愛媛大学理学部紀要 第 24 巻 64–83 ページ，2022 年
Memoirs of the Faculty of Science, Ehime University, vol. 24, p. 64–83, 2022

A brief review of the updated fossil vertebrate fauna of the upper
Eocene Ergilin Dzo Formation, southeastern Mongolia
モンゴル南東部の上部始新統エルギリン・ゾー層における最新の化石脊椎動物相

Takehisa Tsubamoto, Khishigjav Tsogtbaatar, Tsogtbaatar Chinzorig and Naoko Egi鍔本武久，ヒシグジャウ＝ツォクトバートル，ツォクトバートル＝チンゾリグ，江木直子

愛媛大学理学部紀要 第 24 巻 64–83 ページ，2022 年
Memoirs of the Faculty of Science, Ehime University, vol. 24, p. 64–83, 2022

A brief review of the updated fossil vertebrate fauna of the upper
Eocene Ergilin Dzo Formation, southeastern Mongolia
モンゴル南東部の上部始新統エルギリン・ゾー層における最新の化石脊椎動物相

Takehisa Tsubamoto1, Khishigjav Tsogtbaatar2, Tsogtbaatar Chinzorig2,3 and Naoko Egi4
鍔本武久 1，ヒシグジャウ＝ツォクトバートル 2，ツォクトバートル＝チンゾリグ 2,3，江木直子 4
1Earth’s Evolution and Environment, Department of Mathematics, Physics, and Earth Sciences, Graduate School of
Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime Prefecture 790-8577, Japan1

愛媛大学 大学院理工学研究科 数理物質科学専攻 地球進化学講座

2

Institute of Paleontology, Mongolian Academy of Sciences, P.O. Box 46/650, Chingeltei District-15160, Horoo-4, S.
Danzan Street 3/1, Ulaanbaatar, Mongolia

2

3

North Carolina Museum of Natural Sciences, 11 W. Jones Street, Raleigh, NC 27601, USA

3

4

モンゴル科学アカデミー 古生物学研究所
ノースカロライナ自然科学博物館

National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba 305-0005, Japan4

国立科学博物館

Abstract.
We briefly review the fossil vertebrate fauna of the upper Eocene Ergilin Dzo Formation ofsoutheastern Mongolia. The Ergilin Dzo vertebrate fauna currently consists of 104 species of fiveclasses: two species of the Osteichthyes, one species of the Amphibia, nine species of the Reptilia, 11
species of the Aves, and 81 species of the Mammalia. The Ergilin Dzo mammalian fauna currently
consists of 11 orders, including six species of the Eulipotyphla, one species of the Anagalida, two speciesof the Mesonychia (= Acreodi), one species of the Cimolesta, two species of the Leptictida, four speciesof the Rodentia, four species of the Lagomorpha, five species of the Carnivora, eight species of theHyaenodontida (= Hyaenodontidae), 13 species of the Artiodactyla, and 33 species of the Perissodactyla.
In terms of the collected specimen numbers, the brontotheriid and rhinocerotid perissodactyls andruminant artiodactyls are dominant among the vertebrate taxa of the formation.
Key words: Ergilin Dzo Asian Land Mammal Age (ALMA), Ergilin Dzo fauna, faunal list, Mammalia,
Eocene, VertebrataIntroduction
The upper Eocene Ergilin Dzo Formation (= Ergilin
Dzo Svita in Russian literature) of southeastern Mongolia
has been famous for yielding many terrestrial vertebrate
fossils, including fish, amphibians, reptiles, birds, andmammals, since the early 20th Century (Berkey andGranger, 1923; Matthew and Granger, 1923a, 1923b,
1924, 1925a, 1925b; Osborn, 1923, 1924, 1925; Berkey
and Morris, 1927; Wetmore, 1934; Burke, 1941; Kretzoi,
1942; Granger and Gregory, 1943; Rozhdestvenskiy,
1949; Belyayeva, 1952, 1954; Gromova, 1952a,
2022 年 1 月 11 日 受付
2022 年 3 月 14 日 発行

1952b, 1954, 1958, 1959; Trofimov, 1952, 1957,
1958; Yanovskaya, 1954, 1976, 1980; Kozlova, 1960;
Dashzeveg, 1964, 1965, 1966, 1970, 1974, 1975, 1976a,
1976b, 1985; Radinsky, 1965, 1967; Van Valen, 1967;
Kielan-Jaworowska and Dovchin, 1968; Młynarski,
1968; Wood, 1970; Shevyreva, 1972; Belyayeva etal., 1974; Gabunia and Dashzeveg, 1974; Kurochkin,
1976, 1981; Yanovskaya et al., 1977; Reshetov, 1979;
Kurochkin and Dashzeveg, 1979; Devyatkin, 1981;
Lucas, 1982; Wall, 1982; Dashzeveg and Devyatkin,1986; Russell and Zhai, 1987). The fossil mammals
from the formation define the type fauna of the Ergilian

2022 年 3 月 14 日 受理

- 64 -

Received: 11 January, 2022; Accepted: 14 March, 2022
Published: 14 March, 2022

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

100˚E
90˚E

95˚E

105˚E

110˚E

115˚E
50˚N

Ulaanbaatar

MONGOLIA

Dorno
Gobi
Aimag

45˚N
Distributional area of
the Ergilin Dzo Formation

46˚ N

Sain Shand

44˚ N
Dzamyn Ude

Khoer Dzan

Erenhot

Ergilin Dzo(Erlianhaote)Gua Teg

CHINA
100 km112˚ E
42˚ N
106˚ E108˚ E110˚ E

Figure 1. Map of Mongolia showing the distributional area of the upper Eocene Ergilin Dzo Formation, showing threeof the fossil localities of the formation: Ergilin Dzo, Gua Teg, and Khoer Dzan localities (after Tsubamoto and Tsogtbaatar,
2008).

