|
Post by brobear on Oct 16, 2021 15:40:42 GMT -5
www.bearbiology.org/wp-content/uploads/2017/10/McLellan_Reiner_Vol_9.pdf A REVIEW OF BEAR EVOLUTION. Abstract. Ursidae is a young family, evolving from early canids during the late Oligocene and early Miocene, about 20-25 million years ago. The family has frequently been divided into subfamilies. Although debated, these often include: (1) Hemicyoninae, (2) Agriotheriinae, (3) Tremarctinae, (4) Ursinae, and (5) Ailuropodidae. Based on scattered literature published over the past century, we trace the evolutionary lineage of the various genera and species found in these subfamilies; most are extinct, 8 species remain. Many if not most of the relationships have been disputed for many years and we may be far from the definitive history. Speculated causes of extinction usually involved climate change and competition. Primitive man may have been the major competitor of some extinct species and modem man is definitely a major influence on bear evolution today.
|
|
|
Post by brobear on Jul 1, 2022 1:34:29 GMT -5
The Brown Bear/Cave Bear Connection:
|
|
|
Post by brobear on Jul 1, 2022 1:38:22 GMT -5
Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America www.researchgate.net/publication/301568754_Ancient_mitochondrial_DNA_reveals_convergent_evolution_of_giant_short-faced_bears_Tremarctinae_in_North_and_South_America The Tremarctinae are a subfamily of bears endemic to the New World, including two of the largest terrestrial mammalian carnivores that have ever lived: the giant, short-faced bears Arctodus simus from North America and Arctotherium angustidens from South America (greater than or equal to 1000 kg). Arctotherium angustidens became extinct during the Early Pleistocene, whereas Arctodus simus went extinct at the very end of the Pleistocene. The only living tremarctine is the spectacled bear (Tremarctos ornatus), a largely herbivorous bear that is today only found in South America. The relationships among the spectacled bears (Tremarctos), South American short-faced bears (Arctotherium) and North American short faced bears (Arctodus) remain uncertain. In this study, we sequenced a mitochondrial genome from an Arctotherium femur preserved in a Chilean cave. Our molecular phylogenetic analyses revealed that the South American short-faced bears were more closely related to the extant South American spectacled bear than to the North American short-faced bears. This result suggests striking convergent evolution of giant forms in the two groups of short-faced bears (Arctodus and Arctotherium), potentially as an adaptation to dominate competition for megafaunal carcasses.
|
|
|
Post by brobear on Jul 1, 2022 1:43:16 GMT -5
Evolutionary history of bears: It's complicated Date:June 11, 2014 Source:Senckenberg Research Institute and Natural History Museum www.sciencedaily.com/releases/2014/06/140611093447.htm Summary:Several bear species that today only occur in America or in Asia have hybridized in their evolutionary history, researchers have discovered. The Beringia land bridge, which in former times connected the habitats of these species, might have enabled their encounter. A new large-scale study is based on the comparison and analysis of genetic material of all bear species that still exist. According to researchers of the LOEWE Biodiversity and Climate Research Centre (BiK-F), Goethe University Frankfurt and the U.S. Wildlife Service several bear species that today only occur in America or in Asia have hybridized in their evolutionary history. The Beringia land bridge, which in former times connected the habitats of these species, might have enabled their encounter. The large-scale study is based on the comparison and analysis of genetic material of all bear species that still exist. The results have been published recently in the journal Evolution and Molecular Biology. If in documentaries or in the zoo -- everyone has seen and knows about brown bears, polar bears and pandas. However, there are several other bear species in Asia and South America that are less well-known, such as the sloth bear, the Asiatic or the spectacled bear. There are eight bear species that still exist worldwide. Despite many years of research, the exact relationships between them remain unresolved. Who with whom? Polar bear and brown have hybridized Previous analyses of genetic material of polar bears and brown bears have proven already that the two species have hybridized during their long evolutionary history. This behavior can still be observed today and the ongoing climate change drives the bear even closer. It is therefore likely that there have been similar exchanges of genetic material between other species of the bear family. ... as well as brown bears and black bears To shed light on this, a team of the German Biodiversity and Climate Research Centre (BiK-F) and the Goethe University Frankfurt in cooperation with colleagues from the US have now analyzed certain genome parts of all bear species alive today. "We were able to show that several bear species have hybridized during their evolutionary history. The exchange can still be traced in the genetic makeup of today's bears," says the lead author of the study, Verena Kutschera (BiK-F). This mix-up makes it difficult to classify some gene fragments as belonging to a particular species. Beringia land bridge serving as an intercontinental meeting point Surprisingly, several bear species which nowadays live on different continents have also taken part in the mating and thus gene exchange. This may have been possible because the significantly lower sea level during past ice ages resulted in a land bridge between Asia and North America, the Beringia land bridge. Thus the ancestors of today's bear species, e.g. of the Asiatic black bear and the American black bear, had the opportunity to meet and to mate. Darwin's species tree is insufficient to map complicated relationships All eight bear species that occur today have well adapted to their present habitat and differ physically very much. A prime example for this is polar bears and black bears. Nevertheless, the speciation of some individual genes has not finished yet which additionally complicates the research of the evolution of bears. With new molecular methods more gene parts might be discovered in the genomes of mammal species that could originate from other species. Apparently separate genetic lineages turn out to have merged -- sometimes repeatedly -- during the evolutionary history and exchanged genetic material with each other. "The traditional pedigree already used by Darwin is not always suitable to map evolutionary history in full detail. So-called phylogenetic networks a more useful to depict the genetic mix-up that we have found," comments evolutionary biologist Prof. Dr. Axel Janke, BiK-F, leader of the research team. The study demonstrates that evolution often is not a linear process; thanks to modern molecular methods it's complex processes are finally revealed.
