Plastic smells like supper for some seabirds. When the ubiquitous material ends up in the ocean, it gives off a chemical that petrels, prions and shearwaters often use to locate food, researchers report November 9 in Science Advances. That might lead the birds to ingest harmful junk instead of a real meal.

Researchers at the University of California, Davis let small beads of three common plastics linger off the coast of California. After a few weeks, the once-clean plastic accumulated grit, grime and bacteria that gave off an odiferous gas called dimethyl sulfide (SN: 2/20/16, p. 20). Phytoplankton give off the same gas, and certain seabirds use the odor as a cue that dinner is nearby. Birds that rely more heavily on dimethyl sulfide as a beacon for a nearby meal are more likely to ingest plastic than birds that don’t, the team found. Other marine animals that use the cue could also be fooled.

NEW ORLEANS — Chronic sleep problems are associated with atrial fibrillation — a temporary but dangerous disruption of heart rhythm — even among people who don’t suffer from sleep apnea. An analysis of almost 14 million patient records has found that people suffering from insomnia, frequent waking and other sleep issues are more likely than sound sleepers to experience a condition in which the upper chambers of the heart quiver instead of rhythmically beating, allowing blood to briefly stagnate.

“Even if you don’t have sleep apnea, is there something about sleep disruption that puts you at a higher risk of fibrillation,” said Gregory Marcus, a cardiologist at the University of California, San Francisco. “We should put a higher priority on studying sleep itself.” Marcus and Matthew Christensen, from the University of Michigan, presented their results November 14 at the annual meeting of the American Heart Association.
People with atrial fibrillation have double the risk of having a heart attack, and up to five times the risk of stroke. Although the heart condition can be a consequence of aging, its prevalence is rising at about 4 percent per year for reasons that aren’t totally explained. In the United States, about 5 million people currently have the condition, and that number is expected to rise to 12 million by 2030.

A large body of studies has found that sleep apnea, which occurs when a person stops breathing during the night, can lead to atrial fibrillation and a host of other health concerns. Identifying a risk of atrial fibrillation among people with no sleep apnea is unexpected, says Richard Becker, director of the University of Cincinnati Heart, Lung & Vascular Institute, who was not part of the study.

Marcus, Christensen and colleagues analyzed data from three different sources, including the California Healthcare Cost and Utilization Project, a database of almost 14 million patients. They also drew on records from more than 4,600 participants of Health eHeart Study who had filled out a sleep survey, and from the Cardiovascular Health Study, which has tracked more than 5,700 people for more than a decade. Those data allowed the researchers to follow patients over time, tracking which came first — the fibrillation or the sleep issues. The researchers included a variety of sleep disorders, such as insomnia, nighttime waking and shortened periods of rapid eye movement, or REM, sleep.

Among the results: People who frequently woke had a 33 percent greater chance of developing atrial fibrillation in one analysis, and a 47 percent higher chance in another. For the eHeart group, insomnia increased the odds by 17 percent. And among more than 14 million California records studied, insomnia increased the odds of future atrial fibrillation by 36 percent. Analysis of a subgroup undergoing sleep studies showed that less REM sleep also was associated with a higher probability of developing atrial fibrillation.

The study can’t explain why a lack of sleep even with normal breathing might hurt the heart, but the authors hypothesize that the mechanism could be tied to the body’s stress response.

Becker believes that cardiologists should emphasize sleep just as they do diet and exercise for lifestyle management. To workaholic, screen-fixated Americans, “this study sends a powerful message about wellness as a continuum throughout the day and night,” he says. “It offers clinicians and the public a 360-degree view of what is important for good health.”

Bedbugs give me nightmares. Really. I have dreamt of them crawling up my legs while I lie in bed. These are common bedbugs, Cimex lectularius, and after largely disappearing from our beds in the 1950s, they have reemerged in the last few decades to cause havoc in our homes, offices, hotels and even public transportation.

Now there’s a new nightmare. Or rather, another old one. It’s the tropical bedbug, C. hemipterus. Its presence has been confirmed in Florida, and the critters could spread to other southern states, says Brittany Campbell, a graduate student at the University of Florida in Gainesville, who led a new study that tracked down the pests.

Tropical bedbugs can be found in a geographic band of land running between 30° N latitude and 30° S. In the last 20 years or so, they’ve been collected from Tanzania, Sri Lanka, Malaysia, Australia, Rwanda and more. Back in 1938, some were collected in Florida. There were more reports of the species in the following years, but none since the 1940s.

