Rhinotitanium
| Rhinotitanium | ||||||||||||
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-PaleozoologicalMuseumOfChina-May23-08.jpg)
Skull of Rhinotitan |
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| Temporal occurrence | ||||||||||||
| Middle Eocene ( Sharamurunian ) | ||||||||||||
| 41.1 to 37.7 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Rhinotitanium | ||||||||||||
| Granger & Gregory , 1943 | ||||||||||||
Rhinotitan is an extinct genus of the Brontotherien , which is found mainly in East Asia and lived in the Middle Eocene 41 to 37 million years ago. Within the Brontotherien it represented a rather large representative of this fossil unpaired ungulate group , but it did not have as pronounced bony horns as the later forms. The majority of the finds were discoveredin Inner Mongolia from 1922 to 1923 during the third Asian expedition of the American Museum of Natural History .
features
Rhinotitan was a large representative of the Brontotheria, but did not reach the size of Embolotherium or Megacerops . Characteristic was the 66 to 78 cm long skull, which was relatively narrow and had little protruding zygomatic arches . In contrast to other horn-bearing shapes, the skull did not have such a distinct saddle at the forehead line. The occiput was also not so markedly elongated, but rather designed at right angles. The nasal bone was straight and hardly curved. In the area of the characteristic bony horns at the transition from the nasal bone to the frontal bone , both bones were clearly widened. The horns themselves had a long oval shape and protruded diagonally upwards at an angle of 45 °, but only represented slight elevations. They were clearly separated from one another and protruded in front of the orbit . This, in turn, was comparable to Embolotherium above the second molar . The intermaxillary bone had a downwardly directed shape, the nasal space between this and the nasal bone was very extensive and reached to the rearmost premolar .
The massive lower jaw reached a length of 54 to 61 cm and could be up to 13 cm high. The teeth had the full number of teeth of early mammals, whereby the following dental formula gives: . The two inner incisors each had a hemispherical to spoon-like shape and were relatively small, while the outer one was conically pointed and larger. This made it resemble the canine tooth directly following it , but which was even larger in shape. The subsequent diastema reached a width of 2.5 to 4 cm. The molars increased in size from front to back, but were generally low-crowned ( brachyodont ). The posterior premolars were partially molarized while the posterior molars were clearly elongated. The last molar could be over 8 cm long. The W-shaped course of the tooth enamel on the chewing surface of the upper molars was also characteristic of Brontotheria.
The postcranial skeleton is partially known, the limbs resembled those of the other Brontotheria and ended in four rays in front and three in back. This ancient characteristic of the odd ungulate is only known from the tapirs today. The humerus measured almost 50 cm, the radius 48 cm. The longest long bone was the thigh bone with almost 68 cm, while the shin reached 46 cm. The central ray ( Metapodium III) was most strongly developed in the hands and feet . The forefoot was a bit larger than the hindfoot, characteristic of numerous odd ungulates. The metacarp III reached 21 cm, the metatarsus III 20 cm in length.
References
Finds of rhinotitan are only known from northern East Asia , significant finds are in the Chinese autonomous region of Inner Mongolia . The first finds came to light in 1922 and 1923 during the Third Asiatic Expedition of the American Museum of Natural History and were discovered in the Erlian Basin near Ula Usu and Baron Sog. They camped in the Shara Murun Formation , which belongs to the Middle Eocene . 17 finds were discovered alone, including three complete skulls, several lower jaws and remains of fore and hind legs. A mandibular fragment was one of the first Brontotherium fossils to reach the American Museum of Natural History in 1923 and was used by Henry Fairfield Osborn for the first description of Rhinotitan mongoliensis (then Protitanotherium mongoliense ), a species that is largely no longer recognized today. Additional material was discovered in the aftermath of World War II .
Paleobiology
Adult rhinotitan canine teeth are highly variable and indicate possible sex dimorphism . The larger and more robust canines can probably be associated with male animals. Varying canine sizes within the two sexes, which could also be observed in other Brontotheria such as Gnathotitan and Parvicornus , are typical of phylogenetically older animals with nonexistent or only small horns, while this difference was lost again in the more modern with large horns. Such dimorphic formations of the front set of teeth (canines and incisors) are also known among the ungulates living today and often occur in those who have no or only slightly pronounced head weapons, such as horses or, to an extreme extent, in turning water . These variations are interpreted with a polygynous way of life.