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T. Tsubamoto et al. 鍔本武久ほか

Asian Land Mammal Age (Russell and Zhai, 1987;
Dashzeveg, 1993; Ducrocq, 1993; Ducrocq et al., 1995;
Meng and McKenna, 1998). Despite the recent progressof the discoveries and descriptions of its vertebrate
fossils (Gabunia and Dashzeveg, 1988; Lange-Badréand Dashzeveg, 1989; Dashzeveg, 1991, 1996a, 1996b;
Dashzeveg and Russell, 1992; Dashzeveg and Hooker,
1997; Lopatin, 1997, 2005, 2020; Vislobokova, 1998;
Lavrov, 1999, 2019; Tsubamoto et al., 2006, 2008, 2010,2011a, 2011b, 2012a, 2012b, 2013a, 2013b; Tsubamoto
and Tsogtbaatar, 2008; Mihlbachler, 2008; Egi et al.,2009, 2016; Tsubamoto, 2010; Suzuki et al., 2010;
López-Torres and Fostowicz-Frelik, 2018; Iijima et al.,2019) since Russell and Zhai (1987), who summarized
the Paleogene mammals of Asia, the current compositionof its fossil vertebrate fauna is not well documented dueto the lack of comprehensive reviews based on the latest
data. Here, we briefly review the fossil vertebrate faunaof the formation.
Geological and paleontological settings
The Ergilin Dzo Formation (Dashzeveg, 1993) (=Ardyn Obo Formation by Berkey and Granger, 1923)
is distributed in the southern part of Dornogobi Aimag(eastern Gobi Desert), southeastern Mongolia (Figures
1–4; Dashzeveg, 1993, fig. 1; Clarke et al., 2005, fig.
1; Tsubamoto and Tsogtbaatar, 2008, fig. 1). There areseveral fossil localities of the formation (Yanovskaya
et al., 1977; Russell and Zhai, 1987; Dashzeveg,
1993, 1996a; Saneyoshi et al., 2010): Ergilin Dzo(sublocalities: Novozhilov Hills, Sevkhul Khuduk,
Ergil Obo [= Ardyn Obo], Ergil Ula, Ikh Uldziyn,
Amar Uldziyn, Aman Us, Aman Usny Khyar, Shavag[= Zavag], Bayan Tsav Obo, Khetsu Tsav, and Sangin
Obo), Gua Teg, Khoer Dzan (sublocalities: Ikh Dzan
and Baga Dzan), and a locality near the Dzamyn Ude
Railway Station. Nevertheless, it should be noted that
more precise geological surveys are indeed necessary
to test whether the deposits of all the localities cited
above are really assigned to the single ‘formation,’ ina strict sense, in terms of the current guidelines of thelithostratigraphic units in geology. This is because there
is no key bed (e.g., characteristic tuff bed useful for the
stratigraphic correlation) in the formation, and because
the formation consists of fluvial deposits (Saneyoshi etal., 2010; contra Dashzeveg, 1993; Dill et al., 2005),
which generally contain little evidence useful for the
stratigraphic correlation.
Dashzeveg and Devyatkin (1986) and Dashzeveg(1993) subdivided the formation into six members: instratigraphic ascending order, the Khubsugul, Zangut,
Sevkhul, Shavag, Ergilin, and Khetsu Tsav members(Figure 2). Most of the vertebrate fossils come from the

Sevkhul and Ergilin members according to Dashzeveg
and Devyatkin (1986) and Dashzeveg (1993). At the
Ergilin Dzo locality, all members of the formation are
exposed (Dashzeveg, 1993). Around the uppermost partof the formation (= around the Khetsu Tsav Member)at the Ergilin Dzo locality, many fossil specimens of
the Amynodontidae (Mammalia, Perissodactyla) werecollected during the 2004 and 2008 field seasons (Suzuki
et al., 2010; Tsubamoto et al., 2010). It should be notedthat the Khetsu Tsav Member is not distributed (orcannot be observed due to the erosion) at the Khoer Dzanlocality, which is one of the most fossiliferous localities
in the formation (Dashzeveg, 1993).
The Ergilin Dzo Formation is currently correlated
to the upper Eocene on the basis of the comparison
with the contemporaneous terrestrial mammalian fauna.
The formation was traditionally correlated to the lower
Oligocene (e.g., Dashzeveg, 1966, 1970; Liskun andBadamgarav, 1977; Belyayeva et al., 1974; Dashzeveg,
1974; Yanovskaya et al., 1977; Russell and Zhai, 1987).
Later, Dashzeveg and Devyatkin (1986) and Dashzeveg(1991, 1993, 1996a, 1996b) stated that there is the
Eocene-Oligocene boundary between the Shavag and
Ergilin members (Figure 2). More recently, Ducrocq(1993), Ducrocq et al. (1995), Meng and McKenna(1998), and Tsubamoto et al. (2004, 2008) concluded
that all of the formation is correlated to the upper Eocene.
The Khetsu Tsav Member (Figure 2) yields brontotheriid
perissodactyl fossils (Yanovskaya et al., 1977; Russell
and Zhai, 1987), strongly implying the upper Eocene
correlation for the member (Berggren and Prothero,
1992; Prothero, 1994). As another information on thegeological age of the formation, Sakamoto et al. (2021)
performed a preliminary paleomagnetostratigraphic
study of the formation at the Ergilin Dzo locality andimplied that there is at least one geomagnetic reversal
within the formation.
The paleoenvironment of the Ergilin Dzo Formation
is estimated to be relatively hot/warm and humid witha relatively-closed area on the basis of the presence of
the Brontotheriidae (Mammalia, Perissodactyla) and thedominance of the low-crowned plant-eating mammals(Prothero, 1994; Tsubamoto et al., 2005). This is also
supported by the cenogram analysis of the Ergilin Dzo
fossil mammalian fauna by Ducrocq et al. (1995).
Nevertheless, the very few collected specimen number(currently only one specimen) of the crocodyliforms andthe absence of the primates (Mammalia) imply that the
paleoenvironment of the fauna appears to be more arid
with some more open areas than the contemporaneous
faunas of the southern and middle part of eastern Eurasia,
such as the late middle Eocene Heti fauna (Rencun and
Zhaili faunas) of central China, the late middle Eocene
Pondaung fauna of Myanmar, and the late Eocene Krabi- 66 -

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

Ergilin Dzo Formation

gravelly sandstones
Khetsu Tsav Member Poorly-sortedwith cross lamination

Ergilin Member
Shavag Member
Sevkhul Member
Zangut Member
Khubsuguk Member

Yellowlish gray sandstones
with minor mudstones
Mudstones withvery minor gravelly sandstones
Well-sorted white sandstones
with red mudstones
White sandstones
with minor mudstones
Red mudstones

Figure 2. Generalized composite
stratigraphy of the upper Eocene Ergilin Dzo
Formation suggested by Dashzeveg (1993), withsome comments from Saneyoshi et al. (2010) andTsubamoto et al. (2011a).

A

B

C

D

Figure 3. Some photos at the Ergilin Dzo locality (Figure 1) in 2004. A, landscape of the Ergilin Dzo locality around the
Ergil Obo (= Ardyn Obo) sublocality; B, close-up of the Ergil Obo (= Ardyn Obo) sublocality; C, mode of occurrence of aright mandible with teeth of the Amynodontidae; D, right and left mandibles with teeth of the Amynodontidae in situ before
plaster jacketing.

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T. Tsubamoto et al. 鍔本武久ほか

A

B

C

D

E

F

G

H

Figure 4. Some photos at the Ikh Dzan sublocality of the Khoer Dzan locality (Figure 1) in 2004. A–G, landscapes of the
Ikh Dzan sublocality; H, mode of occurrence of a left mandible with p4–m2 of Hyaenodon incertus.

- 68 -

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

fauna of Thailand (Russell and Zhai, 1987; Ducrocq etal., 1995; Tong, 1997; Tsubamoto et al., 2004, 2005).

requirements of crocodyliforms during the late Eocene(Iijima et al., 2019).

