Sinomammoth
| Sinomammoth | ||||||||||||
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Lower jaw of Sinomammut with graphic reconstruction |
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| Temporal occurrence | ||||||||||||
| Upper Miocene | ||||||||||||
| 11.62 to 5.333 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Sinomammoth | ||||||||||||
| Mothé , Avilla , Zhao , Xie and Sun , 2016 | ||||||||||||
Sinomammut is a now extinct genus from the order of the proboscis , which waswidespreadin eastern Asia in the Upper Miocene 11 to 5 million years ago. So far, only one lower jaw is known. Due to the characteristic tooth structure, it iscounted tothe Mammutidae family. The lower jaw is elongated, but there were no lower tusks. The closest relative is most likely the genus mammoth , which was foundin North America until the Pleistocene . The find was discovered in 1999 and was first assigned to a representative of another line of proboscis. The classification in the new genus Sinomammut then took place in 2016.
description
Sinomammut is so far only known about a single right lower jaw branch, which is only fragmentarily preserved on the ascending articular process, the articular surface is missing. The lower jaw as a whole was built relatively robust, the horizontal bone body had a rounded cross-section, it widened significantly towards the rear. The symphysis was narrow and long, alveoli for the mandibular tusks were not formed. In the lower jaw stuck nor the second and the third molar . The second is completely chewed off and does not reveal any diagnostic features, although it originally consisted of three transverse ridges ( trilophodont ). The third molar was already fully developed. It had a length of 16.7 cm and a width of 8.25 cm. There were four ridges on the chewing surface. In outline, it was square in shape, narrowing towards the back, so that the tooth on the fourth ridge was only 6.35 cm wide. Due to the dimensions, the teeth of Sinomammut were rather wide and not as narrow as in the representatives of the Gomphotheriidae, corresponding to other Mammutidae . The chewing surface had the zygodontic structure typical of mammoths . Each bar was divided into two half-lists, each consisting of a main hump on the edges of the teeth. This was followed by a smaller cusp on the inside of the tooth, both cusps were firmly connected to one another by a fusion strip, so that a continuous sharp edge was created. Behind the last ridge of the third molar was a small cingulum, a protruding bulge made of tooth enamel, which in Sinomammut consisted of six small cusps. The cingulum continued weakly developed along the inner and outer longitudinal sides of the tooth.
Location
The remaining lower jaw was discovered in 1999 at the Yanghecun site south of Changdao in Xihe County in the western Chinese province of Gansu . The site is in the Xihe Linxian Basin . The subsoil here consists of Devonian deposits, which in turn are covered by sediments from the Paleogene and the Neogene . The Neogen reaches a thickness of up to 1000 m in the Xihe Linxian Basin and can be divided into two, so far unnamed sub-units. At the Yanghecun site, especially in the northern and southern areas, deposits of the Upper Miocene and Lower Pliocene are exposed, which are again around 220 m thick. They begin with a thin, dark brown clay / siltstone layer and a limestone breccia , which is then followed by reddish brown silty claystones in which conglomerates are embedded. The entire sequence of layers at the Yanghecun site goes back to a former lake. The remains of Sinomammut were about 60 m above the base of the red-brown clay / silt stones. The exact age is given with the local stratigraphic level of the Baodean , the age of which is between 8.3 and 5 million years.
Systematics
Sino mammoth is a genus from the extinct family of Mammutidae in the order of Rüsseltiere (Proboscidea). Within the proboscis, the trilophodontic second molar refers the Mammutidae to the superordinate group of the elephantiformes , which by this feature distinguish themselves from the phylogenetically older proboscis with only two transverse ridges on the first two molars ( bilophodont ). The latter are often grouped together as the Plesielephantiformes . The early Elephantiformes include the two groups of the Mammutidae and the Gomphotheriidae , which appeared around the same time. The two groups of shapes are distinguished, among other things, on the basis of their tooth structure. The mammoths have zygodontic molars, while many gomphotheria have a bunodontic chewing surface pattern.
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Internal systematics of the Mammutidae according to Mothé et al. 2016
Losodokodon as the oldest known representative of the mammoths is not taken into account here, as it has only been passed down with upper jaw teeth. |
Both tooth patterns have paired rows of cusps that are perpendicular to the longitudinal axis of the molars and thus form the individual ridges. As a rule, a central furrow divides each ridge into two half-ridges. Small side humps are often formed along the median furrow in every half ridge. In contrast to the bunodont teeth of the gomphotheria, the side cusps in the mammoths are not free, or the space between the main cusp is not filled by further, again smaller cusps, rather both cusps are connected by a sharp fusion ridge, so that a continuous ridge is created.
