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Post by brobear on Oct 16, 2020 13:41:29 GMT -5
Ursus minimus Pliocene, small bear, perhaps ancestor of the brown bear and of the "black" bears. Ursus etruscus Pleistocene. This bear has no significant skeletal differences with the Tibetan black. Everything suggests a direct lineage between the two species. Ursus deningeri Pleistocene, a cave bear the size of the European brown Ursus spelaetus Pleistocene, the iconic cave bear.
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Post by King Kodiak on Oct 16, 2020 16:48:03 GMT -5
Reply #24: good pic brobear. Ursus etruscus evolved from Ursus minimus. Also, remember that Ursus etruscus gave rise to Ursus spelaeus, Ursus deningeri, and Ursus arctos. Another lineage of Ursus etruscus gave rise to the black bears.
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Post by brobear on Oct 16, 2020 17:30:08 GMT -5
Reply #24: good pic brobear. Ursus etruscus evolved from Ursus minimus. Also, remember that Ursus etruscus gave rise to Ursus spelaeus, Ursus deningeri, and Ursus arctos. Another lineage of Ursus etruscus gave rise to the black bears. Actually ( it is my understanding ) that Ursus minimus gave rise to Ursus etruscus and to the black bears. One group of Ursus etruscus in Europe gave rise to the cave bears while another group of Ursus etruscus in Asia gave rise to the brown bears. *Edit and add: Some experts believe that possibly the Asiatic black bear might be Ursus etruscus.
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Post by King Kodiak on Oct 16, 2020 17:41:03 GMT -5
This is the evolution of the Ursus genus, Ursus minimus gave rise to Ursus etruscus, then Ursus etruscus gave rise to the cave bear lineage, the brown bear lineage, and the black bear lineage:
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Post by brobear on Oct 16, 2020 17:52:03 GMT -5
en.wikipedia.org/wiki/American_black_bear Despite living in North America, American black bears are not closely related to brown bears and polar bears; genetic studies reveal that they split from a common ancestor 5.05 million years ago (mya). American and Asian black bears are considered sister taxa and are more closely related to each other than to the other modern species of bears. According to recent studies, the sun bear is also a relatively recent split from this lineage. A small primitive bear called Ursus abstrusus is the oldest known North American fossil member of the genus Ursus, dated to 4.95 mya. This suggests that U. abstrusus may be the direct ancestor of the American black bear, which evolved in North America. Although Wolverton and Lyman still consider U. vitabilis an "apparent precursor to modern black bears", it has also been placed within U. americanus. The ancestors of American black bears and Asian black bears diverged from sun bears 4.58 mya. The American black bear then split from the Asian black bear 4.08 mya. The earliest American black bear fossils, which were located in Port Kennedy, Pennsylvania, greatly resemble the Asian species, though later specimens grew to sizes comparable to grizzly bears. From the Holocene to the present, American black bears seem to have shrunk in size, but this has been disputed because of problems with dating these fossil specimens. The American black bear lived during the same period as the giant and lesser short-faced bears (Arctodus simus and A. pristinus, respectively) and the Florida spectacled bear (Tremarctos floridanus). These tremarctine bears evolved from bears that had emigrated from Asia to North America 7–8 ma. The giant and lesser short-faced bears are thought to have been heavily carnivorous and the Florida spectacled bear more herbivorous, while the American black bears remained arboreal omnivores, like their Asian ancestors. The American black bear's generalist behavior allowed it to exploit a wider variety of foods and has been given as a reason why, of these three genera, it alone survived climate and vegetative changes through the last Ice Age while the other, more specialized North American predators became extinct. However, both Arctodus and Tremarctos had survived several other, previous ice ages. After these prehistoric ursids became extinct during the last glacial period 10,000 years ago, American black bears were probably the only bear present in much of North America until the migration of brown bears to the rest of the continent.
