Late Eocene Entelodonts (Mammalia: Artiodactyla) From Inner Mongolia, China

9 Pages·1996·3.5 MB·

by  S G Lucas

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PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
109(2):397-405. 1996.
Late Eocene entelodonts (Mammalia: Artiodactyla) from
Inner Mongolia, China
Spencer G. Lucas and Robert J. Emry
(SGL) New Mexico Museum of Natural History and Science,
1801 Mountain Road N.W., Albuquerque, New Mexico 87104, U.S.A.;
(RJE) Department of Paleobiology, National Museum of Natural History,
Smithsonian Institution, Washington, D.C. 20560, U.S.A.
—
Abstract. Previously undescribed specimens ofEntelodon from the lateEo-
cene (Ergilian) of Nei Monggol, China represent two species, small and large.
We identify the small species as Entelodon gobiensis (Trofimov, 1952), because
this is the oldest valid name available for a relatively small species of Asian
Entelodon. E. diconodon (Trofimov, 1952) is a nomen dubium, and it is prob-
able that E. ordosius (Young & Chow, 1956), E. major Biryukov, 1961 and
E. orientalis Dashzeveg, 1965 are junior subjective synonyms of E. gobiensis
(Trofimov, 1952). The large species is Entelodon dirus Matthew & Granger,
1923, a species previously known only from its holotype M3, but to which we
now refer a lower jaw with p2-m3. In Asia, Entelodon is more common in
strata of Ergilian (late Eocene) age; its Shandgolian (early Oligocene) occur-
rences are few. Entelodonts originated in Asia during the middle Eocene, im-
migrated to North America (late Eocene) and Europe (early Oligocene) and
persisted until late Oligocene in Eurasia and North America. The last entelo-
donts, from the early Miocene of North America, apparently arose from a
separate, latest Oligocene emigration from Asia.
Entelodonts were a family of Eocene- Ergilian, Shandgolian) as it was established
Miocene giant suiform artiodactlys, some by Russell & Zhai (19—87).
with skulls nearly one meter long. They are Abbreviations used. When used in den-
especially well represented in the fossil rec- tal notations upper case letters denote upper
ord in western North America (Peterson (skull) teeth and lower case letters denote
1909) and western Europe (Brunet 1979). lower (dentary) teeth. Ins—titutional abbre-
In Asia, the oldest entelodonts {Eoentelo- viations used are: AMNH American Mu-
don) are of middle Eocene (Irdinmanhan) seum—of Natural History, New York;
age, and the group persisted until the late IVPP Institute of Vertebrate Paleontology
Oligocene. The genus Entelodon is known and Paleoanthropology, Beijing; KAN
from the late Eocene (Ergilian) to early Oli- Kazak—h Academy of Sciences, Almaty;
MAN
gocene (Shandgolian), and two genera, Mongolian Academy of Sciences,
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Paraentelodon and Neoentelodon, are of Ulan Bator; PIN Paleontological Institute
late Oligocene (Tabenbulukian) age. In this of the Russian Academy of Sciences, Mos-
article, we describe a sample of Entelodon cow.
from the late Eocene ofNei Monggol (Inner
Mongolia), China (Fig. 1), and clarify the Systematic Paleontology
taxonomy of the Asian species of Entelo-
don in Asia. We use the Asian "land mam- Family Entelodontidae Lydekker, 1883
mal age" terminology (e.g., Irdinmanhan, Genus Entelodon Aymard, 1847
398 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
0-^
Fig. L MapofEntelodonlocalitiesinAsia. 1,Houldjin,BaronSogandUrtynOboformations,NeiMonggol,
China; 2, Cajiachong Formation, Yunnan, China; 3, Ergilin Dzo svita, Mongolia; 4, Kusto svita, Zaysanbasin,
Kazakhstan; 5, Iwaki Formation, Japan; 6, Chilikta svita at Kursay near Lake CheLkar Teniz, Kazakhstan; 7,
Qingshuiying Formation, Lingwu, Ningxia, China; 8, "indricothere" svitaatDulygaly-Zhilanchik, Kazakhstan.
