Iranotherium
| Iranotherium | ||||||||||||
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Skull of Iranotherium |
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| Temporal occurrence | ||||||||||||
| late Miocene ( Tortonium ) | ||||||||||||
| 9.5 to 7 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Iranotherium | ||||||||||||
| Ringström , 1924 | ||||||||||||
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Iranotherium is an extinct genus of rhinos and belongs to the Elasmotheriini, close relatives of the rhinos living today, which are characterized by a large body and teeth with high crowns. It lived in the late Miocene and is found mainly in East and South Asia . A proven, extremely clear sexual dimorphism isimportant for Iranotherium . The name is made up of the name of the area where the first known fossils were found ( Iran ) and the Greek word θηρίον (thērion) for "animal".
features
Iranotherium was a large representative of the rhinoceros, but did not reach the dimensions of the simultaneously occurring or subsequent genera of the Elasmotheria. The animals are known from some very well-preserved skull finds. This was between 71 and 78 cm long, very elongated and narrow. The occiput was clearly elongated and acute-angled, so that the animals had a low head posture. It had a pronounced bulge at the point of attachment of the neck muscles, which was strongly angled in the middle when viewed from above. The nasal bone was strongly built and drawn out long and narrowed significantly in the front area. In addition, it showed a clearly rounded shape in the side view. The typical ossification of the nasal septum of the later Elasmotheria were not yet developed in Iranotherium . Roughened structures on the surface of the nasal bone indicate on the one hand the position of the horn on the middle area of the nasal bone, on the other hand, due to the strong expression of these formations, they indicate that it must have been quite large. The forehead line between the nasal and occiput continued to show a very noticeable saddle. The eye socket was above the center of the rearmost molar .
The lower jaw was narrow but sturdy and was about 54 cm long. He had a strong symphysis that reached the middle of the third premolar . In the dentition, as in all later Elasmotheria, the anterior teeth consisting of the incisors and canines were missing and therefore had a reduced number of teeth. The molars were pushed well forward and included three premolars and three molars, so that the teeth formula of adult animals follows read: . The deciduous dentition still had the anterior premolars. The premolars were largely molarized, but the first was only small in size. In contrast, the posterior premolars were more like the molars in size. Of these, the second molar had the largest dimensions in the dentition. The crowns of the posterior molars were very high (hypsodont) , but did not yet reach the values of the later elasmotheria. The maximum height was 10 cm. They contained a lot of dental cement , but had only slightly curved enamel folds , which had not yet developed the strong angled molars of the following genera.
The found material of the trunk (vertebrae, ribs) and the musculoskeletal system (long bones, hand and foot bones), comprising only a few skeletal elements, shows hardly any characteristic features that distinguish it from other representatives of Elasmotheria.
Fossil finds
Remains of Iranotherium come largely from South and East Asia . Significant finds are known from Maragha and Kerjavol (both Iran ). Especially from Maragha, in addition to a relatively complete skull, which also has the rear molars, there are also some postcranial skeletal elements, such as B. the first cervical vertebra ( atlas ). The finds represent the type specimen of the genus. Further finds came to light in the Linxia Basin in the northern Chinese province of Gansu . These come from the reddish colored clay deposits of the Upper Miocene Liushu Formation , with a skull of a young male and that of a fully grown female animal in the village of Houshan, while the lower jaw of an adult bull was found in the village of Shanzhuang. Several isolated tooth finds and remains of the musculoskeletal system as well as ribs were found in the also Upper Miocene Loh formation near Builstyn Khudag in the valley of the Gobi lakes ( Mongolia ).
Paleobiology
Above all, the existing and largely complete skull finds enable a differentiation of the sex differences in Iranotherium , which has so far been possible with only a few fossil rhino species. The bulls had a generally more robust skull structure and a broader nose bone with a rounded front, while this tapered to a point in cows. The roughening of the nasal bone shows that males had a much larger horn than females, which they probably used more often in domination and mating battles. A very striking difference are hemispherical bone hypertrophies on the outer areas of the cheekbones , as shown by the skulls of Moragha and the sub- adult find by Houshan. These are interpreted as stronger muscle attachment points for the masseter muscles ( musculus masseter and musculus temporalis ) in bulls, which shows that bulls are generally more robust.