Then, in 2015, researchers at the Insect Identification Laboratory at the University of Florida identified bedbugs sent to the lab from a home in Brevard County, Florida, as tropical bedbugs. To confirm the analysis, researchers went to the home and collected more samples. They were indeed tropical bedbugs, the team reports in the September Florida Entomologist.

The family thought that the bedbugs must have been transported unknowingly into the house by one of the people who lived there. But no one living in the home had traveled outside the state recently, let alone outside the country. This suggests that tropical bedbugs can be found elsewhere in Florida, the team concludes.

Additional evidence comes from the Florida State Collection of Arthropods, which holds two female tropical bedbugs that, according to their label, were collected in Orange County, Florida, on June 11, 1989, from bedding. “Whether this species has been present in Florida and never disappeared, or has been reintroduced and remains in small populations, is not currently known,” the researchers write.

Why hasn’t anyone noticed? Well, people don’t usually send bedbugs to entomologists when they have an infestation, and your average victim isn’t going to notice the difference between the two species. “Both species are very similar,” Campbell says. Not only do they look alike, but they also both “feed on blood, hide in cracks and crevices and have similar lifestyles.” Plus, there’s been little research directly comparing the two species, she notes, so scientists don’t know how infestations might differ.

Just to give us all a few more nightmares, Campbell points out something else: While there’s probably no reason to worry that the creepy critters will spread as climate change warms the globe, she says that there is a potential for the species to move north “because humans provide nice conditions for bedbugs to develop.”

When I first found out my daughter existed, she was about half the size of a mini chocolate chip.

I was six weeks pregnant; she was four weeks into development. (The pregnancy timer officially begins two weeks before conception.) Already, the structures that would become her eyes had formed rudimentary orbs and the four tiny chambers of her heart were taking shape. At this stage of development, the embryo’s heart is huge, like a dumpling squeezed inside the torso.

You can see this early human heart and what happens before and after it develops with a new tool, the 3-D Atlas of Human Embryology, published November 25 in Science. The atlas chronicles the very first stages of human development — when growth is literally exponential and an embryo is building bodily systems that will be in place for a lifetime.

Embryologist Bernadette de Bakker and colleagues at the Academic Medical Center in Amsterdam created the atlas to help students, doctors and researchers better understand what goes on in those earliest weeks.

“We might know more about the moon than about our own development,” de Bakker says. Even today, human embryology textbooks often rely on pictures of chick or mouse embryos to describe how humans grow. Any human embryonic data used “is often based on just one or two specimens,” she says.
And that’s a problem because, as de Bakker has discovered, not all human embryos are the same.
Her team photographed nearly 15,000 cross sections of human embryos from the Carnegie Collection, a famous set of historical specimens collected from hysterectomies and abnormal pregnancies or miscarriages. De Bakker and colleagues uploaded the photos into a computer program, and then, using digital pencils and drawing pads, traced and labeled every organ and structure in every photo. It took some 75 people roughly 45,000 hours to complete.
What they (and we) have gained is a remarkable look at humans’ first metaphorical steps — the steady developmental march that, eventually, takes an embryo from a bundle of cells to babyhood.

Here are some landmarks in the first 60 days of development (links are to PDFs; save and open in Adobe Reader X or higher for interactive features):

Days 15-17: The embryo and all the membranes that surround it are no bigger than a speck of dust. The embryo itself is a speck within the speck, and consists of just three layers of cells. From these layers, all organs and body structures will form.

Days 19-21: What a difference a few days make. The embryo is now about the size of a pinhead and has laid the early groundwork for the heart, gut, skin, muscles, skeleton and brain.

Days 21-23: A furrow of tissue that gives rise to the brain and spinal cord has now begun to fold together, forming the neural tube. If the furrow doesn’t close properly, the spinal cord could protrude from the backbone, a birth defect called spina bifida.

Days 28-32: The embryo, now at the half mini-chocolate-chip size, starts to take on a textbook look, fledgling head and lower body curled toward each other — a rough draft of the classic fetal position.

Days 35-38: Short paddlelike arms and the first nubs of legs have emerged. The embryo is now almost the size of a ladybug.

