Discovery of the First Early Cenozoic Euprimate (Mammalia) from Inner Mongolia

2007·0.5 MB·English

by  Xijun Ni

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3571, 11 pp., 3 figures May 16, 2007
Discovery of the First Early Cenozoic Euprimate
(Mammalia) from Inner Mongolia
XIJUN NI,1,2 K. CHRISTOPHER BEARD,3 JIN MENG,2 YUANQING WANG,1
AND DANIEL L. GEBO4
ABSTRACT
Although it is widely thought that euprimates originated in Asia, the fossil record of early
euprimates remains sparse there. We describe herein a new omomyid euprimate, Baataromomys
ulaanus,n.gen.etsp.,basedonanisolatedrightlowerm2fromBumbanianstrataatWulanboerhe
in the Erlian Basin of Inner Mongolia, China. In terms of the size and proportions of m2,
Baataromomys ulaanus is intermediate between Eurasian and North American species that are
usually assigned to Teilhardina. Morphologically, m2 of Baataromomys differs from that of
Teilhardina and North American small-bodied omomyids (including Anemorhysis, Tetonoides,
Trogolemur, and Sphacorhysis) in having a smaller paraconid that is less fully connate with the
metaconid, a lower entoconid, a weaker crest connecting the metaconid with the entoconid, and
aweakerbuccalcingulid.ThenewtaxonismuchsmallerandlowercrownedthanSteinius,agenus
commonly regarded as a basal omomyid. Despite the substantial difference in size, the m2s of
Baataromomys and Steinius share some important features, including a very broad talonid basin
and a relatively low hypoconid and cristid obliqua. Given its early occurrence and primitive
anatomy,Baataromomysmayeventuallyhelptoclarifythephylogeneticrelationshipsamongbasal
omomyids, but more complete specimens will be required to test this possibility. Baataromomys
brandti from the basal Wasatchian zone Wa-0 in the northern Bighorn Basin, Wyoming, was
previouslyallocatedtoTeilhardina.However,several dentalfeatures sharedbyB. brandtiandB.
ulaanus suggest that they are closely related. The co-occurrence of Baataromomys in Asia and
NorthAmericaindicatesthatsmall-bodiedeuprimateswereabletodispersalacrosstheBeringian
regionnearthe Paleocene–Eocene boundary.
1Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, 100044, China
([email protected]).
2DivisionofPaleontology,AmericanMuseumofNaturalHistory.
3SectionofVertebratePaleontology,CarnegieMuseumofNaturalHistory,Pittsburgh,PA15213.
4DepartmentofAnthropology,NorthernIllinoisUniversity,DeKalb,IL60115.
CopyrightEAmericanMuseumofNaturalHistory2007 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3571
INTRODUCTION Altanius hasmore recentlybeeninterpretedas
either a basal euprimate or a plesiadapiform
Euprimates, or primates of modern aspect, (Rose and Krause, 1984; Gingerich et al.,
include living lemurs, lorises, tarsiers, and
1991; Beard and Wang, 1995; Ni et al., 2005).
anthropoids, as well as extinct taxa such as
Aside from the specimen described here, the
adapiforms and omomyids that are closely
onlyotherBumbanianomomyidsdescribedto
relatedtothem(e.g.,Szalayand Delson,1979;
date are Kohatius and Teilhardina asiatica.
Szalayetal.,1987;RoseandBown,1991;Rose
Kohatius is a poorly documented omomyid
et al., 1994). To date, the oldest undoubted
from the Kuldana Formation of northern
euprimate fossils have been recovered from
Pakistan that apparently includes multiple
earliest Eocene strata in North America,
species, only one of which, K. coppensi, has
Europe, and Asia (Gingerich, 1986, 1993; Ni
been named (Russell and Gingerich, 1980,
et al., 2004). One potential exception, the
1987;Thewissenetal.,1997).Thephylogenet-
poorly documented Altiatlasius koulchii from
ic relationships of Kohatius remain unclear.
