A solitary bison in Yellowstone National Park. Amelia Templeton/NPR hide caption

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Institute for Marine Mammal Studies veterinary technician Wendy Hatchett takes a skin sample from a dead bottlenose dolphin that was found on Ono Island, Ala., and brought for examination to Gulfport, Miss., on Tuesday. Patrick Semansky/AP hide caption

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Researchers found that as groups of black-tailed prairie dogs and other rodents became larger, it also became easier to identify individuals. Kimberly Pollard/UCLA hide caption

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Some 16,000 years ago, people may have been curling up next to the fire with red foxes. iStockphoto.com hide caption

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An American black bear from the Kenai Peninsula in Alaska. A new study found that a bear's metabolism in hibernation drops by nearly 75 percent while its body temperature falls just slightly. Oivind Toien/Institute of Arctic Biology, University of Alaska, Fairbanks hide caption

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A mature Atlantic tomcod collected from the Hudson River. These tomcod evolved to handle excessive amounts of industrial pollutants, like PCBs and dioxin, in the water. Science/AAAS hide caption

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Daisy Mae, a miniature Vietnamese potbellied pig, lounges on a couch in West St. Paul, Minn. Vincent J. Musi/National Geographic hide caption

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The crew of the whaling vessel Yushin Maru #3 uses their water cannons against Sea Shepherd's Delta team (foreground) in a Zodiac boat during clashes in the Southern Ocean. The photo was taken on Jan. 1 by the Sea Shepherd Conservation Society. Gary Stokes/AFP/Getty Images hide caption

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Fleas push off the ground from the ends of their legs, not from the part of the leg that resembles a knee. Gregory Sutton hide caption

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The Pacific walrus has to wait to be placed on the endangered species list. AP hide caption

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Researchers have sequenced the genome of the common water flea, Daphnia, shown in this false-color micrograph. About 35 percent of the genes are brand new to science. Jan Michels/Christian-Albrechts-Universitat zu Kiel hide caption

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