], female; 275593 [125034], male. April
,
Lun˜g District, Lang Son Province, Vietnam. 16: 275602 [125044], male. April 19: 275627
The specimen was fixed in 10% formalin for [125069],male;275644[125086],male.April23:
several days before being transferred to 70% 275688 [125130], male. April 24: 275692
ethanol for storage. A liver sample was [125134], male; 275693 [125135], ear with
collected prior to fixation and placed in lysis attached bit of furry skin only. April 25:
buffer before its ultimate transfer to the 275711[125153],male;275712[125154],female.
8 AMERICAN MUSEUMNOVITATES NO. 3517
Fig.4. AliveTonkinomysdaovantieni(AMNH275593).Notetheunpigmenteddistalportionofthetail
andtheblazeofwhiteontheforehead.Otherexternaltraitsaredescribedinthetext.PhotographedbyD.P.
Lunde, April2004.
GEOGRAPHIC DISTRIBUTION: Tonkinomys Professor Tien was educated in Hanoi under the French
daovantieni is currently known only from the colonial Administration. He taught several generations of
Vietnamese scientists and carried his Biology Faculty
type locality, but the species probably occurs
through the difficult years after his country gained its
in suitable forested habitats throughout the
freedom. Though Professor Tien’s principal works and
karst landscapes of northern Vietnam (identi- manyofhispaperswereinmammalianzoology,hisadvice,
fied as the ‘‘Vietbac Karst Zone’’ by Tuyet, his academic research, and most importantly his student
1998:187;ortheCaobangandBacsonregions support was never limited to this. Certainly, all senior
biologistsinnorthernVietnamtodaygladlycallProfessor
by Głazek, 1966), and possibly in southern
Tientheirteacher.Itishardtocalculatetheimportanceof
China (see the distributions of karst outcrops thisgentleandthoughtfulmaninthehistoryofVietnam’s
mapped in Tuyet, 1998, and Zhang, 1989). science.HewasthefatherofhisfieldinVietnam.Hisloss
DIAGNOSIS: Becausedaovantieniistheonly was a great blow for us, though he left for the world an
incalculablelegacyofstudiesoftherichbiologyofVietnam,
known species of Tonkinomys, generic and
and ascholarly tradition for those who will follow in his
specific diagnoses are the same.
footsteps.
ETYMOLOGY: Wearehonoredtonamethis
distinctive gray-furred and short-tailed lime- The biodiversity surveys undertaken in
stone endemic after the late Ða`o Va˘n Tieˆ´n, northern Vietnam during the past decade that
who when he died on May 3, 1995, at the age havecontributedsosignificantlytoknowledge
of78,wasemeritusprofessorofbiologyatthe ofmammaliandiversityinthatcountrycanbe
National University of Hanoi. Our esteem for viewed as extensions of earlier vertebrate
this Vietnamese scholar is reflected in the surveys in northern Vietnam from 1957 to
obituary prepared by Groves and Weitzel 1971initiatedandmanagedbyProfessorTieˆ´n.
(1995: 15216): His results generated large and important
2006 MUSSERETAL.: NEW RODENTFROM VIETNAM 9
terize live Tonkinomys daovantieni (figs. 4, 5;
table 1). Detailed descriptions of its external
features, skull, and dentition are provided
below.
External traits: The dense fur covering
upperparts of head and body is grayish black
with burnished highlights, and consists of
three types of hairs. The soft underhairs (up
to12 mmlong)aregrayfortheirentirelength.
The overfur layer (up to 15 mm thick) is
formed by wide, flexible, and grooved spines,
each pale gray for most of its length and
tipped with brown or black. Scattered guard
hairs project 5210 mm beyond the overhairs,
the basal half of each is gray, the distal half
black.Thecombinationofhairtypesandtheir
pigmented banding patterns imparts a thick
and semispinous texture, and a burnished,
grayish black tone to the upperparts. The
dorsal pelage is less spiny along the sides of
thebody,appearsespeciallysoftandgrayover
the shoulders and hips, and gradually blends
into thesofterand shorter(up to8 mm thick)
dark gray fur covering the underparts. That
coat is formed by soft underhairs mixed with
soft, wide, and grooved spines; both kinds of
hairs are gray for their entire lengths.
