Orientolophus
| Orientolophus | ||||||||||||
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Lower jaw and teeth of Orientolophus , 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 | ||||||||||||
| Orientolophus | ||||||||||||
| Ting , 1993 | ||||||||||||
Orientolophus is an extinct genus of the very early odd- toed ungulates . Their fossil record is based on a single upper jaw fragment from northwestern China . This dates to the transition from the Paleocene to the Eocene and is therefore around 56 million years old. The genus is one of the earliest records of the odd ungulate. From a systematic point of view, a classification in the line of development of today's rhinos and tapirs is likely. The name of the form took place in 1993, but it was based on a more extensive fossil record, some of which included several species. Only one species is recognized today.
features
Orientolophus is a very early representative of the odd ungulate. There is currently only a single upper jaw fragment that can be assigned to the genus. In addition to the last milk premolar, this also contains the first two molars . In agreement with other early unpaired ungulates, the molars had a humped ( bunodonte ) chewing surface with four main cusps arranged in pairs (para and metaconus on the cheek side and hypoconus and protoconus on the tongue side; in relation to the upper molars). With Orientolophus the humps had a steep conical shape. In addition, the paraconus towered over the metaconus, while both cusps on the tongue side were about the same size, but generally did not reach the height of the cusps on the cheek side. Between each pair of cusps, enamel ridges ran across the longitudinal axis of the teeth so that the teeth were given a bilophodontic character (with two ridges). The Lophodontia was more developed in Orientolophus than in Cymbalophus , Sifrhippus and Erihippus , forms which are associated with the earliest horses . However, it did not reach the level of expression found in Karagalax or Cambaylophus , which in turn belong to the tapir - rhino kinship complex. There are also individual further features on the molars that separate Orientolophus from the other early odd- toed ungulates. The first molar had a more rectangular shape than is known from Cymbalophus , for example . Compared to Erihippus , the Paraconus was more clearly asymmetrical in shape with a flattened half on the cheek and a flared half on the tongue side. Between the main bumps of a groin there were smaller minor humps, those on the tooth cheek side were relatively smaller than, for example, in the other horse-related species mentioned. On the other hand, in Karagalax or Cambaylophus, various side humps were extremely weak or not at all developed. One of the side bumps that Paraconul stood at Orientolophus addition, closer to the Protoconus than at Paraconus. On the tongue side there was a cingulum, a low bulge of tooth enamel, which was confined to the middle section of the tooth. In contrast to Cymbalophus , the cingulum was fully developed on the cheek side of the tooth in the area of the paraconus. The length of the two anterior molars was 7 mm each, the width 8 mm each.
Fossil finds
The so far only find of Orientolophus , a hardly weathered upper jaw fragment, came to light in the mid-1980s in the Lingcha formation south of Lingcha in the Hengyang Basin in the southern Chinese province of Hunan . The Hengyang Basin extends over an area of around 5200 km² and is known for its wealth of paleogenic fossils. The first fossil remains were published as early as the mid-1940s, when they were considered to be the oldest mammalian remains in southern China. The finds are stored in the so-called Red beds (also called Hengyang Red beds or Hengyang sandstones ), which are widespread in the Hengyang Basin. Within the sediment sequence , two stratigraphically separated fauna horizons can be distinguished: from a geological point of view, the lower one belongs to the Limuping Formation and, in addition to numerous reptiles, also produced finds of the Pantodonta , an ancient branch of the higher mammals . 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 . According to isotope examinations and analyzes of magnetostratigraphy , a position in the transition area from the Paleocene to the Eocene around 56 million years ago is probable for the upper find horizon (locally stratigraphically called Bumnabium ). The lower one dates to the end of the Paleocene (locally stratigraphically called Gashatum ).
Systematics
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Possible family relationship of Orientophus within the early odd- toed ungulates according to Bai et al. 2018
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Orientolophus is a genus from the order of the odd ungulate . Within the order, the genus belongs to a very early branch related to the tapirs and rhinos . The tapirs and rhinos including their immediate (extinct) close relatives together form the higher taxon of the Ceratomorpha or, including the also extinct Ancylopoda (such as the Chalicotheria ), the Tapiromorpha . Opposite it are the Hippomorpha with today's horses and the extinct Brontotheriidae . According to today's perspective, Orientolophus is classified more in the stem group of the Ceratomorpha with possibly closer connections to Karagalax and Cambaylophus . Both are primeval tapiromorpha, largely from southern Asia, which are documented on the one hand from the Mami-Khel formation in northern Pakistan and on the other hand from the Cambay Shale formation in western India. A Lower Oocene origin is estimated for each rock unit. A more precise assignment of Orientolophus to a specific family has not yet been made.
