Arctotherium

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Arctotherium
Live reconstruction of Arctotherium bonariense from 1913

Live reconstruction of Arctotherium bonariense from 1913

Temporal occurrence
Lower Pleistocene to Upper Pleistocene
1.2 million years to 11,000 years
Locations
Systematics
Laurasiatheria
Predators (Carnivora)
Canine (Caniformia)
Bears (Ursidae)
Short-snouted bears (tremarctinae)
Arctotherium
Scientific name
Arctotherium
Burmeister , 1879

Arctotherium was a genus of short-snouted bears (Tremarctinae) from the early Pleistocene and Holocene. The genus lived in South America about 1.2 million to 11,000 years ago. With Arctotherium angustidens it contained one of the largest known bears in the history of the earth.

features

Arctotherium was characterized by a massive and short, not very high skull, which had a uniform, convexly curved forehead line. The nasal bone was flat and also short, the zygomatic arches well developed. The orbit had a very typical, round shape and a slightly outward position to the side. Further features that separate the genus from the spectacled bear and the North American Arctodus were wider molars and also larger dimensions in the last premolar .

Fossil finds

Arctotherium is known from numerous sites in South America , ranging from northern Venezuela to Patagonia . Most of the finds come from the pampas region in Argentina . Here, among other things, remains of teeth from El Rodeo in the north-west of the country were discovered, which are to be placed in the late Pleistocene. The fossil-rich deposits of the Rio Luján in northeast Argentina are about the same age , while the remains of La Plata are to be found in the end of the Old Pleistocene.

Paleobiology

size

A specimen of A. angustidens , the remains of which were found in the form of a foreleg in La Plata in the Argentine province of Buenos Aires , was estimated to weigh approx. 980 to 2,040 kg based on the approx. 62 cm long humerus . The most likely value is assumed to be around 1,590 to 1,750 kg. This specimen was almost 5 times as heavy as the average polar bear and 15 times as heavy as a spectacled bear , and the cave bear ( Ursus spelaeus ) found in the Pleistocene of Europe was also surpassed. However, it is believed that some sexual dimorphism occurred within the species of Arctotherium and females became significantly smaller. A. angustidens itself died out around 800,000 years ago. The following species, A. bonariense , A. tarijense , A. vetustum and A. wingei were much smaller, so A. wingei as the smallest member of this bear genus weighed around 100 to 150 kg, while A. tarijense still weighed around 200 to weighed a maximum of 400 kg.

nutrition

Arctotherium believed to be omnivorous, feeding on both carnal and vegetable resources. In A. angustidens in particular , numerous broken molars have been demonstrated, which may have been caused by chewing on very solid material such as bone. It is therefore assumed that he had a clearly carnivorous way of life and thus consumed even more meat. The following species were more similar in their diet to today's spectacled bears due to the signs of wear on their teeth, possibly they ate more vegetable material. It is believed that the bears were "forced" into a plant-based diet by other predators that later immigrated from North America, such as the Smilodon populator .

Systematics

Arctotherium belongs to the subfamily of the short-snouted bears (Tremarctinae), which is only found in America. The subfamily separated into several lines in the late Miocene , about 7.3 million years ago. The most original form is Plionarctos from the transition from Miocene to Pliocene , which only occurred in North America . It is accompanied by the genus Tremarctos , which also includes today's spectacled bear ( Tremarctos ornatus ) and is the only relative still alive today; both representatives are placed on the line of spectacled bears. The second line is that of the short- snouted bears , which includes the genera Arctodus , which also produced very large animals, Arctotherium and Pararctotherium . Arctodus appeared as early as the late Pliocene in North America, while Arctotherium only appeared in the early Pleistocene and was native to South America . Its ancestors came with the Great American Fauna Exchange from North to South America.

Within the genus Arctotherium , five types are distinguished:

  • A. angustidens Gervais & Ameghino , 1880
  • A. bonariense Gervais , 1852
  • A. tarijense Ameghino , 1902
  • A. vetustum Ameghino , 1885
  • A. wingei Ameghino , 1902

swell

Individual evidence

  1. ↑ E. Trajano, H. Ferrarezzi: A fossil bear from northeastern Brazil, with a phylogenetic analysis of the South American extinct Tremarctinae (Ursidae). In: Journal of Vertebrate Paleontology. Volume 14, No. 4, 1994, pp. 552-561.
  2. ↑ a b Borja Figueirido, Leopoldo Héctor Soibelzon: Inferring palaeoecology in extinct tremarctine bears (Carnivora, Ursidae) using geometric morphometrics. In: Lethaia. Volume 43, 2010, pp. 209-222.
  3. ^ A b Daniel A. García López, Pablo E. Ortiz, M. Carolina Madozzo Jaén, M. Sebastián Moyano: First Record of Arctotherium (Ursidae, Tremarctinae) in Northwestern Argentina and its Paleobiogeographic Significance. In: Journal of Vertebrate Paleontology. Volume 28, No. 4, 2008, pp. 1232-1237.
  4. ^ A b c Francisco J. Prevosti, Sergio F. Vizcaíno: Paleoecology of the large carnivore guild from the late Pleistocene of Argentina. In: Acta Palaeontologia Polonica. Volume 51, No. 3, 2006, pp. 407-422.
  5. ↑ a b c d Leopoldo Héctor Soibelzon, Blaine W. Schubert: The largest known bear, Arctotherium angustidens, from the Early Pleistocene Pampean region of Argentina: Withe a discussion of size and diet trends in bears. In: Journal of Paleontology. Volume 85, No. 1, 2011, pp. 69-75.
  6. ↑ Leopoldo Héctor Soibelzon, Viviana Beatritz Tarantini: Estimación de la masa corporal de las especies de osos fósiles y actuales (Ursidae, Tremarctinae) de la America del Sur. In: Revista del Museo Argentino de Ciencias Naturales. Volume 11, No. 2, 2009, pp. 243-254.
  7. ↑ Shaenandhoa Garcia-Rangel: Andean bear Tremarctos ornatus natural history and conservation. In: Mammal Review. Volume 42, No. 2, 2012, pp. 85-119.