Say Aaaah Zoo’s Aardvark Gets 2 Teeth Pulled

Getting a tooth pulled is never fun, but it’s especially irksome if you’re an aardvark. Ali, an aardvark at the Cincinnati Zoo, recently learned this lesson firsthand after two infected teeth landed her in the dentist’s chair.

Aardvarks, the only extant species in the order Tubulidentata, are unusual animals — and they have unusual teeth, said Jack Easley, a Kentucky-based veterinarian who specializes in dentistry. Easley was one of several veterinarians who helped extract Ali the aardvark’s two problematic teeth last month at the Cincinnati Zoo.

Unlike most other mammals, aardvarks don’t have enamel in their teeth. (Enamel is the hard, visible part of the tooth that covers up the more sensitive tissues beneath it.) These soft teeth typically serve aardvarks well, because in their native African habitat, the animals only eat easy-to-chew insects like termitesand ants, Easley told Live Science. [Photos: World’s Cutest Baby Wild Animals]But in zoos, aardvarks don’t always eat soft insects, which may not be readily available. Instead, they eat a special, pelleted feed or some other manufactured food, said Easley, who noted that, sometimes, this diet can lead to dental disease. Ali, who is 11 years old, is also middle-age for an aardvark, which may have contributed to the decline in her dental health, he added.

Zoo staff first noticed that there was a problem with the animal’s health back in January, when Ali developed a weird-looking, swollen eye. The problem seemed to be resolved with a dose of antibiotics, but when the medication was finished, the ulcer came back, said Jenny Nollman, an associate veterinarian at the Cincinnati Zoo.

“When it didn’t clear up completely, we investigated it further,” Nollman told Live Science. “That’s when we got into the CT [cat scan] and MRI [magnetic resonance imaging] — the more advanced imaging — to try to really get a better diagnosis.”

In July, zoo staff accompanied Ali to a nearby hospital to try to pinpoint the root of the problem. The CT scan and MRI suggested that what appeared to be an eye problem was actually a tooth problem, Nollman said. That’s when zoo vets reached out to Easley, one of very few veterinarians in the United States who is board-certified in veterinary dentistry.Ali the aardvark’s two infected teeth. Unlike most mammals, aardvarks don’t have a hard layer of enamel covering the crown of their teeth.

Two of Ali’s molar teeth were so infected that the bone and tissue supporting her teeth had formed what’s known as a periodontal pocket, Easley said. This led to the formation of a fistula, or an abnormal passageway between two body parts that are not usually connected. In Ali’s case, the fistula formed between her sinus and the periorbital sac (the tissue surrounding the eyeball), causing her eyeball to look inflamed and leak out pus.

To fix this problem, Easley and another certified veterinary dentist traveled to Cincinnati to pull out Ali’s infected teeth. But there was one small problem: Unlike humans, aardvarks can’t say “ah.”

In addition to having weird teeth, aardvarks have strange mouths. The animals have long tongues and deep oral cavities, with the teeth located all the way in the back (about 12 inches, or 30 centimeters, inside their mouths). These oral openings are very small, measuring only 1.5 inches (4 cm) across, according to Easley.

To reach inside Ali’s mouth, Easley had to make a small incision in the animal’s cheek. After removing the two infected molars, the veterinarians packed the hole left by the extracted teeth with an antibiotic-coated gauze material and left Ali to heal over the next three to six weeks.

Yesterday (Sept. 1), Nollman performed a checkup, and the resilient little aardvark seemed to be doing quite well, she said, though it will take Ali a few more weeks to fully heal.

“[Ali] has not missed a beat through this whole thing,” Nollman said. “Her appetite has never decreased, and she has been very active.”

Iguana Relative Shows How Lizards Spread Worldwide

An 80-million-year-old lizard discovered in southern Brazil has provided a surprising clue about how these reptiles evolved, and where they once lived, according to a new study.

