A Revision of the Didelphid Marsupial Genus Marmosa Part 1. The Species in Tate's ‘Mexicana’ and ‘Mitis’ Sections and Other Closely Related Forms

2010·10.4 MB·English

by  Rogério V. Rossi

A REVISION OF THE DIDELPHID MARSUPIAL
GENUS MARMOSA
PART 1. THE SPECIES IN TATE’S ‘MEXICANA’
AND ‘MITIS’ SECTIONS AND OTHER CLOSELY
RELATED FORMS
ROGE´RIO V. ROSSI
Universidade Federal de Mato Grosso
Instituto de Biocieˆncias
Departamento de Biologia e Zoologia
Av. Fernando Correˆa da Costa s/n, Cuiaba´, MT,
Brazil, CEP 78060-900
ROBERT S. VOSS
Department of Mammalogy
American Museum of Natural History
DARRIN P. LUNDE
Department of Mammalogy
American Museum of Natural History
BULLETINOFTHEAMERICANMUSEUMOFNATURALHISTORY
Number334, 83pp., 30figures, 8tables
Issued June3,2010
CopyrightEAmericanMuseumofNaturalHistory2010 ISSN0003-0090
CONTENTS
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Materials and Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Ontogenetic Variation and Sexual Dimorphism. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Comparative Morphology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
External Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Craniodental Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Species Accounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Marmosa mexicana. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Marmosa zeledoni. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Marmosa isthmica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Marmosa robinsoni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Marmosa xerophila . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Marmosa simonsi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Marmosa rubra. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2
ABSTRACT
We revise the nominal species of mouse opossums currently synonymized with Marmosa
mexicanaMerriam,1897,andM.robinsoniBangs,1898,whichincludeallofthetrans-Andean
taxacurrentlyassignedtothenominotypicalsubgenusofMarmosa.Inaddition,weredescribe
two other species that appear to be closely related to M. mexicana and M. robinsoni based on
morphological or molecular citeria: M. rubra Tate, 1931, and M. xerophila Handley and
Gordon, 1979. Based on first-hand examination of holotypes and other material (about 1500
specimens in total), we additionally recognize M. isthmica Goldman, 1912, and M. simonsi
Thomas,1899(bothcurrentlysynonymizedwithM.robinsoni),andM.zeledoniGoldman,1917
(currently synonymized with M. mexicana), as valid species. For each of the seven species
recognizedasvalidherein(M.mexicana,M.zeledoni,M.isthmica,M.robinsoni,M.xerophila,
M.simonsi,M.rubra),wedescribeandillustratediagnosticexternalandcraniodentalcharacters,
tabulatemeasurementdatafromadultspecimens,listallknownexamplesofsympatry,andmap
geographicrangesbasedonspecimensexamined.Thespeciesnewlyrecognizedasvalidherein,
all of which occur in Central America and/or northwestern South America, substantially
increase the known diversity of trans-Andean mouse opossums, but it is not currently known
whether ornot theserepresenta distinctradiationwithinthegenusMarmosa.
INTRODUCTION within Gracilinanus (see Voss et al., 2004,
2005).
Species of the genus Marmosa, commonly
Despite these refinements, the taxonomic
known as mouse opossums (fig. 1), are long-
status of Marmosa remains problematic
tailed, black-masked, pouchless didelphid
because all molecular phylogenies published
marsupials that inhabit a wide range of
todateindicatethatthegenus(asunderstood
tropical and subtropical habitats from Mex-
by Gardner and Creighton, 1989) is para-
ico to Argentina. Marmosa was last revised
phyletic with respect to Micoureus (fig. 2).
