Eurybelodon

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Eurybelodon
Temporal occurrence
Middle Miocene
12.6 to 9 million years
Locations
Systematics
Tethytheria
Russell animals (Proboscidea)
Elephantimorpha
Elephantida
Gomphotheria (Gomphotheriidae)
Eurybelodon
Scientific name
Eurybelodon
Lambert , 2016

Eurybelodon is an extinct pachyderm genus , it becomes a subfamily of Amebelodontinae within the family of Gomphotheriidae counted. The genus is based on a few fossil remains consisting of jaw and tusk fragments that came tolightin the US state of Oregon . The animals lived in wooded lake landscapes of the Middle Miocene about 13 to 9 million years ago. Special features of the fossil material can be found in the laminated structure of the tusks and their complete coverage by tooth enamel , the molars are also characterized by a rather original construction for gomphotheria. First, the remains were assigned to a different representative of the proboscis; due to different characteristics, a reassessment took place in 2016.

features

Eurybelodon is a representative of the Amebelodontinae, of which only individual jaw elements and tusk fragments are available so far . The upper tusks were oval in cross-section with a greater height versus width. About 14 cm in front of the tip, the width of the tusks was about 4.8 cm, the height about 6.2 cm. In the longitudinal direction they bent slightly downwards. The lower tusks were strikingly flat and clearly indented on the upper side. The width away from the body was 15.5 cm, the width near the body was 13.2 cm, the average height was 3.3 cm. They were twisted in lengthways. Inside, both the upper and lower tusks had a characteristically concentric laminated structure, which differs from the tubular structures of Platybelodon or Torynobelodon . Likewise, the outer shell of the upper and lower tusks was completely covered by ribbed tooth enamel . In this feature, Eurybelodon differs from most of the more modern proboscis animals, which only have a narrow lateral melting band. Only the second and third molar of the posterior dentition are known, both of which had a bunodontic chewing surface pattern typical of gomphotheria with humped cusps in a parallel arrangement. Two larger cusps each formed a ridge that ran transversely to the longitudinal direction of the teeth. It is noticeable that the last molar in Eurybelodon only had three complete ridges and an indicated fourth ridge. This is comparatively conservative for gomphotherias, since gomphotherium had four complete teeth on this tooth, whereas Platybelodon had five complete ones. The tooth humps on the pretrit (more heavily chewed) side of the tooth had a distinctive cloverleaf pattern. The length of the third molar was 15.3 cm and the width 7 cm. No diagnostic features could be observed on a 39 cm long mandibular fragment. On the horizontal bone body it was 14.5 cm high and the symphysis was 22 cm wide.

Fossil finds

The only known fossil material of Eurybelodon came to light in the upper section of the Juntura Formation near the town of Juntura in Malheur County in the southeast of the US state of Oregon . The rock unit is about 380 m thick and consists of three layers, of which the upper one is particularly fossil-bearing. It comprises a sequence of different clay and sandstones with tuffs and pumice stones turned on . The deposits are interpreted as the remains of former flood plains and lakes that extended within moderately humid forest landscapes. These existed at an average annual temperature of 13 ° C and an annual precipitation of 880 mm. On the basis of radiometric age determinations , the layers can be dated to the Middle Miocene about 13 to 9 million years ago (locally stratigraphically Clarendonian ). The significant mammal fauna from this area of ​​the Juntura Formation is known as Black Butte local fauna . It consists of insectivores , rodents , lagomorphs , carnivores and various ungulates such Couple and perissodactyls . Some extinct beavers in riparian forests and camels and horses in open areas can be rated as special landscape indicators. In addition to the Eurybelodon , mammoths from the more primitive group of the Mammutidae are also found among the trunk animals . Eurybelodon is represented with at least two lower jaws and individual tusk remnants . All the material is heavily fragmented, the longest tusk fragment reaches a length of 50 cm.