Until now, researchers had found acrodontans only in the Old World, including Africa and Asia. (This is a type of lizard is called an iguanian that has teeth fused to the top of its jaws, a group that includes chameleons and bearded dragons.) But the newfound fossil, a partial lower jaw of a new species of acrodontan, shows that they lived in the New World much earlier than thought.

The fossil suggests that acrodontans managed to distribute themselves worldwide before the ancient supercontinent Pangaea broke up about 200 million years ago, the researchers said. [Image Gallery: 25 Amazing Ancient Beasts]

“This fossil is an 80-million-year-old specimen of an acrodontan in the New World,” study co-author Michael Caldwell, a biological sciences professor at the University of Alberta in Canada, said in a statement. “It’s a missing link in the sense of the paleobiogeography and possibly the origins of the group, so it’s pretty good evidence to suggest that back in the lower part of the Cretaceous, the southern part of Pangaea was still a kind of single continental chunk.”

The jaw, photographed from different angels, of Gueragama sulamerica.
Credit: Tiago Simoes and Adriano Kury

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Paleontologists discovered the fossil in the rock outcrops of desert that dates to the late Cretaceous in the Brazilian municipality of Cruzeiro do Oeste. The researchers named the new species Gueragama sulamericana — guera meaning “ancient” in native Brazilian; “agama” in reference to agamid, a family of iguanian lizards; and “sulamericana” meaning “from South America” in Portuguese.

The jaw is missing a few teeth, but has room for 18 of them, and the teeth almost uniformly increase in size from the front to the back of the mouth, the researchers found.

During the Late Cretaceous, G. sulamericana lived in an arid desert environment, although evidence of ancient wetlands suggests that water was available seasonably, the researchers said. G. sulamericana also had company. Other fossil findings, including “hundreds of bones” of the pterosaur species Caiuajara dobruskii, show that larger animals lived there, too, the researchers wrote in the study.

G. sulamericana may have lived in burrows to avoid extreme daytime heat, just as some modern lizards do today, the researchers added.

Surprise finding

Among living lizards, iguanians comprise one of the most diverse groups, with more than 1,700 species. Previous research has found that acrodontan iguanians dominated the Old World, and nonacrodontan iguanians (such as iguanas) dominated the New World, particularly the American South, Caldwell said.

The oldest known acrodontans are from the early to middle Jurassic period in present-day India. However, now researchers know that acrodontans had spread elsewhere in the world by the late Cretaceous, the researchers said.

“This Gueragama sulamericana fossil indicates that the group is old, that it’s probably southern Pangaean in its origin,” Caldwell said. “After the [Pangaean] breakup, the acrodontans and chameleon group dominated in the Old World, and the iguanid side arose out of this acrodontan lineage that was left alone on South America.”

Eventually, nonacrodontans replaced acrodontans in the Americas. But nonacrodontans remain as natives in the Old World, the researchers said.

“This is an Old World lizard in the New World at a time when we weren’t expecting to find it,” Caldwell said. “It answers a few questions about iguanid lizards and their origin.”

The Science of Adorable What It Takes to Win CuteOff

Science Twitter has gone full squee. Biologists are tweeting pictures of their adorable research subjects in a #CuteOff, and the results are downright nom-able.

Baby elephants? Adorbs. Pert-nosed pikas? Too cute. Hummingbird nestlings? Heart-stopping. Meanwhile, #TeamHerpetology is making a strong showing with shots of baby sea turtles that fit in the palm of a hand, and #TeamEntomology is showing how sweet bugs can be.

“I don’t generally think of fish as cute, but there were some alarmingly cute fish,” said Anne Hilborn, a doctoral student and cheetah researcher at Virginia Tech who helped launch the hashtag.

While the #CuteOff may open eyes to wildlife conservation, it’s also an opportunity to look at what really makes people squee. What are the essential ingredients of cute? Based on the types of animals posted — and previous scientific research on adorableness — here are seven features that could help an animal win a cuteness contest. (This #CuteOff emerged on Twitter following a perhaps, ahem, more salacious animal contest, the #JunkOff.)