Days 44-48: It’s now a slightly bigger ladybug, and leg bones and hand and finger bones have formed. The liver, suddenly, has ballooned in size, filling much of the lower half of the body cavity.

Days 51-53: Chubby fingers have sprouted from once clublike hands. Toes are not visible yet, but toe bones are in place. The embryo is roughly marble-sized.

Days 56-60: The embryonic brain is a giant bulbous globe now, more than a third of the entire body — which is about the size of a cherry tomato. Skinny arms and legs fold close, and a plate of skull has started to stretch across the back of the head.

Give it another 30 weeks or so and that tiny embryo will grow to the size of a bowling ball. Comparatively, a little chocolate chip doesn’t seem like much. But development-wise, it goes through something pretty huge.

Fewer teenagers in the United States used drugs in 2016 than in previous decades. The positive news comes from an annual survey of almost 45,500 U.S. students in grades eight, 10 and 12.

“There’s a lot of good news here,” says pediatrician Sharon Levy of Boston Children’s Hospital. Public health messages from pediatricians, educators and others seem to be sinking in, she says. “I think that’s fabulous. Substance use is one of the most important — yet modifiable — behavioral health issues of adolescents.”
Adolescents’ use of many of the substances, including alcohol and cigarettes, hit an all-time low since the survey, known as the Monitoring the Future study, began collecting data 42 years ago. Heroin, methamphetamines, inhalants and stimulants also hit lows this year.

E-cigarettes have been particularly concerning as more adolescents gave the new devices a try, reaching a high in 2015 (SN: 5/28/16, p. 4). For the first time, the number of students who vape is declining, the survey found. In 2015, 16.3 percent of 12th-graders reported vaping in the last 30 days. In 2016, that fell to 12.5. Similar declines were evident among eighth- and 10th-graders.
In a happy surprise, misuse of prescription opioid use decreased in the last five years among 12th–graders. The drop was “a big surprise,” particularly against a backdrop of a much wider opioid epidemic in the general population (SN: 9/3/16, p. 14), Nora Volkow, the director of the National Institute on Drug Abuse in Bethesda, Md., said December 13 at a news briefing.
The news isn’t all good, though. Marijuana bucked the declining trends, at least for 12th-graders. In 2016, about 6 percent of 12th-graders said they use marijuana daily — a number that hasn’t changed much in the last five years.

Researchers don’t yet know why the rates for many drugs are down, but one idea is that the drop in illegal drugs may stem in part from reductions in alcohol and tobacco use. “There is a connection there,” Lloyd Johnston, a social psychologist at the University of Michigan in Ann Arbor who led the survey, said in the news briefing.

The survey and the information it produces is “extremely important,” Levy says, “but it’s not everything.” Other measures of kids’ drug use, such as rates of substance use disorders, will offer a fuller view of how adolescents interact with drugs, she says.

Macaque monkeys would be quite talkative if only their brains cooperated with their airways, a new study suggests.

These primates possess the vocal equipment to speak much as people do, say evolutionary biologist and cognitive scientist W. Tecumseh Fitch of the University of Vienna and colleagues. But macaques lack brains capable of transforming that vocal potential into human talk. As a result, the monkeys communicate with grunts, coos and other similar sounds, the scientists conclude December 9 in Science Advances.

“Macaques have a speech-ready vocal tract but lack a speech-ready brain to control it,” Fitch says.

His team took X-ray videos of an adult macaque’s vocal tract while the animal cooed, grunted, made threatening sounds, smacked its lips, yawned and ate various foods. Measures of shifting shapes during these vocalizations allowed the researchers to estimate what types of speech sounds the monkey could potentially utter.
Monkeys, and presumably apes, have mouths, vocal cords and other vocal tract elements capable of articulating at least five vowel sounds, the researchers say. These consist of vowel pronunciations heard in the words bit, bet, bat, but and bought.
Consonant sounds within monkeys’ reach include those corresponding to the letters p, b, k, g, h, m and w, the scientists add.

An animal that can voice those vowels and consonants is capable of making understandable statements in English and many other languages, they conclude.

The new findings expand monkeys’ gab potential beyond that described in a pioneering 1969 study led by anthropologist and cognitive scientist Philip Lieberman, Fitch claims. Lieberman, now at Brown University in Providence, R.I., devised a computer model of a macaque’s speech potential based on measures of a cadaver monkey’s vocal tract.
Lieberman regards the new study as a replication of his 1969 report. Both investigations find that monkeys can emit a partial range of vowel sounds, Lieberman says. Each paper also determines that two especially distinctive vowel sounds, found in the words beet and boot, lie outside macaques’ vocal realm.

