Aprotodon

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Aprotodon
Temporal occurrence
38 to 15.97 million years
Locations
  • Central Asia, South Asia, East Asia
Systematics
Higher mammals (Eutheria)
Laurasiatheria
Unpaired ungulate (Perissodactyla)
Rhinocerotoidea
Rhinoceros (Rhinocerotidae)
Aprotodon
Scientific name
Aprotodon
Forster Cooper , 1915

Aprotodon is an extinct genus of rhinos , it lived from the Upper Eocene to the Lower Miocene 38 to 16 million years ago. Aprotodon was mainly found in what is now central to eastern Asia . Fossil finds are rather rare, the rhinoceros genus is largely only known from skull and tooth finds. Particularly noteworthy are the long and curved lower incisors, which protruded up to 20 cm from the mouth. The shape and size of the incisors, but also the characteristic structure of the mandibular symphysis , initially led to an incorrect assignment of aprotodon to the hippopotamus .

features

Aprotodon were rather primitive, but large representatives of the rhinos, whose smaller forms reached around 1.1 t in body weight. However, the genus is only known through remains of skulls, lower jaws and a few isolated teeth. A deformed skull was 48 cm long, while the width at the zygomatic arches was up to 14.5 cm. The occiput was rather short and rectangular and thus ensured a high head posture. The nasal bone had a graceful shape and was relatively elongated at 16 cm in length. In addition, it had only a small thickness, which was only 8 mm at the front tip. The absence of roughening on the surface of the nasal bone shows that no horns were formed. The forehead line was rather straight, with small, rib-like elevations formed behind the orbit . The interior of the nose between the nasal bone and the intermaxillary bone was very extensive and reached to the end of the last premolar , the height of the interior of the nose was around 4.5 cm.

The lower jaw had a rather delicate shape and was 4.5 cm high in the area of ​​the second premolar. The height of the lower jaw bone was roughly the same in the area of ​​the rear teeth and was only about twice the height of the teeth. The symphysis had a broad shape and increased significantly from the last premolar towards the front, so that it reached up to 10 cm in width at the front end. In addition, it was heavily dented in places and its entire structure is reminiscent of that of today's hippos . The canine and part of the incisors were reduced in the dentition . The lower incisors in particular, each consisting of the second (I2), had a characteristic shape. They were conical in shape and strongly curved upwards and reached lengths measured over the bend from 35.5 to 43.4 cm, with direct lengths from 29.5 to 34.7 cm. The cross-section at the base was oval and measured approximately 4.3 x 3.4 cm. The tooth crown and tooth root had about the same length, so that the teeth looked up to 20 cm out of the mouth. This is a more distinctive feature than related species. The lower incisors in Chilotherium reached a maximum crown length of 12 cm, while in the giant Brachypotherium they still measured 11 cm. The dimensions of the incisors, as well as the mandibular symphysis, are similar to the massive canine teeth of the hippopotamus, which can be up to 53 cm long measured over the curvature, with direct lengths of 36 cm (each including the tooth root).

The posterior dentition was separated from the incisors by a diastema . Premolars and molars had low ( brachyodontic ) to moderately high crowned ( hypsodontal ) tooth crowns. The premolars were hardly molarized and thus deviated from the molars. The entire back row of teeth reached 20 cm in length, with the tooth size increasing towards the rear. The anterior premolar was about 1.5 cm long, while the last molar was 4.5 to 5.0 cm long.

