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Apr 29, 2011 19:29:30 GMT -9
Post by grrraaahhh on Apr 29, 2011 19:29:30 GMT -9
Arctodus Simus Factoid:Spread across the North American continent and spanning the middle Irvingtonian through the Rancholabrean and becoming extinct during the last glacial maximum ≤11,400 BP; fossil remains of the nomadic Giant Short Faced Bear are scarce; they are found in little over a hundred localities. At the famous Southern California Rancho La Brea Tar Pit, a small total of thirty individual specimens (three shelve racks) have been recovered of the Giant Short Faced Bear. "Cox (1991) and Scott and Cox (1993) showed that some large specimens were present at Rancho La Brea, but that the measurable sample is skewed towards females (the majority of adult specimens) and adolescent males, where long-bone epiphyses were not fused (S. Cox, pers. comm. to Richards, 26 July 1989; Agenbroad and Mead, 1986; Cox, 1991; Scott and Cox, 1993)."Richards et al. (1996).
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Jun 10, 2011 10:06:33 GMT -9
Post by warsaw on Jun 10, 2011 10:06:33 GMT -9
Ekhm...
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Jul 1, 2011 11:32:42 GMT -9
Post by grrraaahhh on Jul 1, 2011 11:32:42 GMT -9
Soibelzon et al. 2009.
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Jul 2, 2011 17:40:06 GMT -9
Post by grrraaahhh on Jul 2, 2011 17:40:06 GMT -9
Kurten (1966, 1967) recognized two genera and at least seven species of short-faced Pleistocene bears, subfamily Tremarctinae: the Neotropical Tremarctos ornatus (the only living species); T. floridanus, Arctodus pristinus, and A. simus from North America; and A. bonariensis, A. pamparus, and A. brasiliensis from South America. Other poorly known species from South America include Arctodus enectum (Paula Couto, 1960) and A. angustidens (Kragiievich, 1926). Several genera were created for the American fossil bears (see Kraglievich, 1926, and Kurten, 1966, 1967, for taxonomic revision). For instance, Paulo Couto recognized two genera (Paula Couto, 1960) or subgenera (Paula Couto, 1979) of South American extinct bears, Arctotherium and Pararctotherium, the latter including Arctodus brasiliensis. Kurten (1967) considered all tremarctine genera, except Tremarctos, as junior synonyms of Arctodus. Kurten's classification was followed by Perea and Ubilla (1983, 1985), who distinguished two morphological patterns in the extinct genus Arctodus: pattern "G" (large forms) and pattern "P" (small forms). They assigned A. brasiliensis, with some restrictions, to pattern "P," characterized by inflated frontal region and auditory bullae, U -shaped postpalatine margin, lateral margin of mesopterygoid fossa independent from the styloid apophysis, and foramen rotundum emerging in the orbit independent of the alisphenoid canal. A. brasiliensis, and represents a considerable extension to the northeast of the geographic range of South American tremarctines. The bear from Ubajara is compared to the known species of Tremarctinae, and its systematic position is discussed. A phylogenetic hypothesis of the genera of Tremarctinae is presented. We recognize Arctotherium as a separate genus, including the extinct South American tremarctines, with two subgenera: Arctotherium and Pararctotherium. SOUTH AMERICA OVERVIEW- The bear from Ubajara is classified as A. (P.) brasiliense (comb. nov.).
- The measurements of the Ubajara skull, mandible, and teeth are presented as well as those of other specimens previously assigned to A. brasiliense.
- The differences in size and proportions between these specimens and the closely related A. pamparum and A. bonariense can be appreciated in the ratio diagrams.
- No major qualitative differences between the specimen from Ubajara and those previously assigned to A. brasiliense from Minas Gerais State were found.