1. Big Eyes

Big eyes, full heart, can’t lose. It’s pretty clear that a wide pair of peepers pushes an animal high in the cuteness ratings. Whether it’s a puffer fish or a pygmy possum, many of the animals Tweeted in the #CuteOff are blessed in the eye department. Even plants are getting in on this action: Atmospheric scientist Brian DiNunno tweeted about the doll’s-eye plant (Actaea pachypoda), which has fruit that looks like a stalk full of googly eyes. (These eyes, however, can kill you — the berries contain toxins that can cause cardiac arrest in humans.)

Big eyes may be so alluring because they remind people of human babies. Huge eyes trigger a caregiving response in adult humans, research finds, as do other babylike features such as chubby cheeks, a protruding forehead, and a small nose and mouth. A 1979 study in the journal Infant Behavior and Development reported that even among babies, those with more infantile features were perceived as cuter. The baby-loving response appears to be deeply embedded, even in nonparents.

“Cute infants at all ages tend to have large foreheads, large eyes, small features and narrow faces below the eyes,” the researchers wrote in the 1979 paper. It’s not hard to see how animals with similar features can trip the brain’s cuteness detector.

2. Youth

Given that infantlike features prompt paroxysms of glee, it’s no surprise that baby animals were #CuteOff front-runners. Infant sooty mangabeys? Yes, please.

Humans respond to baby animal cuteness in the same way they respond to baby human cuteness, according to a 2013 study published in the journal Behavioural Processes. The researchers found that women were more sensitive to the appeal of infant animals than were men, and that people who had higher levels of empathy also found baby animals more heart-melting than did people with lower empathy levels.

This love of baby animals may have spilled over from the evolutionary drive to protect infants of one’s own species, the researchers wrote. But bonds with animals can also contribute to well-being, the researchers noted, so perhaps baby animal cuteness stands on its own two (or four) feet.

3. Tininess

If you can’t be a baby, at least stay the size of one. That seems to be one message of the #CuteOff, which featured a cascade of pictures of almost absurdly small creatures. [Photos: See the World’s Cutest Baby Wild Animals]

The link between smallness and cuteness isn’t as well established as the link between babylike features and cuteness. But the connection is certainly there. (Evidence: Buzzfeed has done a listicle.) Without research, it’s only possible to speculate. Perhaps small things simply remind people of babies. Or perhaps, as posited in a 2012 article by a museum studies professor in Insite Magazine, miniature things remind people of toys and give people a sense of power because they know they have control over something so small.

4. Being a mammal

#CuteOff was officially kicked off by herpetologists, who tweeted a picture of a teeny, tiny lizard and declared premature victory.

But it soon became clear that mammals were going to dominate the #CuteOff feed, much to the chagrin of scientists who study less-vaunted taxons.

“There was some talk about the inverts [invertebrates] and the fish joining up to challenge mammals, because mammals are always thought of as cute,” Hilborn said. “It was interesting to see biology rivalry and cooperation come out over Twitter.”

Humans are mammals, of course, so perhaps it’s no surprise that people are drawn to other fuzzy species. Which brings us to our next winning feature …

5. Fur

#TeamEntomology made a strong #CuteOff showing by showcasing species with features not normally associated with insects. The teddy bear ant (Tetramorium pulcherrimum) is a forest dweller in Africa that has what looks like a fine dusting of fur all along its back.

Fuzzy bees, moths and flies also made a showing. To explain the appeal of fuzz, let’s get wildly Freudian and blame mothers. Bear with us: In the 1950s, psychologist Harry Harlow did a series of famous experiments in which monkeys were “raised” by food-bearing “wire mothers” (really, wire frames with monkeylike faces) and terry cloth surrogates, which didn’t dispense food. Even though the wire mothers provided sustenance, the baby monkeys always snuggled back up with their terry-cloth “moms” when not nursing. The studies were groundbreaking, introducing the notion of psychological attachment not based simply on nourishment.

What can we take away from Harlow’s work? Primates really like cuddly things. Is it too much of a stretch to say that a furry ant might trip those same brain circuits?

