Rise of the Mammals

Sixty-six million years ago, an asteroid wiped out the dinosaurs in a fiery global catastrophe. But we know little about how their successors, the mammals, recovered and took over the world. Now, hidden inside ordinary-looking rocks, an astonishing trove of fossils reveals a dramatic new picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species—from cheetahs to bats to whales to humans—that rule our planet today.

Amazing fossils reveal how mammals took over after an asteroid wiped out the dinosaurs.

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Explore the intimate connections between the landscape, the colonizing of the continent, and the emergence of our industrial world. Beginning with Native American ancestors who crafted hunting weapons from stone traded across hundreds of miles, the program shows how pre-Columbian civilizations developed an expert knowledge of the landscape and its resources. With the arrival of Europeans, North America’s hidden riches became to key to prosperity, from the gold rush to today’s oil and gas boom. As a result, human activity has transformed the continent on a scale that rivals the geological forces that gave birth to it billions of years before. Yet, scientists warn of sleeping giants like the Cascadia fault, and the earthquake/tsunami one-two punch it could unleash on the Pacific Northwest. Even as we re-mold the continent to suit our needs, geologic processes inexorably continue, and they raise potential risks of catastrophe to our human civilization.

How has the land shaped our lives, from the arrival of the first Americans to today?

Making North America: Human

Day the Dinosaurs Died Hero

A seven-mile-wide asteroid collided with Earth 66 million years ago, triggering a chain of events that coincide with the end of the dinosaurs. But experts have long debated exactly what happened when the asteroid struck and how the giant beasts met their end. Now, scientists have uncovered compelling new clues about the catastrophe—from New Jersey to the wilds of Patagonia—and an international expedition of scientists has drilled into the impact crater off the coast of Mexico, recovering crucial direct evidence of the searing energy and giant tsunami unleashed by the asteroid. Join NOVA as scientists piece together a chillingly precise unfolding of the Earth’s biggest cataclysm, moment by moment, and discover how our early mammalian ancestors managed to survive and repopulate the Earth. (Premiered December 27, 2017)

Experts drill into the impact crater of an asteroid that created a worldwide cataclysm.

Day the Dinosaurs Died

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Evolution

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The Denver Basin preserves a pristine record of ecosystem recovery.
At Corral Bluffs, Colorado, paleontologist Tyler Lyson discovers rare mammal fossils that paint a picture of the first million years after an asteroid killed the dinosaurs.
Paleontologist Makes &quot;Game-Changing&quot; Fossil DiscoveryPublished: October 25, 2019Tyler Lyson: I grew up in basically the middle of nowhere in Southwestern North Dakota. But this area just happened to be the epicenter for understanding the extinction of the dinosaurs.Everything alive today can trace its ancestry back to the survivors of this mass extinction event — the extinction that wiped out the dinosaurs 66 million years ago.But I&#x27;ve always been fascinated, I&#x27;ve always been interested in the recovery.…going from the age of the dinosaurs to the Modern Age, the Age of the Mammals.When I moved here to Colorado, I was really excited to move to Denver. Denver is situated right in the middle of the Denver Basin which just happens to preserve the recovery of an ecosystem.There&#x27;s only a few places in the world where we have the rocks of the right age.I think the discovery that we have here in Colorado is a complete game changer.Simply because we have amazing vertebrates, amazing plants, and an amazing timeline.So those three things together, it&#x27;s a bit like the holy trinity of paleontology.We are and will continue to make some major progress in understanding the recovery.It’s, I mean, amazing.

The Denver Basin preserves a pristine record of ecosystem recovery.