thelatePaleoceneofMorocco,isoftendebated
Teilhardina asiatica is based on a partial skull
astheworld’sonlyknownPaleoceneeuprimate
and relatively complete lower dentition from
(Sige´ etal.,1990;Godinot,1994;Hookeretal.,
the Lingcha Formation in Hunan Province,
1999; Beard, 2006). The relatively modern
China (Ni et al., 2004). According to the
anatomy, high taxonomic diversity, and broad
phylogenetic analysis of Ni et al. (2004),
geographicrangeofearliestEoceneeuprimates
T.asiatica is closely related to T. belgica,
suggest that the group as a whole originated
a species that occurs in earliest Eocene strata
sometime before the beginning of the Eocene.
of Belgium and France. In agreement with
This conclusion is corroborated by molecular
Szalay (1982), Ni et al. (2004) found that
approachestophylogenyreconstruction,which
North American species that are often
typically recognize euprimates as one of three
referred to Teilhardina may actually be more
living members of the Euarchonta, along with
closely related to younger and more derived
tree shrews (Scandentia) and flying lemurs
North American omomyids, such as Tetonius,
(Dermoptera) (e.g., Eizirik et al., 2004).
Tetonoides, and Anemorhysis. With the excep-
Given the wide geographic distribution of
tion of ‘‘Teilhardina’’ brandti, which was
the earliest fossil euprimates, it is not surpris-
originally described as the earliest Teilhardina
ing that specialists have so far failed to reach
from North America (Gingerich, 1993) and is
any consensus regarding their ancestral place
transferred to the new genus from Inner
oforigin.Thehierarchicallynestedpositionof
Mongolia here, systematic revision of these
euprimates within the superodinal clades
EuarchontaandEuarchontoglires,whoseoth- North Americanspecies is beyond the scope of
erprincipalmembersareallwidelythoughtto this study. We provisionally refer them to
have originated in Asia, points toward an Teilhardina (e.g., as ‘‘Teilhardina’’ americana)
Asian origin for euprimates as well (Beard, in this paper.
1998, 2006; Beard and Dawson, 1999; Ni et The new euprimate was discovered by
al., 2005). Despite the strong biogeographic screenwashing matrix from the Gomphos
signal provided by this phylogenetic context, bed at Wulanboerhe in the Erlian Basin of
some recent workers continue to advocate Inner Mongolia in 2003. Meng et al. (2004)
a Gondwanan origin for euprimates (e.g., described dental and postcranial remains of
Miller et al., 2005). the gliriform mammal Gomphos elkema from
Although phylogenetic evidence suggests this site, which they called ‘‘Huheboerhe’’.
that euprimates originated in Asia, the fossil The locality is close to the site ‘‘7 miles
record of early euprimates remains sparse southwest (235u) of Camp Margetts’’ of the
there. The phylogenetic affinities of Altanius Central Asiatic Expeditions. Locality and
orlovi, a tiny species known from Bumbanian stratigraphic data for Wulanboerhe have
strata in the Nemegt Basin of Mongolia, are been published (Meng et al., 2004; Bowen et
currently disputed. Originally described as an al., 2005). New field observations indicate
omomyid (Dashzeveg and McKenna, 1977), that Paleogene beds of the Wulanboerhe-
2007 NI ETAL.: ASIAN CENOZOICEUPRIMATE 3
Huheboerhe-Nuhetingboerhe area consist of American ‘‘Teilhardina’’ species in having
three lithological units: the Nomogen, a smaller paraconid that is more closely
Arshanto, and Irdin Manha formations. At appressed to the metaconid, and a relatively
the Wulanboerhe transect, only the Nomogen lower hypoconid and cristid obliqua. m2
and Arshanto formations are present, con- further differs from that of North American
trary to Meng et al. (2004) and Bowen et al. ‘‘Teilhardina’’ species in having a lower en-
(2005). The Gomphos bed occurs in the upper toconid, a much weaker crest connecting the
part of the Nomogen Formation, the lower entoconid with the metaconid, and a weaker
part of which yields a typical late Paleocene buccal cingulid.
(Gashatan)fauna,characterizedbythepresence INCLUDEDSPECIES: TeilhardinabrandtiGin-
ofLambdopsalis,Prionessus,andPalaeostylops. gerich, 1993:322.
