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Early mammals like this rat-sized species Liaoconodon hui coexisted with feathered dinosaurs like Sinotyrannus in the temperate ecosystems of the Cretaceous in what is now Liaoning in northern China. Illustration by Davide Bonadonna

An explosion of dazzling fossil finds reveals that ancient mammals evolved a wide variety of adaptations allowing them to exploit the skies, rivers and underground lairs. This avalanche of discovery is also stirring up debate: some researchers disagree over which fossil groups are true mammals and the shape of the mammal family tree.

Nature | 11 min read

Illustration: Davide Bonadonna; Design: Wes Fernandes

Chemicals released by bacteria in the gut seem to influence how mice recover from fear — an ability linked to chronic anxiety and post-traumatic stress disorder. Mice that were trained that a certain sound meant a painful shock were able to forget the association after some time with a painless version of the tone. But mice treated with antibiotics to wipe out the microbiome were never able to get over the learned fear. When researchers looked closer, the bacteria-free mice had changes to their brains and different chemicals flooding their bodies.

Science | 5 min read

Reference: Nature paper

Nature Index Young Universities 2019

OPINION

Twelve years ago, Brazilian climate scientist Carlos Nobre and his colleagues calculated the tipping point for the Amazon rainforest: if its area shrunk by 40% of its expanse in the 1970s, it could not grow back — and as much as 70% of the original forest could transform to drier, hotter savanna. (Now, with rising global temperatures, deforestation and fires, that margin has shrunk even further.) Nobre calls on his country to turn against the anti-science movement and restore Brazil’s status as an international conservation inspiration.

Nature | 5 min read

A vibrant community of do-it-yourself microscopists have developed advanced, custom microscopy that can visualize dynamic processes in their native biological context like never before. But their work has outpaced commercialization, meaning that many biologists can't get their hands on the best equipment. Imaging-focused biologists Rory Power and Jan Huisken call for a new kind of shareable, configurable and portable microscopes.

Nature Methods | 5 min read

INFOGRAPHIC OF THE WEEK

The prospect of a regular meal brings humpback whales (Megaptera novaeangliae) to a salmon hatchery in Alaska that releases young fish every April. The whales’ predictable pattern gave researchers the first opportunity to film whales from above to confirm their amazing hunting technique. First the whales create a bubble net to corral their prey. Then they use their exceptionally long pectoral flippers to herd the fish right into their mouths.National Geographic, 8 min read

Reference: Royal Society Open Science paper (M. M. Kosma et al./Royal Soc. Open Sci./CC BY 4.0)