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Post by grrraaahhh on Jan 8, 2011 18:20:56 GMT -9
What a BEAST!!! The Largest Known Bear, Arctotherium angustidens, from the Early Pleistocene Pampean Region of Argentina: With a Discussion of Size and Diet Trends in BearsAbstract The South American giant short-faced bear (Arctotherium angustidens Gervais and Ameghino, 1880) is one of five described Arctotherium species endemic to South America and it is known for being the earliest, largest, and most carnivorous member of the genus. Here we report an extraordinarily large A. angustidens individual exhumed from Ensenadan sediments (early to middle Pleistocene) at Buenos Aires Province, Argentina. Based on overall size, degree of epiphyseal fusion, and pathologies, this bear was an old-aged male that sustained serious injuries during life. Body mass of the bear is estimated and compared to other ursid species based on a series of allometric equations. To our knowledge, this specimen now represents the largest bear ever recorded. In light of this discovery, we discuss the evolution of body size in Arctotherium (from large-to-small) and compare this to bears that exhibited different evolutionary trajectories. We suggest that the larger size and more carnivorous nature of A. angustidens, compared to later members of the genus, may reflect the relative lack of other large carnivores and abundance of herbivores in South America just after the Great American Biotic Interchange. www.bioone.org/doi/abs/10.1666/10-037.1?journalCode=pleo shaggygod.proboards.com/index.cgi?board=americaspleistocene&action=display&thread=329&page=1#1294531184Ulna comparison between A. angustidens vs. U.m.tyrannusUrsus maritimus tyrannus (B.M. 24361 Kew Bridge specimen)L, total length of the ulna. PD, greatest proximal diameter, measured anteroposteriorly from the tip of the coronoid process to Margo dorsalis. SD, inner diameter of the semilunar notch, measured vertically. BS, minimum transverse breadth of shaft. This is in the distal portion of the shaft, at some distance above the capitulum. The extreme constriction lies close to the capitulum in the Brown Bear and the spelaeids, but higher on the shaft in the Polar Bears, including the Kew specimen. 1 L, length; PD, maximum proximal diameter; SD, inner diameter of semilunar notch; BS, minimum shaft diameter.Ursus maritimus tyrannusUlna measurements L: e485 PD: a95 SD: 44 BS1: 27.6 Ursus maritimus tyrannus (Plate # 2 Ulnae)Kurten, Bjorn 1964, The evolution of the Polar Bear Ursus maritimus Phipps.Arctotherium angustidensUlna measurements Greatest length: Right; Left, 570. Greatest width of olecranon processWidth from posterior border to tip of coronoid process: Right, 108; Left, 109. Least distance from sigmoid notch to posterior border: Right, 66; Left, 70. Greatest diameter of distal epiphyses: Right, 63; Left, 62.5.
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Post by grrraaahhh on Jan 8, 2011 18:44:47 GMT -9
Follow up on Ursus maritimus tyrannus (B.M. 24361 Kew Bridge specimen):
B.M. No. 24361 is a bear ulna of gigantic proportions. The specimen is well preserved, but the distal epiphyse is missing, so that the bone evidently belonged to a subadult animal. There is also slight damage to the distal end of the diaphyse, the olecranon, and the coronoid process, but the essential characters are well preserved. The fragment has a total length of about 440 mm. as preserved. In a very large subadult recent Polar Bear (U.Z.I. No. 3), the length without distal epiphyse is 387 mm., and the total length 428 mm. Thus the full length of the fossil bone may be estimated at a minimum of 485 mm. As far as I know this is the longest ursine ulna on record. The large Pleistocene tremarctines (Arctodus) of the Americas were unusually long-legged bears, and in some cases their limb bones attain similar or greater dimensions. The maximum record from Potter Creek Cave in northern California is 446 mm. (U.C. No. 3426), and from Rancho La Brea, Los Angeles, 475 mm. (L.A.C.M. No. Z32); and a tremendous specimen from the Irvingtonian, or Californian Middle Pleistocene, attains the almost incredible length of 591 mm (Kurten, 1964).
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Post by grrraaahhh on Jan 8, 2011 20:00:41 GMT -9
Ratio diagram Kurten (1964) comparing ulna of Ursus maritimus tyrannus with other bear ulnae: link
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Post by grrraaahhh on Jan 9, 2011 10:25:59 GMT -9
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Post by grrraaahhh on Jan 10, 2011 11:59:06 GMT -9
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Post by grrraaahhh on Jan 10, 2011 22:52:57 GMT -9
Greetings international visitors (you are welcomed to join). RE: 591 mm ulna length, it is confirmed. Using Kurten's weight estimate of 590-630 kg for the large specimen from Hay Springs, we calculated the weight of the Salt Lake County specimen to be in the range of 620-660 kg. This weight calculation was based on Kurten's (1967) estimates of "fairly lean individuals" but conveys an idea of the large size of these animals. Fattened bears might weigh several tens of kilograms more than this estimate (Nelson & Madson 1983). However.... The specimen described here has an estimated body mass ranging from 983 to 2,042 kg depending on the equations considered (Tables 3 and 4). The highest predicted value is probably unrealistic, although the size of this individual is much higher than other known specimens (see Table 5). All predicted body masses based on humeral measurements are shown in Table 3. The mean and median (considering all equations) are 1,588 and 1,749 kg respectively. Thus, we suggest that the body mass of this gigantic bear was between these two values. To our knowledge, this makes the A angustidens described here the largest known bear, and probably the most powerful terrestrial carnivoran of the late Cenozoic (Soibelzon & Schubert 2011).
