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In one of the tallest trees on Earth, a tan, mottled salamander ventures out on a fern growing high up on the trunk. Reaching the edge, the amphibian leaps, like a skydiver exiting a plane.

The salamander’s confidence, it seems, is well-earned. The bold amphibians can expertly control their descent, gliding while maintaining a skydiver’s spread-out posture, researchers report May 23 in Current Biology.

Wandering salamanders (Aneides vagrans) are native to a strip of forest in far northwestern California. They routinely climb into the canopies of coast redwoods (Sequoia sempervirens). There — as high as 88 meters up — the amphibians inhabit mats of ferns that grow in a suspended, miniature ecosystem. Unlike many salamanders that typically spend their days in streams or bogs, some of these wanderers may spend their whole lives in the trees.
Integrative biologist Christian Brown was studying these canopy crawlers as a graduate student at California State Polytechnic University, Humboldt in Arcata, when he noticed they would jump from a hand or branch when perturbed.

Now at the University of South Florida in Tampa, Brown and his colleagues wondered if the salamanders’ arboreal ways and proclivity to leap were related, and if the small creatures could orient themselves during a fall.

Brown and his team captured five each of A. vagrans, a slightly less arboreal species (A. lugubris), and two ground-dwelling salamanders (A. flavipunctatus and Ensatina eschscholtzii). The researchers then put each salamander in a vertical wind tunnel to simulate falling from a tree, filming the animals’ movements with a high-speed camera.

In all of 45 trials, the wandering salamanders showed tight control, using their outstretched limbs and tail to maintain a stable position in the air and continually adjusting as they sailed. All these salamanders slowed their descents’ speed, what the researchers call parachuting, using their appendages at some point, and many would change course and move horizontally, or glide.

“We expected that maybe [the salamanders] could keep themselves upright. However, we never expected to observe parachuting or gliding,” Brown says. “They were able to slow themselves down and change directions.”
A. lugubris had similar aerial dexterity to A. vagrans but glided less (36 percent of the trials versus 58 percent). The two ground huggers mostly flailed ineffectively in the wind.

The wandering salamanders’ maneuverable gliding is probably invaluable in the tops of the tall redwoods, Brown says. Rerouting midair to a fern mat or branch during an accidental fall would save the effort spent crawling back up a tree. Gliding might also make jumping to escape a hungry owl or carnivorous mammal a feasible option.

Brown suspects that the salamanders may also use gliding to access better patches to live. “Maybe your fern mat’s drying out, maybe there’s no bugs. Maybe there are no mates in your fern mat, you look down — there’s another fern mat,” Brown says. “Why would you take the time to walk down the tree and waste energy, be exposed and [risk] being preyed upon, when you could take the gravity elevator?”

There are other arboreal salamanders in the tropics, but those don’t live nearly as high as A. vagrans, says Erica Baken, a macroevolutionary biologist at Chatham University in Pittsburgh who was not involved with the research.

“It would be interesting to find out if there is a height at which [gliding] evolves,” she says.

A. vagrans’ relatively flat body, long legs and big feet may allow more control in the air. Brown and his colleagues are now using computer simulations to test how body proportions could impact gliding.

Such body tweaks, if they do turn out to be meaningful, wouldn’t be as conspicuous as the sprawling, membraned forms seen in other animals like flying snakes and colugos that are known for their gliding (SN: 6/29/20; SN: 11/20/20). There may be many tree-dwelling animals with conventional body plans that have been overlooked as gliders, Brown says. “The canopy world is just starting to unfold.”

In the unceasing battle against dust, humans possess a deep arsenal of weaponry, from microfiber cloths to feather dusters to vacuum cleaners. But new research suggests that none of that technology can compare to nature’s secret weapon — biological soil crusts.