The Ergilin Dzo fossil vertebrate fauna

Aves
The avian (bird) fauna consists of five orders,seven families, nine genera, and 11 species (Table1). The birds from the formation were reported andcited by Wetmore (1934), Kozlova (1960), Kurochkin(1976, 1981), and Yanovskaya et al. (1977). Ergilornis
minor was first described as a new genus and species
Proergilornis minor by Kozlova (1960) (Table 2).
The species was assigned to the genus Ergilornis by
Kurochkin (1981). Clarke et al. (2005) considered that
the Ergilornithidae is synonymous with the Eogruidae,
although we provisionally and conservatively retain the
Ergilornithidae in this article.

The Ergilin Dzo vertebrate fauna currently consistsof five classes, 22 orders, 49 families, 77 genera, and104 species (Table 1). A list of some synonyms ofthe vertebrate taxa discovered from the formation are
indicated in Table 2. Other synonyms and early versionsof the faunal list are provided mainly by Belyayeva etal. (1974), Devyatkin (1981), Yanovskaya et al. (1977),
Russell and Zhai (1987), Dashzeveg (1993), Meng and
McKenna (1998), Tsubamoto et al. (2004), and Lopatin(2020).
Osteichthyes
The bony fish fauna consists of two orders, twofamilies, two genera, and two species (Table 1). The two
fish from the formation, Amia sp. and Parasilurus sp.,were cited by Yanovskaya et al. (1977). The siluriform
specimen from the formation figured by Tsubamoto etal. (2006) might perhaps be assigned to Parasilurus sp.
of Yanovskaya et al. (1977).
Amphibia
Only one species (indeterminate urodelan) of theAmphibia has been reported (Table 1). It was citedby Yanovskaya et al. (1977), although it has not been
described yet.
Reptilia
The reptilian (excluding birds) fauna consists of threeorders, seven families, nine genera, and nine species(Table 1). The reptiles from the formation were studiedor cited by Matthew and Granger (1923b), Młynarski(1968), Ckhikvadze (1972), Dashzeveg (1974, 1993),
and Yanovskaya et al. (1977). According to Yanovskaya
et al. (1977), six species (four families) of turtles
and two species (two families) of lizards have beenrecognized in the formation (Table 1). The testudinid
tortoise (or turtle), Ergilemys insolitus, was firstdescribed as a new species Testudo insolitus by Matthew
and Granger (1923b). Later, this species was assigned
to the genus Geochelone by Młynarski (1968); and thisrevised classification was followed by Dashzeveg (1974).
G. insolitus was assigned to the new genus Ergilemys as
the type species by Ckhikvadze (1972) (Table 2); andthis revised classification was followed by Yanovskaya
et al. (1977) and Dashzeveg (1993). Palaeochelys?
elongata was renamed as ?Melanochelys elongata
by Ckhikvadze (1971) (Table 2). Iijima et al. (2019)
described a crocodyliform tooth. This discovery impliedthat southeastern Mongolia probably fulfilled thermal

Mammalia
The fossil mammals from the formation were mainly
summarized by Belyayeva et al. (1974), Yanovskaya etal. (1977), Devyatkin (1981), Russell and Zhai (1987),
Dashzeveg (1993), and Lopatin (2020). The Ergilin Dzo
mammalian fauna based on the progress of recent studies
are briefly reviewed below.
The Ergilin Dzo fossil mammalian fauna
The mammalian fauna of the Ergilin Dzo Formation
currently consists of 11 orders of 81 species (Table1): six species of the Eulipotyphla, one species of the
Anagalida, two species of the Mesonychia, one speciesof the Cimolesta, two species of the Leptictida, four
species of the Rodentia, four species of the Lagomorpha,
five species of the Carnivora, eight species of theHyaenodontida, 13 species of the Artiodactyla, and 33
species of the Perissodactyla. In terms of the species
diversity, the perissodactyls are dominant in the fauna (33perissodactyl species among the 81 mammalian species
and the 104 vertebrate species). In terms of the collected
specimen numbers, brontotheriid and rhinocerotid
perissodactyls and ruminant artiodactyls are dominantamong the vertebrate taxa from the formation (e.g.,
Tsubamoto et al., 2010).
Eulipotyphla
Three families, six genera, and six speciesof eulipotyphlans (= ‘insectivorans’) have beenrecognized (Yanovskaya et al., 1977; Russell and Zhai,
1987; Lopatin, 2005). Lopatin (2005) described anindeterminate tupaiodontine changlelestid, Oligochenus
grandis (Erinaceidae, Galericinae), and Amphechinus
sp. (Erinaceidae, Erinaceinae, Amphechinini; McKennaand Bell, 1997) from the formation. However, he did
not mention the other eulipotyphlans from the formation- 69 -

T. Tsubamoto et al. 鍔本武久ほか

Table 1. Composite fossil vertebrate faunal list of the Ergilin Dzo Formation. The list was compiled mainly after
Kurochkin (1976, 1981), Yanovskaya et al. (1977), Russell and Zhai (1987), Dashzeveg (1993), and Meng and McKenna
Table(1998),
with1.other references. Selected references for the citation of each species in the Ergilin Dzo fauna are indicated insquare brackets at each species.
OSTEICHTHYES
Amiiformes
Amiidae
Amia sp. [Yanovskaya et al., 1977]
Siluriformes
Siluridae
Parasilurus sp. [Yanovskaya et al., 1977]
AMPHIBIA
UrodelaFamily indet.
Gen. et sp. indet. [Yanovskaya et al., 1977]
REPTILIA
Chelonia
Testudinidae
Ergilemys insolitus (Matthew and Granger, 1923b) Ckhikvadze, 1972 [Yanovskaya et al., 1977]
Platysternidae
Gen. et sp. indet. [Yanovskaya et al., 1977]
Emydidae?Melanochelys elongata (Gilmore, 1931) Ckhikvadze, 1971 [Yanovskaya et al., 1977]
Chrysemys sp. [Yanovskaya et al., 1977]
Gen. et sp. indet. [Yanovskaya et al., 1977]
Trionychidae
Gen. et sp. indet. [Yanovskaya et al., 1977]
Lacertilia
Family indet.
Gen. et sp. indet. [Yanovskaya et al., 1977]
Iguania
AgamidaeGen. et sp. indet. [Yanovskaya et al., 1977]
Crocodyliformes
Family indet.
Gen. et sp. indet. [Iijima et al., 2019]
AVES
Gruiformes
Grues
RallidaeGen. et sp. indet. [Kurochkin, 1976]
Gruoidea
Ergilornithidae
Ergilornis minor (Kozlova, 1960) Kurochkin, 1981 [Yanovskaya et al., 1977]
Ergilornis rapidus Kozlova, 1960 [Yanovskaya et al., 1977; Kurochkin, 1981]
Ergilornis sp. [Kurochkin, 1981]
Eogruidae
Eogrus sp. [Yanovskaya et al., 1977]
Sonogrus gregalis Kurochkin, 1981
Anseriformes
Anseres
AnatidaeGen. et sp. indet. [Kurochkin, 1976]
Ciconiiformes
ArdeaeArdeidaeGen. et sp. indet. [Kurochkin, 1976]
Cygninae
Gen. et sp. indet. [Kurochkin, 1976]
Falconiformes
Accipitridae
Gen. et sp. indet. [Kurochkin, 1976]
Charadriiformes
Lari
Family indet.
Gen. et sp. indet. [Kurochkin, 1976]- 70 -

Table 1.

