"Amynodon" sinensis
Extinct species of mammal
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"Amynodon" sinensis is a species of amynodont, an extinct family of odd-toed ungulates (perissodactyls) related to modern rhinoceroses. "A". sinensis is known from relatively fragmentary fossil material from the Late Eocene of China. The species was originally described as a species of Amynodon, but phylogenetic analyses recover it outside of that genus, which is generally restricted to North American fossils. "A". sinensis has also been classified in the genus Sianodon, as Sianodon sinensis.
| "Amynodon" sinensis Temporal range: | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Perissodactyla |
| Superfamily: | Rhinocerotoidea |
| Family: | †Amynodontidae |
| Species: | †"Amynodon" sinensis |
| Binomial name | |
| "Amynodon" sinensis | |
| Synonyms | |
Despite the poor material, "A". sinensis occupies an important phylogenetic position as one of the most primitive amynodonts known from Asia. "A". sinensis was the smallest known amynodont, estimated to have weighed just 127 kilograms (280 lbs).
History of research
Amynodon sinensis was described by Otto Zdansky in 1930,[1] based on fossils found in Late Eocene strata in Henan, China.[2] The relatively fragmentary fossils[2] included two associated lower jaw fragments (the type specimen), fragments of both right and left upper jaws, and isolated teeth.[1] Zdansky compared the fossils to the amynodont taxa known in his time, and referred them to the genus Amynodon.[1] An additional lower jaw, with two teeth preserved (M1 and M3; the first and third molar), was later discovered at the same locality as Zdansky's type specimen and was referred to A. sinensis by Yang Zhongjian in 1937.[3]
In 1965, Zhou Mingzhen and Xu Yu-Xuan referred A. sinensis to the genus Sianodon, as S. sinensis.[4] Zhou and Xu revised the diagnosis of S. sinensis and referred additional fossil material to the species, including two fossils from the same locality as Zdansky's type specimen: a right maxilla preserving P4–M3 (the fourth premolar to third molar; V.3018), a lower jaw fragment that preserves M2 and M3 (V.3018.1).[4] Additional fossils reported by Zhou and Xu included V.3019 (an upper jaw fragment preserving P4–M3 from Yuanqu, Shanxi) and V.3024 (an upper jaw fragment preserving M1–M3 from Tungchang, a village in Xichuan, Henan). V.3024 is from the same locality as the type specimens of fellow amynodonts Lushiamynodon obesus and Sianodon chiyuanensis.[4] Zhou and Xu noted that the assignment of many fossils to S. sinensis was provisional, as the fossils show considerably variation in their dental features and belong to at least two late Eocene faunal zones.[4]
In 2017, Alexander Averianov, Igor Danilov, Jin Jianhua, and Wang Yingyong suggested that Sianodon as traditionally understood is not a valid genus. S. sinensis was found separate from other species in a phylogenetic analysis, and Averianov et al. referred to it under its original combination, albeit with quotation marks: "Amynodon" sinensis.[2] The genus Amynodon as currently understood is generally restricted to fossils found in North America.[5] Averianov et al. further suggested that three fragmentary species of Sianodon found in Henan—S. chiyuanensis, S. honanensis, and S. mienchiensis—could represent primitive amynodonts and possibly the same animal as "A". sinensis.[2]
Description
Classification
"A". sinensis occupies an important phylogenetic position as one of the most primitive amynodonts known from Asia.[2] The cladogram below presents amynodont relations per the phylogenetic analysis of Averianov et al.:[2]
| Amynodontidae |
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