SAN FRANCISCO — Zika causes fetal brain cells neighboring an infected cell to commit suicide, David Doobin of Columbia University Medical Center reported December 6 at the annual meeting of the American Society for Cell Biology. In work with mice and rats, Doobin and colleagues found hints that the cell death might be the body’s attempt to limit the virus’ spread.

The scientists applied techniques they had used to investigate a genetic cause of microcephaly to narrow when in pregnancy the virus is most likely to cause the brain to shrink. Timing of the virus’s effect varied by strain. For one from Puerto Rico, brain cell die-off happened in mice only in the first two trimesters. But a strain from Honduras could kill developing brain cells later in pregnancy.

SAN FRANCISCO — Earth’s innards are cooling off surprisingly fast.

The thickness of new volcanic crust forming on the seafloor has gotten thinner over the last 170 million years. That suggests that the underlying mantle is cooling about twice as fast as previously thought, researchers reported December 13 at the American Geophysical Union’s fall meeting.

The rapid mantle cooling offers fresh insight into how plate tectonics regulates Earth’s internal temperature, said study coauthor Harm Van Avendonk, a geophysicist at the University of Texas at Austin. “We’re seeing this kind of thin oceanic crust on the seafloor that may not have existed several hundred million years ago,” he said. “We always consider that the present is the clue to the past, but that doesn’t work here.”
The finding is fascinating, though the underlying data is sparse, said Laurent Montési, a geodynamicist at the University of Maryland in College Park. Measuring the thickness of seafloor crust requires seismic studies, and “you don’t have that everywhere; there’s nothing in the South Pacific, for example.” Still, he said, “it’s amazing that we can see the signature of the cooling of the Earth.” The finding could help explain why supercontinents such as Pangaea break apart, he added.

Earth’s mantle is made up of hot rock under high pressures. As material rises toward Earth’s surface, pressures drop and the rock starts melting. This molten material can spew onto the surface at mid-ocean ridges and construct new crust. When mantle temperatures are hotter, the melt zone is larger and the resulting crust is thicker. Near the upper boundary with the crust, mantle temperatures range from about 500° to 900° Celsius.

Comparing the thickness of oceanic crust of different ages, Van Avendonk and colleagues discovered that 170-million-year-old crust is 1.7 kilometers thicker on average than fresh crust. Chemical analyses of lava rocks suggest Earth’s mantle has cooled about 6 to 11 degrees on average every 100 million years over the last 2.5 billion years. But since the mid-Jurassic about 170 million years ago, the mantle has cooled around 15 to 20 degrees on average per 100 million years, the researchers estimate. While scientists expected the mantle to cool over time as heat left over from Earth’s formation and from radioactive decay dissipates, this degree of cooling was surprising.

Plate tectonics is causing this rapid cooldown, the researchers proposed. The sinking, shifting and formation of plates drive convection in the planet’s interior that shifts heat. This process also controls how fast different regions of the mantle cool. While mantle temperatures below the Pacific Ocean have decreased around 13 degrees per 100 million years, the mantle below the Atlantic and Indian oceans has cooled about 37 degrees per 100 million years.

The difference between the oceans is their distance to continents. The Atlantic and Indian oceans opened when the Pangaea supercontinent ripped apart. Before then, the underlying mantle was covered by continental crust, which served as an insulating blanket that kept mantle temperatures toasty, Van Avendonk proposed. As Pangaea split and the continents shifted, the mantle beneath the young oceans began cooling much faster. Over that same time period, the Pacific Ocean was largely isolated from the continents and cooled more gradually.
The insulating effect of the Pangaea supercontinent could help explain what drives Earth’s cycle of supercontinent formation and breakup, Montési said. Heat may build up underneath supercontinents, ultimately generating a massive rising plume of hot rock that splits the landmass apart. “This could explain why you get a breakup about 100 million years after you get a supercontinent assembled,” he said.

Imperfections in supersized diamonds are a bummer for gem cutters but a boon for geologists. Tiny metal shards embedded inside Earth’s biggest diamonds provide direct evidence that the planet’s rocky mantle contains metallic iron and nickel, scientists report in the Dec. 16 Science.

The presence of metal in the mantle is “something that’s been predicted in theory and experiments for a number of years, but this is the first time that we have samples that give us physical evidence,” says Evan Smith, a geologist at the Gemological Institute of America in New York City who led the study.
Understanding the composition of the mantle can help scientists figure out how it drives plate tectonics, and how elements like carbon and oxygen are cycled and stored in the Earth.

Diamonds form in the mantle when carbon-containing compounds are compressed and heated to great temperatures (SN: 4/30/16, p. 8). During this process, traces of other elements can sneak in as “inclusions.” Inclusions make the mineral less valuable as a gemstone, and chunks with many such imperfections are often rejected by jewelers. But to scientists, such stowaways are priceless: They provide some of the only physical evidence available of what’s going on deep inside Earth.
Smith and his colleagues used lasers to identify inclusions in samples from some of Earth’s largest diamonds. Some diamonds like these were originally hundreds or even thousands of carats. The Cullinan Diamond, for instance, was as big as two stacked decks of cards and weighed 621 grams, or more than a pound.
By analyzing the inclusions in 53 diamond samples, Smith’s team found that the megadiamonds formed much deeper than ordinary diamonds — hundreds of kilometers down, in a different part of the mantle.