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Post by grrraaahhh on Feb 1, 2011 7:23:53 GMT -9
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Post by grrraaahhh on Feb 3, 2011 9:44:35 GMT -9
More media on A. angustidens: Standing at 11 Feet: World's Largest Known Bear UnearthedThe fossils of the largest known bear to have ever lived have been found, a giant that was the most powerful land carnivore of its time, scientists said. The remains were unearthed during the construction of a hospital in La Plata City, Argentina. It was a South American giant short-faced bear (Arctotherium angustidens), the earliest and largest member of its genus (its group of species of bears). This titan lived between 2 million to 500,000 years ago, with its closest living relative being the spectacled bear (Tremarctos ornatus) of South America. Based on measurements of the fossil's leg bones and equations used to estimate body mass, the researchers say the bear would have stood at least 11 feet tall (3.3 meters) on its hind legs and would have weighed between 3,500 and 3,855 pounds (1,588 and 1,749 kilograms). In comparison, "the largest record for a living bear is a male polar bear that obtained the weight of about 2,200 pounds (1,000 kg)," said researcher Leopoldo Soibelzon, a paleontologist at the La Plata Museum. "During its time, this bear was the largest and most powerful land predator in the world," researcher Blaine Schubert, a paleontologist at East Tennessee State University in Johnson City, told LiveScience. "It's always extremely exciting to find something that's the largest of its class — and not just a little bit larger, but quite a bit larger." Although this bear probably had an omnivorous diet, flesh likely dominated. Megafauna or large creatures likely played an important role in what it ate, and potentially included giant ground sloths, now-extinct relatives of elephants, camels, tapirs, and armadillo-like creatures known as glyptodonts. "This does not imply that active hunting was its primary strategy for feeding, since its large size and great power may have permitted the bear to fight for prey hunted by other Pleistocene carnivores such as the saber-toothed cat," Schubert said. "Scavenging megaherbivore carcasses was probably another frequent way of feeding." The research team's analysis of the bear's bones suggests it was an old male that survived a number of serious injuries during life. These might have come from battles with other males, while hunting megafauna, or during fights with other carnivores over a carcass. The scientists also suggested the reason why this species might have grown so huge. When bears arrived in South America after the land bridge between the Americas appeared about 2.6 million years ago, there were relatively few other large predators there at the time, with the exception of the saber-toothed cat. The bears then grew, taking advantage of the large amount of prey, researchers suggested. The species eventually became extinct after more carnivores evolved in South America. Soibelzon and Schubert detailed their findings in the January issue of the Journal of Paleontology. www.livescience.com/animals/worlds-largest-bear-fossils-unearthed-110201.html
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Post by grrraaahhh on Feb 6, 2011 23:07:01 GMT -9
Largest recorded North American Arctotherium fossils. Ulna: 591 mm (Ivringtonian, Alameda County, CA). Ulna measurements:UC 40086:A: - B: 105 C: 62 D: - E: - A. Greatest Length. B. Proximal diameter from tip of coronoid progress to Margo dorsalis. C. Smallest diameter from bottom of semi circular notch to Margo dorsalis.. D. Inner diameter of semi circular notch. E. Least transverse diameter of shaft, above capitulum. UC 44686:A: 591 B: - C: 65 D: 47 E: 35.2 A. Greatest Length. B. Proximal diameter from tip of coronoid progress to Margo dorsalis. C. Smallest diameter from bottom of semi circular notch to Margo dorsalis.. D. Inner diameter of semi circular notch. E. Least transverse diameter of shaft, above capitulum. Extra (largest femur) ...... Femur Measurements:UC 44687A. 678 B. a165 C. 77 D. 62 E1. 134 A. Greatest Length. B. Greatest proximal width. C.Caput diameter. D. Least transverse width of shaft. E1. Greatest distal width over epicondyles. Source: Kurten (1967). Stay tuned...there are more large North American specimens.
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Post by arctodus on Feb 14, 2011 4:02:44 GMT -9
Hello, thanks for theses good informations. But i would like understand some points please:
First, according to your informations,
tyrannus ulna has a total length of 485mm. Arctotherium ulna has a total length of 570mm. Arctodus simus UVP015 ulna has a total length of 591 mm.