Immediately above the Gomphos bed are red GEOLOGICAL RANGE: Bumbanian of Inner
beds that contain a species of perissodactyl Mongolia and earliest Wasatchian (Wa-0) of
similar to Pataecops parvus and an arctostylo- Wyoming.
pid similar to, but significantly larger than, ETYMOLOGY: Baatar,Mongolian,hero,wide-
Palaeostylopsmacrodon.WefollowMengetal. ly used as Mongolian first name; and omomys,
(2004) in referring the Gomphos bed to the Greek,shoulder-mouse.
Bumbanian Land Mammal Age.
Institutionalabbreviationsusedinthisreport
Baataromomys ulaanus, new species
are as follows: IVPP, Institute of Vertebrate
figure 1
Paleontology and Paleoanthropology, Chinese
Academy ofSciences(Beijing,China);MNHN,
Museum National d’Histoire Naturelle (Paris, HOLOTYPE: IVPPV14614,anisolatedright
France); UM, University of Michigan Museum m2; only known specimen.
ofPaleontology(AnnArbor,Michigan);USGS, TYPE LOCALITY AND AGE: Wulanboerhe,
United States Geological Survey (Denver, Erlian Basin, Inner Mongolia. Bumbanian of
Colorado); USNM, United States National Inner Mongolia.
Museum of Natural History (Washington, DIAGNOSIS: m2 differs from that of B.
D.C.); UW, University of Wyoming Geolo- brandti in having a weaker paracristid and
gical Museum (Laramie, Wyoming). a paraconid that is more lingual and less
mesial in position.
SYSTEMATIC PALEONTOLOGY ETYMOLOGY: Ulaan, Mongolian, red. The
only known specimen was recovered from
PRIMATESLINNAEUS,1758 a prominent Bumbanian red bed in the Erlian
Basin.
OMOMYIDAETROUESSART,1879
Baataromomys, new genus DESCRIPTION
TYPESPECIES: Baataromomys ulaanus,new The single isolated right lower molar
species. (fig. 1) can be confidently identified as m2
DIAGNOSIS: Smaller than all other omo- because its trigonid is mesiodistally com-
myids except Teilhardina, Anemorhysis, Teto- pressed and lingually closed. The tooth as
noides, Trogolemur, and Sphacorhysis. m2 a whole is remarkably bunodont and low-
differs from that of Trogolemur, Sphacorhysis, crowned, and most of its individual cusps
Anemorhysis, and Tetonoides inhavinga smal- and crests are relatively blunt and rounded.
lerparaconidthatislessfullyconnatewiththe The molar has a relatively square occlusal
metaconid; a lower, less projecting entoconid; outline, being 1.79 mm long, 1.47 mm wide
amuchweakercrestconnectingthe metaconid at the trigonid, and 1.52 mm wide at the
with the entoconid; a weaker buccal cingulid; talonid. In terms of its size and proportions,
and in lacking a mesially expanded and shelf- m2 of Baataromomys ulaanus falls between
like paracristid. m2 differs from that of samples of Eurasian Teilhardina and North
Teilhardina asiatica, T. belgica, and North American ‘‘Teilhardina’’ (fig. 2).
4 AMERICAN MUSEUMNOVITATES NO. 3571
The trigonid as a whole is slightly inclined
mesially. The weakly developed paracristid
descends the mesial face of the protoconid
beforeturninglinguallytounitethelattercusp
with the paraconid. The tip of the protoconid
and the buccal arm of the protocristid are
worn to expose the dentine, forming a small
depression that tapers distolingually. The
metaconid is roughly the same size as the
protoconid and is situated almost directly
lingual to the latter cusp. Its distolingual
corner forms a blunt and insignificant ridge,
the postmetacristid, that descends the lingual
face of the postvallid. The mesial surface of
the metaconid is smooth, bearing no trace of
a premetacristid. The lingual arm of the
protocristid projects buccally from the meta-
conid, meeting the buccal arm of the proto-
cristid near the midline of the tooth. A
transverse line of dentine joins the tip of the
metaconid with the lingual arm of the proto-
cristid. The wear facets on the protocristid
suggestthat thecrest wasveryblunt,and that
its lingual and buccal arms probably did not
form a continuous shearing crest. The para-
conid is very small, occurring at the mesiolin-
gual corner of the trigonid. A tiny pit of
dentine is exposed at the apex of the para-
conid, indicating that the cusp was low even
when it was unworn. No crest connects the
paraconid and metaconid. The topography of
the internal part of the trigonid is unusual in
that the region between the protoconid and
metaconid is actually elevated above the level
of the protocristid and paracristid.
