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It doesn’t have to be this way.

The world already has the know-how and tools to dramatically reduce emissions from fossil fuels — but we need to use those tools immediately if we hope to forestall the worst impacts of climate change. That’s the message of the third and final installment of the massive sixth assessment of climate science by the United Nations’ Intergovernmental Panel on Climate Change, which was released April 4.

“We know what to do, we know how to do it, and now it’s up to us to take action,” said sustainable energy researcher Jim Skea of Imperial College London, who cochaired the report, at a news event announcing its release.
Earth is on track to warm by an average of about 3.2 degrees Celsius above preindustrial levels by the end of the century (SN: 11/26/19). Altering that course and limiting warming to 1.5 degrees or even 2 degrees means that global fossil fuel emissions will need to peak no later than the year 2025, the new report states.

Right now, meeting that goal looks extremely unlikely. National pledges to reduce fossil fuel emissions to date amount to “a litany of broken climate promises,” said United Nations Secretary-General António Guterres at the event.

The previous two installments of the IPCC’s sixth assessment described how climate change is already fueling extreme weather events around the globe — and noted that adaptation alone will not be enough to shield people from those hazards (SN: 8/9/21; SN: 2/28/22).

The looming climate crisis “is horrifying, and I don’t want to sugarcoat that,” says Bronson Griscom, a forest ecologist and the director of Natural Climate Solutions at the environmental organization Conservation International, based in Arlington, Va.

But Griscom, who was not an author on the new IPCC report, says its findings also give him hope. It’s “what I would call a double-or-nothing bet that we’re confronted with right now,” he says. “There [are] multiple ways that this report is basically saying, ‘Look, if we don’t do anything, it’s increasingly grim.’ But the reasons to do something are incredibly powerful and the tools in the toolbox are very powerful.”

Tools in the toolbox
Those tools are strategies that governments, industries and individuals can use to cut emissions immediately in multiple sectors of the global economy, including transportation, energy, building, agriculture and forestry, and urban development. Taking immediate advantage of opportunities to reduce emissions in each of those sectors would halve global emissions by 2030, the report states.

Consider the transportation sector, which contributed 15 percent of human-related greenhouse gas emissions in 2019. Globally, electric vehicle sales have surged in the last few years, driven largely by government policies and tougher emissions laws for the auto industry (SN: 12/22/21).

If that surge continues, “electric vehicles offer us the greatest potential [to reduce transportation emissions on land], as long as they’re combined with low or zero carbon electricity sources,” Diana Ürge-Vorsatz, the vice chair of the IPCC’s Working Group III, said at the news event. But for aviation and long-haul shipping, which are more difficult to electrify, reduced carbon emissions could be achieved with low-carbon hydrogen fuels or biofuels, though these alternatives require further research and development.

Then there are urban areas, which are contributing a growing proportion of global greenhouse gas emissions, from 62 percent in 2015 to between 67 and 72 percent in 2020, the report notes. In established cities, buildings can be retrofitted, renovated or repurposed to make city layouts more walkable and provide more accessible public transportation options.

And growing cities can incorporate energy-efficient infrastructure and construct buildings using zero-emissions materials. Additionally, urban planners can take advantage of green roofs, urban forests, rivers and lakes to help capture and store carbon, as well as provide other climate benefits such as cleaner air and local cooling to counter urban heat waves (SN: 4/3/18).

Meanwhile, “reducing emissions in industry will involve using materials and energy more efficiently, reusing and recycling products and minimizing waste,” Ürge-Vorsatz said.

As for agriculture and forestry, these and other land-use industries contribute about 22 percent of the world’s greenhouse gas emissions, with half of those emissions coming from deforestation (SN: 7/13/21). So reforestation and reduced deforestation are key to flipping the balance between CO₂ emissions and removal from the atmosphere (SN: 7/9/21; SN: 1/3/22). But there are a lot of other strategies that the world can employ at the same time, the report emphasizes. Better management of forests, coastal wetlands, grasslands and other ecosystems, more sustainable crop and livestock management, soil carbon management in agriculture and agroforestry can all bring down emissions (SN: 7/14/21).

