(left to right): DAVID MOSKOWITZ; GAO ET AL./SCIENCE 2019; Bob Wick/BLM

Top stories: last wild caribou in the lower 48, glowing brains, and ancient fossils under threat

The contiguous United States just lost its last wild caribou

The last caribou known to inhabit the contiguous United States has been removed from the wild. This week, a team of biologists working for the Canadian province of British Columbia captured the caribou—a female—in the Selkirk Mountains just north of the U.S.-Canada border. They then moved it to a captive rearing pen near Revelstoke as part of a controversial, last-ditch effort to preserve highly endangered herds.

Microscope captures intricate images of glowing brains at record speed

Expansion microscopy allows scientists to label individual neurons and trace their thinnest tendrils to chart their connections. But the process takes an excruciatingly long time, and it can “burn out” the fluorescent labels. Now, researchers have come up with a new method that can image an entire fly brain in exquisite detail in just 62.5 hours.

Scientists sue to protect Utah monument—and fossils that could rewrite Earth’s history

Thousands of fossils pepper Bears Ears National Monument, a sweep of buttes and badlands in southwestern Utah whose rich paleontological and archaeological record persuaded former President Barack Obama to designate the area a national monument. But in December 2017, President Donald Trump slashed its size by 85%, prompting the typically apolitical Society for Vertebrate Paleontology to sue—along with environmentalists, archaeologists, outdoor companies, and five Native American tribes. Paleontologists fear a ruling against them would have devastating consequences for Bears Ears, just as they are starting to uncover fossils there that could rewrite Earth’s early history.

The bacteria in your gut may reveal your true age

The billions of bacteria that call your gut home may regulate everything from your ability to digest food to how your immune system functions. But scientists know very little of how that system, known as the microbiome, changes over time—or even what a “normal” one looks like. Now, researchers studying the gut bacteria of thousands of people around the globe have come to one conclusion: The microbiome is a surprisingly accurate biological clock, able to predict the age of most people within years.

How hagfish launch slime missiles that swell 10,000 times in size

When a hagfish runs into a hungry shark, the eellike creature squirts out a dollop of goo that—in just a few tenths of a second—expands into a slimy mess 10,000 times its original size, choking the shark and chasing it away. Now, a new study suggests hagfish can’t take all the credit for this gooey defense. Motions in seawater might be the reason the slime can spread into a large cloud so quickly.