Yes, you say? Oh, hush. Look, a fuzzy teen bee:

6. Smiling faces

Let’s bring our cute-related theorizing back to solid ground. You know what’s cute? Dolphins. You know why? They always look like they’re smiling.

Smiles make people more approachable, research finds. People also judge a smiling person as more likeable and smarter than a nonsmiling person, reported a 1982 paper in The Journal of Social Psychology.

The appeal of smiles clearly extends to animal faces, a fact that #TeamHerpetology exploited to good effect. Frogs, snakes and lizards may lack fur, but they can plaster on some adorable grins.

 

Why Animal Genitals Are Important to Science

Did you know that male black widow spiders have corkscrew-shaped genitals? Or that barnacle penises are up to eight times the length of barnacle bodies? Or that echidnas have frankly horrifying four-headed dangly bits?

If you’ve been following scientists on Twitter in the past week or so, you probably do. That’s because biologists have gone wild posting junk shots of their research subjects, from meerkats to cheetahs to some truly bizarre ants. The #JunkOff hashtag took off last week, and not entirely for sophomoric reasons: Animal genitalia are actually a major window into how evolution works.

“It all goes back to the basis of animal behavior and evolution,” said Anne Hilborn, a doctoral student at Virginia Tech and cheetah researcher who launched #JunkOff and helped start the warmer-and-fuzzier follow-up hashtag, #CuteOff.

Wild junk

As #JunkOff illustrates, the world of genitals is … diverse. And maybe a little scary. But really, let’s focus on the diversity. [The 9 Weirdest Animal Penises]

Alligators, for example, have enormous, permanently erect penises made of connective tissue called collagen. Instead of inflating with blood like most mammalian penises, the alligator penis pops out of the cloaca (the alligator all-purpose genital and waste opening) with the help of rubber-bandlike tendons and muscles. And, yes, there is video.

Even creepier are the detachable genitalia of the male orb-web spider (Nephilengys malabarensis). The “palps,” or sperm-transferring organs, of these spiders stay attached to the female when mating is done, in part so they can keep working if the female spider decides to chow down on her mating partner — these spiders are sexual cannibals. Similarly, black widow males leave the tips of their corkscrew genitalia inside the female. Leaving genitals behind may save spiders energy in the long run. [Animal Sex: 7 Tales of Naughty Acts in the Wild]

Even paleontologists got into the #JunkOff fun, tweeting pictures of dire-wolf penis bones that were preserved in the La Brea Tar Pits in Los Angeles. Yes, many mammal penises have actual bones, also known as baculums. Dogs have them, as do chimpanzees, bears and walruses. (Chimps also have penis spines, a feature that humans — fortunately? — have lost.)

And let’s not give females’ short shrift: Many mammalian females have an analogous genital bone, the baubellum, which sits below the clitoris. This bone, also called the os clitoridis exists in many rodents, as well as bats and some primates. Perhaps the craziest clitoris out there belongs to hyenas, which is about 7 inches (18 cm) long and looks almost like a penis. Female hyenas give birth through it.

“It’s one of my favorite ice-breaking conversation topics at parties when I don’t know what to say,” Hilborn said.

(R)evolutionary genitalia

If the eyes are the windows to the soul, the junk is the window to evolution. Genitalia are important because they’re front and center in sexual selection — and that means that private parts are thought to evolve faster than other body parts.

Very closely related species often have dramatically different genitals, biologist Julia Klaczko, who researches lizard genitalia at the University of Campinas in Brazil, told Live Science in January. Klaczko and her team measured the rate of evolution in lizard hemipenes, the penis-equivalents for snakes and lizards. They then compared the rate of hemipene change with the rate of change in lizard limb length and throat flaps called dewlaps.

They found that male genitalia evolve six times faster than limbs or dewlaps, explaining the large diversity seen in lizard hemipenes. It’s possible that females are picky about penises, so males are constantly evolving new, better options. Or perhaps the penis evolution is an example of an evolutionary arms race, in which males and females both evolve genitals in an effort to gain the most control over fertilization.

