AMYNODONTIDAE SCOTT AND OSBORN, 1883

Bai, Bin, Wang, Yuan-Qing, Li, Qian, Wang, Hai-Bing, Mao, Fang-Yuan, Gong, Yan-Xin & Meng, Jin, 2018, Biostratigraphy and Diversity of Paleogene Perissodactyls from the Erlian Basin of Inner Mongolia, China, American Museum Novitates 2018 (3914), pp. 1-60 : 12-14

AMYNODONTIDAE SCOTT AND OSBORN, 1883

Rostriamynodon Wall and Manning, 1986

Only one species of Rostriamynodon , R. grangeri ( fig. 2E ), is known from the “Irdin Manha Formation,” 2 mi east of Camp Margetts ( Wall and Manning, 1986). The species is known from a complete skull and mandible (AMNH FM 107635), and likely was unearthed from the Irdin Manha Formation, rather than the Arshanto Formation ( Bai et al., 2017). Rostriamynodon grangeri was considered to be a primitive member of the amynodontids ( Wall and Manning, 1986).

Caenolophus Matthew and Granger, 1925b

Two species of Caenolophus , C. promissus and C. obliquus , have been named from the Shara Murun Formation at Ula Usu ( Matthew and Granger, 1925b; Radinsky, 1967). Caenolophus promissus is known from a maxilla with P3–M3 (AMNH FM 20297) and a mandible with m1–2 (AMNH FM 20304) ( Matthew and Granger, 1925b). Caenolophus obliquus is known from a maxilla with DP3–DP4, P3–M2 (AMNH FM 20296) ( Matthew and Granger, 1925b). Caenolophus was originally assigned to the Hyracodontidae ( Matthew and Granger, 1925b) , but Radinsky (1967) suggested its affinity with the amynodontids.

Sharamynodon Osborn, 1936

Osborn (1936) briefly described a nearly complete skeleton of “ Amynodon ” monogoliensis (AMNH FM 20278) from the Shara Murun Formation at Ula Usu ( fig. 2F ). Kretzoi (1942) considered the species as a new genus, Sharamynodon . Xu (1966) reported additional material of the species from the same horizon and locality. Wall (1981) also referred a partial skeleton (AMNH FM 21601) to the species from the Shara Murun Formation (gray beds), 4 mi north of Baron Sog Lamasery.

Sianodon Xu, 1965

Only one species of Sianodon , S. ulausuensis , has been reported from the Shara Murun Formation at Ula Usu ( Xu, 1966). The species is known from a nearly complete skull (IVPP V 3215). Sianodon ulausuensis is more primitive than S. bahoensis in having a relatively longer facial part and three upper incisors. Xu (1966) also assigned a maxilla with M2–3 (IVPP V 3221) to Sianodon sp. from the same horizon and locality.

Lushiamynodon Chow and Xu, 1965

Only one species of Lushiamynodon , L. sharamurenensis , has been reported from the Shara Murun Formation at Ula Usu ( Xu, 1966). The species is known from an incomplete juvenile cranium with DP1–M1 (IVPP V 2892), a juvenile mandible (IVPP V 2892.1), a posterior part of the cranium (IVPP V 2892.2), and some postcraninal material ( Xu, 1966). A mandible with m2–3 (IVPP V 3217) of L. sharamurenensis also has been reported from the “same horizon” at “Ulan Shireh Obo,” which was situated about 30 km northeast of Ula Usu. The so-called “Ulan Shireh Obo” (= Ulan Shireh) is located in the North Mesa, north of Tukhum Sumu, with the deposits of Ulan Shireh Formation roughly equivalent to the Irdin Manha Formation ( Chow and Rozhdestvensky, 1960; Wang et al., 2012).

Gigantamynodon Gromova, 1954

Only one species of Gigantamynodon , G. promisus , has been reported from the Shara Murun Formation at Ula Usu ( Xu, 1966). The species is known from a mandible with p2–m3 (IVPP V 3218) and many postcranial specimens (IVPP V 3218.1-28). However, Wall (1989) considered Gigantamynodon a nomen dubium (Lucas and Emry, 1996; Lucas et al., 1996).