“Not only are [these diamonds] very large and very valuable, but they appear to be very special in terms of their origin,” says Graham Pearson, a geochemist at the University of Alberta in Canada who wasn’t part of the study. Other minerals brought up from such a depth don’t preserve chemical clues to their environment in the same way.

In the deep diamonds, Smith found inclusions made of a mixture of solidified iron, nickel, carbon and sulfur, surrounded by a thin skin of methane and hydrogen.

Aside from the molten metal core, most iron inside Earth is thought to be incorporated into other minerals, not as a stand-alone metal, says Pearson.

But the metallic inclusions suggest that the part of the mantle where the large diamonds formed contains iron and nickel as metals. And the fact that the metals hadn’t reacted with other elements to form compounds suggests that the diamonds’ birthplace probably contains very little oxygen.

Smith thinks the metallic mixture was probably molten at the time the diamonds were forming. Instead of being sprinkled throughout like grated parmesan on spaghetti, ribbons of iron and nickel might have rippled through the mantle like gooey cheddar-jack through mac-and-cheese.

“You need very special conditions to get a metallic melt,” says Catherine McCammon, a geologist at the University of Bayreuth in Germany. So the idea that diamonds carry evidence of these conditions in the mantle is “pretty mind-blowing.”

Hollywood space flicks typically feature one type of hero: astronauts who defy the odds to soar into space and back again. But now a group of behind-the-scenes heroes from the early days of the U.S. space program are getting their due. Black female mathematicians performed essential calculations to safely send astronauts to and from Earth’s surface — in defiance of flagrant racism and sexism.

These “computers” — as they were known before the electronic computer came into widespread use — are the subject of Hidden Figures. The film focuses on three black women — Katherine Johnson (played by Taraji P. Henson), Dorothy Vaughan (Octavia Spencer) and Mary Jackson (Janelle Monáe) — and their work at NASA’s Langley Research Center in Hampton, Va., during the run-up to John Glenn’s orbit of the Earth in 1962.
A mathematics virtuoso, Katherine Johnson calculated or verified the flight trajectories for many of the nation’s space milestones. The film showcases her work on two: the first American in space (Alan Shepard), and the first American to orbit the Earth (John Glenn). But Johnson also had a hand in sending the first men to the moon, during the Apollo 11 mission, and when the Apollo 13 astronauts ran into trouble, Johnson worked on the calculations that helped them get home safely.

Mary Jackson worked on wind tunnel experiments at Langley, where she tested how spacecraft performed under high winds. The film follows Jackson as she overcomes obstacles of the Jim Crow era to become NASA’s first black female engineer. Though the movie focuses on her triumphant rise, after decades in that role, Jackson grew frustrated with the remaining glass ceilings and moved into an administrative role, helping women and minorities to advance their careers at NASA.
Johnson and Jackson got their start under the leadership of Dorothy Vaughan, who led the segregated group of “colored computers,” assigning black women to assist with calculations in various departments. As electronic computers became more essential Vaughan recognized their importance and became an expert programmer. A scene where she surreptitiously takes a book from whites-only section of a public library — a guide to the computing language FORTRAN — is a nod to Vaughan’s prowess with the language.
Electronic computers were so unfamiliar in the 1960s that everyone from engineers to astronauts felt more confident when a human computer calculated the numbers. After a room-sized IBM mainframe spits out figures for his trajectory, John Glenn requests, “Get the girl to check the numbers” — meaning Johnson. In the film, that request culminates in Johnson running a frantic last-minute check of the numbers and sprinting across the Langley campus while Glenn waits. In reality, that process took a day and a half.

For spaceflight fans, Hidden Figures provides an opportunity to be immersed in a neglected perspective. The women’s stories are uplifting, their resilience impressive and their retorts in response to those who underestimate them, witty.

But viewers should be aware that, although the main facts underpinning the plot are correct, liberties have been taken. Some of the NASA higher-ups in the film — including Johnson’s supervisor Al Harrison (Kevin Costner) — are not real people. And presumably because number crunching tends to be a bit thin in the suspense department, the filmmakers have dramatized some scenes — Johnson is pictured in Mission Control during Glenn’s flight, but in reality she watched it on television — which seems a shame because the contributions of these women don’t need to be exaggerated to sound momentous.

GRAPEVINE, TEXAS — A mysterious, recurring blast of cosmic radio waves finally has a home address. For the first time, astronomers have definitively traced a fast radio burst back to its source: a faint galaxy about 2.5 billion light-years away. The finding confirms a decade-long suspicion that these outbursts originate well outside our galaxy, although the mystery as to what’s causing them remains unsolved.

“Now with the first proven distance, we can see how remote and how bright the source must be,” Sarah Burke-Spolaor, an astrophysicist at West Virginia University, said January 4 at a meeting of the American Astronomical Society. For roughly five milliseconds, the burst outshined all the stars in its own galaxy and rivaled the luminosity of blazing disks of gas that swirl around supermassive black holes, said Burke-Spolaor, one of the researchers involved with the project.
Fast radio bursts have stumped astronomers since the first one was reported in 2007 (SN: 8/9/14, p. 22). Since then, 17 more bursts have been detected by several radio telescopes around the world. In nearly every case, the outburst lasted just a few milliseconds and was never seen again. Only one, first detected at the Arecibo Observatory in Puerto Rico in 2012, has been seen multiple times (SN Online: 12/21/16).