Thetalonidislongerandslightlywiderthan
the trigonid. The hypoconid is the dominant
cusp, but it and the cristid obliqua remain
relativelylowandblunt.Thelingualsurfaceof
the hypoconid is smooth and slopes down to
thetalonidbasin.Itsbuccalanddistalsurfaces
are continuous, forming a rounded distobuc-
cal corner. The cristid obliqua joins the distal
wall of the trigonid beneath the protoconid,
resulting in a shallow hypoflexid. The buccal
Fig. 1. Baataromomys ulaanus, n. gen. et sp.,
holotype, IVPP V14614, isolated right m2. A, arm of the postcristid is low and blunt,
Occlusal view; B, lingual view; C, buccal view. connecting the hypoconulid with the cristid
Scalebarindicates 1.00 mm. obliqua at about a right angle. The tip of the
hypoconidisworntoexposeasmallroundpit
ofdentine.Thecristidobliquaisslightlyworn,
exposing a tiny line of dentine. The entoconid
forms the distolingual corner of the talonid.
2007 NI ETAL.: ASIAN CENOZOICEUPRIMATE 5
Fig. 2. Size of m2 in the holotypes of Baataromomys ulaanus, n. gen. et sp. and B. brandti, shown in
relation to those of Eurasian Teilhardina and North American ‘‘Teilhardina’’. Measurements of North
American ‘‘Teilhardina’’ are taken from Bown and Rose (1987). Vertical and horizontal axes are
inmillimeters.
This cusp is much smaller and lower than the leaving the talonid basin open lingually. The
hypoconid, so that the deepest point of the lingual arm of the postcristid is insignificant
talonid basin lieslingualtothe midline of this and fuses seamlessly with the transversely
structure. The mesiobuccal surface of the elongated hypoconulid. The hypoconulid is
entoconid is smooth but concave, forming worn, exposing the dentine. No significant
the distolingual border of the talonid basin. cusp remains, but it must have been relatively
The entocristid is very low and blunt. It does large in its unworn condition, based on the
not connect with the weak postmetacristid, exposedislandofdentine.Nosulcusisformed
6 AMERICAN MUSEUMNOVITATES NO. 3571
between the entoconid and hypoconulid, nor Donrussellia. For example, both have very
between the hypoconulid and hypoconid. A broad and shallow talonid basins, with hypo-
thinbutdistinctcingulidsurroundsthebuccal conid and entoconid cusps that are not very
halfofthetooth.Itoriginatesfromthebaseof elevated. In buccal view, the hypoconid and
the paracristid at its mesiobuccal side, con- cristid obliqua on m2 in Baataromomys are
tinues distobuccally, envelops the hypoconid, very low, like those of Donrussellia and in
and terminates just below the buccal side of contrast to those of Teilhardina. Like
the hypoconulid. Donrussellia, Baataromomys retains a small
but distinct hypoconulid on m2.
COMPARISONS Altanius orlovi differs markedly from
Baataromomys ulaanus in many aspects of
Baataromomys differs enough from other m2 morphology. In Altanius, m2 is smaller,
basal omomyids that it is also necessary to relativelynarrower,andmuchhighercrowned
compare it with basal adapiforms, such as than that of Baataromomys. The trigonid of
Donrussellia, as well as the enigmatic primate m2inAltaniusismuchhigherthanitstalonid,
Altanius (fig. 3). bears three high and conical cusps, and has
Thetrigonidofm2inB.ulaanusdiffersmost a more triangular occlusal outline. The para-
notably from that of Donrussellia gallica and conid is slightly larger than the metaconid on
D.provincialisinthepositionofthemetaconid m2 in Altanius, and these cusps are fused at
and the orientation of the protocristid. In their bases to form a lingual pair of trigonid
Donrussellia, the metaconid of m2 is more cuspsthatarehigherthantheprotoconid.The
distal in position, which contributes to the protoconid and hypoconid of Altanius are
relative isolation of this cusp. The relatively morepointedandbearmoresignificantbuccal
distallocationofthemetaconidinDonrussellia ridges, whereas the hypoconulid is much
also results in a more oblique, rather than weaker. In Altanius, the cristid obliqua of m2
transverse, orientation for the protocristid. In is connected to the postvallid below the
contrast, the metaconid of m2 in protoconid-metaconid notch, resulting a very
Baataromomys is located only slightly distal deep hypoflexid. In contrast, the cristid
to the protoconid, so that the protocristid is obliqua of Baataromomys is more buccally
nearly transverse. In addition to the wider oriented, thereby forming a very shallow
separationbetween the paraconidand metaco- hypoflexid. The talonid basin of Altanius is
nid on m2 in Donrussellia compared with much deeper and narrower than that of
Baataromomys, the paraconid in the former Baataromomys, and its lingual side is closed
genus is relatively larger and its base is not by a relatively large entoconid and a high
fusedwiththebaseofthemetaconid.Inlingual entocristid.These important differences inm2
view,thetrigonidofm2inDonrusselliaismore morphology rule out any possibility of close
deeply notched as a result. These lower molar affinitiesbetweenAltaniusandBaataromomys.