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Post by brobear on Oct 16, 2020 18:14:45 GMT -5
bearsoftheworld.net/ursus_minimus.asp Yes; you are correct Kodiak. Quote: The Ursus minimus, also known as the Auvergne bear, evolved from Protursus about 5.3 million years ago and existed for roughly 3.5 million years during the Pliocene. It is an ancestor of all bears of the genus Ursus, and the immediate ancestor of the Etruscan bear.
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Post by King Kodiak on Oct 16, 2020 18:35:29 GMT -5
Bear evolution is a hard thing and sometimes confusing. Even biologists dont agree sometimes and have contradicting information. But at least we have a general knowledge of bear evolution.
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Ursinae
Oct 16, 2020 21:35:37 GMT -5
Post by OldGreenGrolar on Oct 16, 2020 21:35:37 GMT -5
So all bears owe their existence to Ursus minimus.
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Post by King Kodiak on Oct 16, 2020 23:44:05 GMT -5
So all bears owe their existence to Ursus minimus. Only the bears of the Ursus genus. The panda bear, the sloth bear, the spectacled bear, and the sun bear are not included.
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Ursinae
Oct 17, 2020 0:25:35 GMT -5
Post by brobear on Oct 17, 2020 0:25:35 GMT -5
So all bears owe their existence to Ursus minimus. Only the bears of the Ursus genus. The panda bear, the sloth bear, the spectacled bear, and the sun bear are not included.Reply #28: American and Asian black bears are considered sister taxa and are more closely related to each other than to the other modern species of bears. According to recent studies, the sun bear is also a relatively recent split from this lineage. *Both the sun bear and the sloth bear are Ursinae bears. animalmentor.com/wild-life/mammals/types-of-bears/
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Ursinae
Oct 17, 2020 0:52:19 GMT -5
Post by King Kodiak on Oct 17, 2020 0:52:19 GMT -5
Yes, but Ursinae is at subfamily level. When it comes down to the genus level, sun bears, sloth bears, panda bears, and Andean bears did not evolve from Ursus minimus.
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Ursinae
Oct 17, 2020 1:00:43 GMT -5
Post by brobear on Oct 17, 2020 1:00:43 GMT -5
Yes, but Ursinae is at subfamily level. When it comes down to the genus level, sun bears, sloth bears, panda bears, and Andean bears did not evolve from Ursus minimus.
reply #28: " According to recent studies, the sun bear is also a relatively recent split from this lineage." The experts are divided as to the sun bear and sloth bear being of the Ursus genus. But they are all in agreement that both are of the Ursinae subfamily. The giant panda and the Andean bear are far more primitive bears. I'm not saying you're wrong. But the sun bear is closely associated with the black bears and ( somehow ) the sloth bear is associated with the brown bears.
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Ursinae
Oct 17, 2020 1:09:33 GMT -5
Post by King Kodiak on Oct 17, 2020 1:09:33 GMT -5
Well yeah, like i said before, some experts disagree and have contradicting info. i know that the sun bear is sometimes listed as "Ursus malayanus", But officially, it is still "Helarctos malayanus" in most sites. Same with the sloth bear, it is still officially "Melursus ursinus". As for their subfamily, yes, both are Ursinae.
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Ursinae
Oct 17, 2020 1:28:09 GMT -5
Post by brobear on Oct 17, 2020 1:28:09 GMT -5
From topic: Pleistocene sloth bear - Melursus theobaldi The fossilized skulls of a bear once named Melursus theobaldi found in the Shivaliks from the early Pleistocene or early Pliocene are thought by certain authors to represent an intermediate stage between sloth bears and ancestral brown bears. Reply #28 here: According to recent studies, the sun bear is also a relatively recent split from this lineage. ( black bears ). *So, classification is debatable, but DNA relationships are real. The giant panda is the most primitive of bears ( barely a bear ) and the Andean bear is more closely related to the giant panda than to the Ursinae bears.
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Ursinae
Oct 17, 2020 1:39:24 GMT -5
Post by King Kodiak on Oct 17, 2020 1:39:24 GMT -5
I went to the Wikipedia page for this phrase but unfortunately there is no source given. It would be nice to see a brand new bear evolution tree with this supposed recent split of the sun bear, but we dont have any. Up to now, only Wikipedia is stating this but no original source given.
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Ursinae
Oct 17, 2020 1:56:17 GMT -5
Post by brobear on Oct 17, 2020 1:56:17 GMT -5
academic.oup.com/mbe/article/31/8/2004/2925840 Bears in a Forest of Gene Trees: Phylogenetic Inference Is Complicated by Incomplete Lineage Sorting and Gene Flow Ursine bears are a mammalian subfamily that comprises six morphologically and ecologically distinct extant species. Previous phylogenetic analyses of concatenated nuclear genes could not resolve all relationships among bears, and appeared to conflict with the mitochondrial phylogeny. Evolutionary processes such as incomplete lineage sorting and introgression can cause gene tree discordance and complicate phylogenetic inferences, but are not accounted for in phylogenetic analyses of concatenated data. We generated a high-resolution data set of autosomal introns from several individuals per species and of Y-chromosomal markers. Incorporating intraspecific variability in coalescence-based phylogenetic and gene flow estimation approaches, we traced the genealogical history of individual alleles. Considerable heterogeneity among nuclear loci and discordance between nuclear and mitochondrial phylogenies were found. A species tree with divergence time estimates indicated that ursine bears diversified within less than 2 My. Consistent with a complex branching order within a clade of Asian bear species, we identified unidirectional gene flow from Asian black into sloth bears. Moreover, gene flow detected from brown into American black bears can explain the conflicting placement of the American black bear in mitochondrial and nuclear phylogenies. These results highlight that both incomplete lineage sorting and introgression are prominent evolutionary forces even on time scales up to several million years. Complex evolutionary patterns are not adequately captured by strictly bifurcating models, and can only be fully understood when analyzing multiple independently inherited loci in a coalescence framework. Phylogenetic incongruence among gene trees hence needs to be recognized as a biologically meaningful signal. Our understanding of evolutionary processes relies on a backbone of phylogenetic inferences from molecular data, but recombination imposes limits on the resolution that can be obtained from a single autosomal locus. High-resolution phylogenies can be obtained in multilocus analyses. In traditional phylogenetic analyses, several loci are concatenated and analyzed as one “superlocus.” However, incomplete lineage sorting (ILS), a process by which ancestral polymorphisms can persist through species divergences up to several million years, and gene flow across species boundaries caused by introgressive hybridization generate gene tree discordance, hampering species tree estimation (Tajima 1983; Pamilo and Nei 1988; Leaché et al. 2014). These evolutionary processes are not considered in phylogenetic analyses of concatenated data and can result in inconsistent phylogenetic estimates and high statistical support for an incorrect species tree topology (Kubatko and Degnan 2007).
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Ursinae
Oct 17, 2020 1:57:23 GMT -5
Post by brobear on Oct 17, 2020 1:57:23 GMT -5
Continued: Bears (Ursidae) are emerging as a prominent example of a mammalian family with a complex speciation history, showing discrepancies among mitochondrial and nuclear phylogenies (Yu et al. 2007; Krause et al. 2008; Nakagome et al. 2008; Pagès et al. 2008; Hailer et al. 2012, 2013; Miller et al. 2012; Cahill et al. 2013). Within bears, the ursine subfamily comprises the American and Asian black bear (Ursus americanus, U. thibetanus), sun bear (Helarctos malayanus), sloth bear (Melursus ursinus), brown bear (U. arctos), polar bear (U. maritimus), plus numerous extinct taxa. In addition, bears also include the giant panda (Ailuropoda melanoleuca) and spectacled bear (Tremarctos ornatus). In phylogenetic analyses of genes from the nuclear genome, the placement of the sun bear, sloth bear, and Asian black bear remained unclear (Yu et al. 2004; Nakagome et al. 2008; Pagès et al. 2008). These analyses were performed using a combination of intron and exon sequences, rendering it difficult to interpret whether nodes with low statistical support resulted from insufficient resolution or from actual conflict in evolutionary signals among loci. Moreover, in these studies only one (consensus) sequence per species was analyzed and data from several markers were concatenated, precluding the identification of paraphyletic relationships among species.
