Black Bear portrait 26

by Mitch Shindelbower

Title

Black Bear portrait 26

Artist

Mitch Shindelbower

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Photograph

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One of our local bear while living in Lake Tahoe...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).[2] 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.[2][3][page needed] According to recent studies, the sun bear is also a relatively recent split from this lineage.[4][page needed]

A small primitive bear called Ursus abstrusus is the oldest known North American fossil member of the genus Ursus, dated to 4.95 mya.[5] This suggests that U. abstrusus may be the direct ancestor of the American black bear, which evolved in North America.[2][6] Although Wolverton and Lyman still consider U. vitabilis an "apparent precursor to modern black bears",[7] it has also been placed within U. americanus.[6]

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.[2][8] The earliest American black bear fossils, which were located in Port Kennedy, Pennsylvania, greatly resemble the Asian species,[9] though later specimens grew to sizes comparable to grizzly bears.[10] From the Holocene to the present, American black bears seem to have shrunk in size,[2] but this has been disputed because of problems with dating these fossil specimens.[7]

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 the Americas 7–8 ma.[11] The giant and lesser short-faced bears are thought to have been heavily carnivorous and the Florida spectacled bear more herbivorous,[12] 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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July 3rd, 2021

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