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Sluggish memories might be captured via RNA. The molecule, when taken from one sea slug and injected into another, appeared to transfer a rudimentary memory between the two, a new study suggests.

Most neuroscientists believe long-term memories are stored by strengthening connections between nerve cells in the brain (SN: 2/3/18, p. 22). But these results, reported May 14 in eNeuro, buoy a competing argument: that some types of RNA molecules, and not linkages between nerve cells, are key to long-term memory storage.
“It’s a very controversial idea,” admits study coauthor David Glanzman, a neuroscientist at UCLA.

When poked or prodded, some sea slugs (Aplysia californica) will reflexively pull their siphon, a water-filtering appendage, into their bodies. Using electric shocks, Glanzman and his colleagues sensitized sea slugs to have a longer-lasting siphon-withdrawal response — a very basic form of memory. The team extracted RNA from those slugs and injected it into slugs that hadn’t been sensitized. These critters then showed the same long-lasting response to touch as their shocked companions.

RNA molecules come in a variety of flavors that carry out specialized jobs, so it’s not yet clear what kind of RNA may be responsible for the effect, Glanzman says. But he suspects that it’s one of the handful of RNA varieties that don’t carry instructions to make proteins, the typical job of most RNA. (Called noncoding RNAs, these molecules are often involved in manipulating genes’ activity.)

But even the few scientists who question whether the strength of nerve cell connections is the key to long-term memory storage don’t necessarily buy Glanzman’s ideas. The fact that untrained slugs become more sensitive to touch after RNA injection is “amazing,” says biochemist Tomás Ryan of Trinity College Dublin, who wasn’t part of the study. “But it doesn’t go far enough to say that the memory has been transferred.”

After a giant asteroid hit Earth about 66 million years ago, the planet’s climate went on a roller coaster ride.

The space rock’s impact set off tsunamis and wildfires before climate-chilling clouds of sulfur gas engulfed the planet for decades, wiping out most life (SN: 11/25/17, p. 14). As these clouds dissipated, billions of tons of carbon dioxide, which spewed into the atmosphere when the asteroid hit, fueled roughly 100,000 years of global warming, new data suggest. Analyzing fossilized fish bits hints that the influx of the greenhouse gas raised the temperature of the ocean on average by 5 degrees Celsius, scientists report online May 24 in Science.
It’s not surprising that the climate heated up after the collision, which left a 200-kilometer-wide crater centered around what’s now Chicxulub, Mexico, says Johan Vellekoop, a geologist at KU Leuven in Belgium. But finding evidence to back up the warming claim has been challenging.

A common way to estimate past temperatures on Earth is to measure the proportion of heavier to lighter forms of oxygen in the carbonate shells left behind by dead invertebrates. Animals incorporate different oxygen forms into shells, teeth and bones at different rates depending on temperature. But carbonate fossils from around the time of the impact aren’t well enough preserved to be a reliable thermometer.

Instead, paleogeologist Ken MacLeod of the University of Missouri in Columbia and colleagues analyzed those same types of oxygen ratios in a crushed jumble of fish bones, teeth and scales — a different way to measure past temperatures. The team collected sediment samples from a section of rock in what’s now El Kef, Tunisia, that records the transition between the periods before and after the impact in its layers. (Samples from 2 meters of rock laid down before the impact and 6.6 meters laid down after the strike recorded almost 250,000 years of geologic history.) Back in the lab, the researchers spent hours peering through microscopes to sort out glassy, amber fish teeth and mineralized scales and measure the oxygen content within them.
The ratio of heavier oxygen to lighter decreased by about 1 percent in the fish bits collected after the impact compared with those pieces from before the impact, the team found. That change translates to an increase in seawater temperature of about 5 degrees Celsius — a substantial amount.
The elevated temperatures persisted for about 100,000 years before the planet cooled down again, an analysis of fish debris collected from different levels of rock showed. While the study looked only at ocean temperature, air temperature would probably reflect that increase, too, MacLeod says.

“It’s a pretty robust result,” says Clay Tabor, a climate scientist at the University of Connecticut in Hartford. But getting similar results from sites elsewhere in the world would boost the case that this was a global effect and not a local fluke, he says.

The story is far from over, MacLeod agrees. It’s not clear how long after the impact the warming began, for instance. His team hopes to analyze fish debris from other sites that might reveal finer-scale changes in temperature.

Nothing against trees. But maybe it’s better not to get too dependent on them if you want to survive a big flaming space object crashing into Earth.

The asteroid impact that caused a mass extinction 66 million years probably also triggered the collapse of forests worldwide, a new investigation of the plant fossil record concludes. Needing trees and extensive plant cover for nesting or food could have been a fatal drawback for winged dinosaurs, including some ancient birds. Reconstructing the ecology of ancient birds suggests that modern fowl descended from species that survived because they could live on the ground, an international research team proposes in the June 4 Current Biology.
“You probably would have died anyway regardless of habitat,” says study coauthor Daniel Field, an evolutionary paleobiologist at the University of Bath in England. “But if you could get along on the ground, you at least had a shot at surviving across this devastated landscape.”