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Jul 2, 2011 17:41:12 GMT -9
Post by grrraaahhh on Jul 2, 2011 17:41:12 GMT -9
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Aug 14, 2011 1:40:19 GMT -9
Post by grrraaahhh on Aug 14, 2011 1:40:19 GMT -9
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Aug 28, 2011 9:50:31 GMT -9
Post by grrraaahhh on Aug 28, 2011 9:50:31 GMT -9
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Oct 23, 2011 14:38:10 GMT -9
Post by grrraaahhh on Oct 23, 2011 14:38:10 GMT -9
"North American giant short-faced bears have been ascribed at times to various taxa and have undergone several revisions: Arctotherium simum Cope, 1879 (genus from Bravard, 1857); Arctotherium yukonense Lambe, 1911; Arctotherium californicum Merriam, 1911; Dinarctotherium merriami Barbour, 1916; Tremarctotherium simum (Cope, 1879) (genus from Kra-glievich, 1926; used by Rinker, 1949); Arctodus nebrascensis (used by Berger, 1930; genus from Leidy, 1854); and Arctodus simus nebrascensis (used by Frick, 1930). These taxa are now considered to be junior synonyms of Arctodus simus (Cope, 1879), subfamily Tremarctinae, family Ursidae (Kurten, 1963). At one time, all North American Arctodus fossils were tentatively referred to a single species, Arctodus pristinus Leidy, 1854, and thought to be highly variable (Firby, 1968; Kurten, 1963). As more specimens became available, two species were recognized (Kurten, 1967). Arctodus pristinus Leidy, 1854 (junior synonym: Ursus haplodon Cope, 1896) was a relatively lightly built form with slender bones, relatively longer jaws, and smaller teeth than the larger A. simus. A. pristinus has been recognized with certainty only in eastern North America from middle Irvingtonian through Rancholabrean deposits (Kurten, 1967; Kurten and Anderson, 1980). A. simus is larger, has a more robust dentition and skeleton, a shorter face, and relatively longer limbs than A. pristinus. Remains of A. simus are found throughout North America (except in the southeast) and also date from middle Irvingtonian through Rancholabrean times (Kurten, 1967; Kurten and Anderson, 1980). Kurten (1967) recognized two subspecies of A. simus: the larger A. s. yukonensis from Yukon Territory, Alaska, and Nebraska and the smaller A. s. simus recovered throughout the rest of North America." Richards et al. (1996). "The Tremarctinae are a monophyletic group; Ursinae is their sister group (Trajano and Ferrarezzi, 1994; Talbot and Shields, 1996). Plionarctos and Tremarctos constitute the ‘spectacled bears’ clade, a basal group of the Tremarctinae, and Arctodus and Arctotherium conform to the ‘short-faced bears’ clade. Within the clade formed by the Arctotherium species." Soibelzon et al. (2005).
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Oct 24, 2011 8:46:49 GMT -9
Post by grrraaahhh on Oct 24, 2011 8:46:49 GMT -9
"North American giant short-faced bears have been ascribed at times to various taxa and have undergone several revisions: Arctotherium simum Cope, 1879 (genus from Bravard, 1857); Arctotherium yukonense Lambe, 1911; Arctotherium californicum Merriam, 1911; Dinarctotherium merriami Barbour, 1916; Tremarctotherium simum (Cope, 1879) (genus from Kra-glievich, 1926; used by Rinker, 1949); Arctodus nebrascensis (used by Berger, 1930; genus from Leidy, 1854); and Arctodus simus nebrascensis (used by Frick, 1930). These taxa are now considered to be junior synonyms of Arctodus simus (Cope, 1879), subfamily Tremarctinae, family Ursidae (Kurten, 1963). At one time, all North American Arctodus fossils were tentatively referred to a single species, Arctodus pristinus Leidy, 1854, and thought to be highly variable (Firby, 1968; Kurten, 1963). As more specimens became available, two species were recognized (Kurten, 1967). Arctodus pristinus Leidy, 1854 (junior synonym: Ursus haplodon Cope, 1896) was a relatively lightly built form with slender bones, relatively longer jaws, and smaller teeth than the larger A. simus. A. pristinus has been recognized with certainty only in eastern North America from middle Irvingtonian through Rancholabrean deposits (Kurten, 1967; Kurten and Anderson, 1980). A. simus is larger, has a more robust dentition and skeleton, a shorter face, and relatively longer limbs than A. pristinus. Remains of A. simus are found throughout North America (except in the southeast) and also date from middle Irvingtonian through Rancholabrean times (Kurten, 1967; Kurten and Anderson, 1980). Kurten (1967) recognized two subspecies of A. simus: the larger A. s. yukonensis from Yukon Territory, Alaska, and Nebraska and the smaller A. s. simus recovered throughout the rest of North America." Richards et al. (1996). "The Tremarctinae are a monophyletic group; Ursinae is their sister group (Trajano and Ferrarezzi, 1994; Talbot and Shields, 1996). Plionarctos and Tremarctos constitute the ‘spectacled bears’ clade, a basal group of the Tremarctinae, and Arctodus and Arctotherium conform to the ‘short-faced bears’ clade. Within the clade formed by the Arctotherium species." Soibelzon et al. (2005). The North American short-faced bears have been variously placed in the genera Arctodus, Arctotherium, Tremarctotherium, Dinar ctotherium, Tremarctos, and Ursus. Clearly, their closest affinities lie with the South American "Arctotherium" (Pararctotherium), with which they may be regarded as congeneric; the generic name Arctodus takes precedence. Kraglievich (1926) points out a number of differences between the North and South American forms, which must be regarded as distinct species, but not distinct genera as Kraglievich inferred.