Most radio telescopes can provide only a fuzzy idea of where on the sky a burst comes from. But the repetitive nature of this burst, dubbed FRB 121102, gave astronomers a heads up of where to point the Very Large Array, a network of radio dishes near Socorro, N.M., which could provide a sharper image.

“We have imaged the burst itself with the VLA and pinpointed where it is on the sky,” said Shami Chatterjee, an astrophysicist at Cornell University. Over the span of six months, the VLA detected nine outbursts coming from the same direction as previous repetitions. A persistent glow of radio waves also comes from the same spot. Further observations with the Gemini telescope in Hawaii revealed that the radio outbursts coincide with a faint galaxy. By measuring how much the expansion of the universe has stretched the light coming from the galaxy, the researchers were able to measure the distance to the source of the burst.
The findings appear in a paper in the Jan. 5 Nature and two papers in the Jan. 10 Astrophysical Journal Letters.
“Without a doubt, this is a landmark event,” said Duncan Lorimer, an astrophysicist at West Virginia University who was not involved with these studies but did discover the first radio burst roughly a decade ago. “There’s no question about the validity of the result.”

The host galaxy is tiny. “We’re barely able to distinguish it from a star,” said project member Shriharsh Tendulkar, an astrophysicist at McGill University in Montreal. It has roughly one one-thousandth of the stars as the Milky Way and is less than one-tenth as wide. “That’s weird,” he said. One favored explanation for fast radio bursts is that they come from neutron stars, the dense cores left behind after a massive star explodes. But if neutron stars are responsible, then astronomers expect to find bursts in places with lots of stars, Tendulkar said.

Tracing FRB 121102 back to a dwarf galaxy doesn’t rule out neutron stars as a source. The gas in dwarf galaxies is more pristine than in other locales such as the Milky Way — with relatively low amounts of elements heavier than helium. Such gas makes it easier for massive stars to form. More heavyweight stars lead to more neutron stars, which could lead to more radio bursts.

Some of the new data, however, also suggest that the source sits near a supermassive black hole, indicating that perhaps the radio blast is somehow connected to gas and dust swirling down the black hole’s gravitational throat.

“We’ve made this huge breakthrough in getting the distance, and it still doesn’t want to let its identity be known,” Lorimer said.

With a host galaxy in hand, astronomers can now point telescopes covering a broad range of the electromagnetic spectrum — from radio waves to gamma rays — at the galaxy to learn more about the burst’s home. One thing that researchers will look for is whether or not the bursts have a steady beat; all the detections so far have appeared randomly. If the signal has a regular period, then something that is spinning (like a neutron star) might be the culprit. Pinpointing more radio bursts and seeing if they originate in dwarf galaxies could also help researchers figure out if this object is unusual or typical of all radio bursts.

A protein that sounds the alarm when the body encounters something painful also helps put out the fire.

Called Nav1.7, the protein sits on pain-sensing nerves and has long been known for sending a red alert to the brain when the body has a brush with pain. Now, experiments in rodent cells reveal another role for Nav1.7: Its activity triggers the production of pain-relieving molecules. The study, published online January 10 in Science Signaling, suggests a new approach to pain management that takes advantage of this protein’s dual role.
“This is very interesting research,” says neuroscientist Munmun Chattopadhyay of Texas Tech University Health Sciences Center El Paso. The findings suggest that when opiates are given for certain kinds of pain relief, also targeting Nav1.7 might lessen the need for those pain relievers, Chattopadhyay says. That could reduce opiate use and their associated side effects.

The new research also solves a puzzle that has frustrated researchers and pharmaceutical companies alike. People with rare mutations in the gene for making Nav1.7 feel no pain at all. That discovery, made more than a decade ago, suggested that Nav1.7 was an ideal target for controlling pain. If a drug could block Nav1.7 activity, some kinds of pain might be eradicated (SN: 6/30/12, p 22). Yet drugs designed to do just that didn’t wipe out people’s pain.

“It seemed so obvious and simple,” says study leader Tim Hucho, a neuroscientist at the University Hospital Cologne in Germany. “But it was not so simple.”

Then in 2015, researchers reported that mice and people with nonfunctioning Nav1.7 not only felt no pain, but they also made higher than normal levels of pain-relieving opioids naturally produced by the body. When these researchers, led by John Wood of University College London, gave the opiate-blocker naloxone to a woman with the rare pain-eradicating mutation, she felt pain for the first time.

“It was astonishing,” says Hucho, whose collaborators on the new research include Wood.
Pain-sensing proteins like Nav1.7 work by prompting nerve cells to send electrical signals. But in this case, Nav1.7 was influencing a nonelectrical process — it was somehow cranking up the activity of genes in charge of making in-house opioids. “It turned the whole field upside down,” Hucho says.