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

Table 1.—continued.
MAMMALIA
Eulipotyphla
Changlelestidae
Tupaiodontinae
Ictopidium? sp. [Yanovskaya et al., 1977]
Gen. et sp. indet. [Lopatin, 2005]
Erinaceidae
Galericinae
Oligochenus grandis Lopatin, 2005
Erinaceinae
Amphechinini
Amphechinus sp. [Lopatin, 2005]
Palaeoscaptor? sp. [Yanovskaya et al., 1977]
Soricidae
Soricinae
Gen. et sp. indet. [Russell and Zhai, 1987]
Anagalida
Anagalidae
Zofiagale ergilinesis López-Torres and Fostowicz-Frelik, 2018
Mesonychia (= Acreodi)
Mesonychidae?Mongolestes hadrodens Szalay and Gould, 1966 [Dashzeveg, 1985, 1993; Russell and Zhai, 1987; Tsubamoto et al., 2012a; This study]
Hapalodectidae?Metahapalodectes sp. [Dashzeveg, 1993; This study]
Cimolesta
Pantolesta
Pantolestidae
Dyspterninae
Gobiopithecus khan Dashzeveg and Russell, 1992 [Tsubamoto et al., 2011b]
Leptictida
Didymoconidae
Ergilictis reshetovi Lopatin, 1997
Ardynictis furunculus Matthew and Granger, 1925a [Russell and Zhai, 1987]
Rodentia
Cylindrodontidae
Ardynomys silentiumis (Shevyreva, 1972) [Dashzeveg, 1993]
Ardynomys olseni Matthew and Granger, 1925a [Dashzeveg, 1993]
Ardynomys sp. [Dashzeveg, 1993]
Cricetidae
Eucricetodon sp. [Russell and Zhai, 1987]
Lagomorpha
Ochotonidae
Desmatolagus robustus Matthew and Granger, 1923a [Russell and Zhai, 1987; Dashzeveg, 1993]
Desmatolagus gobiensis Matthew and Granger, 1923a [Burke, 1941; Gureyev, 1960; Sych, 1975; Dashzeveg, 1993]
Desmatolagus ardynense Burke, 1941 [Dashzeveg, 1993]
Family indet.
Gen. et sp. indet. [Russell and Zhai, 1987]
Carnivora
Nimravidae
Nimravus mongoliensis (Gromova, 1959) [Dashzeveg, 1996b, Peigné, 2003; Egi et al., 2016]
Eofelis sp. [Egi et al., 2016]
Amphicyonidae
Gen. et sp. indet. [Egi et al., 2009]
Family indet.
Asiavorator gracilis (Matthew and Granger, 1924) Egi et al., 2016 [Dashzeveg, 1996b]
Alagtsavbaatar indigenus (Dashzeveg, 1996b) Egi et al., 2016
Hyaenodontida
Hyaenodontidae
Hyaenodontinae
Hyaenodon pumilus Lavrov, 2019
Hyaenodon chunkhtensis Dashzeveg, 1985 [Tsubamoto et al., 2008]
Hyaenodon eminus Matthew and Granger, 1925a [Tsubamoto et al., 2008]
Hyaenodon pervagus Matthew and Granger, 1924 [Tsubamoto et al., 2008]
Hyaenodon incertus Dashzeveg, 1985 [Tsubamoto et al., 2008]
Hyaenodon mongoliensis (Dashzeveg, 1964) Van Valen, 1967 [Tsubamoto et al., 2008]
Hyaenodon gigas Dashzeveg, 1985 [Wang et al., 2005; Tsubamoto et al., 2008; This study]
Proviverrinae
Gen. et sp. indet. [Tsubamoto et al., 2008]- 71 -

Table 1.

T. Tsubamoto et al. 鍔本武久ほか

Table 1.—continued.

