Marine monsters Ancient aquatic reptiles called ichthyosaurs ruled the seas for much of the Mesozoic era, when dinosaurs reigned. These marine creatures evolved from land-dwelling reptiles and quickly diversified in the early Triassic period into a vast variety of agile swimmers, including some that were the biggest marine predators of their time. Read more in How giant marine reptiles terrorized the ancient seas

Sampling Mars In 2020, NASA plans to send a rover to Mars to collect and store tubes of rock and dirt. If it succeeds, it will be the first step in bringing carefully documented Martian samples back to Earth for study. Engineers are now designing the robotic system to gather the samples — and they have to make it excruciatingly clean, so as not to contaminate any possible traces of Martian life. Read more in The $2.4-billion plan to steal a rock from Mars

Tracking trouble in the Arctic Many shorebird populations are declining steeply around the globe, and those that nest in the Arctic are among the hardest hit. Read more in What’s killing the world’s shorebirds?

What the numbers say about refugees The biggest concentrations of displaced people lie far from the spotlight. Read more in our special issue on human migration.

Top genes A tour through the most studied genes in biology reveals some surprises. Read more in The most popular genes in the human genome.