The shock wave from the strike probably flattened trees within a radius of 1,500 kilometers, Field says. Wildfires ignited around the planet and then came the acid rain. Clouds of ash and dust may have darkened the sky for several years, and researchers suspect that photosynthesis waned. Yet some lucky birds, but no other dinosaurs, survived the hellscape.

For clues to what made a survivor, researchers turned to fossilized pollen from before and after the fiery impact. Abundant kinds of flower-bearing and cone-bearing plants left pollen just before the asteroid hit and again starting about a thousand years afterward. In between those times of diversity, however, ferns dominated, the team notes. A kind of “disaster flora,” ferns (making spores instead of flowers and seeds) do well at recolonizing land. Seed plants, however, weren’t thriving.

Analyzing evolutionary histories of modern birds supports the idea of tree dependence as a vulnerability for the earliest fowl, the researchers say. Specialists in bird evolution now generally agree on the lowest, oldest branches of the bird family tree, Field says. The bottommost one, for instance, includes such modern species as ground-dwelling ostriches and smaller, flight-capable birds called tinamous, which might be more like the ancient birds that dodged extinction.
Working backward along these low branches, researchers used fossils and known bird traits to reconstruct the most likely lifestyles of the earliest survivors. These probably weren’t tree-dependent birds, the researchers conclude.

The glory days of dinosaurs had had plenty of flying tree-dwellers. So far, paleontologists have identified at least 80 kinds of what are called “opposite birds,” the Enantiornithes (SN: 2/4/17, p. 26). “If you saw one flying around today, you’d say, ‘Well, that’s a bird,’ ” Field explains. Their feet looked like those of birds that perch on tree limbs, so he’s not surprised that a fossil of an opposite bird from this probably arboreal group has never been found in rock formed after the dino doomsday.

What did happen, however, was that when trees and forests came back after the disaster, birds quickly evolved arboreal lifestyles, the team says.

Many people don’t realize that birds almost died off during the mass extinction, too, says paleontologist Stephen Brusatte of the University of Edinburgh who has studied bird evolution but was not involved in the new study. What let the few survivors squeak through, he says, has been a mystery for a long time. The whole scenario of a ground-dweller’s advantage and then a return to the trees “makes a lot of intuitive sense.”

The veteran Opportunity rover isn’t dead yet. Currently, the craft is in a deep sleep to ride out a massive Martian dust storm, NASA officials said in a briefing on June 13. The rover may wake itself up when the storm ends.

Opportunity is enveloped in a vast dust storm that grew from a small patch spotted on May 30 to cover a quarter of the planet by June 12 (SN Online: 6/11/18). Too little sunlight is reaching the rover’s solar panels, so Opportunity is in low-power mode — just barely enough to run the rover’s internal clock — until its batteries can charge again. The team hasn’t heard from Opportunity since June 10, and no transmissions are expected until the storm clears.
The Martian summer is just beginning, so the rover should stay warm enough to survive for a long time in this mode, said Opportunity’s project manager John Callas, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

“When the skies clear and the rover begins to power up, it should be able to communicate with us,” he said.
That’s not to say the team isn’t worried. Based on past storms, the wait could be anywhere from a few weeks to a few months.
“It’s like you have a loved one in a coma in the hospital,” Callas said. “You have the doctors telling you that, ‘OK, you just have to give it time and she’ll wake up,’… but if it’s your 97-year-old grandmother, you’re going to be very concerned. And so we are. By no means are we out of the woods here.”

Opportunity landed on Mars on January 25, 2004, and was supposed to last 90 Martian days. It has now spent 5,113 Martian days driving more than 45 kilometers.

About 99 million years ago, tiny frogs hopped through a wet, tropical forest — and an unlucky few ran afoul of some tree sap. Four newly described frog fossils, preserved in amber, offer the earliest direct evidence of ancient frogs living in a humid tropical clime — just as many modern amphibians do.

None of the frog fossils is complete, making it difficult to place the frogs within their family tree: One has a partial skull and another a froggy outline, although CT scanning revealed no remaining skeletal material inside the impression. So researchers dubbed all four fossils Electrorana limoae (electrum for “amber” and rana for “frog”) in a study published June 14 in Scientific Reports. Anatomy-wise, the ancient frogs most resemble a modern group that includes fire-bellied toads.

The fossil record contains relatively few frogs, despite the amphibians’ more than 200-million-year history. The frog fossils that do exist suggest that frogs have looked distinctly — well, froggy — for hundreds of millions of years, says study coauthor David Blackburn, an amphibian biologist at the Florida Museum of Natural History in Gainesville. “The aspects that make them diverse are not their skeletons, it’s their ecologies, natural histories, reproductive modes. Things that are really hard to find in the fossil record.”

That’s what makes the amber specimens so interesting: The chunks also contain preserved spiders, velvet worms and bamboo — all pointing to a tropical environment. Such paleoecological evidence offers scientists a rare glimpse into the life and times of tropical frogs of old.