Watch: A grizzly bear in Yellowstone rushes for its life, but from what?

In Yellowstone National Park, a photographer captured a grizzly bear racing for safety while being pursued by another animal.

Last Monday, Bo Welden, a naturalist and guide with Jackson Hole EcoTour Adventures, requested his Instagram followers

As you may expect, the answer is a bison. More specifically, a mother bison guarding her calf along the Lamar River.

"A mother bison showed this grizzly bear that he is not the biggest baddest beast on the landscape," Welden said.

"Seeing this role reversal while on tour with Jackson Hole EcoTours guests was truly AMAZING!" 

We were taken aback to see this incident in real time."The quickness of these animals stands out.

Grizzly bears can reach speeds of nearly 40 mph, but sprinting bison can only reach 35 mph.

It's unusual to see both animals running at full or nearly full pace.

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