I don't understand, all people say that tyrannus is taller and bigger than arctodus, nevertheless ulna arctodus is much longer than ulna tyrannus... Do you know what is the height of UVP015 when it was standing on his legs? Same question about tyrannus please.
Then, do you know measurements about skull of arctotherium (largest males)?
This polar bear may reach 3.3 meters standing on his legs, how do you explain that a polar bear which has an ulna of 440mm is as tall as arctotherium angustidens which has an ulna of 570mm...?
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Post by grrraaahhh on Feb 14, 2011 7:03:46 GMT -9
Hello, thanks for theses good informations. But i would like understand some points please: First, according to your informations, tyrannus ulna has a total length of 485mm. Arctotherium ulna has a total length of 570mm. Arctodus simus UVP015 ulna has a total length of 591 mm. I don't understand, all people say that tyrannus is taller and bigger than arctodus, nevertheless ulna arctodus is much longer than ulna tyrannus... Do you know what is the height of UVP015 when it was standing on his legs? Same question about tyrannus please. Then, do you know measurements about skull of arctotherium (largest males)? This polar bear may reach 3.3 meters standing on his legs, how do you explain that a polar bear which has an ulna of 440mm is as tall as arctotherium angustidens which has an ulna of 570mm...? Quick reply (this is a busy day for me). I will try to log in later eve. - 591 mm Ulna is a California not Utah specimen (see previous post - reply # 8).
- The operative word is "all the people"? Looking at the actual data, there is little fossil specimen data for U.m.tyrannus and in my amateur opinion some of the popular online reconstruction comparisons are incorrect.
- Regarding the largest collected skull, please view the following thread for reply # 7.
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Post by grrraaahhh on Feb 14, 2011 7:11:59 GMT -9
FYI .... there are other LARGE North American Arctotherium fossil specimens. I am in the process of organizing these data and plan to post relating data including photos for comparisons in the not too far future.
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Post by grrraaahhh on Feb 14, 2011 7:41:08 GMT -9
UVP 015 Lake Bonville, Utah Specimen & Material:
Femoral measurements (mm)
UVP 015/1
Greatest length: 723 Greatest proximal width: 191 Caput diameter: - Least transverse width of shaft: 64 Greatest distal width over condyles: 152
Tibial measurements (mm)
UVP 015/2
Greatest length: 524 Greatest proximal width: 152 Least width of shaft: 50.15 Greatest distal width: 119
UVP 015/3
Greatest length: 522 Greatest proximal width: 155 Least width of shaft: 50 Greatest distal width: 119
Width of shaft in percent of total length of the tibia in Arctodus simus
Arctodus simus (Salt Lake County)
Number of Specimens: 2 Range: 9.6 Mean: 9.6
Measurements (mm) of pelvis in Arctodus simus.
UVP 015/7
Ilium, length from rim of acetabulum to anterior border: 273± Ilium, greatest width: 239± Ilium, least width of neck in front of acetabulum: 84 Acetabulum, transverse diameter: - Obturator foramen, greatest anteroposterior diameter: 127 Obturator foramen, greatest dorsoventral diameter: -
Measurements (mm) of vertebral centra in Arctodus simus
UVP 015/4 L2?
Length: 66 Width: 93 Depth: 66
UVP—Utah Vertebrate Paleontology, Utah Division of State History
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Post by arctodus on Feb 14, 2011 7:48:05 GMT -9
Thanks a lot, when you will have the time (and if you can because i suppose it's not easy), could you give or estime the height (when they are standing on their legs): UVP015, Tyrannus, and the specimen which has an ulna of 591mm.
Finally, which are the most big bones?
Arctotherium in north America were bigger than the huge specimen found in south america?
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Post by grrraaahhh on Feb 14, 2011 20:28:24 GMT -9
Thanks a lot, when you will have the time (and if you can because i suppose it's not easy), could you give or estime the height (when they are standing on their legs): UVP015, Tyrannus, and the specimen which has an ulna of 591mm. Finally, which are the most big bones? Arctotherium in north America were bigger than the huge specimen found in south america? I would describe myself as an enthusiast not a paleontologist especially as it relates to fossil reconstruction and modeling. What information I find I share in the hopes of pooling data (some forms of data are more desired including foreign and technical report literature). In short, all I am doing is forwarding the data and happy to do so. I would say there are a handful of North American GSFB specimens that are in the ballpark range of A.angustidens as it relates to size. Some of them have a longer ulna, some of them have a longer humerus. RE: U.m. tyrannus, its fossil history stops with its ulna. There are varying debates about this beast, some argue the bear was more brown bear than polar bear, some think the fossil ulna belonged to a very large brown bear, and of course the original theory that the bear was the first form of polar bear. Personal note, there's a lot of technical work I have to do this week as they relate to my computers which is impacting my ability to forum post (less so).
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