These biocrusts are thin, cohesive layers of soil, glued together by dirt-dwelling organisms, that often carpet arid landscapes. Though innocuous, researchers now estimate that these rough soil skins prevent around 700 teragrams (30,000 times the mass of the Statue of Liberty) of dust from wafting into the air each year, reducing global dust emissions by a staggering 60 percent. Unless steps are taken to preserve and restore biocrusts, which are threatened by climate change and shifts in land use, the future will be much dustier, ecologist Bettina Weber and colleagues report online May 16 in Nature Geoscience.
Dry-land ecosystems, such as savannas, shrublands and deserts, may appear barren, but they’re providing this important natural service that is often overlooked, says Weber, of the Max Planck Institute for Chemistry in Mainz, Germany. These findings “really call for biocrust conservation.”

Biocrusts cover around 12 percent of the planet’s land surface and are most often found in arid regions. They are constructed by communities of fungi, lichens, cyanobacteria and other microorganisms that live in the topmost millimeters of soil and produce adhesive substances that clump soil particles together. In dry-land ecosystems, biocrusts play an important role in concentrating nutrients such as carbon and nitrogen and also help prevent soil erosion (SN: 4/12/22).

And since most of the world’s dust comes from dry lands, biocrusts are important for keeping dust bound to the ground. Fallen dust can carry nutrients that benefit plants, but it can also reduce water and air quality, hasten glacier melting and reduce river flows. For instance in the Upper Colorado River Basin, researchers found that dust not only decreased snow’s ability to reflect sunlight, but it also shortened the duration of snow cover by weeks, reducing flows of meltwater into the Colorado River by 5 percent. That’s more water than the city of Las Vegas draws in a year, says Matthew Bowker, an ecologist from Northern Arizona University in Flagstaff who wasn’t involved in the new study.

Experiments had already demonstrated that biocrusts strengthened soils against erosion, but Weber and her colleagues were curious how that effect played out on a global scale. So they pulled data from experimental studies that measured wind velocities needed to erode dust from various soil types and calculated how differences in biocrust coverage affected dust generation. They found that the wind velocities needed to erode dust from soils completely shielded by biocrusts were on average 4.8 times greater than the wind velocities need to erode bare soils.

The researchers then incorporated their results, along with data on global biocrust coverage, into a global climate simulation which allowed them to estimate how much dust the world’s biocrusts trapped each year.

“Nobody has really tried to make that calculation globally before,” says Bowker. “Even if their number is off, it shows us that the real number is probably significant.”

Using projections of future climate conditions and data on the conditions biocrusts can tolerate, Weber and her colleagues estimated that by 2070, climate change and land-use shifts may result in biocrust losses of 25 to 40 percent, which would increase global dust emissions by 5 to 15 percent.

Preserving and restoring biocrusts will be key to mitigating soil erosion and dust production in the future, Bowker says. Hopefully, these results will help to whip up more discussions on the impacts of land-use changes on biocrust health, he says. “We need to have those conversations.”

Punishing headbutts damage the brains of musk oxen. That observation, made for the first time and reported May 17 in Acta Neuropathologica, suggests that a life full of bell-ringing clashes is not without consequences, even in animals built to bash.

Although a musk ox looks like a dirty dust mop on four tiny hooves, it’s formidable. When charging, it can reach speeds up to 60 kilometers an hour before ramming its head directly into an oncoming head. People expected that musk oxen brains could withstand these merciless forces largely unscathed, “that they were magically perfect,” says Nicole Ackermans of the Icahn School of Medicine at Mount Sinai in New York City. “No one actually checked.”
In fact, the brains of three wild musk oxen (two females and one male) showed signs of extensive damage, Ackermans and her colleagues found. The damage was similar to what’s seen in people with chronic traumatic encephalopathy, a disorder known to be caused by repetitive head hits (SN: 12/13/17). In the musk ox brains, a form of a protein called tau had accumulated in patterns that suggested brain bashing was to blame.

In an unexpected twist, the brains of the females, who hit heads less frequently than males, were worse off than the male’s. The male body, with its heavier skull, stronger neck muscles and forehead fat pads, may cushion the blows to the brain, the researchers suspect.