Artiodactyla (sensu Prothero et al., 2022)
Anthracotheriidae
cf. Bothriodon sp. [Tsubamoto and Tsogtbaatar, 2008]
Gen. et sp. indet. [Tsubamoto and Tsogtbaatar, 2008]
Entelodontidae
Entelodon gobiensis (Trofimov, 1952) Brunet, 1979 [Russell and Zhai, 1987; Lucas and Emry 1996b; Tsubamoto et al., 2011b]
Brachyhyops trofimovi (Dashzeveg, 1976b) [Russell and Zhai, 1987; Wang and Qiu, 2002; Tsubamoto et al., 2011b]
Brachyhyops? sp. [Trofimov, 1952; Brunet, 1979; Russell and Zhai, 1987; Tsubamoto et al., 2011b]
Ruminantia
Hypertragulidae
Praetragulus gobiae (Matthew and Granger, 1925b) Vislobokova, 1998 [Russell and Zhai, 1987]
Praetragulus electus Vislobokova, 1998
Lophiomerycidae
Lophiomeryx angarae Matthew and Granger, 1925b [Russell and Zhai, 1987]
Lophiomeryx sp. [Russell and Zhai, 1987]
Leptomerycidae
Miomeryx altaicus Matthew and Granger, 1925b [Russell and Zhai, 1987]
Miomeryx sp. [Russell and Zhai, 1987]
Gobiomeryx dubius Trofimov, 1957 [Russell and Zhai, 1987]
PecoraCervidae
Eumeryx sp. [Russell and Zhai, 1987]
Perissodactyla
Brontotheriidae
Embolotherium andrewsi Osborn, 1929 [Russell and Zhai, 1987; Dashzeveg, 1993; Mihlbachler, 2008]
Embolotherium grangeri Osborn, 1929 [Russell and Zhai, 1987; Dashzeveg, 1993; Mihlbachler, 2008]
Embolotherium sp. [Russell and Zhai, 1987; Dashzeveg, 1993]
Eubrontotherium clarnoensis Mihlbachler, 2007 [Mihlbachler et al., 2004; Mihlbachler, 2008]
Protembolotherium efremovi Yanovskaya, 1980 [Russell and Zhai, 1987; Mihlbachler, 2008]
cf. Nasamplus progressus (Granger and Gregory, 1943) [Mihlbachler, 2008]
Gen. et sp. indet. [Russell and Zhai, 1987]
Chalicotherioidea
Chalicotheriidae
Schizotherium avitum Matthew and Granger, 1923b [Russell and Zhai, 1987]
Eomoropidae
Eomoropus sp. [Dashzeveg and Devyatkin, 1986; Dashzeveg, 1993]
Rhinocerotoidea
Rhinocerotidae
Ronzotherium brevirostris (Belyayeva, 1954) Heissig, 1969 [Russell and Zhai, 1987; Meng and McKenna, 1998]
Ronzotherium orientale Dashzeveg, 1991
Ronzotherium sp. [Dashzeveg, 1991, 1993]
Eggysodontidae
cf. Allacerops sp. [Dashzeveg, 1991; Qiu and Wang, 1999; This study]
Hyracodontidae (sensu Bai et al., 2020b)
Ardynia praecox Matthew and Granger, 1923b [Radinsky, 1967; Russell and Zhai, 1987; Dashzeveg, 1991, 1993; Bai et al., 2018]
Ardynia sp. [Dashzeveg, 1991]
Armania asiana Gabunia and Dashzeveg, 1988 [Dashzeveg, 1991]
Prohyracodon meridionalis [Dashzeveg, 1993]
Prohyracodon obrutschewi Dashzeveg, 1996a?Prohyracodon parvum Dashzeveg, 1991
Paraceratheriidae (sensu Qiu and Wang, 2007; Bai et al., 2020b)
Juxia borissiaki (Belyaeva, 1959) [Russell and Zhai, 1987; Lucas and Sobus, 1989; Dashzeveg, 1991; Qiu and Wang, 2007]
Paraceratherium parvum (Chow, 1958) [Russell and Zhai, 1987; Lucas and Sobus, 1989; Qiu and Wang, 2007; This study]
Gen. et sp. indet. [Lucas and Sobus, 1989; Dashzeveg, 1991, 1993; This study]
Amynodontidae
Cadurcodon ardynensis (Osborn, 1923) Kretzoi, 1942 [Russell and Zhai, 1987]
Cadurcodon sp. [Russell and Zhai, 1987]
Cadurcotherium progressus (Gromova, 1954) Wall, 1982 [Russell and Zhai, 1987; Meng and McKenna, 1998]
cf. Zaisanamynodon sp. [Wall, 1989; Lucas and Emry, 1996a; Lucas et al., 1996]
Amynodon sp. [Dashzeveg, 1993]
Amynodontopsis lunanensis (Chow et al., 1964) [Dashzeveg, 1993, 1996a]
Sharamynodon mongoliensis (Osborn, 1936) Kretozi, 1942 [Russell and Zhai, 1987; Dashzeveg, 1993]
Tapiroidea or Rhinocerotoidea
Deperetellidae
Teleolophus magnus Radinsky, 1965 [Russell and Zhai, 1987; Dashzeveg and Hooker, 1997; Tsubamoto et al., 2012b]
cf. Deperetella sp. [Dashzeveg and Devyatkin, 1986; Dashzeveg and Hooker, 1997; Tsubamoto et al., 2005; This study]
Tapiroidea
Helaletidae
Paracolodon inceptus (Matthew and Granger, 1925b) Bai et al., 2017 [Russell and Zhai, 1987]
Paracolodon sp. [Russell and Zhai, 1987; Bai et al., 2017; This study]- 72 -

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

Table 2. Synonym list concerning several fossil vertebrate taxa from the Ergilin Dzo Formation. Selected references
Table 2 each synonymy are indicated in the square bracket at each synonymy. Other synonymies concerning theconcerning
mammalian taxa from the Ergilin Dzo Formation are largely indicated in Russell and Zhai (1987), Dashzeveg (1993), andLopatin (2020).
Testudo insolitus = Geochelone insolitus = Ergilemys insolitus[Matthew and Granger, 1923b; Młynarski, 1968; Ckhikvadze, 1972; Dashzeveg, 1974, 1993; Yanovskaya et al., 1977]
Palaeochelys? elongata = ?Melanochelys elongata
Proergilornis minor = Ergilornis minor[Gilmore, 1931; Ckhikvadze, 1971][Kozlova, 1960; Kurochkin, 1981]

Mesonychidae gen. et sp. indet. in Dashzeveg (1985), Russell and Zhai (1987), and Tsubamoto et al. (2012a)= Mongolestes hadrodens in Dashzeveg (1993) = ?Mongolestes hadrodens[This study]
Metahapalodectes in Dashzeveg (1993) = ?Metahapalodectes sp.

[This study]

Ardynomys vinogradovi? = Ardynomys vinogradovi = Ardynomys chihi = Ardynomys olseni[Wood, 1970; Russell and Zhai, 1987; Dashzeveg, 1993; Wang and Meng, 2009]
Morosomys silentiumis = Morosomys silenti = Ardynomys silentii = Ardynomys silentiumis[Russell and Zhai, 1987; Dashzeveg, 1993]

Desmatolagus vetustus = Procaprolagus vetustus = Desmatolagus gobiensis[Matthew and Granger, 1923a; Burke, 1941; Gureyev, 1960; Sych, 1975; Dashzeveg, 1993]]
Cynodictis? sp. = Amphicyonidae gen. et sp. indet.
[Matthew and Granger, 1923b; Dashzeveg, 1974; Yanovskaya et al., 1977; Russell and Zhai, 1987; Egi et al., 2009, 2016]
Megalopterodon mongoliensis = Hyaenodon mongoliensis[Dashzeveg, 1964, 1993; Lange-Badré and Dashzeveg, 1989; Tsubamoto et al., 2008]
Macropterodon zelenovi Lavrov, 1999 = Hyaenodon gigas[Wang et al., 2005; Morlo and Nagel, 2006; Egi et al., 2007; This study]

Aelurogale mongoliensis = Nimravus intermedius from the Ergilin Dzo Fm in Peigné (2003) = Nimravus mongoliensis[Dashzeveg, 1993; Egi et al., 2016]
Brachyodon gobiensis = Ergilgobia gobiensis = Entelodon gobiensis[Trofimov, 1952, 1958; Brunet, 1979; Russell and Zhai, 1987; Dashzeveg, 1993]
Entelodon orientalis = Entelodon gobiensis[Lucas and Emry, 1996b]

Archaeotherium? sp. in Trofimov (1952) = Entelodon? sp. = Brachyhyops? sp.
[Brunet, 1979; Russell and Zhai, 1987; Dashzeveg, 1993; Tsubamoto et al., 2011a]
Eoentelodon = Brachyhyops[Wang and Qiu, 2002; Tsubamoto et al., 2011a]

Lophiomeryx gobiae = Praetragulus gobiae[Matthew and Granger, 1925b; Russell and Zhai, 1987; Vislobokova, 1998]

cited by Yanovskaya et al. (1977), Ictopidium? sp.
(Tupaiodontinae) and Palaeoscaptor? sp. (Erinaceinae,
Amphechinini).
Anagalida
Only one anagalidan species has been reported.
López-Torres and Fostowicz-Frelik (2018) describeda new genus and species of the Anagalidae, Zofiagale
ergilinensis, from the formation at the Ergilin Dzo
locality on the basis of a mandibular fragment with p3–
m3. This is one of the latest records of the anagalids(López-Torres and Fostowicz-Frelik, 2018).