Systematics

Eurybelodon is a genus from the subfamily of the Amebelodontinae within the family of Gomphotheriidae and the order of the trunk animals (Proboscidea). The gomphotheries, in turn, combine developed proboscis with a horizontal tooth change that occurs in today's elephants , in contrast to the earliest representatives of the order, in which the vertical tooth change typical of mammals is still documented. The shovel-like lower tusks are a special characteristic of the Amebelodontinae. They are also considered to be part of the so-called trilophodont gomphotheria because of their anterior molars consisting of three ridges. in some classifications the Amebelodontinae are also listed as an independent family (Amebelodontidae).

The relationships within the Amebelodontinae are still largely under discussion. One reason for this can be found in the construction of the tusks. On the one hand, there are forms in which the tusks consist of concentric laminations. Other representatives such as Platybelodon , Konobelodon and Torynobelodon again have a tubular interior. Some scientists also assign individual proboscis to the Amebelodontinae that do not have shovel-like tusks, such as Progomphotherium and Afromastodon .

The closer relationships between Eurybelodon and other amebelodontins are not clear. The laminated lower tusks make a closer bond with Platybelodon or Torynobelodon rather unlikely. The rear molars with their three complete and fourth indicated groin could speak for a closer relationship to Amebelodon , but this had rather rounded lower tusks and not as flat as in Eurybelodon . The latter occurs among other things with Konobelodon , once considered a subgenus of Amebelodon , but the tusks do not show any noticeable rotations. The posterior molars of the genus also consist of five ridges. Another peculiarity that separates Eurybelodon from other gomphotheria is that both the upper and lower tusks are completely covered with tooth enamel . Most modern proboscis only have a narrow lateral band on the upper tusks here, while the lower ones are free of it. The young elephants of today's elephants still have a thin layer of enamel on their tusks, which is later lost. The process is primarily related to food intake. In the case of Eurybelodon , however, no traces of abrasion can be seen, so that the function of the tusks in the proboscis species remains unclear. The benefits of enamel covering are therefore also unclear.

In a first assessment of the fauna material of the Black Butte local fauna , J. Arnold Shotwell and Donald E. Russell referred the gomphotheria finds to Platybelodon , which occurs quite frequently in North America . More than 50 years later, W. David Lambert recognized that, taking into account the above-mentioned differences, the fossil remains were probably an independent genus. He therefore re- described it in 2016 under the generic name Eurybelodon . He identified an upper tusk fragment as a holotype (specimen number UOMNH F-7977). Lambert also introduced a new species with E. shoshani . The generic name Eurybelodon is derived from the Greek word ευρύ ( eury ) for "wide" and refers to the design of the lower jaw tusks . The suffix -belodon is a frequently used ending in gomphotherias. The specific epithet shoshani honors Jeheskel Shoshani , one of the leading experts on recent and fossil trunk animals, who was killed in a terrorist attack in Addis Ababa in May 2008 .

literature

  • W. David Lambert: Eurybelodon shoshanii, an unusual new shovel-tusked gomphothere (Mammalia, Proboscidea) from the late Miocene of Oregon. Journal of Vertebrate Paleontology 36 (3), 2016, p. E1091352 doi: 10.1080 / 02724634.2016.1091352

Individual evidence

  1. ^ A b c J. Arnold Shotwell and Donald E. Russell: Mammalian fauna of the Upper Juntura Formation, the Black Butte local fauna. Transactions of the American Philosophical Society 53 (1), 1963, pp. 42-69
  2. ^ A b c d W. David Lambert: Eurybelodon shoshanii, an unusual new shovel-tusked gomphothere (Mammalia, Proboscidea) from the late Miocene of Oregon. Journal of Vertebrate Paleontology 36 (3), 2016, p. E1091352 doi: 10.1080 / 02724634.2016.1091352
  3. ^ RG Bowen, WL Gray and DC Gregory: General geology of the Northern Juntura Basin. Transactions of the American Philosophical Society 53 (1), 1963, pp. 22-41
  4. ^ A b Gregory J. Retallack: Late Miocene climate and life on land in Oregon within a context of Neogene global change. Palaeogeography, Palaeoclimatology, Palaeoecology 214, 2004, pp. 97-123
  5. ↑ 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
  6. ^ 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
  7. ↑ 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
  8. ^ 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