Juxia

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Juxia
Skull of Juxia

Skull of Juxia

Temporal occurrence
Middle to Upper Eocene ( Sharamurunian )
41.1 to 37.7 million years
Locations
Systematics
Mammals (mammalia)
Higher mammals (Eutheria)
Laurasiatheria
Unpaired ungulate (Perissodactyla)
Indricotheriidae
Juxia
Scientific name
Juxia
Chow & Chiu , 1964

Juxia is an extinct genus of the odd ungulate from the family Indricotheriidae . This family includes large to very large odd ungulates, which are closely related to the rhinos , but Juxia was a rather smaller representative. The genus lived between 41 and 37 million years ago in the mid and late Eocene and has so far only been found in China and northern India . After the skeleton was built, Juxia was a relatively fast runner who lived on soft, plant-based foods. The genus was first described in 1964.

features

Juxia belonged to the smaller Indricotheriidae ( Indricotheriidae ), its dimensions reached only about half that of the huge Paraceratheriums . Reconstructions assume a head-torso length of around 300 cm, divided into around 60 cm head, 62 cm neck and around 178 cm body. The shoulder reached a height of about 190 cm, the head sat at a height of around 220 to 230 cm. The weight was estimated to be 759 kg. Like Paraceratherium , it had long limbs and a long neck. The incomplete skull was about 60 cm long. It was narrow and elongated with a skull of the same size as the face and brain. The forehead line was clearly convex, on the parietal bone sat a distinctly developed crest . The nasal bone was elongated, but weakly developed and, as in other Indricotheria, had no horn. The interior of the nose reached to the third premolar and was so very extensive. The intermaxillary bone had no contact with the nasal bone. The zygomatic arch was slender and long, and curved upwards at the rear. The occiput was slightly extended and rather rectangular in shape.

The lower jaw was narrow and low in shape with a short symphysis that only reached to the first premolar . Below between the third and fourth premolars was a mental foramen . The ascending branch was wide and low, and the mandibular joint rose only slightly above the occlusal plane. The front edge of the crown process rose steeply. The masseteric fossa emerged as a deep furrow on the ascending branch . With the tooth formula, the dentition comprised the complete dentition of the original mammals. The incisors were not very specialized, only the inner pair of teeth was somewhat larger, but not so much enlarged that it formed clear tusks, as in the later Indricotheria. Each tooth of the front dentition stood at a certain distance from the other. The canine resembled the incisors but was larger. There was a distinct diastema between the canine and the first premolar . The latter was very small, while the next increased significantly in size. The molars were rectangular to triangular in shape. In their structure, they were largely similar to the teeth of rhinos .

The postcranial skeleton is not completely known. The cervical vertebrae were clearly stretched, giving the animal a long neck that was slightly longer than the length of its skull. The limbs were characterized by their slender construction, they were significantly less robust than in the representatives of the Brontotheriidae, which appeared around the same time, and in the related large Indricotheria. As with the other indricotheria, the radius was noticeably longer than the humerus . The former measured 61 cm, the latter 49 cm. The femur reached a good 60 cm, the tibia 59 cm. The limbs each ended in three toes, of which the middle ( Metapodium III) was the largest, while the two much smaller ones (II and IV) each set on at the side. The front feet, however, had an additional fourth, smaller toe. The metapodia were also slender, but did not show any lateral narrowing as in the other indricotheria. The end joints each had distinctive central ribs.

Fossil finds

The genus Juxia has so far only been found in northern China and Mongolia . The fossil record is sparse. The first finds date from the 1920s, which were collected during expeditions of the American Museum of Natural History in Mongolia, but were only later recognized as belonging to Juxia . The best preserved find is a partial skeleton from Ula Usu in Inner Mongolia , which was discovered in 1959 during an expedition by scientists from China and the Soviet Union in the Shara Murun Formation . This find is from the late Ocene era and includes a damaged skull, the lower jaw and numerous skeletal remains of the musculoskeletal system as well as remains of the spine and represents the first document of the genus. Some additional upper jaw fragments come from the same region, but from the Ulan Gochu formation . Other finds, especially isolated teeth, come from the Hedi Formation in the Yuanqu Basin in Shanxi Province and date to the late Middle Eocene. A fragmented skull came to light in the Liyan Basin in Ladakh, India ; the site in today's Himalayas was originally 3000 to 3500 m lower. The reference to Juxia is not shared by all scientists.