trigonid features distinguish Donrussellia from Teilhardina asiatica is the oldest undoubted
all omomyids, so the fact that Baataromomys euprimate known from Asia (Ni et al., 2004).
differs from Donrussellia in these respects is ItcloselyresemblesEuropeanT.belgicabutis
unremarkable. On the other hand, there are morphologically even more primitive. T.
severalwaysinwhichBaataromomysresembles asiatica and T. belgica share some similarities
R
Fig. 3. Schematic drawings of m2 morphology in Baataromomys and a comparative sample of early
Eoceneeuprimates.Allspecimensarescaledtothesamemesiodistallengthandaredepictedinocclusal(left
column), buccal (middle column), and lingual (right column) views. Taxa and specimens illustrated are as
follows:Baataromomysulaanus,holotype,IVPPV14614(A–C);Baataromomysbrandti,holotype,UM99031
(D–F); Teilhardina asiatica, holotype, IVPP V12357 (G–I); ‘‘Teilhardina’’ americana, holotype (reversed),
UW 6896 (J–L); Anemorhysis sublettensis, holotype (reversed), USNM19205 (M–O); Tetonoides pearcei,
holotype,USNM22426(P–R);Steiniusvespertinus,USGS25027(S–U);Donrusselliaprovincialis,holotype
(reversed), MNHNRI-170 (V–X).Each scale barindicates 1.00mm.
2007 NI ETAL.: ASIAN CENOZOICEUPRIMATE 7
8 AMERICAN MUSEUMNOVITATES NO. 3571
in m2 morphology with B. ulaanus, including Baataromomysbrandti, originally referredto
a relatively buccal position of the cristid Teilhardina, is the earliest haplorhine primate
obliqua, a shallow hypoflexid, and a lingually knownfromNorthAmerica(Gingerich,1993).
open talonid basin. On the other hand, Theholotypeofthisspeciesisanisolatedright
differences in m2 morphology between these m2 from the earliest Wasatchian (Wa-0) of
two species of Teilhardina and B. ulaanus are northwestern Wyoming. This species shares
significant. In contrast to the bunodont manysimilaritieswithB.ulaanus.Inbothtaxa,
condition in B. ulaanus, the m2 in T. asiatica the trigonid of m2 is mesiodistally narrow; the
andT.belgicaexhibitsrelativelysharpercusps paraconid, metaconid, and protoconid are
andmoretrenchantcrests.Inocclusaloutline, rounded; the paraconid is not twinned with
thetrigonidofm2inT.asiaticaandT.belgica the metaconid; the talonid basin is broad and
is more triangular than is the case in B. shallow;crests(includingthepostcristid,cristid
ulaanus. While being smaller than the proto- obliqua, entocristid, and postmetacristid) are
conid and metaconid, the paraconid of m2 in lowandblunt;andthehypoconulidisrelatively
T. asiatica and T. belgica is not as reduced as prominent.B.brandtiisdistinguishedfromthe
that of B. ulaanus. In lingual view, the new taxon in having a slightly stronger para-
paraconid on m2 protrudes mesially in T. cristid and a paraconid that is located less
asiatica and T. belgica, but this cusp is fused lingually.