The Iranian finds are connected with the so-called Maragha fauna , whose character animal is the three- toed primeval horse Hipparion . This is also the leading form of the Hipparion fauna from the Linxia basin. Both fauna complexes are regarded as the high point of the development of the Upper Miocene savanna communities . Pollen analyzes from the red sediments of the Liushu Formation of the Linxia Basin revealed a mixture of open and forest landscapes in warm, sometimes dry climates, which are also reflected in the composition of the fauna. Due to the high crowns of the molars of Iranotherium with a high proportion of cement and the low-hanging head, the rhinoceros genus lives in more open landscapes and feeds on silicic acid-rich grasses (grazer) , but the enormous size of the animals also suggests a high proportion of fibrous plant parts.
Systematics
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Internal systematics of the Elasmotheriini according to Sanisidro et al. 2012 and Deng 2008
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Iranotherium belongs to the Elasmotheriini tribe , which is characterized by a generally large to very large physique and high tooth crowns. They represent the sister taxon of the Rhinocerotina, which in turn includes the rhinoceros species living today. Due to the position of the horn on the nasal bone, the genus is closer to the genera Parelasmotherium and Ningxiatherium than to the Elasmotherium, which has a frontal horn . The missing ossification of the nasal septum and the generally not so extremely high crowned teeth still refer to the older representatives of the Elasmotheriini from the Middle Miocene . For the Elasmotherien with nasal horn, the Hungarian paleontologist Miklós Kretzoi (1907-2005) introduced the Subertribus Iranotheriina in 1943.
The rhinoceros genus appeared in the Upper Miocene 10 to 7 million years ago (Upper Vallesian to Lower Turolian ). The earliest finds are all from northern China and Mongolia, so that Iranotherium possibly originated there and only later immigrated to its southern distribution area. It probably emerged from Hispanotherium or Gobitherium , which are also found in East Asia and with which it shares numerous characteristics. The imprecise determination of relationship points to the complex tribal history of the Elasmotheriini.
The first description of Iranotherium and the assignment to the Elasmotherium took place in 1929 by Torsten Ringström . The finds from Maragha are considered a lectotype . The only species recognized today is I. morgani , which was established in 1908 by R. Mecquenem on the basis of the Maragha fossils. Mecquenem recognized the close relationship between the new species and Elasmotherium , but named it Rhinoceros morgani . The skeletal remains from Maragha were identified as Rhinoceros var. Tichorhinus by the paleontologists Hans Pohlig and E. Keyser as early as 1885 ; later, in 1888, E. Kittl referred them to Aceratherium aff. antiquitatis too. A possibly second species, which has not yet been precisely determined, is from the Luh formation in Mongolia. This differs morphologically from I. morgani and shows reminiscences of Hispanotherium and Gobitherium , especially in dental construction , but was already significantly larger than these. Probably connected with its somewhat older age, it represents the basal form of Iranotherium .
Individual evidence
- ↑ a b c d e f g Deng, Tao: New discovery of Iranotherium morgani (Perissodactyla, Rhinocerotidae) from the late Miocene of the Linxia basin in Gansu, China, and its sexual dimorphism. Journal of Vertebrate Paleontology 25 (2), 2005, pp. 442-450
- ↑ a b c d Kurt Heissig: Rhinocerotidae (Perissodactyla, Mammalia). In: Gudrun Daxner-Höck (Ed.): Oligocene-Miocene Vertebrates from the Valley of Lakes (Central Mongolia): Morphology, phylogenetic and stratigraphic implications. Annals of the. Naturhistorisches Museum zu Wien 108 A, 2007, pp. 233–269
- ↑ Deng Tao: Linxia Basin: An Ancient Paradise for Late Cenozoic Rhinoceroses in North China. Paleomammalogy 24 (2), 2010, pp. 103-106
- ↑ Oscar Sanisidro, María Teresa Alberdi, Jorge Morales: The First Complete Skull of Hispanotherium matritense (Prado, 1864) (Perissodactyla, Rhinocerotidae) from the Middle Miocene of the Iberian Peninsula. Journal of Vertebrate Paleontology, 32 (2), 2012, pp. 446-455
- ↑ a b Deng Tao: A new elasmothere (Perissodactyla, Rhinocerotidae) from the late Miocene of the Linxia Basin in Gansu, China. Geobios 41, 2008, pp. 719-728
- ↑ Pierre-Olivier Antoine: Middle miocene elasmotheriine Rhinocerotidae from China and Mongolia: taxonomic revision and phylogenetic relationships. Zoologica Scripta 32 (2), 2003, pp. 95-118