An investigation of rat and mice nerve cells reveals the tug-of-war between Nav1.7’s pain-promoting and pain-relieving powers. Cells with nonfunctioning Nav1.7 have amped up activity in the cellular machinery that kicks off pain relief, Hucho and colleagues report. They suggest that Nav1.7 acts like the axis point in a playground seesaw. When the pain-promoting side is dialed down, the pain-relieving side becomes more dialed up than usual, and cells make more of their in-house opioids.

When opiates are given for pain, the body typically gets used to them and increasing amounts of the drugs are required to have an effect. Yet in the experiments with the rodent cells, this desensitization didn’t happen. The cellular machinery that interacts with the body’s homemade opioids remained sensitive to the pain relievers, even with the uptick in their production.

Taken together, the results suggest that rather than trying to push down on one side of the seesaw to stop pain, a better approach might be moving the axis at the seesaw’s center, says Hucho, tipping the scales toward in-house opioid production, while also dialing down pain promotion. The experimental design by Hucho and University Hospital Cologne colleague Jörg Isensee will make it much easier to explore how manipulations might tip the balance, the researchers say. Much more research is needed before the finding will translate into treating pain in people, but it hints at a new strategy: Rather than trying to stop pain via opiates alone, pain relief might come when such drugs are taken with a Nav1.7 blocker.

Six hours before I gave birth to my son, our labor and delivery nurse started choking.

The cause, we later discovered, was a jar of peanuts that my unsuspecting husband had cracked open for a snack. Our fast-acting (and highly allergic) nurse rushed out of the room and made it to her EpiPen in time. She was OK, to our immense relief, and we managed to not endanger anyone else’s life that night.

But, the scary incident made me want to keep my baby away from peanuts forever.

Don’t do that.

Instead, parents should feed (most) babies peanut-containing foods early and often, new guidelines from the National Institute of Allergy and Infectious Diseases recommend.

“We’re saying that if you introduce peanuts early, you’re going to have a very good chance of preventing peanut allergy,” says Alkis Togias, an allergist at NIAID in Bethesda, Md.

The guidelines, published January 5 in the Journal of Allergy and Clinical Immunology and five other journals, include pages of detailed advice and group kids by different risk factors.

All in all, it’s a lot to process. But in the history of official advice on how to feed your kids, peanuts have always been confusing. Two weeks ago, parents Googling “peanut allergies” might have found guidelines from 2010, which basically said there’s no good reason to avoid peanuts in the first year of life. Or a 2008 report from the American Academy of Pediatrics, which didn’t give a strong statement either way. Or the AAP’s 2000 recommendations, which had some kids avoiding peanuts until age 3.
Last week’s headlines hit upon the apparent contradictions, but the science has actually been steadily marching in one direction — towards peanuts — for years, Togias says.

In 2008, researchers noticed that Jewish kids from the United Kingdom were much more likely to have peanut allergies than Jewish kids from Israel. The reason seemed to be diet-based. Israeli babies usually begin eating peanut-containing foods around 7 months of age. U.K. babies typically wait until after their first birthday.

The results bucked conventional wisdom to delay feeding kids peanuts, and inspired a 2015 trial known as LEAP, for Learning Early about Peanut Allergy. In the trial, 640 babies between 4 and 11 months old with severe eczema and/or egg allergy were divvied up into two groups. One group ate peanut-containing foods. The other avoided them.

It was the first randomized, controlled trial to address the should-I-feed-my-baby-peanuts question. What researchers saw was remarkable: In peanut-fed kids, the incidence of peanut allergy dropped by roughly 70 to 80 percent.

“The results were so impressive that we felt it would be unethical to not come out with these guidelines,” Togias says.

The new guidelines offer different advice depending on certain conditions. For babies without eczema or egg allergies, the guidelines suggest that parents introduce peanut-containing foods around the same time as other solid foods. “There’s really no restriction,” Togias says.
The advice gets tricky for kids with eczema, a skin rash that’s been linked to allergies.

Parents of babies with mild to moderate eczema can stick to the above plan, but peanut-containing foods should be introduced after other solid foods, around 6 months of age. (The allergists I talked to stress that babies should never eat whole peanuts, or even globs of peanut butter — both are major choking hazards.)

Babies with severe eczema and/or an egg allergy should be tested to rule out peanut allergy. If the test is negative, peanut-containing foods get a tentative green light. A doctor can help parents decide if the baby should be fed in the office, or at home with some instructions.

Repeat peanut-feedings is key, says pediatric allergist J. Andrew Bird of UT Southwestern and Children’s Health in Dallas. “Once peanuts are in the diet, they need to stay in the diet,” he says.

It’s unlikely that the United States will see the same drop in peanut allergy reported in the LEAP trial. But even a 50 percent reduction would be huge, Togias says. By his back-of-the-envelope calculation, the U.S. sees roughly 80,000 new cases of peanut allergy every year. “If we cut that in half, we’re saving 40,000 kids right away,” he says.

Still, allergist Katie Allen says the guidelines’ nuanced instructions risk complicating the message that peanuts are OK.

“There’s a lot of merit to these guidelines, but I’m a little worried that the general population will read this and say ‘I’m scared my child has a peanut allergy so I’m going to get him tested,’” says Allen, of Murdoch Childrens Research Institute in Victoria, Australia.

