HELALETIDAE OSBORN, 1892

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 : 8

HELALETIDAE OSBORN, 1892

Heptodon Cope, 1882

Only one species of Heptodon , H. minimus , is known from the Arshanto Formation at Huheboerhe ( Qi, 1987). This species is represented by several mandibles and an isolated m3, and it is characterized by the presence of p1 and relatively distinct cristid obliqua on the lower molars ( Qi, 1987).

Desmatotherium Scott, 1883

Desmatotherium mongoliense was first reported by Osborn (1923b) from the Irdin Manha Formation on the Irdin Manha escarpment. The species has been referred to Helaletes and Irdinolophus ( Radinsky, 1965; Dashzeveg and Hooker, 1997), but recent study confirms its affinity with Desmatotherium ( Bai et al., 2017) . The species has been reported from the Irdin Manha Formation on the Irdin Manha escarpment, Duheminboerhe, Huheboerhe, and Chaganboerhe ( Bai et al., 2017).

Paracolodon Matthew and Granger, 1925a

Paracolodon (= Desmatotherium ) fissus was first reported by Matthew and Granger (1925c) from the Irdin Manha Formation at Camp Margetts ( fig. 2B ). The species was assigned originally to Desmatotherium , and then referred to Helaletes or Colodon ( Radinsky, 1965; Dashzeveg and Hooker, 1997). Based on a partial skull, Bai et al. (2017) recently assigned the species to Paracolodon , suggesting its ancestral relationship with P. inceptus from the Ergilin of Mongolia. Paracolodon fissus is present in the Irdin Manha Formation at Duheminboerhe and Daoteyin Obo.

Qi (1987) named a new species Helaletes medius based mainly on a fragmentary mandible with p4–m3 (IVPP V 5729) from the Arshanto Formation, Wulanboerhe. Bai et al. (2017) questioned the assignment of this species to Helaletes , and noted some similarities with Schlosseria .

Qi (1987) named a new species Homogalax reliquius based on two m 3 specimens (IVPP V 5747, 5748) from Huheboerhe in the Arshanto Formation. The species was assigned initially to Homogalax on the basis of their robust hypoconulids ( Qi, 1987). However, the lack of a “metastylid” and the presence of a relatively long trigonid suggest that the species is more similar to Isectolophus than to Homogalax . Furthermore, Lucas et al. (2003) considered Homogalax reliquius to be a junior synonym of Isectolophus latidens .

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.