Cadurcodon Kretzoi, 1942

Two species of Cadurcodon , C. matthewi and C. houldjinensis , have been reported from the Erlian Basin ( Wall, 1981; Wang et al., 2009). The type species of Cadurcodon matthewi (AMNH FM 26029) was found in the “Ulan Gochu beds” at Jhama Obo ( Wall, 1981). Cadurcodon matthewi is considered to be more primitive than C. ardynensis ( Wall, 1981) . Cadurcodon houldjinensis , known mainly from isolated teeth (e.g., EMM 0126), was discovered from the Houldjin Formation at Houldjin and near the Erenhot Railway Station (Wang et al., 2009). Wang et al. (2009) considered that three specimens of “ Cadurcotherium ” sp. (AMNH FM 19183, field no. 36) from the Houldjin Formation, 5 mi south of Iren Dabasu ( Matthew and Granger, 1923a) should be assigned to C. houldjinensis (m2) or C. ardynensis (P4 and M1/2).

Xu (1966) referred a maxilla with P2–3 (IVPP V 3222), a right m1 (IVPP V 3222.1), and a canine (IVPP V 3222.2) to Cadurcodon sp. from the Urtyn Obo Formation at Urtyn Obo (= Erden Obo). However, their specific stratigraphic horizons are uncertain.

Amynodontopsis Stock, 1933

Two species of Amynodontopsis , A. parvidens and A. tholos , were named by Wall (1981) from the Erlian Basin. The type of A. parvidens , known from a skull and mandible (AMNH FM 26043), was collected from the top of the “Lower White” at Erden Obo. Wall (1981) recognized two different sizes of the species: the small-size group includes AMNH FM 26045, 26046, and 26050; and the large-size group includes AMNH FM 26041, 26042, 26043, and 26051. He attributed the size differences to sexual dimorphism, because all the specimens were collected from the base of the “Middle Red” at Erden Obo, with the exception of AMNH FM 26046 that was recorded from the “Middle Red” bed and AMNH FM 26043 from top of the “Lower White” at Erden Obo. Wall (1981) also referred AMNH FM 26044 from the base of “Middle Red” at Erden Obo to A. parvidens . The species also is known from the following horizons and localities: AMNH 21599 from the base of upper red bed (Ulan Gochu Formation) 4 mi north of Baron Sog Lamasery; AMNH FM 26053 from the “Ulan Gochu beds” at Nom Khong Obo; AMNH 26178 possibly from the “Baron Sog bed” south of Jhama Obo; and AMNH FM 26038 from the “Ulan Gochu Formation” at Jhama Obo ( Wall, 1981).

The holotype of Amynodontopsis tholos , comprising a skull and a lower jaw (AMNH FM 26035), was collected from the top of gray beds (= “Ulan Gochu”) at Ulan Shireh Obo (= Ganggan Obo on East Mesa) ( Wall, 1981). The distribution of the species also includes the “Ulan Gochu beds,” south of Jhama Obo (AMNH FM 26031), and the “Lower White or Gray (pink)” at Nom Khong Obo (AMNH FM 26054, 26055, and 26057). Wall (1981) assigned a mandible (AMNH FM 26053, field no. 786) to A. tholos . However, it contradicts the fact that the specimen is also listed as A. parvidens , as discussed above. The specific stratigraphic horizon where AMNH FM 26053 was collected is uncertain, and is probably below the “Upper Red” bed.

Zaisanamynodon Belyaeva, 1971

Lucas et al. (1996) referred some CAE specimens to Z. borisovi from the Erlian Basin. The species is known from the “Middle White” (AMNH FM 26052, 26049) at Erden Obo, the Baron Sog Formation at Baron Sog Mesa (AMNH FM 21602), the “Ulan Gochu beds” at Ulan Shireh Obo (= Ganggan Obo) (AMNH FM 26034), and the “Houldjin gravels” at Camp Margetts. Lucas et al. (1996) further referred a symphysis with i2 and c (AMNH FM 26170) to Z. borisovi from the “Baron Sog Formation” at Erden Obo.

Figures

FIG. 2. Cranial and mandibular reconstructions of typical Eocene perissodactyls from the Erlian Basin of Inner Mongolia, China. tapiroid A, Lophialetes expeditus; B, Paracolodon fissus; paraceratheriid C, Pappaceras meiomenus; D, Juxia sharamurenensis; amynodontid E, Rostriamynodon grangeri; F, Sharamynodon mongoliensis; brontotheriid G, Protitan grangeri; H, Embolotherium andrewsi. Scale bar equals 10 cm.