The skin prick test used for screening is not that reliable, she says. And a false-positive result could turn people away from peanuts unnecessarily.

Australia’s guidelines are more straightforward, Allen points out. They recommend that all infants be fed allergenic foods, including peanut butter, within the first year of life (around 6 months, but not before 4 months).

For me, that’s an easier message to digest. Already, Bird has picked up on confusion about the U.S. guidelines. “I saw a mom who said, ‘OK, now this is telling me that my peanut-allergic kid should be eating peanuts every day?’”

That answer to that is a big “no.” These guidelines aim to prevent peanut allergies, not treat them, Bird says.

If the core advice does get out there — to pediatricians, and allergists and parents — it may well keep (at least some) kids from having to grab an EpiPen after getting a whiff of peanut. And that’s something any parent could get behind.

For dinosaurs, the end of the world began in fire.

The space rock that stamped a Vermont-sized crater into the Earth 66 million years ago packed a powerful punch. Any animal living within about a thousand miles of the impact zone was probably vaporized, says paleontologist Stephen Brusatte of the University of Edinburgh in Scotland.

“Everything would have been toast.”

But outside of the impact zone, amid the smoking ruins of the battered planet, some survivors emerged.
Life there was no picnic. Wave after wave of life-threatening disasters pummeled the animals that remained, says paleontologist Nicholas Longrich of the University of Bath in England. Earthquakes. Wildfires. Volcanoes. Acid rain. Dust and gunk in the air, blotting out the sun. “It’s this series of biblical plagues,” Longrich says.

With little light, much plant life perished, and entire food webs collapsed. Life would have been like an ancient Hunger Games, with all living creatures as contestants. The odds were not in their favor. From sea to land to lake to sky, animals suffered incredible losses.

“You’re basically losing all the big herbivores, all the big carnivores, apex predators in the oceans, entire guilds — wiped out overnight,” Longrich says. On land, he adds, anything bigger than a beaver went extinct. Just a few places in North America offer a fossil record of the early years after the extinction, he says, but “there’s no evidence for anything over 10 kilos surviving.”

Tyrannosaurus rex, Triceratops, Ankylosaurus and all other nonavian dinosaurs gone.

A lucky few animals managed to cope with the dramatic changes reshaping their environment, Brusatte says. But why exactly some animal groups survived and others bit the dust is still one of paleontology’s biggest mysteries.
New fossil research is now helping scientists peer back through time, offering glimmers of what might have been: How some animals made it through one of the worst extinction events the planet has ever seen — and how mammals, in particular, came to dominate.

Sussing out animals’ survival strategies could offer hints about how animals today might handle a changing climate, Brusatte says. It might even expose the evolutionary drivers that shaped modern life. After the extinction, evolution went wild, he says. The survivors “had a new world to play in — a new world to conquer.”

Cretaceous catastrophe
Near the very end of the Late Cretaceous Epoch, right before the world blew up, one of the largest mammals in North America may have been noshing on bones.

Didelphodon vorax, a honey badger–looking creature with oddly bulbous teeth, was petite by today’s standards — weighing just about five kilograms. But it was no lightweight. “Pound for pound, it had the greatest bite force of any mammal we’ve ever measured,” says paleontologist Gregory Wilson of the University of Washington in Seattle.
Wilson and colleagues estimated Didelphodon’s bite force from the shape of its fossilized skull. The mammal could snap its jaws together with about 50 pounds of force — enough to crush bones and crack shells, the team reported December 8 in Nature Communications.

This fearsome skill wasn’t enough to save it: After the asteroid hit and global disasters descended, Didelphodon went extinct — just like duck-billed dinosaurs and Pteranodon.

The colossal wipeout of Didelphodon and so many others is plain to see in the fossil record. In Montana’s badlands, where Wilson and colleagues hunt for ancient teeth and bones, tributaries of the Missouri River carve steep bluffs into the earth, exposing slabs of sandstone and siltstone rock. Montana is part of the Western Interior, an ancient seaway that once cut a wide aisle through North America from the Gulf of Mexico to the Arctic.

Much of what scientists know about the dino-killing event, called the Cretaceous–Paleogene, or K–Pg, extinction, traces back to this sweeping tract of land. The area has rocks with fossils from before and after the extinction event. “We haven’t found many places in the world like it,” Wilson says. Spain, France and Romania hold a few dinosaur and mammalian fossils from this time period (and a handful of underexplored spots in India and South America may offer more). But so far, the Western Interior is home to the best land-based record scientists have.

In Montana, the rocks capture a snapshot of time from about 2 million years before the extinction to roughly 1.5 million years after. A thin layer of reddish-brown clay marks the before and after of the asteroid’s impact. “It’s a line in the sand, almost literally,” Brusatte says. Within the clay, here and elsewhere in the world, scientists find elevated levels of iridium, a silvery-white metal carried to Earth via asteroid. Though not visible by eye (scientists need chemical tests to spot it), the metallic dust marks a memory of the impact known as Chicxulub.

All around the globe, Brusatte says, scientists see “a knife-edge separation in the rock” before and after Chicxulub hit. “For over 150 million years you have tons and tons of dinosaur bones, and then literally — Bam! There’s nothing.”