Fossil finds

Aprotodon finds are relatively rare and mostly include fragments of the skull and tooth remnants; elements of the body skeleton are not known. Most fossils come from South , Central and East Asia and date from the Upper Eocene to the Lower Miocene 38 to 16 million years ago. From Pakistan and India , especially from the Bugti Mountains of Baluchistan , mainly remains of the upper and lower jaw and individual tooth finds come from. Significant finds were reported mainly from Kazakhstan , where several partial skulls and lower jaw fragments were discovered. A deformed partial skull comes from Akespe in the southwest of the country and belongs to the Lower Miocene. A special feature is a hand skeleton with preserved outer (fifth) finger from the Pavlodar region in the north of Kazakhstan. The outermost finger is no longer found in today's rhinos, they only have three-pronged hands (and feet), in primitive representatives who live in usually have four-pronged hands, this is very rarely detected and greatly reduced in size so that it was functionless. Since the 1980s and 1990s, quite extensive aprotodon fossil remains have been discovered in China . Outstanding is a broken skull and several remains of the lower jaw from Zhangjiaping in the Lanzhou Basin in Gansu Province . These were located in the base area of ​​the middle stratum of the Xianshuihe Formation , which consists of whitish sandstone and dates to the late Oligocene . Skull remains from the Jiaozigou Formation in the Linxia Basin , which is also located in Gansu and which is formed here from yellowish sandstones, also show an Oligocene age , while several isolated teeth, including massive incisors, from the Shangzhuang Formation of the same locality in the lower one Miocene date. The oldest finds include those from the Houldjin Formation in Inner Mongolia , which include a fragment of the lower jaw and a few isolated teeth and are to be placed in the late Eocene. These had already been discovered in 1922 during the Third Asiatic Expedition of the American Museum of Natural History , but were only recognized as remains of Aprotodon in 2009.

Paleobiology

Aprotodon lived from the end of the Eocene to the beginning of the Miocene , a phase that was characterized by climatic cooling. The scanty fossil remains suggest that the rhino genus was not very common. The majority of the finds come from dry climates and is associated with the spread of the giant rhinoceros related Paraceratherium . The broad structure of the mandibular symphysis, which is reminiscent of that of the hippopotamus , leads some experts to assume that the Aprotodon also lived similarly semi-aquatic and inhabited river and lake banks and flooded plains. Especially in the late phase of the appearance of aprotodon , the landscapes were interspersed with coniferous forests , consisting of cypress trees , yews and junipers . Due to the low crown height of the molars, it can be concluded that the main diet consists of soft vegetable foods such as leaves and twigs ( browsing ).

Systematics

Aprotodon is a genus within the rhinoceros family (Rhinocerotidae). Within the rhinoceros, the genus is usually placed in the now extinct subfamily of the Aceratheriinae ; hornless representatives who are considered to be the distant ancestors of the rhinoceros species still alive today. Here is Aprotodon often in the tribe of Teleoceratini directed. Compared to the sister taxon of the Aceratheriini, these are characterized by extremely robust limbs that are greatly shortened in length, and the upper incisor was not reduced in its phylogenetic development. However, a few researchers also refer to aprotodon as the basis of the more modern subfamily Rhinocerotinae . The closest relatives of Aprotodon include Chilotherium and Symphysorrhachis , the latter being the sister genus.

Several types of aprotodon have been described, five are recognized today:

The position of A. fatehjangensis is particularly problematic. Guy Ellcock Pilgrim established the species as early as 1910 using a fragment of the upper jaw from Fatehjang in what is now Punjab and referred to Teleoceras , a genus of rhinoceros actually restricted to North America . Subsequent authors, especially with reference to much more extensive finds, later brought the species in connection with Aprotodon , including Kurt Heissig in 1972 due to numerous tooth remnants and individual leg elements from the Siwaliks, which other scientists also joined. Still other researchers put the form to Brachypotherium , a related genus with sometimes huge representatives of Eurasian and African origins.

It was first described in 1915 by Clive Forster Cooper . It was based on only a few finds of the lower jaw including the symphysis and skull from Dera Bugti in Balochistan . Due to the shape of the symphysis and the extremely long incisors, Forster Cooper put the genus close to the hippopotamus , interpreting the incisors as canines. Later, especially since the first description of Chilotherium in 1924, a similarity between aprotodon and rhinos was recognized, whereupon in 1928 Raymond Vaufrey equated aprotodon with Chilotherium due to the structure of the symphysis of the lower jaw . In the course of new fossil finds, Elisabeth I. Beliajewa reintroduced the genus Aprotodon in 1954 . Based on new skulls from Kazakhstan and China in the 1990s, the systematic assignment of aprotodon to the rhinos could be clearly confirmed.