Hearing those sounds is another issue. Acoustic properties of the vowel sounds monkeys can produce make them relatively difficult for people to identify while listening to someone talk, Lieberman emphasizes. “If monkeys had humanlike brains, they could talk, but their speech would sound indistinct,” he says.

Fitch disagrees. By studying a living monkey’s vocal tract in action, the new study finds that these animals can make a broader range of sounds related to each of the five key vowels than reported by Lieberman, he argues. A talking monkey “would be distinct enough to understand, no worse than a foreign accent,” Fitch says. A computer-generated version of the spoken phrase “Will you marry me?” — based on newly calculated properties of the macaque’s vocal tract — is easily grasped by a listener, although less clear than the same phrase spoken by a human female, Fitch says.

Fitch and colleagues confirm a growing body of evidence that monkeys have speech-ready vocal tracts, says biological anthropologist Adriano Lameira of Durham University in England. It’s too soon, though, to say that monkeys’ brains aren’t at least partially speech-ready, he argues. Recent studies of apes, some conducted by Lameira, find that these close relatives of humans exert considerable control over their vocal tracts, allowing them to learn novel calls containing sounds similar to vowels and consonants. Neural control of various parts of the vocal tract is needed to master these sounds, Lameira says. Little is known about whether monkeys can do the same.

An aptitude for incorporating new sounds into vocal communication possibly originated in ancient primates, laying the evolutionary groundwork for human speech, Lameira proposes.

A part of the brain that’s responsible for recognizing faces seems to grow new tissue throughout childhood. That’s surprising, because brain development during childhood usually involves pruning back neural connections rather than growing new ones, researchers report in the Jan. 6 Science.

The research shows that “pruning isn’t the only game in town,” says Brad Duchaine, a psychologist at Dartmouth College who wasn’t part of the study. “I’m really excited about it.”

Researchers used magnetic resonance imaging, or MRI, to identify regions of the brain’s visual cortex that showed more activity when processing faces versus regions that lit up when processing photos of places like cityscapes or hallways. Then the scientists compared the structures of those regions in 22 kids’ brains (ages 5 to 12) with those of 25 young adults (ages 22 to 28).
The place-sensitive area — the collateral sulcus — didn’t change dramatically between childhood and adulthood. But face-sensitive areas in a region called the fusiform gyrus did.

Adults had denser fusiform gyrus brain tissue than kids and that tissue contained a different composition of cells and proteins, the researchers found.

MRI scans alone can’t reveal exactly what types of cells and structures are behind the increased tissue seen in adults’ fusiform gyrus. But evidence from previous studies suggests that the effect might come in part from increases in dendrites — the fingerlike projections of nerve cells that receive messages from other nerve cells. Dendrites might branch out more, making more connections. Another culprit might be the oligodendrocytes, brain cells that produce nerve cells’ insulating myelin coating. The actual number of nerve cells isn’t increasing, though, says Jesse Gomez, a neuroscientist at the Stanford University School of Medicine who led the study.

The visual cortex contains regions specific to processing many different types of visual stimuli — faces and places but also movement and colors. Since this study compared only facial processing and location processing, it’s not clear yet whether the increase in brain tissue is really limited to facial recognition areas, Duchaine says. But the finding does show that the brain circuits behind different types of visual processing don’t all develop in the same way.

Humans take longer to develop facial recognition skills than other types of visual processing, which could help explain the effect, the researchers propose.
“Throughout development, our social circle grows,” Gomez says. “That might be one reason why the region continues to grow — that piece of hardware in the brain itself just takes time to develop.” The current data can’t pin down the age cutoff for tissue growth, but Gomez and his colleagues are following their subjects over time to try to figure that out.

The team thinks similar tissue growth might occur in other parts of the visual cortex, too. In future studies, they hope to investigate the development of these other specialized regions.

For the millions of people who have taken up the sport of rock climbing, a cliff face is a challenge, a vertical puzzle solved only with the proper placement of hands and feet. Look closely, though, and those crevices and cracks that provide hand- and footholds also provide homes for a variety of plants, invertebrates and other easily overlooked species.