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Ursinae
Oct 17, 2020 1:59:03 GMT -5
Post by brobear on Oct 17, 2020 1:59:03 GMT -5
Continued: Recently, coalescence-based multilocus species tree approaches have been developed (e.g., Heled and Drummond 2010). These analytical advances make it possible to specifically model the complexity of lineage sorting and to incorporate intraspecific variation and heterozygosity within individuals. Accuracy of such multilocus species trees can be additionally improved by sampling several individuals per species, especially at shallow phylogenetic depths at which lineages are not completely sorted (Maddison and Knowles 2006). This is especially relevant in ursine bears, because the fossil record and dated phylogenies of mitochondrial genome sequences suggested a rapid radiation (Wayne et al. 1991; Yu et al. 2007; Krause et al. 2008), including time frames in which ILS is expected (Nichols 2001).
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Ursinae
Oct 17, 2020 2:00:05 GMT -5
Post by brobear on Oct 17, 2020 2:00:05 GMT -5
Continued: Another cause of gene tree discordance can be introgressive hybridization, resulting in gene flow across species boundaries, which can only be estimated when intraspecific variation is considered. Although ILS can be modeled in currently available species tree approaches, they cannot account for gene flow. A recent simulation study showed that gene flow can affect species tree inferences by decreasing posterior clade probabilities, underestimating divergence time estimates, and, in cases of high levels of gene flow, by altering the species tree topology (Leaché et al. 2014). Discordance among loci that differ in ploidy and inheritance mode can be explained by contrasting patterns of female and male gene flow (Chan and Levin 2005). In brown and polar bears, discordance between the mitochondrial gene tree and the nuclear species tree has been found (Hailer et al. 2012, 2013; Miller et al. 2012; Cronin et al. 2013), and explained with introgressive hybridization. Previous studies have also indicated phylogenetic discrepancies between mitochondrial and nuclear genes in American and Asian black bears (Yu et al. 2004; Nakagome et al. 2008; Pagès et al. 2008), suggesting that similar processes may have affected their evolution. To examine whether incongruences among nuclear loci and/or discordance between nuclear and mitochondrial phylogenies can be explained by introgression, coalescence-based multilocus gene flow analyses (e.g., Nielsen and Wakeley 2001; Hey 2010; Yu et al. 2012, 2013) can be used to complement species tree inferences. Thus, to more fully understand the evolutionary history of bears, it is crucial to analyze multiple independently inherited markers with a high resolution in several individuals per species. Such data sets need to be analyzed using coalescence models, tracing the evolutionary histories of individual alleles back in time, from extant individuals to their ancestral populations.
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Ursinae
Oct 17, 2020 2:01:25 GMT -5
Post by brobear on Oct 17, 2020 2:01:25 GMT -5
Continued: We here study the evolutionary history of bears, using a combination of coalescence-based species tree approaches and gene flow analyses. For this purpose, we generated sequence data of 14 independently inherited autosomal introns in 30 individuals and of 5.9 kb from the Y chromosome in 11 males from all eight extant bear species. We combine this with previous data into data sets comprising 29 kb of nuclear sequence and 10.8 kb of mitochondrial sequence to analyze the complexity of phylogenetic signals in bears through multilocus species tree and network analyses, and in statistical model comparisons. Further, we use coalescent-based gene flow analyses to specifically investigate whether remaining conflicts in phylogenetic signals in bears can be explained by introgressive hybridization.
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