That sort of arms race is apparent in ducks. Many species sport long, corkscrew-shaped penises. Females, in turn, have corkscrew vaginas. But the vaginas spiral in the opposite direction as the penises, making it harder for sexually aggressive males to fertilize a female against her will. (And male ducks can get very aggressive. Just ask the discoverer of dead gay duck sex.)

Certain beetles, too, appear to be involved in a genital race — one that leads to the differentiation of new species. Some species of tiny seed beetles have truly intimidating male genitals studded with more than 100 spikes. As male beetles evolve more spikes, researchers found, females evolve tougher genitals to survive mating. This arms race is costly, leading to fewer offspring in species with spikier junk.

“Normally, we think of evolution being adaptive, with organisms becoming better and better adapted to their lifestyle,” study researcher Göran Arnqvist, a biologist at Uppsala University in Sweden, told Live Science in 2007. “Here we have an example of evolution that leads to something bad.”

In many cases, animals keep their private business private. In wild cheetahs, Hilborn said, a couple of males will pick out a female and hang around her for several days — not even leaving to hunt — until she’s ready to mate. Many mating buddies are brothers, but others are unrelated, Hilborn said, and it’s not clear how the female decides which cheetah she mates with.

The Cute and Complicated Science of Raising Twin Pandas

The little panda was cold, low energy and having trouble breathing before its heart stopped beating. But the zoo baby left an indelible mark on its caretakers and admirers before it died, just days after being born to mother Mei Xiang, along with its brother. During its short life, the twin rode atop a lacrosse stick, snuggled with its mother and fed from a bottle, the last of which may have led to its demise.

The final necropsy results aren’t complete, but the butter-stick-size panda likely died when fluid got into its lungs and caused inflammation, a condition called aspiration pneumonia. Veterinarians are unsure whether the cub got the condition during a bottle-feeding blunder or from formula it regurgitated, said Dr. Donald Neiffer, the chief veterinarian at Smithsonian’s National Zoo.

“Whether or not the baby aspirated some of that [regurgitated] material or whether he aspirated material earlier in the day, we don’t know, and we will never know,” Neiffer told Live Science. [See Photos of Mei Xiang’s New Twin Panda Cubs]

Express delivery

The pink and fuzzy cubs are part of a delicate plan, orchestrated on an international level, to preserve the giant panda species and, one day, introduce captive-bred pandas back into the wild. Just 1,864 giant pandas (Ailuropoda melanoleuca) exist in the wild, according to a 2015 panda census. An additional 395 of the roly-poly fur balls live in breeding centers and zoos around the world, said Devin Murphy, a spokesperson for Smithsonian’s National Zoo.

Wild panda numbers increased by about 17 percent in the past decade, according to the 2015 census. American zoos are doing their part to breed and raise the animals, all on loan from China. Right now, there are 13 giant pandas in U.S. zoos, including San Diego Zoo, Memphis Zoo, Zoo Atlanta and the National Zoo.

The new twins were born to Mei Xiang (may-SHONG), the star mother at the National Zoo. Mei Xiang, whose name means “beautiful fragrance,” has three surviving offspring, including Tai Shan (born in 2005), who now lives in China; Bao Bao (born in 2013), who lives at the National Zoo; and the surviving panda twin, which will be named this autumn.The second-retrieved cub squirms as a team examines its weight, length, mouth, heart rate and breathing.

Credit: Pamela Baker-Masson, Smithsonian’s National Zoo

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Each pregnancy is a carefully timed operation, as female pandas are only fertile for about two days a year. (Finding that fertile window can be tricky.) Mei Xiang didn’t go into estrus in 2014, because she was still nursing Bao Bao. But this year, the zoo’s endocrinologists began monitoring the panda’s hormones, a glamorous job that consists of analyzing panda urine on a weekly basis, Murphy said.

