Gobiatherium
| Gobiatherium | ||||||||||||
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Skull of Gobiatherium , holotype |
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| Temporal occurrence | ||||||||||||
| Lower to Middle Eocene ( Arshantan ) | ||||||||||||
| 52 to 46.5 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Gobiatherium | ||||||||||||
| Osborn & Granger 1932 | ||||||||||||
| Art | ||||||||||||
Gobiatherium is a genus of Dinocerata - an extinct group of mammals - from the Lower to Middle Eocene (52 to 46 million years ago) of East and Central Asia . Within this group, the family of Uintatheriidae assigned, so it is with uintatherium and eobasileus closely related. These herbivores belong to the first large forms after the extinction of the dinosaurs . Particularly characteristic features of Gobiatherium were the extremely flat skull and the strongly rounded nose with two small bony horns.
features
Gobiatherium was a large representative of the Uintatheria, but it did not reach the size of its closest relatives Uintatherium and Eobasileus . Overall, it had a generally slimmer build, but the predominant fossil material of this genus consists of skull and dentition remains. The skull of Gobiatherium was up to 68 cm long and was thus shorter than that of Uintatherium or Eobasileus . It was characteristically extremely flat and only reached a height of 8 cm above the premolars , while the zygomatic arches protruded like a wedge and had a maximum distance of 40 cm. On the outermost arch tips there were also prominent bony outgrowths, so that the arches also appeared widened outwards. The occiput was slightly elongated backwards and thus had an acute angle when viewed from the side. In contrast to Uintatherium or Eobasileus , the skull had no very distinct horn formations typical of developed Uintatheria , only two slight osseous swellings were found on the parietal bones, while no such formations occurred in the central skull area. The most striking feature of Gobiatherium , however, was the nasal bone , which had an arched, rounded shape, as a result of which the skull reached a total height of 17 cm in this area. The nasal bone was clearly bent forward at the anterior end and here fused with the medial jawbone through ossification of the nasal septum . Some skulls also had two small swellings of bones similar to those on the parietal bones on the rounded nasal bone. The entire construction of the front muzzle area with the strongly rounded nasal bone is unique among the Dinocerata.
The lower jaw, which was up to 48 cm long, was relatively slim. Compared to Uintatherium, the jawbone was rather low with a height of around 7 cm, and the symphysis had a spatula-shaped structure. Compared to his relatives had gobiatherium addition to the generally reduced upper incisors also no upper canine more, the dental formula was characterized: . Incisors were only found in the lower jaw, as in the other Uintatheria, were rather small and characterized by two cuspid, one behind the other, but overall much thinner and more blade-like than in Uintatherium or Eobasileus . The lower canine resembled the incisors in shape, but was comparatively larger than in other Uintatheria. The diastema behind the canine was quite extensive. The molars had low ( brachyodonte ) crowns and were small, the entire molar row reached a length of 16.3 cm, the last molar was 3.9 cm in length. Typical were the two transverse enamel folds of the individual occlusal surfaces, which give the molars a bilophodontic structure, the enamel folds of the upper jaw teeth had a V-shaped arrangement.
The body skeleton is known only from a few finds. The form of the humerus and thigh bone hardly differed from those of the other developed Dinocerata, as with Uintatherium or Eobasileus there was no third trochanter on the femur . The hand and foot bones of Gobiatherium were generally longer and narrower than those of its relatives.
Fossil finds
Gobiatherium is only known from East and Central Asia . The first finds came to light in 1930 during an expedition by the American Museum of Natural History to Inner Mongolia in 1930 . They were discovered there around 40 km southwest of Iren Dabasu in the Erlian Basin . The first descriptors Henry Fairfield Osborn and Walter W. Granger originally stated the location of the find with the Irdin Manha Formation , which gave the fossil remains an Upper Oocene age. According to new geological investigations, the fossil layers, which among other things also contained Gobiatherium , belong to the underlying Arshanto Formation , which was formed in the Lower and Middle Eocene. The finds of the American Museum of Natural History include at least seven, partly complete skulls, including the complete and barely crushed holotype specimen and the skull of a young animal, as well as isolated lower jaws and remains of the body skeleton. All remains are assigned to the species G. mirificum . For a long time, these were the only known finds of this genus of mammals, only in the 1980s were more fossils discovered. Some come from the Arshanto formation in the Erlian basin and are composed of several upper and lower jaw fragments and isolated teeth. Another lower jaw fragment has been recovered directly from the base of the Arshanto formation. From the Middle Eocene Yuhuangding Formation near Danjiangkou in the Chinese province of Hubei , isolated teeth and a fragment of the lower jaw belonging to the somewhat smaller species G. minutum were discovered from the upper area of the sediment deposits at the end of the 1980s . These supplement some isolated limestone teeth of the same formation that were documented as early as the 1960s, but which came to light near Liguanqiao in the immediately neighboring province of Henan . From the Chonkurchak formation near Toru-Aygyr in Kyrgyzstan, in turn, a complete skull with associated lower jaw has been reported, while some isolated teeth are known from the Chakpaktas River in the Saissan Basin in eastern Kazakhstan .
Paleobiology
Similar to the other representatives of the Dinocerata, the bilophodont molars indicate that the animals feed on soft parts of plants ( browsing ). Due to the non-developed upper maxillary canines, the dentition was less bulky and the lower jaw was not built quite as robustly. It also lacked the lower protrusions of the lower jaw that were typical of Uintatherium and Eobasileus to protect the upper canine. The overall graceful structure of the lower jaw is also evident in the design of the joint there, which, unlike its relatives, is not directed backwards. As a result, it was not possible for Gobiatherium to open its mouth very wide, which should not have been necessary due to the missing canine teeth.
In the opinion of the first authors, a gender dimorphism could possibly be detected in Gobiatherium , which mainly affects the structure of the nasal area. Male animals were said to have a solidly round nasal bone and a bony nasal septum based on a few skulls, with two slight bones on the top tip of the nose and very rarely a small upper canine tooth. Females lacked these characteristics. Later analyzes showed that at least the absence of the bony septum and the small horns can be attributed to weathering and that these features were originally present in all known skulls.
Systematics
Gobiatherium is a genus of the family of Uintatheriidae is, in turn, to order the dinocerata provided. This group of mammals is largely known from North America and East Asia and was the first known giant form among the mammals that developed after the extinction of the dinosaurs during their genetically more recent development phase . The absence of the first premolar and the upper incisors are regarded as common features of all Dinocerata; the only exceptions here are the earliest representatives. The relationship to other mammals is not fully understood, but it is believed that they form a fairly original branch within the heterogeneous group of ungulates . According to current knowledge, the closest relatives are likely to be the South American ungulates ( Meridiungulata ), such as the Pyrotheria or the Xenungulata . The closest relatives still living today are likely to be the odd-toed ungulates .
Within the Uintatheriidae Gobiatherium is placed to the subfamily of the Gobiatheriinae with only this genus as the only member. This subfamily is characterized by the reduction of the upper canine tooth and the overgrown nasal septum . The Gobiatheriinae stand opposite the Uintatheriinae with Uintatherium and Eobasileus as sister group, which in turn are characterized by long and saber-like curved upper canines and several pairs of bony horn formations on the skull. The direct predecessor of Gobiatherium is unknown, since older forms such as Prodinoceras or Bathyopsis differ significantly in their skull morphology and are therefore not directly related. Originally the Gobiatheriinae were introduced by KK Flerov as an independent family Gobiatheriidae in 1952, a revision of the Uintatheriidae in 1961 by Walter H. Wheeler shifted their status to that of the subfamily. Another partial revision of the Uintatherien by William D. Turnbull in 2002 confirmed this taxonomic assignment. However, some researchers see the former partly as an independent family within the Dinocerata due to the different tooth morphologies of the Gobiatheriinae to the Uintatheriinae.
Today there are two types:
Another species G. major , established on the basis of the finds from the Arshanto formation, is now considered a synonym for G. mirificum , while G. monolobotum is regarded as a representative of Eudinoceras from the Pantodonta group.
The genus Gobiatherium was first described in a short essay in 1932 by Henry Fairfield Osborn and Walter W. Granger based on finds from the 1930 expedition of the American Museum of Natural History to Inner Mongolia . The holotype (specimen number AMNH 26624) is a complete, 68 cm long skull, the paratype (AMNH 26630) is a complete lower jaw. The generic name Gobiatherium refers on the one hand to the Gobi desert as a place of discovery, on the other hand the Greek word θήριον ( thêrion ) means "animal". The name was chosen analogous to that of its North American relative Uintatherium , the "animal from the Uinta Mountains ".
Individual evidence
- ^ A b c d e f Henry Fairfield Osborn and Walter W. Granger: Coryphodonts and Uintatheres from the Mongolian expedition of 1930. American Museum Novitates 552, 1932, pp. 1-16
- ↑ a b c d e f Walter H. Wheeler: Revision of the Uintatheres. Bulletin of the Peabody Museum of Natural History Yale University 14, 1961, pp. 1-93
- ^ A b c Spencer George Lucas: Gobiatherium (Mammalia: Dinocerata) from the Middle Eocene of Asia: Taxonomy and biochronological Significance. Paläontologische Zeitschrift 74 (4), 2001, pp. 591-600
- ↑ Jin Meng, Yuanqing Wang, K. Christopher Beard, Chengkai Sun, Qian Li, Xun Jin and Bin Bai: New Stratigraphic Data from the Erlian Basin: Implications for the Division, Correlation, and Definition of Paleogene Lithological Units in Nei Mongol (Inner Mongolia). American Museum Novitates 3570, 2007, pp. 1-31
- ↑ a b Bai Bin: New Materials of Eocene Dinocerata (Mammalia) from the Erlian basin, Nei Mongol (Inner Mongolia). Vertebrata Palasiatica 44 (3), 2006, pp. 250-261
- ↑ a b Cheng Jie and Ma Aneheng: New mammalian materials from the Eocene of the Liguanqiao basin. Vertebrata Palasiatica 28, 1990, pp 228-244
- ↑ Chow Minchen and Tung Yungchen: Notes on some new uintathere materials of China. Vertebrata Palasiatica 6, 1962, pp. 368-371
- ↑ Donald R. Prothero, Earl M. Manning and Martin Fischer: The phylogeny of the ungulates. In: MJ Benton (Ed.): The phylogeny and classification of Tetrapods, Volume 2: Mammals. Systematics Association, Special Volume 35B, Oxford, 1988, pp. 201-234
- ^ Benjamin J. Burger: The systematic position of the saber-toothed and horned giants of the Eocene: The uintatheres (Order Dinocerata). Journal of Vertebrate Paleontology 35 (suppl.), 2015, p. 99
- ^ William D. Turnbull: The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part IV. The Uintatheres. Fieldiana 47, 2002, pp. 1-189
