Workers at the National Geographic Museum in Washington grind the rough edges off a life-size replica of a spinosaurus skeleton. Mike Hettwer/National Geographic hide caption

itoggle caption Mike Hettwer/National Geographic

"The State of the Birds" 2014 report found that red knots (above) and other shorebirds are among the most threatened groups in the U.S. More than half of U.S. shorebird species are on the report's Watch List — species that are currently endangered or at risk. Gerrit Vyn/The Smithsonian Institution hide caption

itoggle caption Gerrit Vyn/The Smithsonian Institution

The granulated surface of the lake bed known as the Racetrack is a favorite destination for tourists — and for scientists who want to investigate trails left by the meandering stones. Momatiuk - Eastcott/Corbis hide caption

itoggle caption Momatiuk - Eastcott/Corbis

Louis E. Pratt, master ivory cutter for Pratt, Read & Co., shows off eight ivory tusks, April 1, 1955. Courtesy of Deep River Historical Society hide caption

itoggle caption Courtesy of Deep River Historical Society

A bed of eel grass (Zostera marina) flutters in the current along the California coast. David Wrobel/Visuals Unlimite/Corbis hide caption

itoggle caption David Wrobel/Visuals Unlimite/Corbis

Our popular image of Homo erectus as the proto-guy who whose human-like traits all emerged at once needs overhauling, some anthropologists say. Sylvain Entressangle/Science Source hide caption

itoggle caption Sylvain Entressangle/Science Source

Being a bit coldblooded has its charms, scientists say. A mammal the size of a T. rex, for example, would have to eat constantly to feed its supercharged metabolism — and would probably starve. Publiphoto/Science Source hide caption

itoggle caption Publiphoto/Science Source

Clint Muhlfeld, an aquatic ecologist with the USGS, holds a native Westslope cutthroat trout in Glacier National Park. Noah Clayton/USGS hide caption

itoggle caption Noah Clayton/USGS

Kalron and his team have set up video cameras that transmit real-time images of the bai via satellite. Courtesy of Maisha Consulting hide caption

itoggle caption Courtesy of Maisha Consulting

A female forest elephant charges, in Dzanga-Sangha Special Reserve in the Central African Republic. Michael K. Nichols/National Geographic/Getty Images hide caption

itoggle caption Michael K. Nichols/National Geographic/Getty Images

Pat Leiggi (right) of the Museum of the Rockies prepares to move a leg bone of the T. rex at the Smithsonian's Natural History Museum in Washington, D.C., on Tuesday. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR