Gnathotitan
| Gnathotitan | ||||||||||||
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Gnathotitan mandibular remains , top (A) the holotype |
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| Temporal occurrence | ||||||||||||
| Upper Eocene ( Irdinmanhum ) | ||||||||||||
| 46.5 to 41.1 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Gnathotitan | ||||||||||||
| Granger & Gregory , 1943 | ||||||||||||
Gnathotitan is a genus from the extinct family of the Brontotherien , primitive members of the odd ungulate . Gnathotherium was one of the largest representatives ofthe Brontotheria,but is only known from a few fossils. Its massive lower jaw, which distinguishes it from all other Brontotheria, was particularly characteristic. Gnathotitan livedin Eastern Asiain the Middle Eocene 46.5 to 41.1 million years ago. The only recognized species within the genus is Gnathotitan berkeyi .
features
Gnathotitan was one of the largest representatives of the Brontotheria and reached a size comparable to that of Embolotherium and Megacerops , but the genus has only been identified through skull and dentition finds. The skull is represented by two upper jaw fragments that reveal only a few features; whether the genus had bony horn formations is unknown. The interior of the nose protruded at least to the second premolar , but is not completely preserved. The orbit was above the second molar , a position comparable to Embolotherium but further back than Megacerops . The lower jaw of Gnathotitan with a length of 80.5 cm is the largest so far that has been discovered in a representative of the Brontotherien. It was extremely solid with a bone body up to 21.5 cm high and a narrow, but very elongated and spatula-shaped symphysis . Especially the height of the lower jaw is atypical for Brontotheria. The teeth are not fully known, the upper incisors are not yet known. In the lower jaw, there were three incisors per jaw arch, which were very large and spoon-shaped. The canine tooth preserved in the upper and lower jaw was variable in size, but always conical in shape. The existing diastema to the posterior teeth reached a length of 4.8 cm. The molars, which consist of four premolars and three molars per jaw branch, were very elongated and low-crowned ( brachyodont ), especially the molars were sometimes enormous, the last one could be up to 11 cm long.
The shape and size of the lower jaw in Gnathotitan are unique to the Brontotheria. It is not certain whether this genus also represented the shape with the largest body size: If the entire chewing surface of Gnathotitan (measured from the first premolar to the last molar) is almost 36 cm long, then Aktautitan , a Middle Eocene representative, shows today's Kazakhstan even reached 39 cm. Megacerops also had a length of up to 39 cm, with Embolotherium this is only 33 cm. However, due to their great variability, the size and shape of the molars are too imprecise for exact body size determinations. Due to different size variables, several genera have been identified that compete for the "title" of the largest known representative of the Brontotherien.
Fossil finds
Gnathotitan is only known from seven fossil finds, two of which were lost again. All of them came to light during the Third Asiatic Expedition of the American Museum of Natural History in 1922 and 1923 . This expedition was led by Walter W. Granger and William King Gregory . All finds come from two locations within the Irdin Manha Formation in Inner Mongolia , which is assigned to the Middle Eocene . The five remains today (two upper jaw and three lower jaw fragments) are in the American Museum of Natural History in New York . Two finds were sent to the Chinese Geological Survey by Henry Fairfield Osborn in 1928 but were lost.
Paleobiology
Although there are only a few finds, the remains of the lower jaw clearly show a sexual dimorphism : Male animals are probably characterized by significantly larger canine teeth, which are noticeably higher than the incisors. Female animals therefore had smaller and less voluminous canine teeth.