by Tate (1933), who recognized several
Obviously, several alternative classifications
species groups that have subsequently been
would be consistent with such results: either
elevated to generic rank (table 1). In the
(1) Micoureus could be regarded as a junior
classification proposed by Gardner and
synonym of Marmosa; or (2) Micoureus
Creighton (1989), the species in Tate’s
could be regarded as a valid subgenus of
‘‘Cinerea Group’’ were referred to the genus
Marmosa;or(3)Marmosacouldberestricted
Micoureus Lesson, 1842; those in his ‘‘Mur-
to M. murina (the type species). Of these,the
inaGroup’’toMarmosaGray,1821;thosein
firstoptionwouldresultinthelossofauseful
his ‘‘Noctivaga Group’’ to Marmosops
andfamiliarnameforawell-supportedclade
Matschie, 1916; and those in his ‘‘Elegans
(Micoureus), whereas the second and third
Group’’toThylamysGray,1843.Mostofthe
alternatives would require that additional
species in Tate’s ‘‘Microtarsus Group’’ were
subgenera or genera be resurrected from
placed in a new genus, Gracilinanus Gardner
synonymy or described as needed to contain
and Creighton, 1989.
the other species currently referred to Mar-
Recent phylogenetic research based on
mosa.
molecular sequence data (e.g., Patton et al.,
1996; Jansa and Voss, 2000; Steiner et al., The interim solution proposed by Voss
2005) has convincingly indicated that Mar- and Jansa (2009), which we adopt herein, is
mosa (sensu Tate) was polyphyletic, and the to recognize Micoureus as a subgenus of
same studies have consistently supported the Marmosa, and to refer all of the species
monophyly of Marmosops, Micoureus, and formerly included in Marmosa to the nomi-
Thylamys as those taxa were recognized by notypical subgenus. In effect, this tactic
Gardner and Creighton (1989). However, a simplymovestheproblemofparaphylyfrom
new genus was proposed for ‘‘Marmosa’’ the generic level (where it affects binomial
canescens by Voss and Jansa (2003), and usage) to the subgeneric level (where it does
othernewgenerawerelaterdescribedfortwo not).Althoughclearlysuboptimal,nofurther
clades formerly concealed by synonymies progress in the classification of this complex
3
4 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.334
Fig.1. Marmosazeledoni,photographedatLaSelvaBiologicalStation,Herediaprovince,CostaRica,
inAugust2005byMarcoTschapka.Zeledon’smouseopossum,formerlysynonymizedwithM.mexicana,
isresurrectedasavalidspeciesinthisreport.ThelocalpopulationatLaSelvawaspreviouslyreportedas
M.mexicanabyTimmetal.(1989),Voss and Emmons (1996)and Sperretal.(2009).
is possible until the phylogenetic relation- mitis, M. ruatanica, and M. simonsi. All of
ships among all of the included species are these were swept into synonymy by Hersh-
worked out. To date, only five of the nine kovitz(1951),whoallegedthatthediagnostic
currently recognized species in the subgenus characters mentioned by Tate were artifacts
Marmosa are represented in published trees, of sexual dimorphism, age, imperfect preser-
and there is reason to believe that additional vation, or clinal variation. Although Hersh-
valid species may be concealed among the kovitz provided no analyses of data to
putative synonyms of several geographically support these claims, his conclusions were
widespreadforms(table 2).Twoofthelatter accepted by subsequent compilers of influen-
are the primary focus of this report. tial checklists (e.g., Cabrera, 1958; Hall and
As currently recognized, Marmosa robin- Kelson, 1959). The nominal taxa of Tate’s
soni includes 13 nominal taxa, of which Tate Mitis Section (for which M. robinsoni is the
(1933)treatedfour asvalidspecies belonging oldest available binomen; Cabrera, 1958)
to his ‘‘Mitis Section’’: M. chapmani, M. extend from Honduras southward to Pana-
2010 ROSSIETAL.:REVISION OFMARMOSA 5
TABLE 1 This report, which is largely based on
Tate’s(1933)GroupsandSectionsofMarmosaand R.V.R.’s thesis research at the Universidade
TheirCurrentClassificationa
de Sa˜o Paulo (Rossi, 2005), summarizes our
conclusions regarding the taxonomy of spe-
Tate’sname Currentname
cies belonging to Tate’s (1933) Mitis Section
CinereaGroup Marmosa(Micoureus) and his ‘‘Mexicana Section.’’ To this we
append redescriptions of Marmosa xerophila
MurinaGroup
Handley and Gordon, 1979, and M. rubra
MurinaSection Marmosa(Marmosa,part)
Tate, 1931. The former is a northern South
MitisSection Marmosa(Marmosa,part)
MexicanaSection Marmosa(Marmosa,part) American form that is morphologically
CanescensSection Tlacuatzin similar to M. robinsoni, whereas the latter is
awesternAmazonianspeciesthatconsistent-
NoctivagaGroup Marmosops(part)
ly appears as thesister taxon of M. robinsoni
MicrotarsusGroup
+ M. mexicana in phylogenetic analyses of
MicrotarsusSection Cryptonanus,Gracilinanus molecular sequence data (e.g., Voss and
LepidaSection Marmosa(Marmosa,part),
Jansa, 2003, 2009; Jansa et al., 2006; Jansa
Marmosops(part)
and Voss, 2005). Despite these indications, it
ElegansGroup Chacodelphys,Thylamys is not our assumption that all of the species
aAfterVossandJansa(2009). treated in this report form a natural group.