Paleontologist Makes "Game-Changing" Fossil Discovery

Stunning new mammal fossils were hiding in plain sight.
Hidden inside ordinary-looking rocks, an astonishing trove of fossils reveals a dramatic new picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species—from cheetahs to bats to whales to humans—that rule our planet today.
Paleontologists Discover New Mammal Fossils Hidden in RocksPublished: October 25, 2019Narrator: In the bluffs outside of Denver, Colorado, paleontologist Tyler Lyson is searching for evidence of a pivotal moment in our evolution: the rise of mammals after the demise of the dinosaurs.Tyler Lyson: The period of time right after the extinction of the dinosaurs, 66 million years ago, is one of the least understood moments in time in all of earth’s history.At Corral Bluffs we find the rocks of the right age.So we are looking for things like mammals, turtles, crocodiles, birds and plants and trying to combine all of that into a reconstruction of the environment.Narrator: Tyler, an experienced dinosaur hunter, was ready to apply his fossil finding techniques to the site.Ian Miller: …so far.Lyson: Hardly, anyway.The old search image was sort of classic paleontology where you go out, walk the bottom of a, of a gully or the base of a cliff and you’d find broken bits of bone.Narrator: Then, you head head uphill, looking for bigger bones weathering out of the dirt. But at Corral Bluffs, the search for early mammals was coming up empty.Lyson: I immediately started searching for bone and not finding anything. So I was pretty frustrated.What could I do to, to find fossils here?Narrator: The fossils were there. Tyler was just looking for them in the wrong way. Until he came across an old specimen in the Museum&#x27;s vault. It was a mammal skull, embedded in a round rock.Lyson: And that&#x27;s when sort of the lightbulb went off and I was like, “Oh, well maybe concretions.”James Hagadorn: Concretions are kinda like nodules—like an egg or a ball that you find in a rock, an ancient rock.Narrator: James Hagadorn is curator of geology at the Denver Museum of Nature and Science. He&#x27;s a colleague of Tyler&#x27;s and has lots of experience with concretions.Hagadorn: So if you have a skull or a tooth or even a bit of poop and it falls to the sea floor or it ends up on the bottom of a lake, um, and gets buried, it is compositionally different than the rest of the sand around it or the mud or whatever.Narrator: With typical fossils, the organic matter would slowly be replaced by minerals, leaving petrified bones within the surrounding sediments. But with concretions, the minerals encase the organic matter as well, creating a distinctive rock within a rock, with a fossil inside.Hagadorn: That kaleidoscope of minerals-get attracted to that tooth or skull or tree root or something, and they start to grow around it layer by layer in the sediment, kind of like a pearl in an oyster.Narrator: The mineral casing can preserve otherwise fragile fossils, just like those of the early mammals Tyler is looking for.Lyson: The concretions form around these bones and it creates this hard protective shell. And then these fossils in their nice protective casings, roll down the hill.And then we crack it open and sure enough we started finding bone inside.Male student: He just found a mammal skull.Lyson: I just found a mammal skull!And that was a complete game changer for this entire project.Narrator: Tyler and the team split open concretion after concretion revealing hundreds of fossils, including dozens of mammals from the period right after the dinosaurs went extinct.Lyson: People have been looking for fossils in Corral Bluffs for over a hundred years and they just didn’t look for concretions. They were looking for actual leaves or they were looking for bones.Narrator: It was an honest mistake. The concretions here are formed by a mineral called apatite, which is not usually associated with terrestrial sites like the Denver Basin.Hagadorn: Apatite is the same mineral that my teeth and bones are made out of and so are yours.In marine settings, in ancient oceanic deposits, they’re pretty common. Prior to working on this project, I had never seen an apatite concretion in a terrestrial setting. It&#x27;s super rare.Narrator: Yet here in plain sight, apatite concretions have been hiding priceless specimens from one of the most important periods in mammal evolution.Hagadorn: Tyler has a paleontological goldmine right there. I mean, there&#x27;s just nothing like it.Wouldn&#x27;t it be cool if you could find more of them? Cause nature repeats itself.Whatever processes led to the formation of those fossils and the preservation of &#x27;em, ought to repeat itself elsewhere in the world.

Stunning new mammal fossils were hiding in plain sight.

Paleontologists Discover New Mammal Fossils Hidden in Rocks

Plants can help us understand how life rebounds after a mass extinction.
Vertebrate fossils can help scientists better understand evolutionary timelines. But plant fossils give paleontologists and paleobotanists a more complete story.
How Fossilized Plants Tell Us About the Evolution of AnimalsPublished: October 25, 2019Ian Miller: Here in the Denver basin, you can see the end of the time of the dinosaurs.And you can see the rocks that tell us about how the world recovered from this mass extinction.But to tell the recovery story, you really need good fossils and you need to be able to place them in time.You need to look for a lot of different kinds of vertebrate fossils.But to see the rest of it we’ve got to find the leaves of plants, wood, fossil wood, and pollen - to see how the plants change.Plants are sort of the keys to helping us understand how the whole world comes back after a great extinction.The first thing we see are the ferns.But one of the big surprises was this incredible abundance of palm spores.This is a world dominated by palms.It’s also where we find the earliest legumes. What we think could be the food source for new groups of mammals to exist here on this landscape.So, you can imagine in a world that’s revegetating and re-diversifying, from a plant perspective…That’s the story that’s really here, this incredible diverse world of the time of the dinosaurs that die off. The ferns, the palms and then this incredible diversification of seed types and the animals that come with it.

