The Whisker Chronicles

Whiskers are also known as vibrissa, from the latin vibrare "to vibrate". Vibrissa are the specialized hairs on mammals and the bristlelike feathers near the mouths of many birds. Their resonant design is symbolic of the energies, good and bad, that are reverberating throughout the natural world. Every living thing is connected and, by birthright, deserves to exist.

Bear Evolution 101

Bear Phylogenetic Tree

I am beginning Bear Month at The Whisker Chronicles with a fairly technical blog in order to elaborate on how very long bears have existed. There are now only a few bear species by comparison to their evolutionary history. I am trying to help readers understand why that is. Many of the issues that affected the evolution of bears and contributed to their decline affected many other species as well. Humans are often influential and directly responsible for animal population declines, but catastrophic events caused decreased animal populations and extinctions before man existed. Exploration of the evolution of bears gives us good reason to ponder this balance and the role of humans in saving what bears remain.

There are now eight bear species and numerous subspecies in more than 65 countries on four continents: North America, South America, Asia and Europe. Bears have been evolving for forty million years and began from small carnivorous mammals around 30-40 million years ago, with the first “true bear” evolving from a bearlike dog in Europe.

Around 16.5-23 million years ago, the Earth’s climate became warmer and drier. This climate change created Drake’s passage between Antarctica and South America and ultimately resulted in a major uplift of the Rocky Mountains in North America and of the Himalayans. The oldest true bear, Ursavus elemensis, who is the original ancestor of all modern bears, originated in subtropical Europe during this time. Also during this period, low sea levels allowed extensive movement of animals back and forth from Africa and Eurasia, and Eurasia and North America. The first branching from the evolutionary tree in bears occurred then in the subfamily Ailuropadidae, the family to which giant pandas belong. Giant pandas appeared in central Asia around 18-22 million years ago.

Declining temperatures continued, causing more drying and a decrease in biodiversity of mammals. A North Atlantic current developed that caused separation of warmer subtropical oceans from those at cooler higher latitudes. Intense Arctic cold fronts in North America affected vegetation while the Himalayans blocked monsoonal winds to Central Asia. During this period there were vast animal extinctions, 60-70% of all Eurasian species and 70-80% of North American species. The initial opening of the Bering Strait is also thought to have been a major contributor to this large extinction event. The Tremarctinae subfamily of short-faced (Old World) bears crossed the Bering land bridge and spread into North America 12-15 million years ago and later became extinct.

Bears appeared in northern Asia about 4-8 million years ago. The Early American black bear appeared in North America, the Asiatic black bear appeared in central Asia and the sun bear appeared in Southeast Asia all around 5 million years ago. By 2.5 million years ago, there was major Arctic glaciation and significant global cooling. Three lines of bears evolved in Europe during this period: black, brown and cave bears.

Around 2 million years ago, black bears and brown bears were already widespread. At 1.5 million years ago, a primitive bear species, either Ursus minimus or a Eurasian bear species, Ursus etruscus, crossed the Bering land bridge to North America and moved south and was extinct by 1.3 million years ago.

The polar bear appeared in Siberia at approximately one million years ago, at which time the Florida cave bear (Ursus tremarctos floridanus) was present in the southeast United States and the brown bear appeared in Asia. All bears that inhabited North and South America 800,000 years ago, during the Ice Age, became extinct except for the Andean bear (Tremarctos ornatus).

Polar bear ancestors evolved from the coastal brown/grizzly bears approximately 500,000 years ago. Cave bears were widely distributed 300,000 years ago and at approximately 100,000 to 250,000 years ago, the brown bear (subspecies include Alaska, Kodiak and grizzly) crossed the land bridge between Asia and North America.  Polar bears became a distinct species during the last great glaciation 70,000 years ago. The modern polar bear was in existence 20,000 years ago.

Also widely distributed in North America, south of the continental ice sheet, were the American black bear, Florida cave bears and a species of short-faced bear. The cave bear became extinct 10,000 to 15,000 years ago. A giant short-faced bear existed in the area now known as Texas around 13,000 years ago. At the end of the last ice age, 10,000 to 11,000 years ago, the brown bear expanded south and the American black bear expanded north. The brown bear became extinct in Africa 88-117 years ago.

Slovak Wildlife Society Esther Tyson, Svetlana Beťková

Slovak Wildlife Society
Esther Tyson, Svetlana Beťková

Today, the following eight species of bears exist: American black bear (Ursus americanus) in North America, brown bear (Ursus arctos) in North America, Europe and Asia, polar bear (Ursus maritimus) in North America, Asia, Europe and the Arctic Ocean, Asiatic black bear (Ursus thibetanus) in Asia, Giant Panda (Ailuropoda melanoleuca) in Asia, Sloth bear (Ursus ursinus) in Asia, Sun bear (Ursus malayanus or Helarctos malayanus) in Asia and the Andean bear (Tremarctos ornatus) in South America.

Thanks for reading. Keep checking in for more details on each species of bear and even on some of the extinct bears. For example, I’m curious about what happened to the African bear. Aren’t you?

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This entry was posted on January 3, 2014 by in Bears, Mammals, Wildlife.
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