with the base of the metaconid in B. ulaanus. ‘‘Teilhardina’’ americana is a relatively
The talonid of m2 in B. ulaanus differs from primitive omomyid. Szalay (1982) argued that
that of T. asiatica and T. belgica in being ‘‘T.’’americanaistooderivedtobereferredto
broader, in having a less elevated hypoconid Teilhardina. Instead, Szalay (1982) synony-
and cristid obliqua (especially apparent in mized ‘‘T.’’ americana with Anemorhysis te-
buccalview),andinhavingamoreprominent nuiculus. Bown and Rose (1987) maintained
hypoconulid. a species-level distinction between ‘‘T.’’ amer-
Kohatius is another early Eocene omomyid icana and A. tenuiculus, but they acknowl-
genus from Asia. Documented specimens, edged the close affinities between them, re-
includingarightm1,asmallfragmentofaleft ferring both species to Teilhardina. Compared
p4, a right mandible fragment preserving p4 with that of B. ulaanus, m2 in ‘‘T.’’ americana
andthealveoliform1–m2,andanisolatedleft has taller cusps and sharper crests. The
p4, are from the Kuldana Formation of paraconid of m2 in ‘‘T.’’ americana is much
northern Pakistan (Russell and Gingerich, larger and protrudes farther mesially than is
1980, 1987; Thewissen et al., 1997). These the case in B. ulaanus, yielding a more tri-
specimens may represent as many as three angular occlusal outline for the trigonid.
differentspecies(RussellandGingerich, 1980, Together, the paraconid and metaconid on
1987; Thewissen et al., 1997). Because m2 m2 in ‘‘T.’’ americana form a massive, bi-
remains unknown for Kohatius, direct com- cusped structure on the lingual side of the
parisons with Baataromomys are not possible. trigonid, while the reduced paraconid of B.
However, m1 of Kohatius has taller cusps and ulaanusseemstobemerelyavestigialappend-
stronger crests than do those on m2 of B. ageofthemetaconid.Asubtlebutcontinuous
ulaanus. Additionally in Kohatius, the para- crestconnects theapices oftheparaconidand
conid and metaconid are widely separated on metaconid on m2 in ‘‘T.’’ americana. This
m1, while these cusps (along with the trigonid structure becomes much better developed in
as a whole) are notable for being closely some younger and more derived North
compressed on m2 in B. ulaanus. Finally, the American omomyids, such as Tetonius,
m1 talonid in Kohatius bears a tall and Tetonoides, and Trogolemur. In B. ulaanus,
projecting entoconid and a relatively tren- no equivalent crest unites the paraconid and
chant entocristid, in contrast to the more metaconid on m2. The talonid of m2 in ‘‘T.’’
bunodont conditions that prevail on m2 in B. americana is much deeper and more fully
ulaanus. These morphological distinctions are closed than that of B. ulaanus. On m2 in ‘‘T.’’
too great to be attributed to different molar americana all of the crests surrounding the
loci alone. talonid basin, as well as the hypoconid and
2007 NI ETAL.: ASIAN CENOZOICEUPRIMATE 9
entoconid, are stronger and more elevated relatively simple cusp pattern, Baataromomys
than is the case in B. ulaanus, but the lacksanycompellingfeaturesincommonwith
hypoconulid remains much less significant. Teilhardina. Because both of the aforemen-
‘‘T.’’ americana also has a stronger buccal tioned characters are almost certainly primi-
cingulid on m2 than does B. ulaanus. tive for Omomyidae, there is no reason to
Steiniushasbeenrankednearthebaseofthe presume that Baataromomys is more closely
omomyid evolutionary radiation based on its relatedtoTeilhardinathanitistoSteinius,for
primitive dental anatomy, despite the fact that example.