The report also includes, for the first time in the IPCC’s reports, a chapter on the “untapped potential” of lifestyle changes to reduce emissions. Such changes include opting for walking or cycling or using public transportation rather than driving, shifting toward plant-based diets and reducing air travel (SN: 5/14/20).

Those lifestyle changes could reduce emissions by 40 to 70 percent by 2050, the report suggests. To enable those changes, however, government policies, infrastructure and technology would need to be in place.

Government policies are also key to financing these transformational changes. Globally, the investment in climate-related technologies needs to ramp up, and quickly, to limit warming below 2 degrees C, the report states. Right now, investments are three to six times lower than they need to be by 2030. And a combination of public and private investments will be essential to aiding the transition away from fossil fuels and toward renewable energy in developing nations (SN: 1/25/21).

Future strategies
Still, reducing emissions alone won’t be enough: We will need to actively remove carbon from the atmosphere to achieve net zero emissions and keep the planet well below 2 degrees C of warming, the report notes. “One thing that’s clear in this report, as opposed to previous reports, is that carbon removal is going to be necessary in the near term,” says Simon Nicholson, director of the Institute for Carbon Removal Law and Policy at American University in Washington, D.C., who was not involved in the report.

Such strategies include existing approaches such as protecting or restoring carbon dioxide–absorbing forests, but also technologies that are not yet widely available commercially, such as directly capturing carbon dioxide from the air, or converting the gas to a mineral form and storing it underground (SN: 12/17/18).

These options are still in their infancy, and we don’t know how much of an impact they’ll have yet, Nicholson says. “We need massive investment now in research.”

An emphasis on acting “now,” on eliminating further delay, on the urgency of the moment has been a recurring theme through all three sections of the IPCC’s sixth assessment report released over the last year. What impact these scientists’ stark statements will have is unclear.

But “the jury has reached a verdict, and it is damning,” U.N. Secretary-General Guterres said. “If you care about justice and our children’s future, I am appealing directly to you.”

A chance alignment may have revealed a star from the universe’s first billion years.

If confirmed, this star would be the most distant one ever seen, obliterating the previous record (SN: 7/11/17). Light from the star traveled for about 12.9 billion years on its journey toward Earth, about 4 billion years longer than the former record holder, researchers report in the March 30 Nature. Studying the object could help researchers learn more about the universe’s composition during that early, mysterious time.

“These are the sorts of things that you only hope you could discover,” says astronomer Katherine Whitaker of the University of Massachusetts Amherst, who was not part of the new study.
The researchers found the object while analyzing Hubble Space Telescope images of dozens of clusters of galaxies nearer to Earth. These clusters are so massive that they bend and focus the light from more distant background objects, what’s known as gravitational lensing (SN: 10/6/15).

In images of one cluster, astronomer Brian Welch of Johns Hopkins University and colleagues noticed a long, thin, red arc. The team realized that the arc was a background galaxy whose light the cluster had warped and amplified.

Atop that red arc is a bright spot that is too small to be a small galaxy or a star cluster, the researchers say. “We stumbled into finding that this was a lensed star,” Welch says.

The researchers estimate that the star’s light originates from only 900 million years after the Big Bang, which took place about 13.8 billion years ago.

Welch and his colleagues think that the object, which they poetically nicknamed “Earendel” from the old English word meaning “morning star” or “rising light,” is a behemoth with at least 50 times the mass of the sun. But the researchers can’t pin down that value, or learn more about the star or even confirm that it is a star, without more detailed observations.

The researchers plan to use the recently launched James Webb Space Telescope to examine Earendel (SN: 10/6/21). The telescope, also known as JWST, will begin studying the distant universe this summer.

JWST may uncover objects from even earlier times in the universe’s history than what Hubble can see because the new telescope will be sensitive to light from more distant objects. Welch hopes that the telescope will find many more of these gravitationally lensed stars. “I’m hoping that this record won’t last very long.”