Plants can help us understand how life rebounds after a mass extinction.

How Fossilized Plants Tell Us About the Evolution of Animals

Amazing fossils reveal how mammals took over after an asteroid wiped out the dinosaurs.
Sixty-six million years ago, an asteroid wiped out the dinosaurs in a fiery global catastrophe. But we know little about how their successors, the mammals, recovered and took over the world. Now, hidden inside ordinary-looking rocks, an astonishing trove of fossils reveals a dramatic new picture of how rat-sized creatures ballooned in size and began to evolve into the vast array of species—from cheetahs to bats to whales to humans—that rule our planet today.

<div class="rich-text">The list of humankind’s scientific accomplishments is long. We’ve unraveled the human genome, harnessed <a href="https://www.pbs.org/wgbh/nova/video/einsteins-quantum-riddle/">quantum mechanics</a>, and sent space probes <a href="https://www.pbs.org/wgbh/nova/article/nasa-celebrates-most-distant-space-encounter/">hurtling past Pluto</a>.Despite decades of research, however, some puzzles remain unsolved—including the female orgasm, whose biological roots have long defied explanation.Now, with the help of some antidepressants and a fluffle of rabbits, a team of researchers may now be a bit closer to unveiling the origins of this elusive experience. Their <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.1910295116">study</a>, published today in the journal PNAS, suggests that the female orgasm is an evolutionary relic—one left over from a distant mammalian ancestor that needed clitoral stimulation to release eggs for fertilization.</div>
 

 
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 <div class="rich-text">This reproductive reflex isn’t present in women of reproductive age, whose ovaries typically pump out eggs monthly, regardless of sexual activity. But mating with a male still triggers ovulation in other, more evolutionarily ancient mammals like rabbits, ferrets, cats, and camels. These animals also happen to have clitorises that reside very near or within their copulatory canals (that is, their versions of the vagina), which could be directly stimulated during mating.Three years ago, this peculiar pattern led biologists <a href="https://www.cincinnatichildrens.org/bio/p/mihaela-pavlicev">Mihaela Pavličev</a> of the University of Cincinnati’s College of Medicine and Günther Wagner of Yale University to propose <a href="https://onlinelibrary.wiley.com/doi/full/10.1002/jez.b.22690">a new theory</a>: The clitoris first arose as a sort of reproductive tripwire that, when set off, would alert the brain that ejaculation was nigh, prompting the release of ovulation-inducing hormones.Eventually, the researchers argued, some mammalian lineages—including our own—branched off from the so-called induced ovulators, instead adopting monthly cycles. As orgasms’ original purpose went obsolete in these animals, the clitoris migrated out of the vagina, becoming more difficult to stimulate during copulation (something that might help explain why orgasm occurs <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5087699/">less reliably</a> in women having sex, Pavličev says). And just like that, orgasm and ovulation went their separate ways.To further test their hypothesis, Pavličev and her colleagues took a more experimental approach. If orgasms were evolutionarily linked to ovulation, they reasoned, then a drug that put a damper on one process should also dial down the other.</div>
 