Among other pertinent issues, the monophy-
ly of Tate’s ‘‘sections’’ has not been tested,
but distinguishing the valid species that each
ma, Peru, Venezuela, and the Lesser Antilles
contains is a necessary step toward a
(Hall, 1981; O’Connell, 1983; Creighton and
genuinely phylogenetic classification of
Gardner, 2008).
mouse opossums.
According to recent phylogenetic results
(fig. 2), Marmosa mexicana is closely related
Materials and Methods
to M. robinsoni. Like the latter, it also
includes several nominal taxa that are cur- SPECIMENS: We examined 1481 specimens
rentlytreatedassynonymsorsubspecies,but
forthisreport,mostofwhicharepreservedas
in this case the current taxonomy follows skins andskulls in thefollowinginstitutional
Tate’s(1933)revision.ThedistributionofM. collections: AMNH, American Museum of
mexicana is less extensive than that of M. Natural History (New York); BMNH, Nat-
robinsoni, but it still extends over 2000 km, ural History Museum (London); FMNH,
from Mexico to Panama (Hall, 1981). FieldMuseumofNaturalHistory(Chicago);
Few nonvolant small mammals have MCZ, Museum of Comparative Zoology,
geographic distributions in Central and HarvardUniversity(Cambridge);MSB,Mu-
SouthAmericaasextensiveasthosecurrently seumof SouthwesternBiology, Universityof
attributed to Marmosa robinsoni and M. NewMexico(Albuquerque);MVZ,Museum
mexicana. The range of habitats occupied ofVertebrateZoology,UniversityofCalifor-
by each of these species is likewise remark- nia (Berkeley); ROM, Royal Ontario Muse-
able, and even a superficial examination of um (Toronto); and USNM, National Muse-
allegedly conspecific skins and skulls reveals um of Natural History (Washington, D.C.).
a surprising degree of morphological varia- ANATOMICAL TERMINOLOGY: Our names
tion. Preliminary sorting of specimens at the for external and craniodental structures of
American Museum of Natural History by Marmosa follow Voss and Jansa (2009),
D.P.L. during a recuration project in the whose anatomical descriptors are largely
early1990ssuggestedthatatleastsomeofthe consistent with standard usage (Brown,
species in Tate’s (1933) Mitis Section were 1971; Brown and Yalden, 1973; Bown and
valid (contra Hershkovitz, 1951), and this Kraus, 1979; Wible, 2003). Principal features
conclusion was independently reached by of the skull are illustrated in figures 3 and 4.
R.V.R. after a much more extensive study WefollowClemens(1966)inusingpositional
of material in other museums. criteria for naming cusps on the stylar shelf
6 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.334
Fig. 2. Phylogenetic relationships of Marmosa (sensu Gardner and Creighton, 1989) and Micoureus
(treated as a subgenus of Marmosa in this report) based on a maximum-parsimony analysis of 7449
characters(includingmorphology,karyotypes,andsequencedatafromfivenucleargenes;VossandJansa,
2009)scoredfor43speciesofRecentdidelphidsandsevennondidelphidoutgroups.Thenumbersabove
and below each branch represent nonparametric bootstrap frequencies and Bremer support values,
respectively. Marmosa isthmica (revalidated in this report) is the correct name for the terminal taxon
labelled Marmosa robinsoni in previous analyses of these data. Marmosa murina is the type species
of Marmosa.