Leeches suck. Most people try to avoid them. But in the summer of 2016, park rangers in China’s Ailaoshan Nature Reserve went hunting for the little blood gluttons.

For months, the rangers searched through the reserve’s evergreen forest, gathering tens of thousands of leeches by hand and sometimes plucking the slimy parasites from the rangers’ own skin. Each time the rangers found a leech, they would place it into a little, preservative-filled tube, tuck the tube into a hip pack and carry on. The work could help aid conservation efforts, at Ailaoshan and elsewhere.

There are many ways to measure how much effort goes into wildlife conservation, but it’s difficult to assess the success of that effort, even in protected areas, says Douglas Yu, an ecologist at the Kunming Institute of Zoology in China.
But bloodthirsty worms may be just the tool for the job. Leeches aren’t picky eaters — they’ll feast on the blood of many different creatures, from amphibians to mammals to fish. Scientists have shown they can extract animal DNA from blood that leeches and other bloodsucking creatures have ingested, what’s known as invertebrate-derived DNA, or iDNA, and identify the source animal.

And some researchers had suggested that iDNA, a type of environmental DNA, could be used to trace the ranges of animals in an area, Yu says (SN: 1/18/22). “We thought we would just actually just try to do it.”

Enlisting 163 park rangers, Yu and colleagues deputized the leech-hunters with gathering the parasites along rangers’ regular patrol routes, which covered all 172 areas of the reserve.

Three months later, the rangers had gathered 30,468 leeches. After extracting and analyzing animal DNA from the leeches’ blood meals, Yu and colleagues detected the presence of 86 different species, including Asiatic black bears, domestic cattle, endangered Yunnan spiny frogs and, of course, humans.

What’s more, the iDNA gave clues to where the animals preferred to roam, the researchers report March 23 in Nature Communications. Wildlife biodiversity was greatest in the reserve’s high-altitude interior, the researchers found, while domestic cattle, sheep and goats were more abundant in the reserve’s lower, more accessible zones. Because most of the wild species detected should be able to inhabit all parts of the reserve, the dichotomy suggests that human activity may be pushing wildlife away from certain areas, Yu says.

Compared with other methods for surveying wildlife, using iDNA from leeches is “really cost- and time-efficient and doesn’t require a lot of expertise,” says Arthur Kocher, an ecologist at the Max Planck Institute for the Science of Human History in Jena, Germany, who was not involved in the study.

Camera traps, for instance, are triggered only by animals of large enough size, and the instruments are expensive. Sight-based surveys require trained observers. With leeches, Kocher says, “there are clear advantages.”

Yu and Kocher both suspect that leeches and other bloodsucking critters, such as carrion flies or mosquitoes, will become more popular wildlife surveillance tools in the future. People are becoming more aware of what iDNA brings to the table, Yu says.

Western banded geckos don’t look like they’d win in a fight. Yet this unassuming predator dines on venomous scorpions, and a field study published in the March Biological Journal of the Linnean Society shows how the lizards take down such perilous prey.

Geckos bite the scorpion and thrash their heads and upper bodies back and forth, body-slamming the scorpion against the ground, new high-speed video reveals. “The behavior is so fast that you can’t see what’s actually happening,” says San Diego State University biologist Rulon Clark. “[You] see the gecko lunge and then see this crazy blur of motion … like trying to watch the wings of a hummingbird.”

Clark first noticed the behavior in the 1990s, during undergraduate fieldwork in the Sonoran Desert near Yuma, Ariz. When he returned with colleagues to study kangaroo rats and rattlesnakes, the team filmed geckos as well. The researchers captured western banded geckos (Coleonyx variegatus) and dune scorpions (Smeringurus mesaensis) in the desert at night (along with harmless arthropods, like field crickets and sand roaches, to compare), and documented the showdowns.
Normal gecko feeding behavior usually involves lunging out, grabbing prey with their mouth, and chomping it, says Clark. With scorpions, it’s totally different after the initial lunge. Such shake feeding is a known method for carnivores and adventurous eaters. For instance, dolphins shake (and toss) octopuses before eating (SN: 4/25/17).