 
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 <div class="rich-text">That’s where the antidepressants come in. Fluoxetine, the active ingredient in Prozac, has the side effect of delaying or preventing orgasms in many human patients. To test its effects in a mammal that still relies on sex for ovulation, the researchers administered the drug to 12 female rabbits for two weeks, then mated all of them to a single male (a little stud named Frank). A day later, the team opened the rabbits up to count how many eggs had egressed from their ovaries. The drugged rabbits released about 30 percent fewer eggs than a group of untreated females that had also coupled with Frank.Pavličev’s team next needed to confirm that fluoxetine was exerting its fertility-compromising effects via the brain—the theoretical intermediary in the sex-induced ovulation pathway—rather than acting on the ovaries directly. So they dosed a new group of rabbits with a hormone that triggers the ovaries to release eggs without involving the central nervous system on the last day of their fluoxetine regimen. This time, the antidepressants had little effect on ovulation.That left just one fertility pathway as a probable culprit: the one with a clitoral jumpstart, brought on by sex with Frank. Whatever fluoxetine was doing to human orgasms, it was doing to rabbit ovulation—likely because the two phenomena use similar machinery, Pavličev says.Given the myriad differences between species as evolutionarily distant as humans and rabbits, “there were so many reasons this might not have worked,” Pavličev says. “But we got a really clear answer.”Of course, rabbits aren’t humans, and researchers don’t know if they (or most other non-human animals) orgasm in the same way people do. (There isn’t an easy way to check.) It’s also possible the rabbits’ downtick in ovulation could be attributed to other effects of fluoxetine, which has been shown to alter the physiology of <a href="https://www.pbs.org/wgbh/nova/article/prozac-may-transcend-generations/">several species</a>, points out <a href="https://cbs.umn.edu/contacts/marlene-zuk">Marlene Zuk</a>, an evolutionary biologist at the University of Minnesota who was not involved in the study.Still, both Zuk and <a href="https://biology.indiana.edu/about/faculty/lloyd-elisabeth.html">Elisabeth Lloyd</a>, a philosopher of science at Indiana University who also wasn’t involved in the study, support the study’s use of rabbits, which helped the researchers answer questions about an apparently ancestral trait. And of the available induced ovulators, rabbits were a good choice, Lloyd says. “Camels would’ve been awkward.”While this study is “well designed and executed,” Lloyd says, the female orgasm still has its mysteries. For instance, it’s unclear why the hormones associated with orgasm and ovulation don’t perfectly overlap. Another lingering question is why women still experience orgasms at all. There’s little reason to stick around in a species that’s supposedly retired your primary function.Lloyd, who authored “The Case of the Female Orgasm,” proposes that modern female orgasms are a byproduct of embryo development, in which the same starting ingredients yield both male and female genitalia. Pressured to retain male orgasms, which go hand-in-hand with ejaculation, our lineage left women with a “fantastic bonus” with no modern function. Female orgasms are to women what nipples are to men, she says.The two theories aren’t necessarily incompatible, Lloyd says. Perhaps ovulation is intertwined with orgasms’ origins, while genital development explains their persistence.(Lloyd also points out that there’s <a href="https://www.sciencedirect.com/science/article/pii/S0003347213002121">no link</a> between orgasms in women and reproductive rate. It makes you wonder, Zuk says, why few have questioned the importance of male orgasms, especially considering that so many other species seem to get by without.)The debate on this subject will inevitably rage on, Pavličev says. But she hopes the research will alleviate some of the stigma surrounding female orgasms. “The lack of female orgasm during intercourse has historically been interpreted as being a problem of women,” she says. “But it’s not. It’s a consequence of female anatomy, which has removed the clitoris from the vagina. There’s nothing [wrong] with women.”</div>
 

 
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Researchers used rabbits and antidepressants to search for a link between orgasm and ovulation in female mammals.

Rabbit study hints at the origins of the female orgasm

<div class="rich-text">The electric eel is the closest thing nature’s got to a living, breathing battery.Running up to eight feet in length, these serpentine swimmers (which actually aren’t true eels, but <a href="https://www.nationalgeographic.com/animals/fish/e/electric-eel/">a type of knifefish</a>) are packed with thousands of cells that can generate their own electricity. Some of their homemade jolts are low-voltage, radar-like pulses that help the fish navigate. When prompted, however, electric eels can also serve up shocks powerful enough to <a href="https://www.nytimes.com/2017/09/14/science/electric-eels-shock.html">incapacitate a horse</a>.</div>
 