AMNH
Entelodon gobiensis (Trofimov, 1952) 26176 merits description as one of
Figs. 2B, D, 3A-C the best preserved upper dentitions of En-
— telodon from Asia. The II is an almostcon-
Referred specimens. From the Baron ical tooth with a very convex labial side,
Sog Formation at Nom Khong Obo, Holy less convex lingual side and a prominent
Mesa, Nei Monggol, China: AMNH 26184, lingual cingulum. Measurements (in mm)
lower jaw with left and right p3 (Fig. 2B- are: length = 16.7; width = 14.6. The 12 is
D). a larger, more caniniform tooth missing the
From the Baron Sog Formation at Urtyn base of the crown, so comparable measure-
Obo, East Mesa, Suiyuan, Nei Monggol, ments cannot be obtained. The 13 is a re-
AMNH
China: 26176, skull fragments and curved tooth, with the crown more trian-
left and right I1-M3 (Fig. 3A-B). gular in cross section than that of the H or
From the Houldjin Formation 7 miles 12. It is very convex labially and has a lin-
west ofCamp Margetts, Nei Monggol, Chi- gual cingulum. Length = 26.8, width =
na: AMNH field number 839, right M3 22.5. The canine is a recurved tooth similar
(Fig. 3C). — to the 13 but lacks the base of the crown.
Description. The upper dentition of The PI is dominated by a single cusp.
VOLUME NUMBER
109, 2 399
Fig. 2. Lowerjaws of Entelodon from the upper Eocene of Nei Monggol, China. A, C, E. dirus, AMNH
26394, lowerjaw with left p2-m3, in lateral (A) and occlusal (C) views. B, D, E. gobiensis, AMNH 26184,
lowerjaw with left and right p3, in lateral (B) and occlusal (D) views, negative reversed foreasiercomparison.
Bar scale = 5 cm.
the paracone. The crown is curved slightly with two roots, one positioned anteriorly
linguad. The labial face ofthe tooth is con- and the other posteriorly. Length = 32.8,
vex, and a ridge extends from the anterior width = 16.9.
end ofthe tooth to the apex ofthe paracone The P3 has a triangular crown dominated
and then to the posterior base ofthe crown. by the paracone, which is deflected slightly
Length = 22.2, width = 10.8. linguad. It has a prominent posterior ridge
The P2 is a larger version of PI except and a less prominent anterior ridge. The
that the paracone is not as lingually deflect- basal cingulum is essentially continuous
ed, and it has a cingulum around the entire around the crown. One large root is present
crown: on the labial face, beneath the par- anteriorly, and there are two fused roots
acone, the cingulum is only weakly devel- posteriorly. Length = 36.9, width = 25.6.
oped. Like the PI, P2 is a trenchant tooth The crown of P4 is subtriangular in oc-
400 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASfflNGTON
Fig. 3. CheekteethofEntelodon fromtheupperEoceneofNeiMonggol, China. A-B,E. gobiensis, AMNH
26176, occlusal view ofleft P3-M3 (A) and right M3 (B). C, E. gobiensis, AMNH field number 839, occlusal
view of right M3. D, E. dims, AMNH 19181 (holotype), occlusal view of right M3. E-F, E. dirus, AMNH
26394, occlusal (E) and labial (F) views ofleft p2-m3. Bar scales = 2 cm.
clusal outline, with its longer axis oriented prominent. The labial cingulum is faintly
transversely. There is a large paracone with developed and a tiny mesostyle is present.
an equally large, closely appressed proto- The well worn condition of this tooth re-
A
cone. basal cingulum is prominent on the sults in two lophs, one connecting the par-
anterior, lingual and posterior margins of acone and the protocone, and the other the
the tooth, and is presentbut weakerlabially. metacone and the hypocone. A strong post-
There is a faint suggestion of a parastyle, hypocone crista is confluent with the pos-
and a convex ectoloph. The tooth has three terior cingulum. It has two divergent roots
divergent roots. Length = 25.5, width = labially and two fused roots lingually. For
29.6. measurements of M1-M3, see Table 1.