it occurs stratigraphically well above the Several of the distinctive molar characters
earliest North American omomyids (Rose and of Baataromomys diverge from conditions
Bown,1991;Roseetal.,1994).Bothspeciesof found in other omomyids, thereby inviting
Steinius are much larger than B. ulaanus, but comparisons with other higher level taxa of
these taxa share many features of molar primates. For example, m2 of Baataromomys
morphology in common. The most significant has bunodont and slightly inflated cusps,
difference between Steinius and Baataromomys trigonidandtalonidof similar width, a cristid
relates to the larger size and more mesial obliqua that reaches the postvallid near the
positionoftheparaconidonm2intheformer. base of the protoconid, a shallow hypoflexid,
On the other hand, both taxa possess very a moderately developed hypoconulid, and
broad talonids and relatively low hypoconids a weak buccal cingulid. These features have
andobliquecristids.Cuspsandcrestsaremore often been considered as derived characters
trenchant inSteinius, whereas the entirecrown amongprimates,andKayandWilliams(1994)
of m2 is more bunodont in Baataromomys. included them in their description of the
Given the large difference in size, the morpho- morphotype of the hypothetical anthropoid
logical similarities between these taxa are ancestor. The potential significance of these
surprising. characters in Baataromomys is difficult to
assess at present, given the very limited
DISCUSSION anatomicalinformationthatiscurrentlyavail-
able for this taxon. Baataromomys may
AlthoughBaataromomysulaanusiscurrent- eventually help to clarify the phylogenetic
ly documented by a single m2, several dental relationships among basal omomyids and
features shared by B. ulaanus and B. brandti other euprimate clades, but more nearly
suggest that they are closely related. These complete specimens of this taxon will be
characters include a mesiodistally compressed required to test this possibility.
trigonid, bunodont and rounded protoconid Along with Teilhardina asiatica, Baataro-
and metaconid cusps, a low talonid with momys ulaanus documents at least modest
a broad basin, and a prominent hypoconulid. diversity in the Asian euprimate radiation at
Despite their widely divergent geographic or near the beginning of the Eocene. Such
provenances, we think that the combination precociouseuprimatediversityinAsiaishardly
of these traits indicates that Asian B. ulaanus surprising. Indeed, early Asian euprimates
and North American B. brandti are more must remain significantly undersampled if the
closely related to each other than either of phylogenetic evidence pointing toward an
them is to other omomyids. We therefore Asian origin for this clade is accurate. On the
transferNorthAmerican‘‘Teilhardina’’brand- other hand, if B. ulaanus and B. brandti prove
ti to the genus Baataromomys. to be as closely related as current evidence
B. brandti was previously interpreted as suggests, then Baataromomys would join nu-
a potential common ancestor for European merous other mammalian taxa indicating
Teilhardina belgica and North American dispersal across the Beringian region near the
‘‘Teilhardina’’ americana (Gingerich, 1993). Paleocene–Eoceneboundary(e.g.,Beard,1998;
Based on our morphological comparisons, B. Beard and Dawson, 1999). Finally, the geo-
brandti shares more features in common with graphic occurrence of Baataromomys ulaanus
B. ulaanus than it does with any species of suggests that forested habitats suitable for
Teilhardina. Aside from its small size and small euprimates must have been present, at
10 AMERICAN MUSEUMNOVITATES NO. 3571
least sporadically, on the Mongolian Plateau Dashzeveg,D.,andM.C.McKenna.1977.Tarsioid
during the early Cenozoic. primate from the early Tertiary of the
Mongolian People’s Republic. Acta Palaeonto-
logicaPolonica22:119–137.
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Alfred L. Rosenberger, Richard F. Kay, and R.F. Kay (editors), Anthropoid origins: new
an anonymous reviewer for instructive dis- visions: 45–64. New York: Kluwer Academic/
cussion and suggestions, Sun Chengkai, Jin Plenum Publishers.
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si—oldest primate of modern aspect from
work, and Mark A. Klingler for help with
NorthAmerica. Nature 320:319–321.
illustrations. Financial support from the
Gingerich, P.D. 1993. Early Eocene Teilhardina
American Museum of Natural History and
brandti: oldest omomyid primate from North
the Carnegie Museum of Natural History is America. Contributions from the Museum of
gratefully acknowledged. Funding was pro- Paleontology,UniversityofMichigan28:321–
vided by grants from the National Natural 326.
Science Foundation of China (40202003 to Gingerich, P.D., D. Dashzeveg, and D.E. Russell.
X.N. and 40532010 to Y.W.) and U.S. 1991.Dentitionandsystematicrelationshipsof
National Science Foundation (BCS 0309800 Altaniusorlovi(Mammalia,Primates)fromthe
early Eocene of Mongolia. Geobios 24:
to C.B. and J.M., and EAR-0120727 to
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