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Up to about 200 years ago, the passenger pigeon was one of the most numerous vertebrate animals on Earth. The species had an estimated 3 to 5 billion individuals at the peak of its existence and had such big flock sizes that they were known to block out the sun. However, this changed during the early 1800s when they…

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Modern bears, while typically thought of as carnivores, actually have a wide variety of dietary preferences. Some eat only meat while others are omnivores, meaning that they eat both meat and vegetation. Cave bears (Ursus spelaeus), an extinct bear species from Europe, are thought to be omnivorous. However, scientists…