The results may highlight an evolutionary balancing act; the animals can endure just enough brain damage to allow them to survive and procreate. High-level brainwork may not matter much, Ackermans says. “Their day-to-day life is not super complicated.”

A massive urban landscape that contained interconnected campsites, villages, towns and monumental centers thrived in the Amazon rainforest more than 600 years ago.

In what is now Bolivia, members of the Casarabe culture built an urban system that included straight, raised causeways running for several kilometers, canals and reservoirs, researchers report May 25 in Nature.

Such low-density urban sprawl from pre-Columbian times was previously unknown in the Amazon or anywhere else in South America, say archaeologist Heiko Prümers of the German Archaeological Institute in Bonn and colleagues. Rather than constructing huge cities densely packed with people, a substantial Casarabe population spread out in a network of small to medium-sized settlements that incorporated plenty of open space for farming, the scientists conclude.
Airborne lasers peered through dense trees and ground cover to identify structures from that low-density urban network that have long eluded land-based archaeologists.

Earlier excavations indicated that Casarabe maize farmers, fishers and hunters inhabited an area of 4,500 square kilometers. For about a century, researchers have known that Casarabe people fashioned elaborate pottery and constructed large earthen mounds, causeways and ponds. But these finds were located at isolated forest sites that are difficult to excavate, leaving the reasons for mound building and the nature of Casarabe society, which existed from about the year 500 to 1400, a mystery.

Prümers’ team opted to look through the Amazon’s lush cover from above, aiming to find relics of human activity that typically remain hidden even after careful ground surveys. The scientists used a helicopter carrying special equipment to fire laser pulses at the Amazon forest as well as stretches of grassland. Those laser pulses reflect data from the Earth’s surface. This technique, called light detection and ranging, or lidar for short, enables researchers to map the contours of now-obscured structures.

Looking at the new lidar images, “it is obvious that the mounds are platforms and pyramids standing on artificial terraces at the center of well-planned settlements,” Prümers says.

Prümers’ team conducted lidar surveys over six parts of ancient Casarabe territory. The lidar data revealed 26 sites, 11 of them previously unknown.

Two sites, Cotoca and Landívar, are much larger than the rest. Both settlements feature rectangular and U-shaped platform mounds and cone-shaped earthen pyramids atop artificial terraces. Curved moats and defensive walls border each site. Causeways radiate out from Cotoca and Landívar in all directions, connecting those primary sites to smaller sites with fewer platform mounds that then link up to what were probably small campsites or areas for specialized activities, such as butchering prey.

The Casarabe society’s network of settlements joins other ancient and present-day examples of low-density urban sprawl around the world, says archaeologist Roland Fletcher of the University of Sydney. These sites raise questions about whether only places with centralized governments that ruled over people who were packed into neighborhoods on narrow streets, such as 6,000-year-old Mesopotamian metropolises, can be defined as cities.

Some past urban settlements organized around crop growing spanned up to 1,000 square kilometers or more in tropical regions. These include locales such as Southeast Asia’s Greater Angkor roughly 700 to 800 years ago and interconnected Maya sites in Central America dating to at least 2,300 years ago (SN: 4/29/16; SN: 9/27/18). Today, extended areas outside large cities, especially in Southeast Asia, mix industrial and agricultural activities over tens of thousands of kilometers.

Clusters of interconnected Casarabe settlements ranged in area from 100 square kilometers to more than 500 square kilometers. Spread-out settlements of comparable area include 6,000-year-old sites from Eastern Europe’s Trypillia culture (SN: 2/19/20).

Tropical forests that have gone largely unexplored, such as Central Africa’s Congo Basin, probably hosted other early forms of low-density urban development, Fletcher predicts.

Only further excavations guided by lidar evidence can begin to untangle the size of the Casarabe population, Prümers says. Whether primary Casarabe sites represented seats of power in states with upper and lower classes also remains unknown, he adds.