Paleobiology

In ungulates, about three quarters of the body weight is carried by the front legs. The construction and position of the legs under the body provide information about the mode of locomotion. Short lower leg sections with an extended elbow joint are typical of lumbering animals, while long lower leg sections and slightly bent elbows indicate fast-moving animals. Juxia has relatively long and slender foot skeleton bones, while the forearm and lower leg are the same or longer than the upper sections of the arm and leg. The reconstructed elbow also formed an angle of about 135 °. The extremely strong central ray of the hands and feet and the significantly reduced two side rays show a tendency towards monodactyly. There is no diaphragmatic vertebra on the thoracic spine (the vertebra that separates the front part of the spine from the back, often the vertebra with the spinous process that marks the highest point of the spine), the spinous processes are usually wide. The lumbar spine is also very long with five to six vertebrae. All of this speaks for a very fast animal with a well mobile spine. On the upper arm there is also an egg-shaped joint head with a surface that is more curved in the longitudinal direction of the body. This enabled wide longitudinal arm movements and reduced lateral outward movements. The midrib on the joints of the metapodia had a similar function, preventing the phalanges from shearing sideways.

The niederkronigen molars are typical of a predominantly soft vegetable diet ( browsing ), perhaps dominated a leaf- and fruit-rich diet. The crest, the low ascending branch of the lower jaw, and the deep masseretica fossa are unusual features in ungulates. As a result, the masseter muscle was probably particularly strong. It can be assumed that vertical movements predominated when chewing and lateral movements hardly occurred. The shape and arrangement of the incisors is also unusual. They are almost the same size, the upper ones are vertical, while the lower ones are oriented forward. When the teeth were closed, the teeth reached into the respective tooth gap of the opposite row of teeth, so that only a small gap between the innermost incisors remained open. It is believed that Juxia ate its food with its incisors, wedging a twig between the gap between the teeth and tearing it off with sideways head movements. The few bone marks on the skull, which could indicate pronounced facial muscles, make particularly mobile lips unlikely.

Systematics

Internal systematics of the family of the Indricotheriidae according to Wang et al. 2016
 Indricotheriidae  


 Pappaceras


   

 Forstercooperia



   

 Juxia


   

 Urtinotherium


   

 Paraceratherium





Template: Klade / Maintenance / Style

Juxia is a genus from the extinct family of the Indricotheriidae , which in turn is part of the superfamily of the Rhinocerotoidea and thus belongs to the close relationship of today's rhinos . Unlike the rhinos, the Indricotheria did not develop a horn. Further anatomical differences can be found, among other things, in the construction of the front dentition. In the case of the Indricotherien, this consists of short, conically shaped incisors, from which a dagger-like pair developed above and below in more modern forms. The rhinos, on the other hand, only have a dagger-like pair in the lower jaw, while the incisors in the upper dentition are chisel-like.

Within the Indricotheria, Juxia represents a basal (primeval) representative. This shows above all the complete, non-reduced mammalian dentition, the hardly specialized incisors and the generally small and slimmer physique with long limbs. It presumably emerged from the Middle Eocene pony-sized Forstercooperia and mainly occurred in the late Middle Eocene and the Lateocene 40 to 34 million years ago. His successors include the gigantic genera Urtinotherium and Paraceratherium . The latter represents the largest known land mammal in the history of the earth.

Juxia was first described in 1964 by the Chinese paleontologists Chow Minchen and Chiu Chan-siang using the partial skeleton from the Shara Muren formation, which functions as a holotype (copy number V 2891). It is Juxia the Latinized version of the Chinese words Ju-xi (巨犀), which means as much as "giant rhinoceros". The only species recognized today is J. sharamurenense , the species name referring to the location of the partial skeleton in the geological formation of the same name . The species name was later corrected in J. sharamurenensis based on the zoological nomenclature . Originally two other species were described with J. borissiaki and J. shoui , but they are largely synonymous with J. sharamurenensis . In parts, the genus Irmequincisoria is also counted to Juxia . This is based on largely isolated teeth and upper jaw remains from the Wucheng Basin in the Chinese province of Henan and was introduced in 1976 with two species: I. mazhuangensis and I. micracis . Other authors see at least J. micracis and J. shoui as two other distinct types of Juxia .