That Arctodus, Tremarctos, and the late Tertiary Plionarctos form a natural group seems also evident, the last-mentioned being ancestral (Thenius, 1958).
The South American fossil arctodonts apparently represent at least three species, ranging in size from the gigantic Arctodus bonariensis (Gervais) through the moderately large Arctodus pamparus (Ameghino) to the very small Arctodus brasiliensis (Lund). In North America there is some local or temporal size differentiation, but nothing like that in South America, and apparently not more than that found within the single species Ursus arctos (Kurten, 1955; 1959). There may have been an oscillation in size, in rapport with the climatic changes, of the same type as that found in Ursus arctos. The largest North American arctodonts occur in Alaska and in the (Illinoian-glacial) Hay Springs. For this reason, there seems no possibility at present of recognizing more than one species from North America. The name of this becomes Arctodus pristinus Leidy. Though the type of the species is but a single M2, there can be no doubt at all of the relationships of this very characteristic and excellently described and figured tooth.
Some of the other species names bestowed on North American arctodont bears may be found to be valid on the subspecies level. The proper subspecific allocation of the Friesenhahn arctodont must await further studies.Bjorn Kurten, 1963.
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Oct 24, 2011 10:58:23 GMT -9
Post by grrraaahhh on Oct 24, 2011 10:58:23 GMT -9
Whether more than one genus of short-faced bears should be recognized is another question. Even if the oversplitting carried out by Ameghino is obviously unrealistic, the two Pampean species (A. bonariensis and A. pamparus) form a group well separated from the North American forms. On the other hand, the third known South American species, Arctodus brasilienis, is somewhat intermediate. Perhaps, pending more detailed investigation and comparison, it would be most useful at present to retain Arctotherium on the subgenus level for the Neotropical forms. Thus the basic differentiation of the Tremarctinae would be reflected in its three genera: Tremarctos for the spectacled bears; Arctodus for the short-faced bears; and Plionarctos for the ancestral Pliocene group.
Bjorn Kurten, 1967.
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Oct 26, 2011 15:25:23 GMT -9
Post by grrraaahhh on Oct 26, 2011 15:25:23 GMT -9
Kurten (1966, 1967) recognized two genera and at least seven species of short-faced Pleistocene bears, subfamily Tremarctinae: the Neotropical Tremarctos ornatus (the only living species); T. floridanus, Arctodus pristinus, and A. simus from North America; and A. bonariensis, A. pamparus, and A. brasiliensis from South America. Other poorly known species from South America include Arctodus enectum (Paula Couto, 1960) and A. angustidens (Kragiievich, 1926). Several genera were created for the American fossil bears (see Kraglievich, 1926, and Kurten, 1966, 1967, for taxonomic revision). For instance, Paulo Couto recognized two genera (Paula Couto, 1960) or subgenera (Paula Couto, 1979) of South American extinct bears, Arctotherium and Pararctotherium, the latter including Arctodus brasiliensis. Kurten (1967) considered all tremarctine genera, except Tremarctos, as junior synonyms of Arctodus. Kurten's classification was followed by Perea and Ubilla (1983, 1985), who distinguished two morphological patterns in the extinct genus Arctodus: pattern "G" (large forms) and pattern "P" (small forms). They assigned A. brasiliensis, with some restrictions, to pattern "P," characterized by inflated frontal region and auditory bullae, U -shaped postpalatine margin, lateral margin of mesopterygoid fossa independent from the styloid apophysis, and foramen rotundum emerging in the orbit independent of the alisphenoid canal.A. brasiliensis, and represents a considerable extension to the northeast of the geographic range of South American tremarctines. The bear from Ubajara is compared to the known species of Tremarctinae, and its systematic position is discussed. A phylogenetic hypothesis of the genera of Tremarctinae is presented. We recognize Arctotherium as a separate genus, including the extinct South American tremarctines, with two subgenera: Arctotherium and Pararctotherium. Original Spanish TextComo ya se expresó, la situación sistemática de los úrsidos fósiles sudamericanos presenta algunas confusiones. Ameghino (1889, Actas Acad. Nac. Cieñe. Córdoba. 5: 315; 1904, op.cit.) y Kraglievich (1926, An.Mus.Nac.Hist.Nat. Buenos Aires. 