 
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 <div class="rich-text">Beneath this electrifying exterior, things get even funkier. Unlike most other fish, electric eels don’t rely on their gills to breathe, instead periodically peeking above water to <a href="https://nationalzoo.si.edu/animals/electric-eel">suck air into their lung-like mouths</a>. During the dry season, females will lay thousands of eggs into nests forged out of their mates’ saliva. And—because DIY electricity just isn’t enough—when they’re f(eel)ing threatened, these suckers can <a href="https://science.sciencemag.org/content/346/6214/1231.abstract">launch themselves at attackers</a> to deliver targeted parcels of pain.There’s a lot that makes the electric eel unique. And for centuries, scientists thought they all comprised a single species—Electrophorus electricus—occupying its own lonely branch on the knifefish family tree. But it turns out electric eels harbor quite the shocking secret: These fish are so nice, they speciated twice.
 <figure class="richtext-image full-width"><img alt="2A - Carlos David de Santana - Electrophorus voltai Xingu River_4 Picture by L. Sousa.jpg" class="richtext-image full-width" height="520" width="800"
 src="/wgbh/nova/media/images/2A_-_Carlos_David_de_Santana_-_Electrophorus_v.width-800.jpg"/><figcaption>Electric eels like Electrophorus voltai are especially fond of slow, shallow waters. “That’s prime real estate,” says Kory Evans, a fish biologist at Brown University. Image Credit: L. Sousa<div class="credit"></div></figcaption>
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 An international team of scientists has found that at least three species of electric eel slither the rivers of South America. One of them, Electrophorus voltai, packs an unexpectedly powerful punch, discharging shocks up to 860 volts. That’s a 30 percent uptick over the previous record—and a stat that earns E. voltai the title of the strongest known living source of electricity.“That’s bonkers,” says <a href="https://koryevans.weebly.com/about.html">Kory Evans</a>, an evolutionary biologist who studies electric fish at Brown University, but was not involved in the study. “The fact that there’s a living organism that has the ability to generate this kind of violent electricity is really shocking, no pun intended.”</div>
 