of the upper molars (not treated in detail by The former include total length (TL), length
Voss and Jansa, 2009) as follows: of tail (LT), length of hind foot (HF), and
Stylar cusp A (styA): A small cusp (often lengthofear(Ear).Lengthofhead-and-body
indistinct) at the anterior end of the stylar (HBL) was calculated by subtracting LT
shelfanterolabialtotheparacone,towhichit from TL.
is sometimes connected by the preparacrista We measured the following 29 cranioden-
(5 ‘‘parastyle’’ of authors). tal dimensions to the nearest 0.01 mm with
Stylar cusp B (styB): A much larger cusp digital calipers while specimens were viewed
(almost always distinct) posterior to styA (if at low magnification under a stereomicro-
present) andlabial to theparacone, to which scope.Exceptasnoted,anatomicalendpoints
it is sometimes connected by the prepara- are illustrated in figures 5 and 6.
crista (5 ‘‘stylocone’’ of authors). GreatestLengthofSkull(GLS):Fromthe
Stylarcusp(s)C(styC):Oneortwosmall anteriormost point of the premaxillae to the
cusps(sometimesindistinctorabsent)poster- posteriormost point of the braincase.
olabial to the paracone and anterolabial to Condylobasal Length (CBL): From the
the metacone. occipital condyles to the anteriormost point
Stylar cusp D (styD): Usually single and of the premaxillae.
sometimesindistinctinMarmosa,thiscuspis Rostral Length (RL): From the anterior-
posterolabial to the metacone, to which it is most point of the nasals to the ventralmost
never directly connected. lacrimal foramen.
Stylar cusp E (styE): A small cusp (often NasalLength(NL):Thegreatestlengthof
indistinct) at the posterior end of the stylar either the right or left nasal bone (whichever
shelf posterolabial to themetacone, to which is longest).
it is always connected by the postmetacrista Palatal Length (PL): From the anterior-
(5 ‘‘metastyle,’’ ‘‘distostyle,’’ ‘‘metastylar most pointofthepremaxillaetothepostero-
spur,’’ or ‘‘metastylar corner’’ of authors). lateral corner of the postpalatine torus.
MEASUREMENTS: We recorded external Length of Maxillary Tooth Row (MTR):
measurements (in millimeters, mm) and From the anterior surface of the base of the
weight (in grams, g) from specimen labels. upper canine to the posterior margin of M4.
2010 ROSSIETAL.:REVISION OFMARMOSA 7
TABLE 2 Length of Upper Molar Series (UMS):
CurrentlyRecognizedSpeciesofMarmosa(Marmosa)a Crown length of the upper molars, from the
anterolabial margin of M1 to the posterior
M.andersoniPine,1972 margin of M4.
M.lepida(Thomas,1888) Length of M4 (LM4): Length (anteropos-
Synonym: grandisTate,1931 teriorormesiodistaldimension)ofthefourth
upper molar crown across the paracone and
M.mexicanaMerriam,1897
metacone.
Synonyms: mayensisOsgood,1913
Width of M2 (WM2): Greatest width
savannarumGoldman,1917
(transverse dimension) of the second upper
zeledoniGoldman,1917b
molar,fromthelabialmarginofthecrownat
M.murina(Linnaeus,1758)
or near the stylar A position to the lingual
Synonyms: bombascaraeAnthony,1922 apex of the protocone.
chloeThomas,1907
Width of M4 (WM4): Greatest width
dorsigera(Linnaeus,1758)
(transverse dimension) of the fourth upper
duidaeTate,1931
molar,fromthelabialmarginofthecrownat
guianensis(Kerr,1792)
or near the stylar A position to the lingual
klagesiJ.A.Allen,1900
macrotarsus(Wagner,1842) apex of the protocone.
madeirensisCabrera,1913 Height of Upper Canine (HC): Height
maraniiThomas,1924 (vertical dimension) of C1, from the exposed
meridionalisMiranda-Ribeiro, labial base to the tip of the tooth.