The genus Juxia was not always independent . In 1967 Leonard B. Radinsky saw no major differences to Forstercooperia and equated the former with the latter described earlier. This was viewed critically by other experts due to the somewhat different set of teeth and additional anatomical features such as the nasal interior that extends significantly further back in Juxia . Therefore, Spencer George Lucas and fellow researchers removed the synonymity again in 1981. Since then, Juxia has been a recognized genus again.

literature

  • Chow Minchen and Chiu Chan-Siang: An eocene giant rhinoceros. Vertebrata Palasiatica 8 (3), 1964, pp. 264-268
  • Zhan-Xiang Qiu and Ban-Yue Wang: Paracerathere fossils of China. Palaeontologia Sinica 193 (New Series C, 29), 2007, pp. 1–396 (pp. 247–386 in English)

Individual evidence

  1. ↑ a b c d e f g h i j Zhan-Xiang Qiu and Ban-Yue Wang: Paracerathere fossils of China. Palaeontologia Sinica 193 (New Series C, 29), 2007, pp. 1–396 (pp. 247–386 in English)
  2. ↑ a b c d e f Chow Minchen and Chiu Chan-Siang: An eocene giant rhinoceros. Vertebrata Palasiatica 8 (3), 1964, pp. 264-268
  3. ↑ a b c Kurt Heissig: The rhinocerotidae. In: Donald R. Prothero and RM Schoch (eds.): The evolution of perissodactyls. New York, London, Oxford University Press, 1989, pp. 399-417
  4. ↑ a b Qi Tao and Zhou Minzhen: A new species of Juxia (Perissodactyla); Nei Mongol. Vertebrata Palasiatica 27 (3), 1989, pp. 205-208
  5. ↑ Huang Xueshi, Tong Yongshen, Wang Jingwen and Shi Jimming: Discovery of Juxia sharamurenense in Yuanqu Basin. Vertebrata Palasiatica 36 (1), 1998, pp. 54-57
  6. ^ BN Tiwari: A Late Eocene Juxia (Perissodactyla, Hyracodontidae) from Liyan molasse, Eastern Ladakh, India. Journal of the Palaeontological Society of India 48, 2003, pp. 103-113
  7. ↑ Haibing Wang, Bin Bai, Jin Meng and Yuanqing Wang: Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids. Scientific Reports 6, 2016, p. 39607 doi: 10.1038 / srep39607
  8. ^ Leonard B. Radinsky: The families of the Rhinocerotoidea (Mammalia, Perissodactyla). Journal of Mammalogy 47 (4), 1966, pp. 631-639
  9. ^ A b Leonard B. Radinsky: A review of the Rhinocerotoid Family Hyracodontidae (Perissodactyla). Bulletin of the American Museum of Natural History 136 (1), 1967, pp. 1-47
  10. ↑ Demberelyin Dashzeveg: A new Hyracodontid (Perissodactyla, Rhinocerotoidea) from the Ergilin Dzo formation (Oligocene Quarry 1) in Dzamyn Ude, Eastern Gobi Desert, Mongolia. American Museum Novitates 3178, 1996, pp. 1-12
  11. ↑ Donald R. Prothero, Earl Manning and C. Bruce Hanson: The phylogeny of the rhinocerotoidea (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 87, 1986, pp. 341-366
  12. ↑ Wang Jingwen: A New Genus of Forstercooperiinae from the Late Eocene of Tongbo, Henan. Vertebrata Palasiatica 14 (2), 1976, pp. 104-111
  13. ^ Spencer George Lucas and Jay C. Sobus: The systematics of Indricotheres. In: Donald R. Prothero and R. Schoch (Eds.): The evolution of Perissodactyls. New York, Oxford University Press, 1989, pp. 358-378
  14. ^ A b Donald R. Prothero: Rhino giants: The palaeobiology of Indricotheres. Indiana University Press, 2013, pp. 1-141 ISBN 978-0-253-00819-0
  15. ↑ Spencer G. Lucas, Robert M. Schoch and Earl Manning: The Systematics of Forstercooperia, a Middle to Late Eocene Hyracodontid (Perissodactyla: Rhinocerotoidea) from Asia and Western North America. Journal of Paleontology 55 (4), 1981, pp. 826-841

Web links

Commons : Juxia  - collection of images, videos and audio files
  • The Paleobiology Database Juxia