 
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 <div class="rich-text">The <a href="https://www.nature.com/articles/s41467-019-11690-z">study</a>, published today in the journal Nature Communications, triples the membership of the genus Electrophorus, which now includes the OG E. electricus, as well as newcomers E. voltai and E. varii. (Does this make electric eels less special? Maybe it boosts their appeal by a factor of three.)In truth, though, the discovery has been a long time coming. Since their discovery in 1766 by Swedish zoologist Carl Linnaeus, electric eels have been found all over Greater Amazonia, lurking wherever the water’s fresh, calm, and chock full of invertebrate snacks.That’s an enormous range for a single species—essentially the top half of a continent, Evans says. Animals that spread into such diverse geographical regions tend to split off into separate species, especially if disparate groups lose contact with one another along the way. That should have been the case for electric eels, which, with their penchant for shallow, slow-moving waters, aren’t exactly the most cosmopolitan of fish.Researchers have been trying to “break up” E. electricus for years, says Evans, who praised the new paper. “My first thought was, ‘Oh, they finally did it!’”
 <figure class="richtext-image full-width"><img alt="4A - Carlos David de Santana - Aerial view_typical electric eel Upland habitat_Coppename River_Suriname Picture by de Santana.jpeg" class="richtext-image full-width" height="600" width="800"
 src="/wgbh/nova/media/images/4A_-_Carlos_David_de_Santana_-_Aerial_view_typ.width-800.jpg"/><figcaption>The highland regions of Greater Amazonia, the stomping grounds of Electrophorus electricus and Electrophorus voltai. Image Credit: C. David de Santana<div class="credit"></div></figcaption>
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 There’s a few reasons it took 250 years to get to this point, says study author <a href="https://electriceel2013.wixsite.com/electric-fishes">David de Santana</a>, a zoologist and fish biologist at the Smithsonian’s National Museum of Natural History. For one, the trio of species his team teased apart all look remarkably similar, save for a few subtle discrepancies, like the shapes of their skulls. Even now, with three clear-cut bins to sort them into, picking apart their physical differences takes an exacting eye. According to de Santana, who studies fish morphology for a living, “this was my hardest work yet.”The crux of the matter came down to a combination of intensive field work and modern genetic sequencing. De Santana and his colleagues spent the better part of four years traipsing through the river basins of Greater Amazonia, wrangling fish out of muddy streams, swamps, and plains throughout Brazil, French Guiana, Guyana, and Suriname.Back in the lab, DNA extracted from 107 specimens revealed three distinct groups of animals. While the trio appear to share a common ancestor, they ultimately split from each other in two bouts: once about 7.1 million years ago, when E. varii branched off, and again 3.6 million years ago, when E. electricus and E. voltai went their separate ways.Nowadays, the three species don’t have much to do with one another. While E. electricus was once thought to dominate the entire Amazonian region, de Santana’s team has narrowed its range to the Guiana Shield, a northerly geological formation home to highlands with rapids and waterfalls. South of this is a similar region called the Brazilian Shield, which appears to be the main stomping grounds of E. voltai. De Santana thinks the fast-flowing waters may have helped shape the two closely-related species’ relatively flat heads.The geographic outlier of the bunch, then, is E. varii, a more bulb-headed fish that lurks in the lowlands of the Amazon Basin, where the waters are murky and sluggish.
 <figure class="richtext-image full-width"><img alt="4B - Carlos David de Santana - typical electric eel Lowland habitat Picture by D. Bastos.png" class="richtext-image full-width" height="529" width="800"
 src="/wgbh/nova/media/images/4B_-_Carlos_David_de_Santana_-_typical_electri.width-800.png"/><figcaption>The lowland regions of Greater Amazonia, where Electrophorus varii is known to lurk. Image Credit: D. Bastos<div class="credit"></div></figcaption>
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 Not to be outdone, E. voltai managed to distinguish itself in its own way. When the researchers hooked electrodes up to some of the fish to suss out their shock factor, one E. voltai specimen managed to pump out a whopping 860 volts of electricity.The team only hooked six fish up to their oscilloscope, and de Santana suspects researchers have yet to crown the world’s most electrifying eel. (De Santana, who’s received his fair share of shocks, adds that the jolts are brief, and “not so bad.” That said, you would not want to get cornered by a dozen or so pissed off electric eels at once—a real concern, considering the team believes the fish sometimes hunt in packs.)It’s still not totally clear what originally drove the three Electrophorus species apart, de Santana says. But his team is now hard at work disentangling more of the differences that exist between them—and it’s very possible that a few more species have yet to be uncovered.Evans suspects the new species designations won’t slither down smoothly for everyone. “Usually when you split up species...it gets controversial,” he says. “But genetically, [these electric eels] sort out nicely, and it’s hard to argue with that.”<a href="https://kmallenneuro.com/">Kate Allen</a>, a neuroscientist and fish biologist at Johns Hopkins University who was not involved in the study, agrees, pointing out that at least 250 species of electric fish exist in South America (though Electrophorus are the only ones that weaponize their zap). “It’s kind of weird that there would only be one species of electric eel given the diversity in the rest of their group,” she says.
 <figure class="richtext-image full-width"><img alt="3A - Carlos David de Santana - Electrophorus varii Rio Negro 2 Picture by D. Bastos.jpg" class="richtext-image full-width" height="228" width="800"
 src="/wgbh/nova/media/images/3A_-_Carlos_David_de_Santana_-_Electrophorus_v.width-800.jpg"/><figcaption>The newly described electric eel species Electrophorus varii swims through murky, slow-flowing lowland waters. Image Credit: D. Bastos<div class="credit"></div></figcaption>
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 Regardless of where species lines are drawn, though, simply having a more comprehensive catalog of these funky fish could be a boon for scientists in a variety of fields, de Santana says. Electric eels inspired Italian physicist Alessandro Volta to design the first battery in 1799; centuries later, researchers are still studying them to develop <a href="https://www.ncbi.nlm.nih.gov/pubmed/26766594">more efficient</a> <a href="https://www.ncbi.nlm.nih.gov/pubmed/29239354">power sources</a>. Other Electrophorus aficionados are exploring applications in the <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/cmdc.201500104">treatment of neurodegenerative disease</a>, or <a href="https://jeb.biologists.org/content/216/13/2501">designing robots</a> modeled on the fish’s elongated anal fin, which allows it to swim backward or forward, or simply hover in place.For these reasons and more, de Santana stresses the importance of preserving biodiversity in the Amazon, where <a href="https://www.theguardian.com/environment/2019/aug/23/amazon-fires-what-is-happening-anything-we-can-do">thousands of fires</a> currently rage amidst widespread deforestation. The electric eels’ species surprise, he says, is just the latest piece of evidence that many of the region’s biological riches remain unexplored.After all, there’s nothing more conspicuous than an 8-foot-long electric eel leaping out of the water to shock you, Allen adds. If we’re still finding diversity “in such a big, charismatic species,” she says, “that means there’s a lot out there we don’t yet know about.”</div>
 

 
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That earns this fish, Electrophorus voltai, the title of the strongest known living source of electricity.