34:1; 1940, Obras de Geol. Paleont., 3: 557) consideran la existencia, entre otros, de los géneros Arctotherium y Pararetotherium. Paula Couto (1960, Bol. Soc.Bras.Geol. 9(1): 5) opina que sólo éstos 2 géneros son válidos, aunque luego (1979, Tratado de paleomastozoología: 328) ubica a éstos taxa con categoría de subgéneros dentro del género Arctodus y Kurten (1967) mantiene el mismo criterio pero retiene sólo al subgénero (Aretotherium) por razones de practicidad. Nosotros prescindimos de la categoría subgenérica debido a la problemática antedicha e identificamos el material como Arctodus pamparus. Online English TranslationAs already stated, the situation systematically ursids South American fossil presents some confusion. Ameghino (1889, Proceedings Acad. Nac Cien. Córdoba. 5: 315, 1904, op.cit.) And Kraglievich (1926, An.Mus.Nac.Hist.Nat. Buenos Aires. 34:1, 1940, Works Geol. Paleont., 3: 557) consider the existence, among others, gender and Pararetotherium Arctotherium. Paula Couto (1960, Bull Soc.Bras.Geol. 9 (1): 5) believes that only these 2 genera are valid, but later (1979, Treaty of paleomastozoología: 328) places these taxa within the subgenus category Arctodus gender and Kurten (1967) maintains the same approach but retains only the subgenus (Arctotherium) for reasons of practicality. We dispense with the subgeneric category due to the above problem and identified the material as Arctodus pamparus. Perea, D. and M. Ubilla (1983). Original Spanish TextSegún el criterio sustentado por este autor (op. cit.: 3) todos los especímenes que hemos estudiado pertenecerían al género Arctodus. Este criterio resulta particularmente práctico a los efectos de la separación de las formas de Tremarctinae pleistocénicas de aquellas de Tremarctos, aunque, a juzgar por un cúmulo de evidencias empíricas, no reflejaría la realidad biológica. Online English TranslationAccording to the opinion expressed by this author (op. cit.: 3) all specimens that we studied belong to the genus Arctodus. This approach is particularly useful for the purpose of separating the Pleistocene Tremarctinae ways from those of Tremarctos, though, judging by an accumulation of empirical evidence does not reflect biological reality. Perea, D. and M. Ubilla (1985).
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Post by grrraaahhh on Jan 8, 2012 6:20:14 GMT -9
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Jun 15, 2012 5:42:01 GMT -9
Post by grrraaahhh on Jun 15, 2012 5:42:01 GMT -9
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Feb 19, 2013 2:35:34 GMT -9
Post by sarus on Feb 19, 2013 2:35:34 GMT -9
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Mar 27, 2013 7:09:48 GMT -9
Post by grrraaahhh on Mar 27, 2013 7:09:48 GMT -9
Ever wonder why the North American Giant Short Faced Bear (A.simus) did not migrate westward crossing the Beringia land bridge into Siberia? To my understanding, there has not been much written about this topic but what has been speculated is very interesting."Guthrie suggests that a widespread mesic environment in central Beringia may have served as an ecological filter that prevented a few large Pleistocene mammal species from crossing the land bridge from Siberia to Alaska (e.g., woolly rhinos, Coelodonta), and other species from crossing from Alaska to Siberia (e.g., short-faced bears, Arctodus simus). If such an ecological filter existed in central Beringia, it did not prevent most mammal species from crossing the land bridge between the two continents during the Wisconsin (MIS 2-4). This suggests that whatever environmental differences existed between the land bridge and the adjacent regions were probably subtle, and may be difficult or impossible to detect in the fossil record. Future interdisciplinary studies of well-dated records from some of the many volcanic crater lakes in central Beringia may eventually shed light on this question." Source: Late Quaternary vegetation and climate history of the central Bering land bridge from St. Michael Island, western Alaska. PDF LINK: webharvest.gov/peth04/20041015105453/http://climchange.cr.usgs.gov/research/alaska/alaskaPDF/Ager2003QR.pdf"However, we have understoodforalongtimethattherehasbeensomekind of a biogeographic " filter which prevented free exchange of some faunal elements across this specic zone. For example, an arid-adapted species from the west, woolly rhino, Coelodonta, reaches up to the head-waters of the Anadyr River, but fails to go further east. Likewise, the northwestern perimeter of North American camels, Camelops,andtheAmericanlong-leggedkiang-likeequids, Equus (sp?) failed to extend across the strait. The short-faced bear (Arctodus), bonnet-horned muskoxen (Bootherium), and badger (Taxus) are found throughout the interior of Alaska and the Yukon Territory but apparently did not breach this western barrier (Fig. 8)." Guthrie, R.D., 2001. Origin and causes of the mammoth steppe: a story of cloud cover, woolly mammoth tooth pits, buckles, and inside-out Beringia. Quaternary Science Reviews 20, 549–574. www.seas.harvard.edu/climate/seminars/pdfs/Guthrie_2001.pdf
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