Erihippus
| Erihippus | ||||||||||||
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Lower (left) and upper jaw fragments (right) of Erihippus ; the lower jaw forms the holotype |
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| Temporal occurrence | ||||||||||||
| Lower Eocene | ||||||||||||
| 56 to 52 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Erihippus | ||||||||||||
| Bai , Wang & Meng , 2018 | ||||||||||||
Erihippus is a genus of the horse family. Fossil finds come from eastern Asia and are currently composed of a few remains of pine. These date to the transition from the Paleocene to the Eocene around 56 million years ago. This makes Erihippus one of the earliest records of the entire group,along with some North American forms such as Sifrhippus , and it is also the oldest record in Eurasia todate. Differences between the two genera are mainly found in individual tooth features. The Erihippus finds were firstassigned toanother early member of the odd ungulate . In 2018, the fossil remains were reassessed and the reference to the early horses was made.
features
The genus Erihippus is based on a few remains of teeth. It is a very primitive representative of the horses , but so far only the teeth have been described in more detail. In addition to a milk premolar, the permanent molars are mainly known of this. As with other early horse representatives, these had clearly low ( brachyodonte ) tooth crowns and a chewing surface pattern consisting of characteristic cusps, the latter is known as bunodont . Individual ridges were formed between the cusps on the cheek and tongue side, which in turn gave the teeth a certain lophodontia. The front molars each had four main cusps (para- and metaconus on the cheek side and hypoconus and protoconus on the tongue side; based on the upper molars). On the cheek side of the upper molars, the metaconus was clearly offset inward in relation to the paraconus. Both humps were in accordance with Sifrhippus , but different from Orientolophus , clearly separated. On the tongue side, the hypoconus rose offset to the rear compared to the opposite metaconus, while the protoconus was in a line with the paraconus. Individual small bumps were still formed within the transverse ridges, but in some early Tapiromorpha such as Orientolophus these were partially reduced. In contrast to Sifrhippus , Erihippus lacked a tongue- sided cingulum, a low bulge of tooth enamel. The cingula were found on the other sides of the tooth. The cusps of the lower molars were clearly conical in shape. The protoconid and the metaconid were close together, the latter was slightly shifted backwards. It was similar with the hypoconid and the entoconid. In contrast to some other early odd-toed ungulates, the metaconide was not doubled. Cingulids existed here only on the front and back of the tooth. The third lower molar had six cusps, the hypoconulid was formed here relatively large. The second upper molar was 6.9 mm long and 7.6 mm wide. The corresponding dimensions of the second lower molar were 7.5 mm and 5 mm.
Fossil finds
So far, only a few finds of Erihippus are known, these are an upper and a lower jaw fragment. Both specimens are considered to belong to one individual due to similar signs of weathering and wear. These were recovered in the mid-1980s from the Lingcha Formation south of Lingcha in the Hengyang Basin in the southern Chinese province of Hunan . The Hengyang Basin covers an area of around 5200 km² and is known for its paleogenic fossil wealth. The first fossil remains were published as early as the mid-1940s and were considered the oldest mammalian remains in southern China at the time. The main area of discovery of the fossils includes the so-called Red beds (also called Hengyang Red beds or Hengyang sandstones ). They are widespread in the Hengyang Basin. Two stratigraphically separated fauna horizons can be distinguished within the Red beds : the lower one contains numerous reptiles as well as finds of the Pantodonta , an ancient branch of the higher mammals , and from a geological point of view belongs to the Limuping Formation . The upper one is assigned to the Lingcha Formation and includes numerous groups of mammals, including insectivores , rodents , primates , predators , ungulates and various extinct lines such as the Leptictida or Cimolesta . With the help of isotope studies and analyzes of magnetostratigraphy , the upper find horizon in the transition area from the Paleocene to the Eocene was dated around 56 million years ago (locally stratigraphically Bumnabium ). The lower one, however, belongs to the end of the Paleocene (local stratigraphic Gashatum ).
Systematics
Erihippus is a genus of the family of Equidae which also today's modern einhufigen horses includes. In addition to some North American representatives, Erihippus is one of the most original representatives of the group. This appeared relatively suddenly in the transition from the Paleocene to the Eocene . However, the systematics, especially of the earliest representatives of the Equidae, is still much in discussion, as there is some overlap with the Palaeotheriidae , to which the genera Palaeotherium and Hyracotherium belong. Both groups are in a sister group relationship to one another and together form the superfamily of the Equoidea and the intermediate order of the Hippomorpha, which in turn contrasts with the Ceratomorpha with today's tapirs and rhinos within the odd- toed ungulate systematics . Within the Equidae shows Erihippus a close relationship with the North American sifrhippus , which came early in similar appearance. Erihippus' reference to the Equidae shifts the earliest occurrence of the entire group in Eurasia to the transition period from the Paleocene to the Eocene.
The first scientific description of Erihippus was presented in 2018 by a research group led by Bai Bin . The jaw fragments from the Lingcha formation in the southern Chinese province of Hunan served as the basis for this . Among these, a lower jaw with the three preserved molars represents the holotype (specimen number IVPP V-5789.1). The name Erihippus is of Greek origin, it is based on the words eρυ ( eri ) for "old" and ἵππος ( hippos ) for "horse", the latter is a frequently used addition to the name of the horse species. Bai and colleagues introduced E. tingae, a species that they named in honor of Ting Suyin . Ting had already presented the fossil material from Erihippus in a short essay in 1993, but placed it on the genus Orientolophus, which she had created at the time . Orientolophus is a primitive representative of the odd ungulate, whose systematic position is partly under discussion, but the shape may be closer to today's tapirs and rhinos than to horses. In 2018, the research group around Bai then recognized deviations in the tooth structure from some of the findings of the fossil metric that had been associated with Orientolophus . Therefore they separated them out of the genus and described them under the scientific name Erihippus .
literature
- Bin Bai, Yuan-Qing Wang and Jin Meng: The divergence and dispersal of early perissodactyls as evidenced by early Eocene equids from Asia. Communications Biology 1, 2018, p. 115 doi: 10.1038 / s42003-018-0116-5
Individual evidence
- ↑ a b c d e Bin Bai, Yuan-Qing Wang and Jin Meng: The divergence and dispersal of early perissodactyls as evidenced by early Eocene equids from Asia. Communications Biology 1, 2018, p. 115 doi: 10.1038 / s42003-018-0116-5
- ↑ a b Suyin Ting: A preliminary report on an Early Eocene mammalian fauna from Hengdong, Hunan Province, China. Kaupia 3, 1993, pp. 201-207
- ↑ Chung-Chien Young: Note on the first Eocene mammal from South China. American Museum Novitates 1268, 1944, pp. 1-3
- ↑ Suyin Ting, Gabriel J. Bowen, Paul L. Koch, William C. Clyde, Yuanqing Wang, Yuan Wang and Malcolm C. McKenna: Biostratigraphic, chemostratigraphic, and magnetostratigraphic study across the Paleocene-Eocene boundary in the Hengyang basin, Hunan, China. In: Scott L. Wing, Philip D. Gingerich, Birger Schmitz and Ellen Thomas (eds.): Causes and consequences of globally warm climates in the early Paleogene. Geological Society of America Special Papers 369, 2003, pp. 521-535
- ↑ David J. Froehlich: Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society, 134, 2002, pp. 141-256
- ^ Luke T. Holbrook: Comparative osteology of early Tertiary tapiromorphs (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 132, 2001, pp. 1-54