Although paler than the dorsal coat because
Fig. 5. Underparts of Tonkinomys daovantieni it has no dark brown guard hairs, no sharp
(AMNH 275593). The dark grayish black dorsal demarcationexistsbetweendorsalandventral
coat merges gradually into the dark gray venter, fur. A white patch (size ranges from 10 mm
which is broken by a white pectoral patch (found
long and 5 mm wide to 30 mm by 12 mm)
in ten other specimens of the sample of 13).
interrupts the dark gray fur over the chest in
PhotographedbyD.P.Lunde, April 2004.
11ofthe13specimens;theothertwolackthis
chest mark. On the forehead a blaze of white
collections of voucher specimens (currently hairs (expression ranges from a few hairs to
housed at the University of Hanoi), and were a patch 15 mm long and 5 mm wide) con-
summarizedbyhimin1985(Ða`o,1985).That trasting with surrounding dark fur is present
bodyoffielddataandmuseumspecimens,and in nine specimens; four, including the holo-
thescientificresultsderivedfromthemformed type, lack the blaze. Sides of the face and
the foundation of ‘‘Checklist of Mammals in throat are dark gray; the lips, chin, and
Vietnam’’ published nine years later (Ða˘ng et rhinarium are unpigmented. Fur covering the
al.,1994),whichatthetimestoodasthefinest lower limbs is dark gray everywhere, but
and most comprehensive annotated list of shorter than that on the torso.
Vietnam mammals, and today remains not Eyes, relative to head area, are large,
only an important reference, but a tribute to proportionally similar to species of Rattus. A
Professor Tieˆ´n, his students, and his collea- wideunpigmentedringsurroundseachnarrow
gues. and circular, dark brown eyelid. Beyond the
MORPHOLOGICAL DESCRIPTION: Large head eyes, the fur is dark gray covering this part of
andeyes, a stocky body,darkgrayears, short the head, and although somewhat more
and bicolored tail, grayish black (gunmetal) suffused with black, this darker tone does
upperparts, and dark gray underparts charac- not define a facial mask.
10 AMERICAN MUSEUMNOVITATES NO. 3517
The pinnae (external ears) are moderately
large, but not disproportionately expansive
relative to body size. They are dark gray,
somewhat oval in outline, and rubbery in
texture. Short brown hairs (visible only under
magnification) are sparsely scattered over
both outer and inner surfaces, but do not tint
the gray background.
The mystacial vibrissae are either dark
brown or unpigmented, fine, and very long
(upto75 mm);whenlaidagainsttheheadthe
longest projects up to 20 mm beyond the
distal margin of each pinna. The longest in
each pair of superciliary (or supraorbital)
vibrissae (up to 60 mm long) also extend well
past the pinna when appressed against the
head. The short submental and interramal
vibrissae are unpigmented. The few short (up
to 25 mm) genal vibrissae are inconspicuous
and unpigmented for most of their lengths.
Thebaseofthewristsupportsfourmoderate-
ly long (up to 10 mm) unpigmented ulnar
carpal vibrissae, and from the inside of each
heel springs a longer (up to 15 mm) unpig-
mented tarsal vibrissa.
The tail is appreciably shorter than the
length of head and body (LT/LHB 5 83%,
averageof13individuals)anditisthick(range
in 13 specimens is 5.7 mm to 6.3 mm, mea-
sured laterally at midpoint of tail length) and
round in cross section (table 1; fig. 6). The
proximal one-half to three-fourths is dark
brown on dorsal and lateral surfaces (pro-
duced by the brown pigment in scales and
scalehairs).Theventralsurfaceiswhite,asare
allsurfacesofthedistalone-fourthtoone-half
(25%–44% of total tail length among the 13
specimens). In a few specimens, scattered
scales in the unpigmented regions retain very
pale brown pigment, which provides a slight
speckling to the white portion, usually over
the ventral surface. Scales in the overlapping
annuli are moderately large (10 annuli of
Fig. 6. Holotype of Tonkinomys daovantieni. scales per centimeter, counted along basal
Dorsal (left) and ventral (right) views of the tail. one-third of the tail), and beneath each scale
Note increasing length of scale hairs from base to emerge three hairs. These are bristle-like and
tail tip. Basal two-thirds of dorsal and lateral
about as long as two scale annuli (1.0 mm)
surfaces of tail is dark brown, produced by brown
near the base of the tail, but those at the tail
pigmentinbothscalesandscalehairs(a);scalesand
tip are softer and longer (526 mm); there is
scale hairs (c) on underside and distal one-third of
a gradual increase in hair length and texture
thetailareunpigmented.Seetextfordiscussionof
pattern variation within the complete sample. Tail from base to tail tip. Because the hairs are
isroundin cross-section (b). mostly longer than the scale annuli, the tail