Individual evidence

  1. ↑ Deng Tao: Late Cenozoic environmental changes in the Linxia basin (Gansu, China) as indicated by cenograms of fossil mammals. Vertebrata Palasiatica 47 (4), 2009, pp. 282-298
  2. ↑ a b c d e f g Qiu Zhanxiang and Xie Junyi: A new species of Aprotodon (Perissodactyla, Rhinocerotidae) from Lanzhou Basin, Gansu, China. Vertebrata Palasiatica 35 (4), 1997, pp. 250-267
  3. ↑ a b c d Болат У. Байшашов: Первая находка черепа носорога Aprotodon. Известия НАН Республики Казахстан 2, 1994, pp. 54-57
  4. ↑ Chen Shaokun, Deng Tao, Hou Sukuan, Shi Qinqin and Pang Libo: Sexual dimorphism in perissodactyl rhinocerotid Chilotherium wimani from the late Miocene of the Linxia Basin (Gansu, China). Acta Palaeontologica Polonica 55 (4), 2010, pp. 587-597
  5. ↑ Esperanza Cerdeño: Etude sur Diaceratherium aurelianense et brachypotherium brachypus you Miocene Moyen de France. Bulletin du Museum National d'Histoire Naturelle de Paris Series 4 (15) C (1-4), 1993, pp. 25-77
  6. ↑ a b c d e f g Deng Tao: Incisor fossils of Aprotodon (Perissodactyla, Rhinocerotidae) from the Early Miocene Shangzhuang Formation of the Linxia Basin in Gansu, China. Vertebrata Palasiatica, Beijing 51 (2), 2013, pp. 131-140
  7. ^ A b Clive Forster Cooper: New genera and species of mammals from the Miocene deposits of Baluchistan. Annals and Magazine of Natural History (8) 16, 1915, pp. 404-410
  8. ^ Clive Forster Cooper: The extinct Rhinoceroses of Baluchistan. Philosophical Transactions of the Royal Society of London (B) 223, 1934, pp. 569-616
  9. ^ A b Guy E. Pilgrim: The vertebrate fauna of the Gaj Series in the Bugti Hills and the Punjab. Memoirs of the Geological Survey of India (Palaeontologia Indica) New Series 4 (2), 1912, pp. 1-83
  10. ↑ Bolat U. Bayshashov and Spencer G. Lucas: Fifth digit of Aprotodon (Rhinocerotidae) from the Miocene Kalkaman locality, Kazakstan. New Mexico Museum of Natural History and Science Bulletin 67, 2015, pp. 1-4
  11. ↑ a b Deng Tao: Neogene rhinoceroses of the Linxia basin (Gansu, China). Courier Forschungsinstitut Senckenberg 256,2006, pp. 43–56
  12. ↑ Wang Ban-Yue, Qiu Zhan-Xiang, Zhang Quan-Zhong, Wu Li-Jun and Ning Pei-Jie: Large mammals found from Houldjin Formation near Erenhot, Nei Mongol, China. Vertebrata Palasiatica 47 (2), 2009, pp. 85-110
  13. ↑ Deng Tao and W. Downs: Evolution of Chinese Neogene Rhinocerotidae and Its Response to Climatic Variations. Acta Geologica Sinica 76 (2), 2002, pp. 139-145
  14. ↑ Kurt Heissig: The Rhinocerotidae. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York, London, Clarendon Press and Oxford University Press, 1989, pp. 399-417
  15. ↑ Болат У. Байшашов: Новые данные о древних копытных из местонахождения Аяқоз и их биостратиграфия. Геология Казахстана 5/6, 2001, pp. 140–147
  16. ↑ Kurt Heissig: Paleontological and geological investigations in the tertiary of Pakistan. 5. Rhinocerotidae (Mamm.) From the lower and middle Siwalik layers. Bavarian Academy of Sciences, mathematical and natural science class, Abhandlungen 152, 1972, pp. 7–112
  17. ↑ Oliver Chavasseau, Yaowalak Chaimanee, Soe Thura Tun, Aung Naing Soe, John C. Barry, Bernard Marandat, Jean Sudre, Laurent Marivaux, Stéphane Ducrocq and Jean-Jaques Jaeger: Chaungtha, a new Middle Miocene mammal locality from the Irrawaddy Formation, Myanmar. Journal of Asian Earth Sciences 28, 2006, pp. 354-362
  18. ↑ AM Khan, A. Habib, MA Khan, M. Ali and M. Akhtar: New remains of Brachypotherium fatehjangense from Lower Siwalik Hills, Punjab, Pakistan. The Journal of Animal & Plant Sciences, 20 (2), 2010, pp. 79-82