Dinosaurs were among the animal groups hit hardest by the extinction. Others suffered fewer casualties. In what is now northeastern Montana, about half of fish species survived, Wilson reported at an Origins Project workshop at Arizona State University in 2015. Turtles and salamanders seemed to fare the best, losing only roughly a quarter of their species, Wilson and colleagues reported in a series of studies in 2014.

“Most people think that mammals did awesome,” Wilson says. But at least 75 percent of mammals were snuffed out, according to his analysis, which compared fossils present before and after the extinction. Longrich and colleagues put the number even higher: Of 59 mammalian species living in North America during the Late Cretaceous Epoch, about 93 percent died out after the asteroid hit. Those calculations appeared in the Journal of Evolutionary Biology in August 2016.

Still, some species found a way to endure.

Survival strategies
A small body. An aquatic lifestyle. Night vision. An unfussy palate. Any one of these features could have helped survivors withstand the relentless undoing of their ecosystems.

It makes sense. Small animals would have required less food than large ones and may have had an easier time finding shelter. Animals that lived in water could have been buffered from dramatic temperature swings.

Nocturnal animals would have been able to hunt for food when debris-filled skies wrapped the world in gloom. The right diet, in fact, could have been one of the biggest tickets to survival. Among insects, for instance, the difference between survival and demise depended on dietary diversity.

Some insects are adventurous eaters: They feed on lots of different kinds of plants. Other insects are pickier. Leaf miners, for example, typically dine on just one plant species, or a few closely related ones, which made it hard to survive the cataclysm.
These insects burrow through leaves, leaving behind a distinctive trail. Cataloging the trails and other damage patterns on fossil leaves can give researchers a rough idea of the kinds of insects that went extinct — or survived, says Penn State paleontologist Michael Donovan. It’s like a calling card stamped into stone.

Donovan examined 3,646 fossil leaves found in Patagonia, Argentina, from slices of time bracketing the Chicxulub impact. The leaf-mining patterns seen before the impact vanished after the asteroid hit, he and colleagues reported in Nature Ecology & Evolution in 2016.

That suggests a major extinction of leaf-mining insects, a find echoed in previous results from North Dakota. (Though not all perished. Donovan saw new leaf-mining patterns after the extinction.) Other types of leaf damage did persist through the extinction event — damage made by insects that eat many plant species. Unlike leaf miners, these insects took what they could get in the dark days after the impact. “That’s probably a good way to survive,” Donovan says.

This type of strategy may have helped some species adapt to their new habitat, Longrich says, which after the K–Pg extinction “happened to be this post-apocalyptic wasteland world.” It’s like Mad Max of the movies, he says. “A guy who’s super versatile — good at many different things,” Longrich says, “that’s who’s likely to live through an apocalypse.”

Some animals may have already been plugged into the right food chain. When dinosaurs began dying and leaves fell from trees, the bodies and detritus would have littered the ground and washed into rivers and lakes. That would have been a bonanza for the garbage disposal crew. Decaying matter could feed microbes and fish and insects, which could then feed larger animals, like crocodiles and mammals.

Birdlike dinosaurs with beaks could have cracked into another Cretaceous leftover: seeds. The calorie-rich food could have lasted for decades, says paleontologist Derek Larson of the Philip J. Currie Dinosaur Museum in Alberta and the University of Toronto. Other birdlike dinosaurs, with sharp teeth but no beaks, would have had trouble eating seeds. That might explain why they succumbed, while their close relatives — ancestors of modern birds — survived, he and colleagues suggested last year in Current Biology (SN: 5/14/16, p. 11).

Making it as a mammal
Mammals seemed to capitalize on the detritus-based food chain too, Wilson says. He and University of Washington student Stephanie Smith studied fossils found in northeastern Montana from a 1.2-million-year window after the impact. “Fossil mammals are mostly just teeth,” Smith said at the 2016 Society of Vertebrate Paleontology meeting in Salt Lake City. “Luckily, teeth contain a lot of information.”
Smith compared the intricate details of fossil teeth with those from living mammals to learn about the ancient animals’ diets. In Montana, at least, mammals that lived during the first 200,000 years after the extinction event tended to have teeth that were good for crunching insects — “sharp and pointy,” Wilson says. These animals would have had a reliable source of supper. But plant eaters, which have teeth with big basins for grinding and crushing, would have seen their food supplies wither.
For some mammals, a sharp sense of smell could also have offered a competitive edge. Onychodectes tisonensis, a bull dog–sized mammal that lived about 350,000 years after the extinction, had one of the largest olfactory bulbs of any mammal (relative to the cerebrum) — bigger than those found in even expert sniffers like modern dogs and pigs. The smell organs look like two almonds sticking out from the front of the brain, says James Napoli of Brown University in Providence, R.I., who reported the results at the paleontology meeting last year. He and colleagues built a digital model based on a CT scan of an Onychodectes skull unearthed in New Mexico in 1892.

Having big olfactory bulbs means the animal would have been good at nosing out meals, a valuable skill when food is scarce, Napoli says.