The genus Orientolophus was first described scientifically in 1993 by Ting Suyin . The researcher used the material found in the Lingcha formation in the southern Chinese province of Hunan . The holotype (specimen number IVPP V-5789) is the only known find so far, a fragment of the right upper jaw with the preserved posterior milk premolar and the first two molars . The generic name is derived from the Latin word orient for "east" or "Asia" and from the Greek word λόφος ( lophos ) for "hill" or "ridge". In her work, Ting originally assigned two further fossil finds to the genus in addition to the right upper jaw fragment, one left upper and one lower jaw fragment, whereby she assumed that the two maxillary parts belong to one individual. A quarter of a century later, a group of researchers led by Bai Bin ruled out the two left jaw fragments from Orientolophus after a renewed assessment of the Lingcha finds and re-described them under the name Erihippus . Different tooth features were named as arguments for this step. Erihippus is considered to be a very early representative of the horses . Ting himself saw Orientolophus as a possible member of the Isectolophidae in 1993 . This is a group of primeval odd ungulates, which, within the Tapiromorpha , are compared to the Ceratomorpha (tapir-rhinoceros complex) and the Ancylopoda as a sister group , but are considered paraphyletic . Other authors later saw this classification more critically, due to the limited fossil material, Orientolophus was referred to the Tapiromorpha or the Hippomorpha depending on the weighting of the characteristics. However, several of the assessments made on the systematic position of Orientolophus also related to the lower jaw teeth , so that the statements are to be regarded as problematic from today's perspective. After the re-evaluation of the finds in 2018, Bai and colleagues therefore only classified the genus in the basic group of Ceratomorpha.
In addition to the generic name, Ting also introduced the species O. hengdongensis in 1993 , the species name refers to the district of Hengdong , where the exact find location is. The researcher suspected, however, that Hyracotherium gabuniai , introduced in 1979 by Demberelyin Dashzeveg on the basis of some isolated milk teeth from the Naran-Bulak formation in southern Mongolia , could also belong to Orientolophus , but limited this due to the small amount of finds. She later placed the Homogalax namadicus from the same Mongolian site, also created by Dashzeveg with reference to individual teeth, to Orientolophus . Additional tooth finds from the Naran-Bulak Formation then led in 2004 to the reference of the two critical species to the genus Protomoropus , newly established in 2004 , which is close to the Chalicotheria. As a result of this restructuring, only the type species remained in the genus Orientolophus , which, after the revaluation of the finds from the type locality in the Lingcha formation, is only represented by a fossil find.
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
- Suyin Ting: A preliminary report on an Early Eocene mammalian fauna from Hengdong, Hunan Province, China. Kaupia 3, 1993, pp. 201-207
Individual evidence
- ↑ a b c M. C. Maas, ST Hussain, JJM Leiders and JGM Thewissen: A new isectolophid tapiromorph (Perissodactyla, Mammalia) from the Early Eocene of Pakistan. Journal of Paleontology 75 (2), 2001, pp. 407-417
- ↑ a b c Vivesh Kapur and Sunil Bajpai: Oldest South Asian tapiromorph (Perissodactyla, Mammalia) from the Cambay Shale Formation, western India, with comments on its phylogenetic position and biogeographic implications. The Palaeobotanist 64, 2015, pp. 95-103
- ↑ a b c d e Suyin Ting: A preliminary report on an Early Eocene mammalian fauna from Hengdong, Hunan Province, China. Kaupia 3, 1993, pp. 201-207
- ↑ a b c d e f g 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
- ↑ 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
- ↑ a b J. J. Hooker and D. Dashzeveg: The origin of chalicotheres (Perissodactyla, Mammalia). Palaeontology 47 (6), 2004, pp. 1363-1386
- ↑ Spencer George Lucas and Peter E. Kondrashov: Early Eocene (Bumbanian) perissodactyls from Mongolia and their biochronological significance. New Mexico Museum of Natural History and Science Bulletin 26, 2004, pp. 215-220
- ^ Luke T. Holbrook and Joshua Lapergola: A new genus of Perissodactyl (Mammalia) from the Bridgerian of Wyoming, with comments on basal Perissodactyl phylogeny. Journal of Vertebrate Paleontology 31 (4), 2011, pp. 895-901
- ^ Pieter Missiaen and Philip D. Gingerich: New Early Eocene Tapiromorph Perissodactyls from the Ghazij Formation of Pakistan, with Implications for Mammalian Biochronology in Asia. Acta Palaeontologica Polonica 57 (1), 2012, pp. 21-34
- ↑ Bin Bai, Yuanqing Wang, Jin Meng, Qian Li and Xun Jin: New Early Eocene Basal tapiromorph from Southern China and Its Phylogenetic Implications. PlosONE 9 (10), 2014, p. E110806
- ↑ Suyin Ting: Paleocene and early Eocene country mammal ages of Asia. Bulletin of the Carnegie Museum of Natural History 34, 1998, pp. 124–147 ( [1] )