|
|
|
Post by brobear on Jul 1, 2022 1:44:38 GMT -5
A REVIEW OF BEAR EVOLUTION www.researchgate.net/publication/239750226_A_Review_of_Bear_Evolution Ursidae is a young family, evolving from early canids during the late Oligocene and early Miocene, about 20-25 million years ago. The family has frequently been divided into subfamilies. Although debated, these often include: (1) Hemicyoninae, (2) Agriotheriinae, (3) Tremarctinae, (4) Ursinae, and (5) Ailuropodidae. Based on scattered literature published over the past century, we trace the evolutionary lineage of the various genera and species found in these subfamilies; most are extinct, 8 species remain. Many if not most of the relationships have been disputed for many years and we may be far from the definitive history. Speculated causes of extinction usually involved climate change and competition. Primitive man may have been the major competitor of some extinct species and modem man is definitely a major influence on bear evolution today. Members of the bear family, Ursidae, currently inhabit North America, Europe, Asia, and South America. Using generic names suggested by Hall (1981), Nowak and Paradiso (1983), Goldman et al. (1989), and Wayne et al. (1989), species found in Asia include the brown bear (Ursus arctos), Asiatic black bear (U. thibetanus), sun bear (U. malayanus), sloth bear (U. ursinus), and polar bear (U. maritimus). The taxonomic status of the sixth Asian member, the giant panda (Ailuropoda melanoleuca), remains in question, although most evidence suggests that it belongs to Ursidae. Brown bears and polar bears are found in Europe and these 2 species plus the American black bear (Ursus americanus) inhabit North America. The spectacled bear (Tremarctos ornatus) is the only member of Ursidae in South America. Ursidae are placed in the order Carnivora but, except for the largely carnivorous polar bear, bears are omnivorous, feeding mostly on plant material, insects, fish, and mammals. They are generally large, stocky, and powerful animals. All bears are plantigrade, walking on their entire foot. The radius and ulna and the tibia and fibula are separate, which enables bears to rotate their limbs, improving their ability to dig and manipulate food, and facilitating climbing by some species. Bears' teeth reflect their omnivorous habits by lacking the carnassials common in other mammalian carnivores and having flattened molars adapted to crushing and grinding vegetation. Bears' premolars are reduced in size and utility, creating a gap between incisors and molars similar to that found in many herbivorous mammals. Bears are a young family, evolving from early canids during the late Oligocene and early Miocene, about 20- 25 million years before present (MYBP). So recent is this divergence that some taxonomists believe that canids and ursids should be considered as one family and dividing them is due to "custom of more than a century" (Simpson 1945). The majority of students, however, have separated these 2 families but frequently disagree on where the line between canids and ursids, and many other taxonomic boundaries, should be drawn. Recently, the families Ursidae and Otariidae have been placed in the superfamily Ursoidea. These 2 families have been joined with members of the Canoidea superfamily, Canidae, Procyonidae, Mustelidae, and Phocidae, into the suborder Caniformia (Wozencraft 1989). The purpose of this paper is not to create another view of bear evolution and resulting taxonomy. Rather, it is to summarize for the interest of biologists who work with extant species the large body of knowledge that has grown over the past century but is scattered in journals and papers that many of us rarely encounter.
|
|