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New shark mass extinction discovered

Scientists have uncovered a previously unknown mass die-off of sharks, 19 million years ago.

At this time, the oceans swarmed with ten times as many sharks as we have today, but the extinction event killed off more than 70% of them, with a higher death toll in the open ocean compared to coastal waters. The extinction event was even more crippling for sharks than the KT extinction that wiped out the dinosaurs, 66 million years ago.

A subset of shark fossil dermal denticles described in the study.
A subset of shark fossil dermal denticles described in the study. Credit: Leah D. Rubin

But the event is still shrouded in mystery – though scientists can see sharks disappeared from the fossil record 19 million years ago, they don’t know why.

“This interval isn’t known for any major changes in Earth’s history,” said Elizabeth Sibert from Yale University, lead author of the new study in the journal Science. “Yet it completely transformed the nature of what it means to be a predator living in the open ocean.”

Risk-taking mothers protect their infants

Japanese researchers have put mice mums to the test to see why mothers take extra risks to protect their kids. In a study published in Cell Reports, the team studied the brains of female mice to identify which part drives the complicated behaviour of caring for infants – and narrowed it down to neurons in a part of the forebrain that contain a protein called the calcitonin receptor.

The number of these special neurons was higher in mothers than in virgin female, males or fathers – and the connections between these neurons and other parts of the brain changed in females after they gave birth. The researchers also found that silencing the neurons disrupted nurturing behaviours like nest building and watching over pups.

The team also put the mouse mums through a pup retrieval test – putting the pups on an elevated maze. Virgin females refused to go fetch pups in this risky environment, while mother mice always went and retrieved them (but when the calcitonin receptor levels were halved, even mums hesitated and took longer).

A virgin female mouse and a mother mouse are tested on the elevated pup-retrieval maze. As in the example, only mother mice retrieved the pups in this situation (although virgin mice did so willingly in the home cage when it was not dangerous). When the calcitonin receptor was downregulated, mothers also hesitated to take the risk. Credit: RIKEN

Antarctica toastier during last ice age than previously thought

Antarctica is the coldest place on Earth today and it was even colder during the last ice age 20,000 years ago – for decades, research suggested it was a chilly nine degrees Celsius colder than present-day.

But new research, published in Science, has revealed that the continent was actually warmer during this period than we previously thought, only 4 to 5 degrees below current temperatures.

These findings, according to Oregon State University palaeontologist Ed Brook, are critical to understanding the transition from a cold to warm climate – and therefore the transition our planet is undergoing today.

“Antarctica is particularly important in the climate system,” says Brook, a co-author on the paper. “We use climate models to predict the future, and those climate models have to get all kinds of things correct. One way to test these models is to make sure we get the past right.”

To T Cells, orientation matters

Researchers led by Monash University in Melbourne have made a fundamental step in understanding T cells, which play a key role in the body’s immune system by getting rid of viruses and other invading pathogens.

Ice core researcher Don Voigt examines an ice core at the West Antarctic Ice Sheet Divide (WAIS Divide) project. Credit: Photograph by Gifford Wong

The study, published in Science, found that for T cells to be activated, they have to “see” pathogens in a particular way.

“Our study has shown that the orientation in which the T cell receptor binds is a primary factor determining whether the T cell receives an activating signal,” says Monash’s Nicole La Gruta says, co-lead author of the paper.

The result, she says, has “clarified a critical mechanism essential for effective T cell immunity. It is also relevant to the ongoing development of immunotherapies that aim to boost the activation of T cells.”

New view of exceptional cosmic explosion

A specialised observatory in Namibia has recorded the most energetic radiation and longest gamma-ray afterglow of a so-called gamma-ray burst (GRB) to date. The observations – made with the High Energy Stereoscopic System (HESS) – challenge the established idea of how gamma-rays are produced in these colossal stellar explosions, which are the ‘birth cries of black holes’, as the international team reports in the journal Science.

Artist’s impression of a relativistic jet of a gamma-ray burst (GRB), breaking out of a collapsing star, and emitting very-high-energy photons. Credit: DESY, Science Communication Lab

“Gamma-ray bursts…are the biggest explosions in the universe and associated with the collapse of a rapidly rotating massive star to a black hole,” explains Deutsches Elektronen-Synchrotron scientist Sylvia Zhu, one of the paper’s authors. “A fraction of the liberated gravitational energy feeds the production of an ultrarelativistic blast wave. Their emission is divided into two distinct phases: an initial chaotic prompt phase lasting tens of seconds, followed by a long-lasting, smoothly fading afterglow phase.”

The HESS team believe that there’s a promising future for gamma-ray burst detection thanks to next-generation instruments like the Cherenkov Telescope Array, currently being built in the Chilean Andes and Canary Islands.

“The general abundance of gamma-ray bursts leads us to expect that regular detections in the very-high energy band will become rather common, helping us to fully understand their physics,” says HESS spokesperson Stefan Wagner, from Landessternwarte Königstuhl, in Heidelberg, Germany.

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