1936 PalatalBreadth(PB):Measuredacrossthe
moreiriMiranda-Ribeiro,1936 labialmarginsofthefourthmolar(M4)roots.
muscula(Cabanis,1848)
Postpalatal Breadth (PPB): Least breadth
parataThomas,1911
across the anterior processes of the left and
roraimaeTate,1931
right alisphenoids (not illustrated).
tobagiTate,1931
waterhousei(Tomes,1860) Breadth of Basicranium (BB): The least
distance between the anteromedial margins
M.quichuaThomas,1899
of the right and left alisphenoid tympanic
Synonym: musicolaOsgood,1913
processes.
M.robinsoniBangs,1898 Breadth across Tympanic Bullae (BTB):
Synonyms: castaThomas,1911 The greatest distance across the lateral
chapmaniJ.A.Allen,1900 margins of the right and left alisphenoid
fulviventerBangs,1901 tympanic processes.
grenadaeThomas,1911
Length of Tympanic Bulla (LTB): From
isthmicaGoldman,1912b
the anterior curvature of the alisphenoid
luridivoltaGoodwin,1961
tympanic process to the posteriormost point
mimetraThomas,1921c
of the petrosal pars cochlearis.
mitisBangs,1898
nesaeaThomas,1911 Tympanic Bulla Opening (TBO): The
pallidiventrisOsgood,1912 distance between the alisphenoid tympanic
ruatanicaGoldman,1911d process and the rostral tympanic process of
simonsiThomas,1899b the petrosal, measured across the medial
M.rubraTate,1931 margin of ectotympanic.
Width of Ectotympanic (WET): Greatest
M.tylerianaTate,1931
width of the ectotympanic (not illustrated).
M.xerophilaHandleyandGordon,1979 Nasal Breadth (NB): Measured across the
aAfterGardner(2005);synonymsinclude‘‘subspecies.’’ triple-point sutures of the nasal, frontal, and
bRecognizedasavalidspeciesinthisreport. maxillary bones on each side.
cSynonymizedwithM.isthmicainthisreport. BreadthofRostrumacrossCanines(BRC):
dSynonymizedwithM.mexicanainthisreport. Measuredacrossthelabialbasesoftheupper
canines.
BreadthofRostrumbetweenJugals(BRJ):
Measured across the triple-point sutures of
8 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.334
Fig. 3. Dorsal and ventral cranial views of Marmosa murina showing principal osteological features
mentionedinthetext.Abbreviations:als,alisphenoid;atp,alisphenoidtympanicprocess;bo,basioccipital;
bs,basisphenoid;cc,carotidcanal;ect,ectotympanic;fm,foramenmagnum;fpj,frontalprocessofjugal;
fro,frontal;gf,glenoidfossa;gpa,glenoidprocessofalisphenoid;ip,interparietal;jug,jugal;lac,lacrimal;
max, maxillary; mp, mastoid process (of petrosal); nas, nasal; occ, occipital condyle (of exoccipital); of,
orbitalfossa;pal,palatine;par,parietal;pcf,paracaninefossa;pogp,postglenoidprocess(ofsquamosal);
pop, postorbital process; pre, premaxillary; prgp, preglenoid process (of jugal); pro, promontorium (of
petrosal); ps, presphenoid; pt, pterygoid; rtp, rostral tympanic process (of petrosal); sq, squamosal; tcf,
transversecanalforamen; tf, temporal fossa; za, zygomaticarch.
the jugal, lacrimal, and maxillary bones on Zygomatic Breath (ZB): Greatest breadth
each side. across the zygomatic arches.
Least Interorbital Breadth (LIB): Mea- LengthofMandible(LM):Measuredfrom
sured at the narrowest point across the the anteriormost point of the mandible
frontals between the orbits (anterior to the (medial to the alveolus of i1) to the posteri-
postorbital processes, if any). ormost point of the angular process.
PostorbitalConstriction(POC):Measured Length of Lower Molar Series (LMS):
at the narrowest point across the frontals Crown length of the lower molars, from the
betweenthetemporalfossae(posteriortothe anterolingual margin of m1 to the poster-
postorbital processes, if present). olingual margin of m4.