The ml is approximately square, with The M2 is subrectangularin occlusal out-
subequal paracone, metacone, protocone line, and is substantially larger than Ml. It
and hypocone. The anterior cingulum is also differs from Ml in having distinct
P
VOLUME 109, NUMBER 2 401
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Table 1. Measurements (in mmW) of selected upper and lower cheek teeth of Entelodon from Asia. L
maximum antero-posterior length; = maximum transverse width.
Specimen MIL MIW M2L M2W M3L M3W
E. gobiensis
AMNH
26176 29 31 33 34 31 31
AMNH "839" 32 29
IVPP V825.P 31 32
KAN 31-181/54T'' 28 32 33 36 29 32
MAN
27- 25 27 30 34 27 30
MAN
27-2" 29 31 33 37
PIN 473-256<= 25 32 31 39
E. dims
AMNH 19181f
Specimen p4L p4W mlL mlW m2L m2W m3L m3W
E. gobiensis
AMNH "839" 28 23
IVPP V2926.1S 27 21 31 25 29 21
KAN 32-181/547" 40 21 29 23 31 27 33 25
KAN 35(29)3837' 38 20 27 21 31 26 31 24
PIN 473-129J 35 29
PIN 478-126) 32 24
PIN 478-287^ 32 17
E. dims
AMNH
26394 41 22 33 25 38 29 33 25
"Holotype ofE. ordosius (Young & Chow, 1956), ''Holotype ofE. major Biryukov, 1961; "Holotype ofE.
orientalis Dashzeveg (1965); "^Referred specimen ofE. orientalis; '=Holotype ofE. gobiensis (Trofimov, 1952);
fHolotype of E. dims Matthew & Granger, 1923; »Referred specimen ofE. ordosius; ^Holotype ofE. major
Biryukov, 1961; 'Measurements from Emry et al. (1996);JReferred specimen ofE. gobiensis; ^Holotype ofE.
diconodon (Trofimov, 1952).
para- and metaconules, a relatively larger blunt swelling that projects ventrolaterally.
anterior cingulum, and a more distinct la- Two small mental foramina are on the lat-
bial cingulum. eral surface of the horizontal ramus, one
The M3 is subtriangular in occlusal out- under pi and the other under the anterior
line. Its anterior part is very much like that alveolus of p3. The anteroventral aspect of
of M2, but the posterior loph is much nar- the mandibular symphysis is a broad, nearly
rower, and lacks the metaconule. The me- flat, sloping surface. Spacing of the alveoli
tacone is deflected linguad. The hypocone of the canine and anterior premolars indi-
is small but retains a posterior crista con- cates that no diastemata separate these
fluent with the posterior cingulum. teeth. The canine alveolus is large, trihedral
AMNH
The lowerjaw is represented by in cross section and opens anteriorly and
26184. Its horizontal ramus is of nearly dorsally nearly parallel to the inclination of
equal depth throughout and bears two tu- the symphysis. The pi alveolus is a single
bercles, one beneath the pi and anterior al- cavity; its cross section is ovoid with the
veolus of p2, and the other beneath the an- long axis anteroposteriorly oriented. The p2
terior part of ml. The anterior tubercle is a has two separate alveoli, both circular in
convex eminence that is inclined laterally cross section, the posterior much the larger
so that the horizontal ramus dorsal to it is of the two. The p3 is a trenchant tooth with
convex laterally. The posterior tubercle is a a tall, pointed cuspid followed posteriorly
402 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
by a short heel. The p3 is two-rooted, as ordosius do not distinguish it from other
were p4-m3, j—udging from their alveoli. small Entelodon from Asia (Brunet 1979).