Newly described species of electric eel serves up shocks of 860 volts

<div class="rich-text">Being white can make it tough to blend in—if you’re a nocturnal bird, that is.For years, researchers have puzzled over the snowy plumage of some <a href="https://www.allaboutbirds.org/guide/Barn_Owl/id">barn owls</a> (Tyto alba), which makes them stick out like sore thumbs against the black backdrop of night. This lack of camouflage becomes even more apparent when these pearly predators take to the skies beneath a full moon, which can backlight the birds as they descend upon their rodent prey.But these frost-feathered creatures may have good reason not to shirk this lunar spotlight. It turns out that white barn owls actually hunt best when the moon looms large—not in spite of their conspicuous coloration, but because of it.</div>
 

 
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 <div class="rich-text">The driving force behind this counterintuitive trend, described in a <a href="https://www.nature.com/articles/s41559-019-0967-2">study</a> published today in the journal Nature Ecology &amp; Evolution, is a neat visual trick: As light bounces off of bright plumage, it has a deer-in-headlights effect on rodents, triggering a freezing response that makes them easier to catch.In other words, the ghostly plumage of the white barn owl is so visible, it’s scary—and that can mean curtains for its super-skittish prey.“This is a really exciting paper,” says <a href="https://eeb.princeton.edu/people/monica-carlson">Monica Carlson</a>, who studies avian plumage at Princeton University, but was not involved in the study. “Given that we [humans] are a diurnal species...we’re biased toward studying the species we see the most. But this forges new territory in the study of how animals’ colors have evolved.”
 <figure class="richtext-image full-width"><img alt="IMG_1403.jpeg" class="richtext-image full-width" height="597" width="800"
 src="/wgbh/nova/media/images/IMG_1403.width-800.jpg"/><figcaption>Barn owls (Tyto alba) are one of the most widespread birds in existence. They&#x27;re recognizable by their heart-shaped faces, and come in varying shades of auburn and white. Image Credit: Alexandre Roulin, University of Lausanne<div class="credit"></div></figcaption>
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 In a world where predators often rely on camouflage to sneak up on their prey, most nocturnal hunters have evolved coats, scales, hairs, and feathers in hues of brown, gray, or black that match the sunless landscape. Barn owls, whose feathers range from deep russet to luminous white, fly in the face of this trend—and until now, it’s been totally unclear why, says study author <a href="https://www.unil.ch/dee/en/home/menuinst/people/group-leaders/prof-alexandre-roulin.html">Alexandre Roulin</a>, a behavioral biologist at the University of Lausanne in Switzerland. (A quick aside: Though snowy owls <a href="https://www.audubon.org/field-guide/bird/snowy-owl">are also white</a>, that’s more to help them blend into their native Arctic tundra, where they often hunt during the day.)But inklings of inspiration began to dawn on Roulin during the evening jaunts he’d take to capture barn owls for study. On nights when the moon was full, the whitest of the birds would appear to him “like stars crossing the sky,” he says. “They [were] just so visible.”</div>
 