Systematics
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Internal systematics of the Brontotheriina according to Mihlbachler 2009
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Rhinotitan is a genus of the Brontotheriidae family (originally Titanotheriidae). These represent primitive unpaired ungulates , which, due to the structure of their teeth, have a taxonomic proximity to today's horses . Within the Brontotheri, rhinotitan belongs to the subfamily of the Brontotheriinae and to the sub- tribus of the Brontotheriina, which in turn are part of the Brontotheriini tribe. The tribe of the Brontotheriini had originally introduced Bryn J. Mader as a subfamily of the Telmatheriinae, they contained all North American Brontotheri with slight horn approaches. However, in a later investigation he renamed the family Brontotheriinae. Matthew C. Mihlbachler put this subfamily on the rank of tribe in 2008, which now includes all Brontotheria from North America as well as from Eurasia, which have the beginnings of a bony horn formation consisting of the adjacent ends of the frontal and nasal bones. The Brontotheriina as part of the Brontotheriini already have more distinct horn formations. Related genera to Rhinotitan are Protitan and Protitanotherium . From the Brontotheriina, the more modern Brontotheriina developed with clear and large horn formations, which on the one hand are assigned to the Brontottheriita with Megacerops , on the other hand the Embolotheriita with Embolotherium .
Two types of rhinotitanium are recognized today:
- R. andrewsi ( Osborn , 1925)
- R. kaiseni ( Osborn , 1925)
The finds, which were discovered during the Third Asiatic Expedition of the American Museum of Natural History and are now related to Rhinotitan , were originally assigned to other Brontotheria genera by Henry Fairfield Osborn in the 1920s, Protitanotherium for R. andrewsi and Dolichorhinus for R. kaiseni . Walter W. Granger and William K. Gregory established the generic name Rhinotitan in 1943. The reasons for this were differences in the shape of the incisors and the occiput, which are more similar to other Asian Brontotheria than to the assigned North American forms. A third species, Rhinotitan mongoliensis (originally Protitanotherium mongoliense ) determined by Osborn on the basis of a fragment of the lower jaw, is now regarded as the noun dubium , as the associated material shows hardly any diagnostic features. The same applies to the unspecific tooth finds from a coal mine north of Vladivostok , which were the inspiration for the species Rhinotitan orientalis , as well as to the teeth from Lunan in the Chinese province of Yunnan , on the basis of which Rhinotitan quadridens was described. For the generic name Rhinotitan , Granger and Gregory gave no etymological meaning in 1943 , but it is composed of the Greek words ῥίς ( rhīs "nose"; genitive rhinos ) and τιτάν ( titan "titanium" or "giant").
Individual evidence
- ↑ a b c d e Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311, 2008, ISSN 0003-0090 , pp. 1-475
- ^ A b c Walter W. Granger and William K. Gregory: A revision of zhe Mongolian Titanotheres. Bulletin of the American Museum of Natural History 80, 1943, pp. 349-389
- ^ Matthew C. Mihlbachler, Spencer G. Lucas, Robert J. Emry, and Bolat Bayshashov: A New Brontothere (Brontotheriidae, Perissodactyla, Mammalia) from the Eocene of the Ily Basin of Kazakstan and a Phylogeny of Asian `` Horned '' Brontotheres. American Museum Novitates 3439, 2004, pp. 1-43
- ^ A b Henry Fairfield Osborn: Titanotheres and lophiodonts in Mongolia. American Museum Novitates 91, 1923, pp. 1-5
- ^ A b Henry Fairfield Osborn: Upper Eocene and Lower Oligocene Titanotheres of Mongolia. American Museum Novitates 202, 1925, pp. 1-12
- ^ A b Matthew C. Mihlbachler: A New Uintan Horned Brontothere from Wyoming and the Evolution of Canine Size and Sexual Dimorphism in the Brontotheriidae (Perissodactyla: Mammalia). Journal of Vertebrate Paleontology 31 (1), 2011, pp. 202-214
- ^ A b Matthew C. Mihlbachler: A New Species of Brontotheriidae (Perissodactyla, Mammalia) from the Santiago Formation (Duchesnean, Middle Eocene) of Southern California. Proceedings of the San Diego Society of Natural History 41, 2009, pp. 1-36
- ↑ Bryn J. Mader: Brontotheriidae: A systematic revision and preliminary phylogeny of North American genera. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York and London, 1989, pp. 458-484
- ↑ Bryn J. Mader: Brontotheriidae In: Christine M Janus, Kathleen M Scott and Louis L Jacobs (eds.): Evolution of Tertiary mammals from North America, Vol. 1. Cambridge 1998, pp. 525-536
- ↑ Н. М. Яновская: Первая находка Rhinotitan из емейства Brontotheriidae в CCCP. Vertebrata Palasiatica 1 (3), 1957, pp. 187-192
- ↑ Xu Yu-xuan and Chiu Chan-siang: Early Tertiary Mammalian Fossils from Lunan, Yunnan. Vertebrata Palasiatica 6 (4), 1962, pp. 313-332
