Aphanobelodon
| Aphanobelodon | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Middle Miocene | ||||||||||||
| 15.2 to 12.6 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Aphanobelodon | ||||||||||||
| Wang , Deng , Ye , He & Chen , 2017 | ||||||||||||
Aphanobelodon is an extinct pachyderm genus of the family of Gomphotheriidae that of several skeletal remains from northwestern China is busy. They are remnants of adult individuals and of younger animals. In the Middle Miocene , 15 to 13 million years ago, they probably lived in humid landscapes, where they lived on a rather soft vegetable diet. The finds suggest medium-sized representatives of the gomphotheria. They had the family's characteristic flat skull and shovel-like broadened lower tusks. The latter feature refers to Aphanobelodonin the closer relationship of the Amebelodontinae. A special feature of the representatives of Aphanobelodon was that the upper tusks had receded, which is an unusual development in the proboscis . The genus was scientifically introduced in 2017.
features
Aphanobelodon was a medium-sized representative of the gomphotheries. There are several complete skeletons from both adult and younger individuals. On the basis of this, a body weight of around 1300 kg can be concluded for smaller, adult animals, while larger ones weighed around 2070 kg. Young animals found reached body weights between 950 and 1280 kg, while an almost newborn individual weighed around 113 kg. The sizes are clearly below those for today's African and Asian elephants . Was described by Aphanobelodon only the skull so far. This measured between 81 and 102 cm in length, the holotype specimen it is 89.5 cm long. The brain skull took up only 32.2 cm of it. The much larger part with 58.4 cm was formed by the facial skull with the elongated middle jawbone . As a result, the skull was clearly elongated in length. At the side it showed noticeable narrowing, so that the width between the not very bulging zygomatic arches was only 17.4 cm, at the cranium was 14.7 cm. The most striking characteristic of Aphanobelodon was the extended middle jawbone, which began wide and enclosed a large foramen incisivum . Towards the front it narrowed more and more, at the top it had a width of 9.2 cm. This made the entire rostrum look very delicate. It was also directed downwards, a typical characteristic of the Amebelodontinae. When viewed from above, the skull had a bean-shaped nostril. The nose was as usual not very large at the trunk animals and pitched sideways at the rear edge of the nostril on. A nasal process protruded from the center of the nostril . The infraorbital foramen opened in front of the anterior zygomatic arch attachment and was doubled with a large anterior and small posterior depression. In the midline of the incisive fossa (incisor fossa ) there was a forked bone rib, which is missing in other developed representatives of proboscis. The orbit was relatively small, the anterior margin was at the level of the insertion of the broken third molar, while the postorbital process of the posterior margin was at the posterior end of the tooth. When viewed from the side, the skull was generally flattened. The height of the holotype specimen was just under 36 cm. Only the largest skulls were slightly arched. A flat skull is a general characteristic of gomphotheries, but some have a few shapes such as Konobelodon dome-like bulges. The temporal fossa (temporal fossa) was laterally widened, it was framed at the top by a distinctive temporal bar, which in turn delimited the almost rectangular skull. The joints of the occiput for connection to the cervical spine did not protrude very far. The tympanic membrane was not enlarged at the base of the skull . The glenoid pit connecting to the mandible was large. The choans were narrow, to the side of them was a strong pterygoid process with a hook-shaped end.
The lower jaw was between 113 and 155 cm long with a maximum width of 15.2 cm. As with all representatives of the Amebelodontinae, the symphysis at the anterior attachment of the lower jaw was extremely elongated, with the holotype specimen it reached 45.1 cm. At the base, the symphysis began to be relatively narrow, but expanded continuously at the front, so that a scoop-like shape was created. In this feature, Aphanobelodon agrees with Platybelodon , but differs from other Amebelodontinae, whose symphysis does not expand forward. The upper side of the symphysis was indented like a trough, laterally it was bordered by two bone bulges. The front end pulled them out only slightly convex, which mediates between the characteristics of Platybelodon (straight) and Amebelodon (pointed). In side view, the symphysis bent only slightly downwards compared to the lower jaw, which is therefore less pronounced than in Amebelodon and Konobelodon . The horizontal bone body showed a relatively low structure with a maximum height of 12 cm. The ascending branch was about twice as high. The crown process was blunt, the angled process at the rear end of the lower jaw was level with the occlusal plane and was only slightly raised. A large posterior mental foramen opened at the beginning of the row of teeth, a small anterior one also appeared.
