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Long, wide cave with raised patches across ceiling and two people in the distance in silhouette against a light.

A scientist on a caving trip happened to spot dinosaur tracks in the ceiling of Castelbouc Cave in France.Credit: Jean-David Moreau et al./J. Vertebr. Paleontol.

Huge dinosaur footprints found on cave roof

Dinosaur footprints measuring up to 1.25 metres long have been found deep inside a cave in France — on the roof. The tracks were made 166 million to 168 million years ago, when three dinosaurs traversed the shoreline of a sea. The site was then at the planet’s surface, but geological processes have buried and tilted the sediments, and the prints are now on the cave’s roof, 500 metres underground. Researchers say the footprints probably belong to an unknown species of titanosaur, a category of long-necked herbivorous dinosaur that includes some of the largest animals ever to walk on Earth.

Nature | 4 min read

Read more Research Highlights: short picks from the latest papers.

COVID-19 coronavirus outbreak

A biologist in protective clothing removes a sample of coronavirus DNA from a freezer.

Pedro Vilela/Getty

The state of COVID-19 vaccines now

• As of yesterday, there are 78 confirmed COVID-19 vaccine candidates, 5 of which have already entered clinical trials. Get a firm grip on this incredibly fast-moving field with a short, data-driven overview by seven experts at the Coalition for Epidemic Preparedness Innovations (CEPI), one of the world’s leading vaccine funders. (Nature Reviews Drug Discovery | 6 min read)

• Scientists agree that the new coronavirus SARS-CoV-2 was very likely to have originated in bats. Other than that, there are few certainties about how the virus jumped to humans. Pangolins have been suggested as the possible intermediary, but that’s still unproven. It’s also not firmly established that the ground zero of the outbreak was definitely a live-animal food market in Wuhan, China. (The Guardian | 7 min read)

• Members of the world’s largest particle-physics laboratory, CERN, are doing their part to help countries deal with COVID-19 by turning their skills to manufacturing hand sanitizer, 3D-printed masks and face shields. CERN researchers are also designing an open-source ventilator, leveraging their extensive experience in managing gas flows and controls systems. (Nature | continuously updated)

• The Saudi-led coalition fighting in Yemen (supported by the United States and United Kingdom, among other countries) has announced a unilateral two-week ceasefire in the devastating five-year conflict. On 23 March, United Nations chief António Guterres called for a global ceasefire to focus on efforts to stop COVID-19. No cases of the virus have been reported in Yemen, but the battered nation is in no state to fight — or even report — an outbreak. (BBC | 5 min read)

• COVID-19 infections range from asymptomatic to deadly — even among individuals in the same risk group. Infectious-disease researchers Arturo Casadevall and Liise-anne Pirofski explain the five variables behind very different outcomes: the number of viral particles that cause infection, (maybe) genetics, the route by which a virus enters the body, the virulence of the virus and which infections the immune system has fought in the past. (Bloomberg Opinion | 8 min read)

Read the latest coronavirus news, continuously updated on Nature.

Read Nature’s continuously updated selection of the must-read papers and preprints on COVID-19.

Features & opinion

Computer, teach thyself

Further progress in artificial intelligence will require having machines teach themselves, computer scientists say. Machine learning has made impressive breakthroughs in the last decade, in large part through ‘supervised’ training: algorithms go through vast reams of data that have been previously labelled by humans (for example, about pictures being of cats rather than dogs). But ‘self-supervised’ programs (such as AlphaGo Zero) and ‘unsupervised’ techniques can sidestep human labelling, and can perform better at tasks such as discovering new laws of nature or coordinating motion. After all, babies learn how to walk by stumbling around, not by being told which moves are correct. “Humans don’t need that much supervision,” says machine-learning pioneer Yoshua Bengio.

New York Times | 6 min read

Tribology keeps the world rolling

The study of friction and lubricants, called tribology, is an often-neglected field at the confluence of physics, materials science, engineering, nanotechnology and other fields. (How friction works at the microscopic level is not completely understood.) Tribology’s economic impact is immense — for example, a large part of a car’s energy consumption comes from friction between its mechanical components. And a hot question is how to reduce friction in wind turbines to enable them to withstand stronger winds.

Popular Mechanics | 7 min read

Podcast: A plastic-recycling enzyme

Researchers have engineered an enzyme that dissolves one of the world’s most commonly used plastics. The enzyme breaks down polyethylene terephthalate (PET) into its constituent monomers so it can be reused in nearly-new form, researchers tell the Nature Podcast.

Nature Podcast | 16 min listen

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Books & culture

How physics is rocked by the waves of history

Physics thrives on abstract thought and, often, an otherworldly detachment from reality — but up close, the all-too-human business of doing science is messy, writes Sabine Hossenfelder. She reviews an essay collection from physicist and historian of science David Kaiser that reminds us that physics, like any human activity, is influenced by the fears and fashions of history.

Nature | 5 min read

Five best science books this week

Andrew Robinson’s pick of the top five science books to read this week includes life on land, how we see faces and reforming capitalism.

Nature | 3 min read

Where I work

Carole Mundell poses for a portrait on an ornate staircase at the UK Foreign Office building

Carole Mundell is the chief scientific adviser at the UK Foreign and Commonwealth Office and an astrophysicist at the University of Bath.Credit: Leonora Saunders for Nature

Carole Mundell is the chief scientific adviser at the UK Foreign and Commonwealth Office (FCO) and an astrophysicist. “The building’s grandeur contrasts with the humility of the public servants that work here,” says Mundell. “This parallels the humility needed to be a good scientist.” (Nature | 2 min read)

Quote of the day

“Be kind to yourself when setting your hours. It’s a pandemic, not a work retreat.”

Zoologist Lucy Taylor, who continues to study the GPS data from her tracked wild elephants while under lockdown, has some tips for the rest of us. (Nature | 6 min read)