The fact that this delicate, cold-blooded species not known for speed can achieve such physical gyrations is impressive, Clark says. Songbirds called loggerhead shrikes whip larger predators in circles (SN: 9/7/18), but at a lower frequency (11 hertz compared to 14 Hz in geckos). Whiptail lizards also violently shake scorpions, but at unknown speeds. The closest documented match to the speed of gecko shake feeding is small mammals shaking themselves dry; guinea pigs clock in at around 14 Hz, as well.

It’s unclear how common this behavior is among geckos. And aside from generally subduing a venomous foe, how it works — killing the scorpion, immobilizing it, damaging its stinger, or reducing how much venom gets injected — remains a mystery.

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.”

Four billion years ago, lava spilled onto the moon’s crust, etching the man in the moon we see today. But the volcanoes may have also left a much colder legacy: ice.

Two billion years of volcanic eruptions on the moon may have led to the creation of many short-lived atmospheres, which contained water vapor, a new study suggests. That vapor could have been transported through the atmosphere before settling as ice at the poles, researchers report in the May Planetary Science Journal.
Since the existence of lunar ice was confirmed in 2009, scientists have debated the possible origins of water on the moon, which include asteroids, comets or electrically charged atoms carried by the solar wind (SN: 11/13/09). Or, possibly, the water originated on the moon itself, as vapor belched by the rash of volcanic eruptions from 4 billion to 2 billion years ago.

“It’s a really interesting question how those volatiles [such as water] got there,” says Andrew Wilcoski, a planetary scientist at the University of Colorado Boulder. “We still don’t really have a good handle on how much are there and where exactly they are.”

Wilcoski and his colleagues decided to start by tackling volcanism’s viability as a lunar ice source. During the heyday of lunar volcanism, eruptions happened about once every 22,000 years. Assuming that H2O constituted about a third of volcano-spit gasses — based on samples of ancient lunar magma — the researchers calculate that the eruptions released upward of 20 quadrillion kilograms of water vapor in total, or the volume of approximately 25 Lake Superiors.

Some of this vapor would have been lost to space, as sunlight broke down water molecules or the solar wind blew the molecules off the moon. But at the frigid poles, some could have stuck to the surface as ice.

For that to happen, though, the rate at which the water vapor condensed into ice would have needed to surpass the rate at which the vapor escaped the moon. The team used a computer simulation to calculate and compare these rates. The simulation accounted for factors such as surface temperature, gas pressure and the loss of some vapor to mere frost.

About 40 percent of the total erupted water vapor could have accumulated as ice, with most of that ice at the poles, the team found. Over billions of years, some of that ice would have converted back to vapor and escaped to space. The team’s simulation predicts the amount and distribution of ice that remains. And it’s no small amount: Deposits could reach hundreds of meters at their thickest point, with the south pole being about twice as icy as the north pole.

The results align with a long-standing assumption that ice dominates at the poles because it gets stuck in cold traps that are so cold that ice will stay frozen for billions of years.
“There are some places at the lunar poles that are as cold as Pluto,” says planetary scientist Margaret Landis of the University of Colorado Boulder.

Volcanically sourced water vapor traveling to the poles, though, probably depends on the presence of an atmosphere, say Landis, Wilcoski and their colleague Paul Hayne, also a planetary scientist at the University of Colorado Boulder. An atmospheric transit system would have allowed water molecules to travel around the moon while also making it more difficult for them to flee into space. Each eruption triggered a new atmosphere, the new calculations indicate, which then lingered for about 2,500 years before disappearing until the next eruption some 20,000 years later.

This part of the story is most captivating to Parvathy Prem, a planetary scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Md., who wasn’t involved in the research. “It’s a really interesting act of imagination.… How do you create atmospheres from scratch? And why do they sometimes go away?” she says. “The polar ices are one way to find out.”

If lunar ice was belched out of volcanoes as water vapor, the ice may retain a memory of that long-ago time. Sulfur in the polar ice, for example, would indicate that it came from a volcano as opposed to, say, an asteroid. Future moon missions plan to drill for ice cores that could confirm the ice’s origin.