The most noticeable peculiarities of aphanobelodon can be found in the front dentition. In contrast to all other Amebelodontinae, no tusks were formed in the upper jaw . Only the skeleton of an almost newborn young animal had short tusks there. These were obviously not replaced by permanent tusks. Rather, in the adult individuals the alveoli of the upper tusks, which in the proboscis are formed by the middle jawbone, were closed. The greatly enlarged foramen incisivum also speaks against developed tusks. The feature of the missing upper tusks is special in that the proboscis usually reduce the lower ones and keep their upper ones. The Deinotheriidae are an exception here , but they belong to a different and much more primitive line of development. The lower jaw tusks were extremely flat and wide, the feature is more developed than that of Amebelodon or Serbelodon . Inside, the tusks consisted of concentric fine layers, consistent with some other Amebelodontinae, while tubular structures were formed in Platybelodon and Torynobelodon . When viewed from the side, the lower tusks curved slightly upwards; when viewed from above, they were slightly twisted. Overall, however, they only protruded about 15 cm from the alveoli. Their exit width was 11 cm, their height 2.5 cm. At the front they ended in a closed, concave edge that tapered off very sharply and thus formed a cutting edge. It showed clear signs of wear on the surface of the holotype specimen. For the rear teeth of Aphanobelodon was horizontal change of teeth of Elephantimorpha typical, so that only one tooth was each arch claimed simultaneously. In general, the molars had a bunodontic chewing surface, i.e. with humped, parallel cusps. Two large cusps each formed a pair perpendicular to the longitudinal axis of the tooth. The two anterior molars and the last premolar each had a total of three pairs (ridges), which gave them a trilophodontic character. The last molar was long and rectangular in shape and made up of five ridges in both the upper and lower jaw. Small side humps rose between the main humps of each bar. The more strongly chewed ( pretrite ) cusps showed a clover-leaf-shaped pattern in cross-section . On the upper third molar, individual cingula (tooth enamel bulges) were formed laterally and behind, on the lower last molar there was a strong cingulid at the rear end, which also had a cusp. In general, dental cement was strongly developed. In their entire structure, the teeth resembled those of Platybelodon . The upper last molar was 16.3 cm long and 7.1 cm wide in the holotype specimen, the lower one was 18.5 cm long and 6.0 cm wide, respectively.
Fossil finds
The only known finds of Aphanobelodon so far came to light in the Zhangenbao Formation near Tongxin in the Ningxia Autonomous Region in northwestern China . The rock unit is primarily composed of sand and silt stones , in which silt and clay stones are occasionally incorporated. Within the approximately 240 m thick sediment sequence, the remains were found in the middle section (layer 19), which in turn consists of orange-colored silty sandstones with a high proportion of feldspars and gypsum . The deposits go back to a marshland or lake edge area. No other fossil remains were found in the outcrop that contained the Aphanobelodon finds . More than two dozen mammalian taxa from the same stratigraphic position have been documented from the wider area . These include various ungulates such Couple and odd-toed ungulates , but also primates and carnivores . As other representatives of the mammoths were among other Platybelodon and Gomphotherium be occupied. The community is assigned to the local Dingjiaergou fauna, which belongs to the early Middle Miocene around 15 to 13 million years ago. There are several skeletons of Aphanobelodon , which are largely complete and some were found in an articulated position. They come from both adult individuals and young animals.
Paleobiology
The different size variations in the skulls of adult individuals of Aphanobelodon are striking . In addition, the largest skulls have a slightly arched skullcap. Further differences can be found in the position of the posterior margin of the nasal opening, which in large specimens is further set back (behind the postorbital process) than in smaller specimens (at the level of the postorbital process). It is probably a sexual dimorphism , in which the larger skulls belong to males, the smaller ones to females. According to this, bulls weighed around 2000 kg, cows only around 1300 kg, which makes a difference of around 63%. Similar evidence is also found in today's elephants.
Based on the wear marks on the molars, aphanobelodon can be seen as a consumer of mainly soft to mixed vegetable foods . This assumption is supported by the extremely flat lower tusks that taper off like a cutting edge at the front. In their structure, the tusks are similar to those of Platybelodon , which has been analyzed to cut through dense vegetation with them. The more rounded tusks of Amebelodon and Serbelodon , on the other hand, were better suited for digging in harder substrates.
Systematics
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Internal systematics of the Amebelodontinae according to Wang et al. 2017
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Aphanobelodon is a genus from the subfamily of the Amebelodontinae , in turn, a part of the family of Gomphotheriidae within the order of Rüsseltiere forms (Proboscidea). The gomphotheries include developed proboscis with a horizontal tooth change that occurs in today's elephants , in contrast to the earliest representatives of the order, which still had a vertical tooth change typical of mammals. The shovel-like lower tusks can be rated as a special characteristic of the Amebelodontinae. Because of their front molars, which consist of three ridges, they belong to the so-called trilophodont gomphotheria. Sometimes the Amebelodontinae are also run as an independent family (Amebelodontidae).