Compared to the multiform gomphotheries, the mammoths are rather poor in shape, to this day only around half a dozen genera are known. The oldest undoubted representative is Losodokodon from the Upper Oligocene of Africa . The best-known, on the other hand, is mammoth , the type of which, the American mastodon ( Mammut americanum ), still appeared in North America until the end of the Pleistocene . According to molecular genetic studies, the mammoths separated from the gomphotheria and thus from the line of development leading to today's elephants (Elephantidae) in the Upper Oligocene around 24 to 28 million years ago.
From a phylogenetic point of view, Sinomammut is most closely related to mammoth . In contrast to the former, the latter has a rather short lower jaw, which, like Sinomammut, lacks the lower tusks (but can sometimes still appear in a smaller form in mammoths , which is then interpreted as sexual dimorphism ). In contrast, Sinomammut still has a long lower jaw with an extended symphysis. The genus shares this trait with older mammoths such as Eozygodon and Zygolophodon , which, however, still had tusks in the lower jaw. As a result, the long lower jaw can be seen as the original feature of the mammoth, but the loss of the lower tusks as acquired by the Sinomammut and Mammut . The shortening of the lower jaw in the area of the symphysis, where the alveoli of the tusks start, is to be understood as a further evolutionary step. Such a line of development can be proven several times in different families of proboscis, for example in the gomphotheria and the elephants.
Discovery story
The first scientific description of Sinomammut comes from a team of scientists led by Dimila Mothé and was presented in 2016. It is based on the only find so far, a right lower jaw from the West Chinese site of Yanghecun, it also represents the holotype (specimen number GIOTC 0982-9-178). The find was discovered in 1999 by Zhao Desi, a co-author of the first description. It originally consisted of a complete lower jaw, but the left branch was lost during recovery and is only documented by a photo of the situation on site. In 2007, Xie Guangpu, who was also involved in the initial description, published the find under the scientific name Sinomastodon intermedium . Sinomastodon, in turn, is a representative of the gomphotheria, which was introduced in 1986 by Heinz Tobien and colleagues and is characterized by a very short lower jaw, comparable to numerous South American forms of gomphotheria such as Stegomastodon or Cuvieronius . Since the lower jaw of Yanghecun is comparatively long, Wang Shiqi and colleagues placed it at the base of the development of the genus Sinomastodon in 2014 . Two years later, Mothé and her team realized that the molars of the Yanghecun fossil are clearly zygodontic and thus referred the lower jaw to Sinomammut . The generic name refers to the region where it was found with the Latin word sinae (for “Chinese”) and to the mammoth type with mammoth . A species was introduced with Sinomammut tobieni . The specific epithet honors Heinz Tobien, who previously named Sinomastodon .
literature
- Dimila Mothé, Leonardo S. Avilla, Desi Zhao, Guangpu Xie and Boyang Sun: A new Mammutidae (Proboscidea, Mammalia) from the Late Miocene of Gansu Province, China. Anais da Academia Brasileira de Ciências 88 (1), 2016, pp. 65-74 doi: 10.1590 / 0001-3765201520150261
Individual evidence
- ↑ a b c d e Dimila Mothé, Leonardo S. Avilla, Desi Zhao, Guangpu Xie and Boyang Sun: A new Mammutidae (Proboscidea, Mammalia) from the Late Miocene of Gansu Province, China. Anais da Academia Brasileira de Ciências 88 (1), 2016, pp. 65-74
- ↑ a b c Shiqi Wang, Desi Zhao, Guangpu Xie and Boyang Sun: An Asian origin for Sinomastodon (Proboscidea, Gomphotheriidae) inferred from a new Upper Miocene specimen from Gansu of China. Earth Science 57 (10), 2014, pp. 2522-2531
- ↑ Jehezekel Shoshani, William J. Sanders and Pascal Tassy: Elephants and other Proboscideans: a summary of recent findings and new taxonomic suggestions. In: G. Cavarretta et al. (Eds.): The World of Elephants - International Congress. Consiglio Nazionale delle Ricerche, Rome, 2001, pp. 676-679
- ↑ Heinz Tobien: The structure of mastodont molars (Proboscidea, mammalian), Part 2: The zygodont and zygobunodont patterns. Mainz Geoscientific Communications 4, 1975, pp. 195–233
- ↑ Ursula B. Göhlich: Order Proboscidea. In: Gertrud E. Rössner and Kurt Heissig: The Miocene land mammals of Europe. Munich 1999, pp. 157-168
- ^ D. Tab Rasmussen and Mercedes Gutiérrez: A Mammalian fauna from the Late Oligocene of Northwestern Kenya. Palaeontographica Department A 288 (1-3), 2009, pp. 1-52
- ↑ Nadin Rohland, Anna-Sapfo Malaspinas, Joshua L. Pollack, Montgomery Slatkin, Paul Matheus and Michael Hofreiter: Proboscidean Mitogenomics: Chronology and Mode of Elephant Evolution Using Mastodon as Outgroup. PLoS Biology 5 (1), 2007, p. E207