Looking for sulfur will be important when thinking about lunar resources. These water reserves could someday be harvested by astronauts for water or rocket fuel, the researchers say. But if all the lunar water is contaminated with sulfur, Landis says, “that’s a pretty critical thing to know if you plan on bringing a straw with you to the moon.”

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.”

Six years ago, tour guide Brenden Miles was traveling down the Kinabatangan River in the Malaysian part of Borneo, when he spotted an odd-looking primate he had never seen before. He snapped a few pictures of the strange monkey and, on reaching home, checked his images.

“At first, I thought it could be a morph of the silvered leaf monkey,” meaning a member of the species with rare color variation, Miles says. But then he noticed other little details. “Its nose was long like that of a proboscis monkey, and its tail was thicker than that of a silvered leaf [monkey],” he says. He posted a picture of the animal on Facebook and forgot all about it.

Now, an analysis of that photo and others suggests that the “mystery monkey” is a hybrid of two distantly related primate species that share the same fragmented habitat.
The putative offspring was produced when a male proboscis monkey (Nasalis larvatus) mated with a female silvered leaf monkey (Trachypithecus cristatus), researchers suggest April 26 in the International Journal of Primatology. And that conclusion has the scientists worried about the creature’s parent species.

Hybridization between closely related organisms has been observed in captivity and occasionally in the wild (SN: 7/23/21). “But hybridization across genera, that’s very rare,” says conservation practitioner Ramesh Boonratana, the regional vice-chair for Southeast Asia for the International Union for Conservation of Nature’s primate specialist group.

Severe habitat loss, fragmentation and degradation caused by expanding palm oil plantations along the Kinabatangan River could explain how the possible hybrid came to be, says primatologist Nadine Ruppert.

“Different species — even from the same genus — when they share a habitat, they may interact with each other, but they may usually not mate. This kind of cross-genera hybridization happens only when there is some ecological pressure,” says Ruppert, of the Universiti Sains Malaysia in Penang Island.

The state of Sabah, where Kinabatangan River is located, lost about 40 percent of its forest cover from 1973 to 2010, with logging and palm oil plantations being the main drivers of deforestation, a study in 2014 found.
“In certain areas, both [monkey] species are confined to small forest fragments along the river,” Ruppert says. This leads to competition for food, mates and other resources. “The animals cannot disperse and, in this case, the male of the larger species — the proboscis monkey — can easily displace the male silvered leaf monkey.”

Since 2016, there have been some more documented sightings of the mystery monkey, though these have been sporadic. The infrequent sightings and the COVID-19 pandemic has, for now, prevented researchers from gathering fecal samples for genetic analysis to reveal the monkey’s identity. Instead, Ruppert and colleagues compared images of the possible hybrid with those of the parent species, both visually as well as by using limb ratios. “If the individual was from one of the two parent species, all its measurements would be similar to that of one species,” Ruppert says. “But that is not the case with this animal.”

A photograph of a male proboscis monkey mating with a female silvered leaf monkey, along with anecdotes from boat operators and tour guides about a single male proboscis monkey hanging around a troop of female silvered leaf monkeys, has added further weight to the researchers’ conclusion.

The mystery monkey is generating a lot of excitement in the area, but Ruppert is concerned for the welfare of both proposed parent species. The International Union for Conservation of Nature classifies proboscis monkeys as endangered and silvered leaf monkeys as vulnerable. “The hybrid is gorgeous, but we don’t want to see more of them,” Ruppert says. “Both species should have a large enough habitat, dispersal opportunities and enough food to conduct their natural behaviors in the long term.”

Increasing habitat loss or fragmentation in Borneo and elsewhere as a result of changing land uses or climate change could lead to more instances of mating — or at least, attempts at mating — between species or even genera, Boonratana says.

The mystery monkey was last photographed in September of 2020 with swollen breasts and holding a baby, suggesting that the animal is a fertile female. That’s another surprising development, the researchers say, because most hybrids tend to be sterile.