Casarabe culture’s urban sprawl must have encompassed a considerable number of people in the centuries before the Spanish arrived and Indigenous population numbers plummeted, largely due to diseases, forced labor and slavery, says archaeologist John Walker of the University of Central Florida in Orlando.

Whatever Casarabe honchos had in mind as their tropical settlement network spread, he says, “we may have to set aside some of our strongly held ideas about what the Amazon is, and what a city is, to better understand what happened.”

Two mysterious galaxies, devoid of dark matter, could have a smashing origin story.

About 8 billion years ago, researchers propose, two dwarf galaxies slammed into one another. That cosmic crash caused the gas within those two galaxies to split up and form multiple new dwarf galaxies, including the two dark matter–free ones.

A newfound row of dwarf galaxies, more than 6 million light-years long, could have formed in the aftermath of the hypothesized crash, researchers report in the May 19 Nature. If correct, the finding could help solve the mystery of how such unusual dark matter–free galaxies form, and reveal new details about the nature of dark matter.

But other scientists are skeptical that there’s enough evidence to support this backstory. “If this is true, I think it would be really exciting. I just don’t think the bar has been met,” says astronomer Michelle Collins of the University of Surrey in Guildford, England.

In 2018, Yale University astronomer Pieter van Dokkum and colleagues reported a dwarf galaxy with no dark matter (SN: 3/28/18). The invisible, mysterious substance is typically detectable in galaxies via its gravitational effects on stars. When a second dark matter–free dwarf galaxy was found in the vicinity in 2019, it raised an obvious question: How did the two oddball galaxies form? Dark matter is generally thought to form the foundation of all galaxies, gravitationally attracting the gas that eventually forms stars. So some process must have separated the dark matter from the galaxies’ gas.

Scientists have previously seen dark matter and normal matter separate on a very large scale in the Bullet Cluster, which formed when two clusters of galaxies rammed into one another (SN: 8/23/06). Other researchers had proposed that something similar might happen with colliding dwarf galaxies, what van Dokkum and colleagues call “bullet dwarfs.”

In such a collision, the dwarf galaxies’ ethereal dark matter would continue on unperturbed, because the dark matter doesn’t interact with other matter. But the gas from the two galaxies would slam together, eventually forming multiple clumps that would each become its own galaxy, free of dark matter.

Now, van Dokkum and colleagues say that the bullet dwarf idea explains the two previously reported dark matter–free galaxies — and several other galaxies nearby. The two galaxies are moving away from each other as if they had come from the same spot, the researchers say. What’s more, the two galaxies are part of a chain of 11 galaxies aligned in a row, a structure that could have formed in the aftermath of a bullet dwarf collision.
“It’s super satisfying to finally have an explanation for these weird objects,” van Dokkum says.

But, Collins says, “there could be much more done to make it convincing.” For example, she says, the scientists didn’t measure the distances of all the galaxies from Earth. That means some of the galaxies could be much farther away than others, and it could be a coincidence that the galaxies appear to be lined up from our viewpoint.

And the researchers haven’t yet measured the velocities of all the galaxies in the trail or determined whether those galaxies are also missing their dark matter, which would help confirm whether the scenario is correct.

Other scientists are more optimistic. “The origin story is very plausible in my opinion,” says astrophysicist Eun-jin Shin of Seoul National University in South Korea. Shin cowrote a perspective article on the discovery with astrophysicist Ji-hoon Kim, also of Seoul National University, that was also published in Nature.

Computer simulations performed by Shin, Kim and others have shown that bullet dwarfs can produce such dark matter–free galaxies. If confirmed, the bullet dwarf idea could help pin down dark matter’s properties, in particular whether dark matter interacts with itself (SN: 4/5/18).

Van Dokkum and colleagues are planning additional measurements that could confirm or refute the case. But so far, he says, “It has, to me, the ring of truth.”