People who participate in outdoor sports like rock climbing may not think about the environmental impact of what they’re doing. After all, how big of an impact can one person really have on a rock? But there is a potential for harm, notes ecologist Andrea Holzschuh of the University of Würzburg in Germany. Finding evidence of that harm, though, is a challenge — the features that make some cliffs fun to climb, or not, also make for complicated research.

Holzschuh became interested in the effects that climbers are having on the environment in part because she is a climber herself, partial to tackling rocks in the Frankenjura region of Germany, which is noted for having some of the best climbing in Europe. The plants, animals and other species that make the cliffs their home, she notes, are often specialists that have found ways to adapt and even thrive in the extreme conditions found on the rock face. They may be rare or completely absent from nearby spots, and they often are slow-growing and their numbers grow only in spurts.

And then come the climbers, who may trample what grows at the bottom of a cliff, dig out whatever is growing in a crevice to gain a better handhold, spread species not native to the area or taint the rock face with chalk, altering pH or nutrient conditions for whatever is growing there. Rock climbing isn’t quite as impact-free as some might assume.

But scientists haven’t really been able to adequately assess that impact. Holzschuh went looking for research on this topic and found only 22 studies that tested how rock climbing might affect plants or animals. She tossed out six of those studies because they failed to make comparisons with unclimbed areas or had other major design problems that made it impossible to tease out effects. The remaining 16 studies found a variety of impacts on organisms ranging from lichens to snails to cedar trees. Holzschuh’s review appears in the December Biological Conservation.

But what the review really highlights is just how difficult it is to study rock climbing’s potential impacts. Holzschuh says a big challenge is in finding appropriate unclimbed cliff faces to compare to those that rock climbers frequent — ones that share traits such as slope and how much sunlight the face gets. “Often, all cliffs in a regions that are attractive for climbers are climbed and only cliffs that do not resemble the climbed cliffs in all abiotic traits remain unclimbed,” she notes. “Then no reliable study can be conducted.”

And then, of course, there’s the inaccessibility of many cliffs and the difficulty in studying even the accessible ones. “How many people have these skills and the flexibility to work on these projects?” says Michael Tessler of the American Museum of Natural History and Fordham University. Plus, he notes that a subset of rock climbing called bouldering — in which climbers tackle boulders or short cliff faces measuring less than 3.5 meters high, without using safety ropes — is especially popular with younger people. “Professors inherently aren’t always young,” he notes.
Tessler and colleague Theresa Clark of the University of Nevada, Las Vegas published the first ever analysis attempting to quantify the impact of bouldering on the environment. This type of climbing has similar potential for ecosystem damage as roped rock climbing, they note, plus a couple of additional ones: Boulderers often clear the ground below of rocks and logs so that they can place crash pads in case of falls, and they may be more likely to trample anything at the top of a boulder or cliff, rather than coming directly down.

Tessler and Clark tried to measure the impact of climbers at bouldering routes in the Shawangunk Ridge, a popular climbing site in New York where Tessler climbs. They compared transects in climbed boulder routes with transects along nearby unclimbed sections of rock and found differences in lichen, moss and woody plants. None of this added up to a major threat, but conservation managers might want to monitor these activities in remote sites and shut down certain routes that are proving too popular — and potentially too harmful to whatever is growing there, Tessler and Clark suggest in the December Biological Conservation.

While we still can’t really say how much impact climbers might be having on the rocky environments they climb, there is a definite need for more scientists to strap on their climbing shoes and tackle the questions of climbing’s impact. (Try it! It’s lots of fun!) But climbers, too, can do their part, Holzschuh and Tessler say.

“I think climbers can easily minimize their impact on the cliff vegetation if they do not willingly remove vegetation from the cliff to ‘clean’ hand- and footholds in the climbing route. Climbers should not access the cliff plateau [and should] leave this cliff part completely undisturbed,” Holzschuh says. “At the cliff base, bags and gear should be laid down within a small area to reduce the effects of trampling.”

Tessler also has advice. “Boulderers should be aware that even infrequent climbing leaves some impression on rock-associated vegetation,” he says. “They should remove as little vegetation and soil when climbing and establishing climbs. Also, if a climb is wet, dirty or covered in vegetation, maybe go to another one. This is an easy way to ensure that some rock faces can stay more natural.”