Mesonychia (= Acreodi)
Two families, two genera, and two species ofmesonychians is recognized here. In their faunal listsof the Ergilin Dzo Formation, Dashzeveg (1985)
and Russell and Zhai (1987) cited an indeterminate
mesonychid. This mesonychid was reidentified as
Mongolestes hadrodens by Dashzeveg (1993) in his
faunal list of the formation. Dashzeveg (1993) cited asmall mesonychian Metahapalodectes (Hapalodectidae)
from the formation. However, these three studies did notprovide figures or any information on the specimens.
Therefore, the existence of the mesonychians in the
Ergilin Dzo fauna had not been confirmed at that- 73 -

T. Tsubamoto et al. 鍔本武久ほか

Table 2
Table 2.—continued.
Embolotherium insigne = Titanodectes ingens? = Embolotherium loucksii = Embolotherium grangeri[Yanovskaya, 1980; Russell and Zhai, 1987; Dashzeveg, 1993; Mihlbachler, 2008]
Embolotherium ergilense = Embolotherium andrewsi[Dashzeveg, 1975, 1993; Russell and Zhai, 1987; Mihlbachler, 2008]
Metatitan relictus = Parabrontops gobiensis = Eubrontotherium clarnoensis[Russell and Zhai, 1987; Mihlbachler et al., 2004; Mihlbachler, 2007, 2008]
Epimanteoceras robustum = cf. Nasamplus progressus[Russell and Zhai, 1987; Mihlbachler, 2008]

Symphysorrhachus brevirostris = Ronzotherium brevirostris[Heissig, 1969; Russell and Zhai, 1987; Meng and McKenna, 1998]

Allacerops sp. (Rhinocerotidae) in Dashzeveg (1991) = cf. Allacerops sp. (Eggysodontidae) [Qiu and Wang, 1999; This study]
Parahyracodon mongoliensis = Ardynia mongoliensis = Ardynia praecox[Radinsky, 1967; Russell and Zhai, 1987; Dashzeveg, 1991, 1993; Bai et al., 2018]
Prohyracodon sp. in Russell and Zhai (1987) = Prohyracodon meridionalis[Dashzeveg, 1993]

Forstercooperia ergiliiensis = Juxia borissiaki[Russell and Zhai, 1987; Lucas and Sobus, 1989; Dashzeveg, 1991; Qiu and Wang, 2007]
Forstercooperia sp. in Dashzeveg (1991) = deleted[This study]

Indricotherium parvum = Paraceratherium parvum[Russell and Zhai, 1987; Lucas and Sobus, 1989; Qiu and Wang, 2007; This study]
Urtinotherium (or Indricotherium) sp. in Dashzeveg (1991, 1993, 1996a) = Paraceratheriidae gen. et sp. indet.
[Lucas and Sobus, 1989; Qiu and Wang, 2007; This study]
Indricothere or amynodont indet. in Lucas (1982) and Russell and Zhai (1987) = deleted
Caenolophus promissus = Amynodon sp.

[This study][Dashzeveg, 1993]

Hypsamynodon progressus = Cadurcotherium progressus
Amynodon lunanensis = Amynodontopsis lunanensis[Wall, 1982; Russell and Zhai, 1987; Meng and McKenna, 1998][Chow et al., 1964; Dashzeveg, 1996a; Wang et al., 2020]

Gigantamynodon = (nomen dubium) = cf. Zaisanamynodon sp.

[Wall, 1989; Lucas and Emry, 1996a; Lucas et al., 1996]

Amynodon giganteus = Gigantamynodon cessator = cf. Zaisanamynodon sp.
[Wall, 1989; Dashzeveg, 1993; Lucas and Emry 1996a; Lucas et al., 1996]
Deperetella sp. in Dashzeveg and Devyatkin (1986) = Deperetella cf. birmanica in Dashzeveg and Hooker (1997) = cf. Deperetella sp.
[Tsubamoto et al., 2005; This study]
Colodon inceptus = Paracolodon inceptus
Colodon sp. = Paracolodon sp.

[Matthew and Granger, 1925b; Radinsky, 1965; Russell and Zhai, 1987; Bai et al., 2017][Yanovskaya et al., 1977; Russell and Zhai, 1987; Bai et al., 2017; This study]

time. Tsubamoto et al. (2012a) described some dental
fossils of a Mongolestes hadrodens-like indeterminate
mesonychid from the formation. Here, we provisionallyrecognize two mesonychians, ?Mongolestes hadrodens
and ?Metahapalodectes sp., in the faunal list of theformation (Table 2).
Cimolesta
Only one cimolestan species has been reported.
Dashzeveg and Russell (1992) described a dyspternine

pantolestid Gobiopithecus khan from the formation at the
Khoer Dzan locality. Tsubamoto et al. (2011b) describedan additional specimen of G. khan discovered from thesame locality. This species is the only representative of
the Dyspterninae recorded in East Asia.
Leptictida
One family (Didymoconidae), two genera, and two
species of leptictidans have been reported (Matthew
and Granger, 1925a; Russell and Zhai, 1987; Lopatin,- 74 -

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

1997). The Didymoconidae are an endemic group in the
Paleogene of Asia (McKenna and Bell, 1997).
Rodentia
Two families, two genera, and four species of rodents
have been recognized (Matthew and Granger, 1925a;
Wood, 1970; Shevyreva, 1972; Yanovskaya et al., 1977;
Russell and Zhai, 1987; Dashzeveg, 1993). Wood (1970)
and Wang and Meng (2009) considered that Ardynomys
chihi is a junior synonym of Ardynomys olseni (Table2). Dashzeveg (1993) considered that Morosomys
silentiumis (= Morosomys silenti) is assigned to thegenus Ardynomys (Table 2).
Lagomorpha
Possible two families, two genera, and four speciesof lagomorphs have been recognized (Matthew andGranger, 1923a; Burke, 1941; Yanovskaya et al.,
1977; Russell and Zhai, 1987; Dashzeveg, 1993).
Gureyev (1960) established a new genus Procaprolagus
for Desmatolagus vetustus. Later, Synch (1975)
synonymized Procaprolagus vetustus (= D. vetustus)
with Desmatolagus gobiensis (Table 2).
Carnivora
Three families, five genera, and five species ofcarnivorans have been recognized (Matthew andGranger, 1923b; Gromova, 1959; Dashzeveg, 1974,
1996b; Yanovskaya et al., 1977; Russell and Zhai, 1987;
Peigné, 2003; Egi et al., 2009, 2016). Egi et al. (2016)
summarized the carnivoran fauna of the formation.
Hyaenodontida (= Hyaenodontidae)
Hyaenodontidans (or hyaenodontids) were reportedby Matthew and Granger (1925a), Gromova (1952a),Dashzeveg (1964, 1974, 1985), Lange-Badré andDashzeveg (1989), Lavrov (1999, 2019), and Tsubamoto
et al. (2008, 2013a). Tsubamoto et al. (2008) reviewed
the hyaenodontid fauna of the formation and recognized
three genera and eight species of the Hyaenodontidae in
the formation: six species of Hyaenodon, Macropterodon
zelenovi, and an indeterminate proviverrine. Morerecently, Lavrov (2019) described additional one species(Hyaenodon pumilus) and one indeterminate species(Hyaenodon cf. chunkhtensis) from the formation.
Here, we recognize two genera and eight species(seven species of Hyaenodon and an indeterminate
proviverrine) of the Hyaenodontidae in the formation(Table 1). Macropterodon zelenovi established by Lavrov(1999) on the basis of a specimen from the formation
appears to be assigned to Hyaenodon gigas as implied
by Wang et al. (2005), Morlo and Nagel (2006), andEgi et al. (2007). The mandibular specimens describedby Lavrov (2019) from the formation as Hyaenodon