Breadth of Braincase (BBC): Measured Length of m4 (Lm4): Length (anteropos-
immediately above the zygomatic process of terior or mesiodistal dimension) of m4, from
the squamosal on each side. the paraconid to the hypoconulid.
2010 ROSSIETAL.:REVISION OFMARMOSA 9
Fig. 4. Left lateral cranial and mandibular views of Marmosa murina showing principal osteological
features mentioned in the text. Abbreviations: als, alisphenoid; ap, angular process; atp, alisphenoid
tympanicprocess;conp,condylarprocess;corp,coronoidprocess;ect,ectotympanic;exo,exoccipital;fpj,
frontal process of jugal; fr, foramen rotundum; fro, frontal; hpp, hamular process of pterygoid; iof,
infraorbital foramen; ip, interparietal; jug, jugal; lac, lacrimal; lc, lambdoid crest; lf, lacrimal foramina;
maf,massetericfossa;max,maxillary;mef,mentalforamina;nas,nasal;pal,palatine;par,parietal;pc,pars
cochlearis(ofpetrosal);pcf,paracaninefossa;pm,parsmastoideus(ofpetrosal);pop,postorbitalprocess;
pre, premaxillary; rmf, retromolar fossa; sq, squamosal; ssf, subsquamosal foramen; sup, supraoccipital;
zps, zygomatic process ofsquamosal.
Width of m2 (Wm2): Greatest width In the course of this study, we observed
(transverse dimension) of m2, measured substantialontogeneticvariationamongcon-
across the hypoconid and entoconid (not specific specimens assignable to Tribe’s age
illustrated). classes6and7.Inordertotakethisvariation
AGE CRITERIA: The age classification into account for the purpose of taxonomic
employed in this report is a refinement of comparisons, we found it useful to redefine
that proposed by Tribe (1990), which was age classes 6 and 7 and to recognize two
based on the pattern of tooth eruption that additional age classes as follows.
he observed in Marmosopsincanus andother Age class 6: Labial cingulum of P3
small didelphids (including Marmosa). In emergent but slightly dorsal to labial cingu-
these taxa,thedeciduousthirdupper premo- lumofP2(indicatingthepenultimatestageof
lar (dP3) is not replaced until M4 has P3 eruption); M3 and M4 cristae unworn or
erupted; therefore, P3 is the last upper tooth withvery narrowanddiscontinuous stripsof
to erupt. Animals belonging to Tribe’s age exposed dentine.
class 5 have a completely erupted upper Ageclass7:LabialcingulumofP3aligned
molar dentition (M1–4), but dP3 is either with or ventral to labial cingulum of P2
unreplaced or P3 is just starting to erupt. (indicating the complete eruption of P3);
AnimalsbelongingtoTribe’sageclass6have dentine narrowly exposed on all or most
shed dP3, P3 is almost completely erupted, M3 and M4 cristae.
andM4isslightlyworn;specimensinTribe’s Ageclass8:LabialcingulumofP3aligned
age class 7 have P3 fully erupted, and M4 is with or ventral to labial cingulum of P2;
considerably worn. dentine broadly exposed along preparacrista
10 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.334
Fig.5. Anatomicalendpoints of21craniodentalmeasurements of Marmosadefined in thetext.
of M3 but narrowly and discontinuously adults. We additionally distinguish ‘‘young
exposed on at least some of the other cristae adults’’ (specimens in age class 6) from
of M3 and M4. ‘‘mature adults’’ (in age classes 7 to 9).
Ageclass9: LabialcingulumofP3aligned
with or ventral to labial cingulum of P2;
ONTOGENETIC VARIATION AND
dentinebroadlyandcontinuouslyexposedon
SEXUAL DIMORPHISM
most M3 and M4 cristae.
Hereafter, specimens belonging to age Like otherdidelphidmarsupials (Gardner,
class 5 are called subadults, and specimens 1973;Abdalaetal.,2001;Floresetal.,2003),
belonging to age classes 6 to 9 are called young mouse opossums are weaned long