Onychodectes belongs to a weird group of mammals called taeniodonts, says study coauthor Thomas Williamson of the New Mexico Museum of Natural History and Science in Albuquerque. “They have bizarre-looking skulls, enlarged forearms, big claws,” he says. The animals may have survived by digging up and eating tough roots and tubers. “We call them the pigs of the Paleocene.”

Paleontologists don’t know for sure if this group of animals lived through the asteroid crash, or if they arose afterward. There’s just one reported taeniodont fossil from the Late Cretaceous — a partial skull from Alberta, Canada.

If taeniodonts did make it through the impact and its aftermath, an aptitude for rooting out hidden food caches would have been useful. If, instead, the animal group emerged later, Onychodectes could have been one of the early examples of mammalian experimentation.

For more than 150 million years, mammals had been “kept under the thumb of the dinosaurs,” Wilson says. After the extinction, with dinosaurs out of the picture, the “Age of Mammals” could begin.

Boomtime for mammals
In the years after the impact, the world was like a school playground that had banished the big kids.

The animals that survived the early hard years gave rise to a slew of new species able to fill the niches left behind by dinosaurs — and all the other creatures that didn’t make it. Before the impact, humans’ ancestors mostly scurried along the ground. But afterward, with fewer predators and competitors, they were free to try out new lifestyles, like living in trees and gliding.

Placental mammals, a group that includes humans, elephants and most mammals living today, experienced a big evolutionary boom, says Thomas Halliday, a paleobiologist at University College London. “Diversification exploded.”

Without dinosaurs breathing down their necks and with fewer competitors, placental mammals had “freedom to evolve in a variety of new directions,” Halliday says. It’s like they were “exploring almost every aspect of the ways of being a mammal.”

When exactly these mammals arose and how much dinosaurs were holding them back remains controversial: Molecular evidence places their origin tens of millions of years before the dinosaurs died. Fossil evidence puts it closer to the K–Pg extinction.
In a series of papers published in 2015 and 2016, Halliday and colleagues analyzed mammalian fossils to sketch out a clearer picture of placental mammals’ history. First, the team built a family tree focused on placental mammals that lived in the Paleocene, the 10-million-year epoch immediately following the extinction. That’s no easy feat, Halliday says, because these animals tend to lack the kind of standout features that would clearly label them as members of one group or another.

So he and colleagues created an exhaustive catalog of 680 body features (such as skull length, tooth number and molar shape) in 177 genera of extinct and living placental mammals and their close relatives. Presumably, animals that shared features were more closely related than those that didn’t. With so many species, the web of potential relationships was astronomical, Halliday says. “There were more possible arrangements … than there are hydrogen atoms in the universe.” The team plugged the data into a computer, which chugged through all the possibilities and came up with the most likely family tree.

Then, the researchers used the tree to calculate rates of evolution. Placental mammals, they found, probably did originate in the Late Cretaceous, but they evolved three times faster after the extinction event than in the 80 million years before it. “We’re talking about new anatomical innovations,” Halliday says: molars good for grinding leaves, limbs adapted for climbing or swimming.

One of these early innovators was Periptychus carinidens, a muscular animal that walked like a bear and had five toes with “weird little hooves,” says University of Edinburgh paleontologist Sarah Shelley. “It’s not like anything alive today.”

Shelley, Williamson and Brusatte described Periptychus fossils found in New Mexico’s San Juan Basin at the 2016 paleontology meeting. “They have really strange cheek teeth,” Williamson says. The teeth are enlarged and conical with big ridges that run from the base to the tip. He thinks Periptychus used its weird chompers to eat hard objects — seeds, perhaps, or unripe fruit.
Periptychus was among the first plant-eating placental mammals to emerge after the extinction — and for a few million years it flourished. Fossils of the animal have been found from West Texas to eastern Montana, Williamson says. “It must have been a highly successful mammal.” But Periptychus couldn’t cope with changes that came later — it died out about 60 million years ago. The animals “were early experiments,” he says, “but they were ultimately dead ends.”

That’s how it goes with evolution, Halliday says. After the dinosaurs died and mammals tested out different modes of life, some found success and others fizzled. “The most successful strategies are honed and the less successful ones are pared away,” he says.

What’s left is what we have today: more than 5,400 different mammal species spread across the world. But descending from an evolutionary winner doesn’t guarantee a safe future. As species carve out an ever more ideal niche, they become more and more vulnerable to extinction, Halliday says. Animals built for a narrow mode of living tend to have a hard time handling disruptions to their environment. And as the climate changes, some species have already begun to suffer. “In the metaphorical sense, we are in the middle of the asteroid strike right now,” he says.

Already, a changing climate has erased pockets of plants and animals across the globe, John Wiens of the University of Arizona in Tucson reported in December 2016 in PLOS Biology. Further warming in coming decades could ramp up extinctions, he warns.

That’s why studying life and death 66 million years ago is still relevant today, Brusatte says. “It’s not just storytelling about the ancient past,” he says. “It can help us understand our modern world,” and maybe even influence conservation strategies to mitigate some of the changes that are happening now.

Fancy flight tricks are a breeze for a new flying robot. Call it an acrobat.