cf. chunkhtensis appear to be probably assigned toHyaenodon eminus or Hyaenodon chunkhtensis on thebasis of its size and morphology and do not appear toindicate an additional species in the Ergilin Dzo fauna.
Hyaenodon pumilus established by Lavrov (2019) on
the basis of the fossil from the formation is the smallestsized species of the genus in the formation, although
it should be noted that the sizes of p4 and m1 of H.
pumilus are almost identical to those of H. chunkhtensis.
Artiodactyla (sensu Prothero et al., 2022)
Six families, nine genera, and 13 species ofartiodactyls have been recognized.
Anthracotheriidae: Tsubamoto and Tsogtbaatar(2008) recognized two genera and two species (cf.
Bothriodon sp. and a bunodont and small indeterminate
species) of anthracotheriids. The other studies on theanthracotheriids from the formation are as follows:
Matthew and Granger (1923b), Dashzeveg (1974),
Belyayeva et al. (1974), Yanovskaya et al. (1977),
Devyatkin (1981), Dashzeveg and Devyatkin (1986),
Russell and Zhai (1987), Dashzeveg (1993), andTsubamoto (2010).
En te l o d o n ti d a e : Tsu b a m o t o e t a l . (2011a)
recognized two genera and three species ofentelodontids. The other studies on the entelodontids
from the formation are as follows: Trofimov (1952,1958), Dashzeveg (1965, 1976b), Yanovskaya et al.
(1977), Brunet (1979), Russell and Zhai (1987), Lucasand Emry (1996b), Tsubamoto et al. (2013b), andTsubamoto (2015).
Ruminantia: Four families, five genera, and eightspecies of ruminants have been recognized (Matthew andGranger, 1923b, 1925b; Trofimov, 1957; Yanovskaya etal., 1977; Kurochkin and Dashzeveg, 1979; Yanovskaya,
1980; Russell and Zhai, 1987; Vislobokova, 1998). On
the basis of our preliminary unpublished study on theruminant specimens collected from the formation by the
Hayashibara-Mongolian Paleontological Expeditions(Suzuki et al., 2010; Tsubamoto et al., 2006, 2010), atleast three (large-, medium-, and small-sized) speciesof the Lophiomerycidae, which have a mesiolingually
and widely open trigonid basin on the lower molars,appears to be recognized in the formation. Nevertheless,this information is not reflected in Tbale 1 because it istentative.
Perissodactyla
10 families, 24 genera, and 33 species of
perissodactyls have been recognized.
Brontotheriidae: Four genera and seven speciesof the brontotheriids have been recognized (Osborn,
1925, 1929; Granger and Gregory, 1943; Yanovskaya,
1954, 1976, 1980; Belyayeva et al., 1974; Dashzeveg,- 75 -

T. Tsubamoto et al. 鍔本武久ほか

1975; Yanovskaya et al., 1977; Russell and Zhai, 1987;
Mihlbachler et al., 2004; Mihlbachler, 2007, 2008).
Chalicotherioidea: Two family, two genera, andtwo species of chalicotherioids have been recognized(Matthew and Granger, 1923b; Dashzeveg and
Devyatkin, 1986; Russell and Zhai, 1987; Dashzeveg,1993). However, Eomoropus sp. (Eomoropidae) from theformation was only cited by Dashzeveg and Devyatkin(1986) and Dashzeveg (1993) and is neither describednor figured, and thus the presence of Eomoropus andEomoropidae in the formation has not been confirmed
yet. The genus Eomoropus is recorded mainly in the
middle Eocene, except for this alleged record of the
Ergilin Dzo Formation and the record of the late Eocene
Krabi fauna of Thailand (Lucas and Schoch, 1989;
Ducrocq et al., 2021).
Rhinocerotidae: One genus and three species ofrhinocerotids (= true rhinoceroses) have been recognized(Belyayeva, 1954; Heissig, 1969; Russell and Zhai,
1987; Dashzeveg, 1991, 1993).
Eggysodontidae: Dashzeveg (1991) describedsome specimens of Allacerops sp. from the formation
and assigned it to the Allaceropinae within the
Rhinocerotidae. Currently, Allacerops is assigned to
the Eggysodontidae, which are closely related to truerhinoceroses (Wang et al., 2016, Bai et al., 2020b). Qiu
and Wang (1999) doubted the generic identificationof the specimens from the formation described as
Allacerops sp. by Dashzeveg (1991) because thematerials are very poorly preserved and their sizes aremuch smaller than those of Allacerops.
Hyracodontidae (sensu Bai et al., 2020b): Three
genera and six species of hyracodontids have beenrecognized (Matthew and Granger, 1923b; Gromova,
1952b; Kurochkin and Dashzeveg, 1979; Radinsky,
1967; Russell and Zhai, 1987; Gabunia and Dashzeveg,
1988; Dashzeveg, 1991, 1993, 1996a; Bai et al., 2018).
Paraceratheriidae (sensu Qiu and Wang, 2007;
Bai et al., 2020b): three genera and three species ofparaceratheriids (= huge rhinocerotoids) have beenrecognized (Gabunia and Dashzeveg, 1974; Dashzeveg,
1976a, 1991, 1993; Russell and Zhai, 1987; Lucas andSobus, 1989; Qiu and Wang, 2007). Forstercooperia
sp. was described from the formation by Dashzeveg(1991, p. 51–52). According to Dashzeveg (1991,
table 13), it is based on a right mandibular fragmentwith p2–p4 (a specimen of Paleontologo-stratigraphic
section of the Geological Institute of the Mongolian
Academy of Sciences; specimen number: PSS no. 2127), which is as half as that of Juxia borissiaki (=Forstercooperia ergiliiensis) in size. On the contrary,judging from its drawing by Dashzeveg (1991, fig. 23),
the teeth preserved in the specimen are not p2–p4 but
dp2–dp4 because the central tooth preserved on PSS