The relationships within the Amebelodontinae are still largely unclear. The reason for this is the structure of the tusks, which on the one hand consist of concentric laminations in some forms, and in others such as Platybelodon , Konobelodon and Torynobelodon have a tubular interior. In addition, individual proboscis were added to the Amebelodontinae on several occasions , which do not have shovel-like tusks, such as Progomphotherium and Afromastodon . However, despite the existing differences in the internal structure of the tusks , Aphanobelodon has numerous similarities with Platybelodon , for example in terms of the extremely flat and wide shape of the lower tusks. In addition, there are also relationships with Torynobelodon , while Konobelodon may be more closely related to Amebelodon . This suggests that the tubular structure of the tusks is more of a derived feature within the Amebelodontinae that arose several times independently within the group. This may also apply to the front molars with four ridges ( tetralophodont ) that occur in some representatives of platybelodon and konobelodon . Based on phylogenetic investigations from 2017, two closer kin groups can be identified within the Amebelodontinae: on the one hand Konobelodon , Amebelodon and Protanancus (the so-called actual "Amebeldodontinae"), on the other hand Torynobelodon , Platybelodon and Aphanobelodon (the so-called "Platybelodontinae").
The first scientific description of aphanobelodon was made in 2017 by a research team led by Wang Shi-Qi . The basis was the skeleton finds from the Zhangenbao Formation in the Ningxia Autonomous Region in northwestern China. The holotype (copy number HMV 1880) consists of a complete skull with lower jaw and an associated partial skeleton. He likely represents a fully grown female individual. The generic name Aphanobelodon is derived from the Greek word αφανής ( aphanes for "hidden" or "invisible") and refers to the non-existent upper tusks. The addition of the name belodon is often used by representatives of the Amebelodontinae. The only known species named Wang and colleagues A. zhaoi in honor of Zhao Rong, who discovered and excavated the finds.
literature
- Shi-Qi Wang, Tao Deng, Jie Ye, Wen He and Shan-Qin Chen: Morphological and ecological diversity of Amebelodontidae (Proboscidea, Mammalia) revealed by a Miocene fossil accumulation of an upper-tuskless proboscidean. Journal of Systematic Palaeontology 15 (8), 2017, pp. 601-615 doi: 10.1080 / 14772019.2016.1208687
Individual evidence
- ↑ a b c d e f g h i j Shi-Qi Wang, Tao Deng, Jie Ye, Wen He and Shan-Qin Chen: Morphological and ecological diversity of Amebelodontidae (Proboscidea, Mammalia) revealed by a Miocene fossil accumulation of an upper -tuskless proboscidean. Journal of Systematic Palaeontology 15 (8), 2017, pp. 601-615 doi: 10.1080 / 14772019.2016.1208687
- ↑ Jie Ye and Hang Jia: Platybelodon (Proboscidea, Mammalia) from the Middle Miocene of Tongxin, Ningxia. Vertebrata PalAsiatica 24, 1986, pp. 139-151
- ↑ Shi-Qi Wang and Jie Ye: Paleobiological implications of new material of Platybelodon danovi from the Dingjiaergou Fauna, western China. Historical Biology: An International Journal of Paleobiology 27 (8), 2015, pp. 987-997 doi: 10.1080 / 08912963.2014.918967
- ^ W. David Lambert: The Feeding Habits of the Shovel-Tusked Gomphotheres: Evidence from Tusk Wear Pattern. Paleobiology 18 (2), 1992, pp. 132-147
- ↑ María Teresa Alberdi, José Luis Prado, Edgardo Ortiz-Jaureguizar, Paula Posadas and Mariano Donato: Paleobiogeography of trilophodont gomphotheres (Mammalia: Proboscidea). A reconstruction applying DIVA (Dispersion-Vicariance Analysis). Revista Mexicana de Ciencias Geológicas 28 (2), 2011, pp. 235–244
- ^ Jan van der Made: The evolution of the elephants and their relatives in the context of a changing climate and geography. In: Harald Meller (Hrsg.): Elefantenreich - Eine Fossilwelt in Europa. Halle / Saale, 2010, pp. 340-360
- ^ William J. Sanders, Emmanuel Gheerbrant, John M. Harris, Haruo Saegusa and Cyrille Delmer: Proboscidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, London, New York, 2010, pp. 161-251