Bat Bot, a lightweight flier with thin silicone wings stretched over a carbon fiber skeleton, can cruise, dive and bank turn just like its namesake, researchers report February 1 in Science Robotics.

Such a maneuverable machine could one day soar up the towering structures of a construction site, flying in and out of steel beams to help keep track of a building’s progress, study coauthor Seth Hutchinson, a roboticist at the University of Illinois at Urbana-Champaign, said in a news briefing January 31.
Other aerial robots, like some drones, aren’t so agile, relying on four whirling rotor blades to lift off the ground, Hutchinson said. These bots also have trouble flying in the wind, because they can exert force in only one direction, he said. Bat Bot’s flexible wings could make it a more versatile flier.

“Bat flight is the holy grail of aerial robotics,” said study coauthor Soon-Jo Chung, a Caltech aerospace engineer. Bats have more than 40 joints in their wings, which give the animals exquisite control over their flight maneuvers. Chung and colleagues re-created nine of the key joints, so their robot could flap its wings in sync, fold each wing independently and move each of its hind legs up and down. At 93 grams, with a wingspan of 47 centimeters, Bat Bot is roughly the size of an Egyptian fruit bat, Chung said.

An onboard computer and sensors let Bat Bot adjust its movements in midair. But the bot still needs a net to land: A crash could bust its electronics. Sticking the landing is the next step, the researchers said. They want Bat Bot to be able to perch — both right-side up and upside down.

Discoveries in a richly appointed 2,600-year-old burial chamber point to surprisingly close ties between Central Europe’s earliest cities and Mediterranean societies. Dated to 583 B.C., this grave also helps pin down when people inhabited what may have been the first city north of the Alps.

An array of fine jewelry, luxury goods and even a rare piece of horse armor found in the grave indicates that “there were craftsmen working in the early Celtic centers north of the Alps who learned their crafts south of the Alps,” says archaeologist Dirk Krausse of the Archaeological State Office of Baden-Württemberg, Germany.
Previous research has established that speakers of Celtic languages inhabited parts of Europe as early as 3,300 years ago. Celtic iron makers appeared in Central Europe by around 2,700 years ago — marking the beginning of that region’s Iron Age — and founded what’s now called the Hallstatt culture.

The grave and a smaller adjoining burial lie in a German cemetery situated across the Danube River from an early Iron Age hill fort called the Heuneburg. Along with yielding insights into long-distance trade and the timing of Europe’s first Iron Age cities, these graves provide the earliest evidence of Hallstatt people elaborately interring women and even children, Krausse and colleagues report in the February Antiquity.

“The main burial represents one of the oldest examples of an exceptionally rich female grave and serves as further testimony of the important social role of certain women in Hallstatt communities,” says archaeologist Manuel Fernández-Götz of the University of Edinburgh, who did not participate in the new study.
While surveying earthen mounds covering graves at the German site in 2005, Krausse’s team noticed a gold-plated bronze brooch fragment lying on the ground. An excavation revealed that the brooch came from the grave of a 2- to 4-year-old child whose skeleton was surrounded by gold and gold-plated jewelry.
It turned out that the child’s grave was an addition to a larger burial chamber. Because farming activity threatened the site, cranes were used in 2010 to hoist out the chamber and surrounding soil in a block weighing 80 metric tons. Researchers excavated the tomb at Krausse’s facility.

Planks of oak and silver fir formed the chamber. Comparisons of growth rings in the planks with previously dated tree rings in the region indicate that the tomb was built in 583 B.C. Previous excavations over the past decade had suggested that the Heuneburg and several other early Iron Age settlements in Germany and France were the first cities north of the Alps, but the grave provides the most precise date yet. Prior to this find, settlements dating to between 2,200 and 2,000 years ago have traditionally been considered the first Central European cities.

Inside the chamber, the team discovered a 30- to 40-year-old woman’s headless skeleton. Her lower jaw and skull were found at two other spots in the grave. Objects placed on and around the skeleton included gold, bronze, amber and jet jewelry and brooches. Decorative styles of some items showed Mediterranean influences. Researchers also found two pairs of boar tusks mounted on large pendants. Each pair of tusks curves around two bronze strips and bronze bells hanging from a smaller pendant.

Another woman’s skeleton and pieces of bronze jewelry rested in a corner of the chamber. It’s unclear whether both bodies were buried at the same time.

A decorated bronze sheet found near the second skeleton’s feet was a piece of armor, called a chamfron, that covered a horse’s forehead, the researchers say. Traces of plant netting and fur preserved on the inside surface of the sheet come from padding, they suspect. CT scans revealed remains of an iron horse bit at one end of the sheet, where it fit in the mouth.

This is the first chamfron found at a Hallstatt site. It resembles horse armor from around the same time found in several Mediterranean cultures, Krausse says.

“The tide is finally shifting” toward accepting links between early European Iron Age cities and societies south of the Alps, says anthropologist Bettina Arnold of the University of Wisconsin–Milwaukee. She suspects that, as at some other Iron Age graves, the elite woman’s burial chamber was looted or material was removed for ritual reasons shortly after interment. Such burials typically included a wagon and metal vessels, but these are missing in the woman’s spacious grave. “This grave is a puzzle, and Hallstatt culture is still enigmatic,” Arnold says.