no. 21-27 has a mesially elongated trigonid, which is atypical dp3 character of perissodactyls. Therefore, thespecimen might be a juvenile specimen of J. borissiaki.
Consequently, Forstercooperia sp. described byDashzeveg (1991) is deleted from the faunal list of theformation in this paper (Tables 1–2).
It should be noted that a fragmentary dental
specimen described as Hypercoryphodon sp.
(Pantodonta, Coryphodontidae) from the formation by
Kurochkin and Dashzeveg (1979) was assigned to anindeterminate indricothere or amynodont (Perissodactyla,
Rhinocerotoidea) by Lucas (1982). This specimen
appears to be assigned to one of the species of the
Paraceratheriidae or Amynodontidae listed in the Ergilin
Dzo fauna and does not appear to indicate an additional
species in the Ergilin Dzo fauna (Tables 1–2). Therefore,
we delete ‘indricothere or amynodont indet.’, which waslisted in the faunal list of the Ergilin Dzo Formation at
the Khoer Dzan localit by Russell and Zhai (1987), fromthe faunal list of the formation in this paper.
Amynodontidae: Six genera and seven species ofamynodontids have been recognized (Osborn, 1923,
1924, 1936; Gromova, 1954, 1958; Kurochkin andDashzeveg, 1979; Wall, 1982, 1989; Russell and Zhai,
1987; Dashzeveg, 1993, 1996a; Lucas and Emry,
1996a; Lucas et al., 1996). The genus ‘Gigantamynodon
Gromova, 1954’ is now considered to be a nomen
dubium (Table 2; Wall, 1989; Lucas and Emry, 1996a;
Lucas et al., 1996).
Deperetellidae: Two genera and two species ofdeperetellids have been recognized (Russell and Zhai,
1987; Dashzeveg and Devyatkin, 1986; Dashzeveg andHooker, 1997; Tsubamoto et al., 2012b). Dashzeveg and
Devyatkin (1986) cited Deperetella sp. in the formation.
Later, Dashzeveg and Hooker (1997) probably assigned
this taxon to Deperetella cf. birmanica, describing a
fossil specimen. On the other hand, Tsubamoto et al.
(2005) elected a new genus Bahinolophus for Deperetellabirmanica from the middle Eocene Pondaung Formationof Myanmar. Because Bahinolophus is currently endemic
to the Pondaung Formation, here we provisionally cite
the species under discussion discovered from the Ergilin
Dzo Formation as cf. Deperetella sp. (Tables 1–2).
The superfamily to which the Deperetellidae areassigned is currently controversial (Koenigswald et al.,2011; Bai et al., 2019, 2020a, 2020b). This family has
been traditionally assigned to the superfamily Tapiroidea
because of its bilophodont molariforms (Radinsky, 1965;
Bai et al., 2019, 2020a). In contrast, Koenigswald etal. (2011) concluded that this family is assigned to thesuperfamily Rhinocerotoidea because of the presence ofdental cementum in some genera of the family. In thephylogenetic studies by Bai et al. (2020b), on the other
hand, the parsimonious phylogenetic analysis implies- 76 -

Fossil vertebrate fauna of the Ergilin Dzo Formation エルギリン・ゾー層の化石脊椎動物相

the tapiroid affinity of the family, but the Bayesian
phylogenetic analysis implies the rhinocerotid affinity.
Helaletidae: One genus and two species of helaletids
have been recognized (Matthew and Granger, 1925b;
Radinsky, 1965; Yanovskaya et al., 1977; Russell andZhai, 1987; Dashzeveg and Hooker, 1997; Bai et al.,2017). Russell and Zhai (1987) recognized two speciesof the helaletids, Colodon inceptus and Colodon sp.,in the formation. Bai et al. (2017) assigned Colodon
inceptus to the genus Paracolodon. Here, in addition, we
provisionally assign Colodon sp. from the formation to
the genus Paracolodon because the only named speciesof the helaletids from the formation, Paracolodon
inceptus (= C. inceptus), was assigned to the genus
Paracolodon by Bai et al. (2017) (Tables 1–2).
Concluding remarks
The fossil vertebrate fauna of the Ergilin Dzo
Formation currently consists of five classes (theOsteichthyes, Amphibia, Reptilia, Ave, and Mammalia),
22 orders, 49 families, 77 genera, and 104 species,
and its fossil mammalian fauna consists of 11 orders(the Eulipotyphla, Anagalida, Mesonychia, Cimolesta,
Leptictida, Rodentia, Lagomorpha, Carnivora,Hyaenodontida, Artiodactyla, and Perissodactyla),
32 families, 56 genera, and 81 species (Table 1). The
recent discovery of a crocodyliform tooth by Iijima etal. (2019) implies that southeastern Mongolia probably
fulfilled thermal requirements of crocodyliforms during
the late Eocene. In terms of the species diversity,
perissodactyls are dominant in the fauna (Table 1; 33
perissodactyl species among the 81 mammalian species
and the 104 vertebrate species), supporting that the
Ergilian Asian Land Mammal Age is correlated to thelate Eocene (Ducrocq, 1993; Ducrocq et al., 1995; Mengand McKenna, 1998; Tsubamoto et al., 2004, 2008). In
terms of the collected specimens, the brontotheriid andrhinocerotid perissodactyls and ruminant artiodactyls
are dominant among the vertebrate taxa of the formation(e.g., Tsubamoto et al., 2010). Compared with theearly Oligocene mammalian faunas of northern Asia,
taxonomic diversity and collected specimen numbersof the rodents, lagomorphs, and carnivorans appear
to be low in the Ergilin Dzo mammalian fauna on thebasis of the currently available evidence. In contrast,
the perissodactyls in the Ergilin Dzo fauna are morecommon in terms of the relative abundance of thecollected specimens as well as the taxonomic diversity
than those of the early Oligocene faunas of northern
Asia. The taxonomic diversity of the Hyaenodontida
in the Ergilin Dzo fauna is as high as those of the early
Oligocene faunas of northern Asia (Tsubamoto et al.,2008). However, the relative numbers of the collectedhyaenodontid specimens in the Ergilin Dzo fauna arehigher than those in the early Oligocene faunas ofnorthern Asia, on the basis of the specimens collected by
the Hayashibara-Mongolian Paleontological Expeditionsin 2004, 2008, and 2010 (e.g., Suzuki et al., 2010;
Tsubamoto et al., 2006, 2010).
Acknowledgments
We are grateful to Tamotsu Zako (Ehime University,
Matsuyama, Japan) for inviting us to write this paper for
Memoirs of the Faculty of Science, Ehime University.
This manuscript was improved by the critical reviewsof Naoto Handa (Tokyo Metropolitan University,
Hachioji, Japan) and Nao Kusuhashi (Ehime University,
Matsuyama, Japan). This research was supported
by JSPS KAKENHI Grant Numbers 15K05330 and
18H01327 to N. Egi.
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