Systematics
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Internal systematics of the Embolotheriita according to Averianov et al. 2018
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Gnathotitan is a genus from the family of brontotheriidae (originally Titanotheriidae), an extinct mammal group from the group of odd-toed ungulates . Because of the dental structure, the family is considered a distant relative of today's horses . Within the Brontotheriidae Gnathotitan was placed to the subfamily of the Brontotheriinae and to the intermediate tribus of the Embolotheriita. In previous analyzes, Gnathotitan was part of the subfamily Epimanteoceratinae first introduced by Granger and Gregory. The intermediate tribus of the Embolotheriita, on the other hand, originally formed its own subfamily, the Embolotheriinae, which Henry Fairfield Osborn had introduced in 1929 only for Embolotherium . In 2008, however, Matthew C. Mihlbachler moved this to the level of the intermediate tribus. Today, the Embolotheriita with Aktautitan , Metatitan and Embolotherium include other, mostly Asian-widespread genera, and the intermediate tribus of the Brontotheriita with Megacerops as a sister group.
Henry Fairfield Osborn assigned the few finds in his processing of the finds from the Third Asiatic Expedition of the American Museum of Natural History 1925 to the genus Telmatherium , whose representatives are actually much smaller and largely only detectable in North America, but which have numerous fossils in the course of the history of research with their own taxonomic status today . Granger and Gregory corrected this in 1943 and established the genus Gnathotitan . They did not give an etymological origin of the name, but it is made up of the Greek words γνάθος ( gnathos "pine") and τιτάν ( titan "titanium" or "giant"). The only recognized species is Gnathotitan berkeyi , with the addition of the species name berkeyi in honor of the chief geologist of the 1922 and 1923 expedition, Charles P. Berkey, who discovered the first Brontotherien fossils. Osborn gave a lower and upper jaw with the specimen number AMNH 20106 as the holotype . Today only the lower jaw, which is complete except for the missing incisors, is recognized as a lectotype , while the upper jaw has to represent another individual due to deviating metric values on the teeth and was therefore given a new find number.
literature
- Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). In: Bulletin of the American Museum of Natural History. No. 311, June 2008, ISSN 0003-0090 , pp. 1-475, doi : 10.1206 / 0003-0090 (2008) 501 [1: STPABO] 2.0.CO; 2
Individual evidence
- ↑ a b c d e f Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). In: Bulletin of the American Museum of Natural History. 311, 2008, ISSN 0003-0090 , pp. 1-475.
- ^ A b c d Walter W. Granger, William K. Gregory: A revision of the Mongolian Titanotheres. In: Bulletin of the American Museum of Natural History. 80, 1943, pp. 349-389.
- ↑ Matthew C. Mihlbachler, Spencer G. Lucas, Robert J. Emry, Bolat Bayshashov: A New Brontothere (Brontotheriidae, Perissodactyla, Mammalia) from the Eocene of the Ily Basin of Kazakstan and a Phylogeny of Asian `` Horned '' Brontotheres. In: American Museum Novitates. 3439, 2004, pp. 1-43.
- ↑ Bryn J. Mader: Brontotheriidae: A systematic revision and preliminary phylogeny of North American genera. In: Donald R. Prothero, Robert M. Schoch (Eds.): The evolution of perissodactyls. New York / London 1989, pp. 458-484.
- ↑ Alexander Averianov, Igor Danilov, Wen Chen and Jianhua Jin: A new brontothere from the Eocene of South China. Acta Palaeontologica Polonica 63. 2018 doi: 10.4202 / app.00431.2017
- ↑ Wang Yuan, Guo Jianwei, Wang Jingwen: A review of the Chinese Brontotheres. In: YQ Wang, T. Deng (Eds.): Proceedings of the Seventh Annual Meeting of the Chinese Society of Vertebrate Paleontology. Ocean Press, Beijing 1999, pp. 139-147.
- ^ Henry Fairfield Osborn: Embolotherium, gen. Nov., Of the Ulan Gochu, Mongolia. In: American Museum Novitates. 353, 1929, pp. 1-20. ( digitallibrary.amnh.org )
- ^ A b Henry Fairfield Osborn: Upper Eocene and Lower Oligocene Titanotheres of Mongolia. In: American Museum Novitates. 202, 1925, pp. 1-12.