Discussion. Brunet (1979) did much to Hu (1964) referred lower jaw fragments
revise the taxonomy of Asian entelodonts from Urtyn Obo, Nei Monggol, to A. or-
at the generic level. A species-levelrevision dosius. The bilophodonty of the lower mo-
is overdue, and we offer some observations larsjustify assignmenttoEntelodon (Brunet
toward one. 1979). In size and morphology, these teeth
Trofimov (1952) named Entelodon di- cannot be distinguished from other Asian
conodon for a right p4 (he misidentified it small specimens of Entelodon (Table 1).
as a left p2: Brunet 1979) from Kursay near Biryukov (1961) based a new species E.
Lake Chelkar-Teniz in Kazakhstan (Fig 1, major on a skull and lower jaw from Du-
No. 6). The paratype is a right m2 from the lygaly-Zhilanchik in Kazakhstan. This is by
same locality. These specimens cannot be far the most informative type specimen of
distinguished metrically or morphologically any species of Entelodon from Asia, but it
from those ofother small Entelodon species closely resembles in size and morphology
from Asia or from some European Entelo- all the other names species except E. dirus
don, although p4 is relatively smaller(Table and E. diconodon. Biryukov's diagnosis of
1) and has an accessory cuspid on the pos- E. major stressed its large size, massive
terior slope of the trigonid, unlike other skull, flared-out suborbital flanges, infraor-
specimens. We agree with Brunet (1979) bital foramen above P4, short I3-C and C-
that E. diconodon should be considered a Pl diastemata, internal choanae (palatine
nomen dubium. notch) at the level of the posterior end of
Trofimov (1952) named Brachyodon go- M3, and upper sexitubercular upper molars
biensis for a partial skull with badly dam- whose crowns are wider than long. These
aged left P1-M3 from Ergilin-Dzo in Mon- are features of the genus Entelodon, and
golia. Trofimov (1958) replaced the preoc- neither these characters nor size differenti-
cupied name Brachyodon with the name ate E. major from the other relatively small
Ergilobia. Brunet (1979) synonymized Er- Asian Entelodon.
gilobia with Entelodon. The type specimen Dashzeveg (1965) described E. orientalis
is poorly preserved, but metrically it cannot on the basis of a left maxillary fragment
be distinguished from the other relatively with Ml-3, from Khoer-Dzan, Mongolia.
small specimens ofAsian Entelodon (Table His diagnosis emphasized large size, low
1). crowned and sexitubercular upper molars
Young & Chow (1956, p. 41, fig. 4, pi. with anterior and posterior cingula, M3
1, figs. C—D) named Archaeotherium or- with a protoconule but lacking a metaco-
dosius for an Ml (IVPP V 825.1) from nule, and palatine notch at the level of the
Lingwu, Ningxia. They diagnosed the spe- middle of M3. These features and size (Ta-
cies by its large size and brachyodont, sexi- ble 1) do not, however, distinguish the ho-
tubercular upper molar with a prominent lotype, or the referred specimens, ofE. or-
accessory cusp on the labial cingulum. Ac- ientalis from other small specimens of En-
cording to Young & Chow (1956), IVPP V telodon from Asia.
825.1 is indistinguishable from the Ml of It thus seems likely that only one small
Archaeotherium except for its larger size. species ofEntelodon is known in Asia. En-
However, Brunet (1979) argues that this telodon gobiensis (Trofimov 1952) is the
tooth more closely resembles that of Ente- oldest available and valid name forthat spe-
lodon, especially in its heavy labial cingu- cies, given that E. diconodon is a nomen
lum, and created the new combination En- dubium. Entelodon ordosius (Young &
telodon ordosius for it. Nevertheless, the Chow 1956), E. major Biryukov, 1961 and
size and morphology of the holotype of E. E. orientalis Dashzeveg, 1965 are probably
VOLUME 109, NUMBER 2 403
junior subjective synonyms of E. gobiensis slightly bilophodont. The m2 is a larger
(Trofimov, 1952). The specimens of E. go- version of ml, with more distinct lophids,
biensis reported here are the first records of a well developed hypoconulid and a labial
Entelodon from the Baron Sog Formation cingulid. The m3 is well worn but similar
of Nei Monggol. to m2, though it is smaller and has a rela-
tively smaller—talonid.