And if climbing is restricted because, say, rare birds are breeding there, rock climbers should obey the restriction and go climb somewhere else, Holzschuh says. There are plenty of other cliffs to be conquered.

A team of scientists may have given hydrogen a squeeze strong enough to turn it into a metal. But critics vigorously dispute the claim.

Researchers from Harvard University report that under extremely high pressures hydrogen became reflective — one of the key properties of a metal. The feat required compressing hydrogen to 4.9 million times atmospheric pressure, the scientists report online January 26 in Science.

If correct, the result would be the culmination of a decades-long search for a material that could have unusual properties such as superconductivity — the ability to conduct electricity without resistance.
But physicist Eugene Gregoryanz of the University of Edinburgh, who works on similar experiments, decries the study’s publication as a failure of the journal’s review process. Given the evidence presented in the paper, Gregoryanz is skeptical that the claimed pressures were actually reached and notes that the researchers presented results from only one experiment. “How is it possible to do only one experiment and claim such a big thing?” he says.

Physicist Alexander Goncharov of the Carnegie Institution for Science in Washington, D.C., also takes issue with the researchers’ conclusions. “It’s not shown whether they have hydrogen at all at high pressure,” Goncharov says.

Not everyone is so skeptical. “I think there’s a good chance that it’s correct,” says theoretical physicist David Ceperley of the University of Illinois at Urbana-Champaign. The pressure at which the hydrogen became reflective is about where theoretical physicists have calculated that a metal should form, Ceperley says.

Theorists’ calculations also indicate that metallic hydrogen could be a high-temperature superconductor (SN: 8/20/16, p. 18). Most superconductors work only in extreme cold, but metallic hydrogen might function even at room temperature — higher than any other known superconductor. If so, its discovery would raise hopes that superconducting metallic hydrogen could be used in power lines, making transmission of electricity vastly more efficient.

To put the pressure on hydrogen, scientists capture it as a gas between the tips of two diamonds and squeeze them together. It’s no easy task. “The problem in making metallic hydrogen has been that the predicted pressures have been very high,” says physicist Isaac Silvera of Harvard University, a coauthor of the study. “Diamonds always break before you can obtain those pressures.”
To stave off breakage, the scientists smoothed the surface of the diamonds to remove any defects and covered the gems in a thin layer of aluminum oxide to prevent hydrogen from diffusing inside and creating cracks. The researchers also cooled the setup to temperatures of 83 kelvins (−190° Celsius) or below. As the scientists ratcheted up the pressure, the hydrogen first turned black, indicating a possible semiconducting phase, then became reflective, indicating a metal. The metallic hydrogen could be either a solid or a liquid, Silvera says.

But such experiments are tricky — only a few teams of researchers in the world are capable of performing them. One of the pitfalls can be that the hydrogen escapes from the chamber without the scientists realizing it. However, Silvera says, “We’re sure we have hydrogen in there.”

Some previous metallic hydrogen experiments have monitored hydrogen as the pressure is ramped up to help ensure that the hydrogen hasn’t escaped and to study its evolution. To do so, scientists use a technique called Raman spectroscopy, which involves shining a laser through the diamonds and observing the scattered light. But at pressures this high, lasers could cause the diamonds to break, Silvera says. So the researchers used lasers only after the sample had reached the metallic state.

Silvera’s group is not the first to announce the discovery of metallic hydrogen. Earlier claims of finding the metal have been overturned (SN: 12/17/11, p. 9). “It’s not the last word,” says Ceperley. “It should encourage all the other groups to come out and try to reproduce it.”

A roughly 540-million-year-old creature that may have once skimmed shorelines was a real oddball.

Dozens of peculiar, roundish fossils discovered in what is now South China represent the earliest known deuterostomes, a gigantic category of creatures that includes everything from humans to sea cucumbers.

No bigger than a pinhead, the fossils have wrinkly, baglike bodies and gaping mouths that are pleated around the edges like an accordion, researchers report January 30 in Nature. Unlike most other deuterostomes, the animals don’t seem to have an anus. Instead, the ancient oddities, named Saccorhytus coronarius, may have leaked waste (and other bodily fluids like mucus and sex cells) out of tiny holes lining their sides. These holes may have later evolved into gill slits.

A tough, flexible skin would have protected Saccorhytus as it wriggled through grains of dirt, the authors suggest. The find supports previous suggestions that the earliest deuterostomes were actually a kind of water-dwelling worm.