 
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 <div class="rich-text">Dazzling though the birds were to human eyes, Roulin suspected that white barn owls’ ghostly pallor might betray their presence to prey, saddling the birds with a hunting handicap on moonlit nights. But when he and his colleagues dug into their barn owl database—which contained nearly 30 years’ worth of meticulous recordings from 360 nest-boxes in western Switzerland—and overlaid some of the measurements onto the lunar cycle, they discovered the exact opposite to be true.On new moon nights, when the moon was least visible in the sky, white and red owls were equally efficient hunters, and hauled the same number of prey back to the owlets in their nests. As the moon waxed, however, the red owls began to falter. And by the time the full moon rolled around, their nestlings weighed less than those raised by white parents—who, in contrast, seemed entirely unphased by the extra light.To suss out the secrets of the white birds’ relative success, the team rounded up several dozen common voles (Microtus arvalis), a favorite food among barn owls, and placed each rodent in a brightly or dimly lit room that mimicked either the beginning or end of the lunar cycle. Then, because live birds would have been too difficult to test, the team acquired a set of red and white taxidermied barn owls—all immortalized in postures of flight—and flung them at the voles via a 7-foot zipline.Of course, the stuffed birds posed no real threat. But these vulnerable voles were none the wiser. As the owls hurtled down the zipline, most of the rodents froze in fear for several seconds—a common response to an approaching predator, Roulin says. Under new moon conditions, the voles reacted similarly to all the owls the researchers sent their way. But when the room’s “moon” was full, the voles’ paralysis lasted five seconds longer if their assailants were white instead of red.
 <figure class="richtext-image full-width"><img alt="41559_2019_967_MOESM1_ESM.jpg" class="richtext-image full-width" height="300" width="800"
 src="/wgbh/nova/media/images/41559_2019_967_MOESM1_ESM.width-800.jpg"/><figcaption>One of the white (left) and one of the red (right) taxidermied owls used in the study. Image Credit: San-Jose et al., Nature, 2019<div class="credit"></div></figcaption>
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 The stuffed white owls also seemed to draw predatory power from the faux moonlight: The better lit the room was, the brighter the birds glowed—and the longer the voles remained immobile.Motionless prey is much easier to catch, which is great news for (living) white barn owls, Roulin says. In the wild, this terrifying tactic may buy the birds a few extra seconds to swoop in for the kill—explaining, perhaps, their hunting prowess on moonlit nights, when they’re basically “ghosts,” Roulin jokes.“The beautiful thing about this study is that it doesn’t just aim to describe [how the owls’ color affects survival]—it also describes the mechanism behind the process,” says <a href="https://mariadelgado.org/">Maria Delgado</a>, a behavioral ecologist at the University of Oviedo in Spain who was not involved in the study.From a color-challenged rodent’s point of view, there’s one big difference between a red owl and a white one: brightness, generated by light reflecting off their feathers. On a small scale, a predator’s beacon-like glow might compromise its stealth. Taken to an extreme, however, this weakness becomes a strength that exploits rodents’ natural aversion to strong light.
 <figure class="richtext-image full-width"><img alt="News &amp; Views_ 41559_2019_Article_977.jpg" class="richtext-image full-width" height="568" width="800"
 src="/wgbh/nova/media/images/News__Views__41559_2019_Article_977.width-800.jpg"/><figcaption>Given their glimmer, you might expect the whitest barn owls to be terrible hunters when moon looms large. But it turns out that quite the opposite is true. Image Credit: Isabelle Henry<div class="credit"></div></figcaption>
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 That’s exactly what seems to be going on here, Roulin says. In a follow-up experiment, the researchers introduced another taxidermied white owl to the voles—only this time, they coated the bird’s feathers with duck preen wax, a substance that dulls their natural sheen. Faced with this more muted bird, the voles seemed far less flummoxed, and were quicker to unfreeze. “It’s almost like [these waxed birds] were red,” he says.Still, we shouldn’t feel too badly for the browner birds, Roulin adds. The melanin behind their red plumage reinforces feather strength, bolstering the birds against abrasion and fluctuations in temperature. And although white barn owls may shine when the moon is full, their cloak of visibility could come with costs under other circumstances, such as when they’re trying to avoid detection by competitor bird species like carrion crows.Tradeoffs like these are probably why the species hasn’t gone monochromatic. In the wild, the plumage of barn owls spans the spectrum between red and white, and each subtle variation may be ideally suited to its own time and place. Roulin and his team are now surveying barn owl populations worldwide to see if some habitats—such as those with more cloud or tree cover—might favor birds of certain shades.
 <figure class="richtext-image full-width"><img alt="IMG_1346.jpeg" class="richtext-image full-width" height="597" width="800"
 src="/wgbh/nova/media/images/IMG_1346.width-800.jpg"/><figcaption>Depending on the color of their plumage, barn owls might have their own time of the month. Image Credit: Alexandre Roulin, University of Lausanne<div class="credit"></div></figcaption>
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 Plenty of questions remain, with few researchers to answer them, Roulin says. Studying nocturnal animals as a diurnal human isn’t easy: When nighttime field work gets particularly intense, some of Roulin’s students get just four hours of sleep a night.Still, studies like these are crucial for expanding our understanding of the many factors that drive the evolution of plumage, Carlson says. From our perspective, it may seem like there’s little to see after the sun has set. But for nocturnal predators like the barn owl, that couldn’t be further from the truth.“We need to conduct these studies while taking into consideration the ecological niche of the species we’re studying,” she says. After all, taking a different perspective—even one that’s often in the dark—can be pretty illuminating.</div>
 

 
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