Entelodon dirus Matthew & Granger, Discussion. Priorto this report, E. dirus
1923 was known only from its holotype M3. The
AMNH
Figs. 2A, C, 3D-F lowerjaw, 26394, is from the same
stratigraphic level as the holotype, and is
Holotype.—AymW 19181, right M3 from a nearby locality. It is too large to be-
(Fig. 3D) — long to E. gobiensis (Table 1), and its m3
Horizon and locality of holotype. is of appropriate size to occlude with the
Houldjin Formation, 3 mi. (4.8 km) south- holotype M3 of E. dirus, to which we as-
west of Iren Dabasu, N—ei Monggol, China. sign it.
Referred specimens. From the Houldjin
Formation at Overnight Camp, Camp Mar- Biochronology and Paleobiogeography
AMNH
getts area, Nei Monggol, China:
26394, incomplete lower jaw with p2-m3 Entelodon occurs in Asia in strata of late
(Figs. 2A, C, 3E-F). Eocene (Ergilian) and early Oligocene
From the Houldjin Formation 7 miles (Shandgolian) age. The Ergilian occur-
(11.2 km) west of Camp Margetts, Nei rences are: (1) Houldjin, Baron Sog and Ur-
AMNH
Monggol, China: field number 36, tyn Obo formations, Nei Monggol, China
two canine fragments; field number 839, (Matthew & Granger 1923, Hu 1964, this
left p2 and righ—t ml. paper); (2) Cajiachong Formation, Yunnan
Description. The lower jaw has a flat, China (Wang & Zhang 1983); (3) Ergilin
sloping, plate-like symphysis. This orien- Dzo svita, Mongolia (Trofimov 1952, Dash-
tation gives the 11-3 a slightly procumbent zeveg 1976); (4) Kusto svita, Zaysan basin,
flare. The anterior tubercle is a crest or Kazakhstan (Emry et al. 1996); and (5)
ridge that begins under the canine and con- Iwaki Formation, Japan (Tomida 1986).
tinues to beneath the p2-3. The posterior The Shandgolian occurrences are: (1) Chi-
tubercle is a blunt spike under the ml-2 likta svita at Kursay near Lake Chelkar-
juncture. Judging from the sizes of alveoli, Teniz, Kazakhstan (Trofimov 1952); (2)
il < 12 < i3 < c. The canine alveolus is Qingshuiying Formation, Lingwu, Ningxia,
much larger than that of 13 and is round in China (Young & Chow 1956); and (3) "in-
cross section. The pi has a single alveolus, dricothere" svita at Dulygaly-Zhilanchik,
with the cross section an antero-posteriorly Kazakhstan (Biryukov 1961). Entelodon is
elongate oval. There are no diastemata be- much more common and widespread in Er-
tween the teeth. gilian strata than in Shandgolian strata.
The p2 is a two-rooted, trenchant tooth The oldest and most primitive known en-
dominated by a large paraconid. The p3 is telodont is Eoentelodon from the middle
a similar trenchant tooth. Both p2 and p3 Eocene (Irdinmanhan) Xiangshan and Lu-
have a discontinuous cingulid across the meiyi formations of Yunnan, China (Chow
lingual face of the paraconid. The p4 has a 1958; Zhang et al. 1978). The genus has
talonid and accessory cuspid on the pos- been reported from strata as young as late
tero-lingual base of the paraconid slope. Eocene (Ergilian) in Mongolia (Dashzeveg
The p2-4 are inclined slightly posteriad. 1965). Entelodonts first appear in North
The ml is subrectangular in occlusal out- America during the Eocene (Duchesnean)
line. With advancing wear it becomes in the form of Brachyhyops (Lucas 1992),
—
404 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
and first appear somewhat later in Europe, Literature Cited
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ian-Orellan) (Effinger 1987). They declined Haute-LoireetnommeEntelodon. Annalesde
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.
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—
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109, 2 405
— —
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