Zookeepers have also done their part to encourage Mei Xiang to mate naturally with Tian Tian (t-YEN t-YEN), a male giant panda at the National Zoo, but “unfortunately, our pandas have never figured out how to successfully breed,” said Laurie Thompson, a giant panda biologist at Smithsonian’s National Zoo. “They both have positioning issues, so we always have had to artificially inseminate her.”

So, as Mei Xiang’s urinary estrogen levels spiked, zookeepers kept an express delivery of semen on hand from potential father Hui Hui (h-WEI h-WEI), a genetically diverse match, who hails from the Chinese Conservation and Research Center for the Giant Panda in Sichuan. And to increase the likelihood of a pregnancy, veterinarians supplemented the sample with fresh semen from Tian Tian. On April 26 and 27, veterinarians artificially inseminated Mei Xiang.

“Then, we waited,” Murphy told Live Science. “Since pandas have delayed implantation, we just had to wait it out to see when she would start exhibiting behaviors consistent with a pregnancy or pseudopregnancy.” During such false pregnancies, a female panda can snooze a lot, craft bamboo nests, and even cradle foods and toys as if they were real cubs — making it nearly impossible for zookeepers to know if there’s a fetus in the panda’s belly.

Then, on Aug. 19, an ultrasound revealed a fetus, and zoo staff began a 24-hour watch for a delivery. Shortly after, on the morning of Aug. 22, Mei Xiang went into labor. [In Photos: Giant Panda Mei Xiang Gives Birth]

Twin birth

The first cub popped out at 5:35 p.m. EDT.

“I believe there was a cheer and high-fiving,” said Thompson, who was watching the panda cam with colleagues in another room.

Mei Xiang looked so calm that Thompson emailed the zoo’s panda team, saying it didn’t appear that a twin was on the way. But at 10:07 p.m., Mom surprised everyone by delivering a second cub.

Zookeeper Shellie Pick cares for the smaller panda cub in the incubator on Aug. 24. At the time, Pick was weighing the cub, stimulating it to go to the bathroom and taking its temperature.
Credit: Heather Roberts, Smithsonian’s National Zoo

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“When they’re born, they come out screaming, so there was a little, squealy thing on the ground, and she [Mei Xiang] had one that she was already holding,” Thompson said. “She was figuring out how to pick up the second one without dropping the first one, and she wasn’t really able to do it.”

Immediately, the zookeepers began to follow a “twin protocol” used by panda experts in the United States and China. The caretakers dressed in scrubs, approached Mei Xiang’s den and grabbed the squirmy cub that was on the ground — the larger of the twins.

Newborn cubs can’t regulate their own temperature, so zookeepers put the cub in a heated and humidified incubator, said panda-keeper Juan Rodriguez. Then, they did a medical checkup, and put the cub they’d retrieved to bed in the incubator.

Newborn cubs feed every 2 hours, so the zookeepers prepared for a cub swap. They put the larger twin on the ground about 3 feet (1 meter) away from Mei Xiang. When she heard it crying, she put down the smaller twin, allowing zookeepers to whisk that cub away after Mei Xiang picked up its brother. Soon, the smaller twin was in the incubator and then getting a medical checkup.

“The little one was really feisty,” Rodriguez said. “He tried to jump out of the scale area. We had to wrap him up like a burrito to get a good weight on him.”

The panda team was tired, but the twins were doing well.

Lacrosse-stick solution

The swaps went without a hitch, until Aug. 24, when a curious thing happened: Whenever zookeepers would put a squealing cub on the ground near Mei Xiang, she wouldn’t retrieve it. Instead, she would act as if the cub in her possession were crying, and tend to it.

The lacrosse stick that the panda team used to help swap the panda twins.
Credit: Smithsonian’s National Zoo

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“We had to change the process a little bit,” Rodriguez told Live Science. “We had to bring the cub closer, so she could actually visualize it a little bit better and realize, ‘Oh, this is the cub that’s crying, not the one on me.'”

Zookeepers couldn’t enter Mei Xiang’s den, for safety reasons — after all, she’s still an undomesticated, protective mamma bear, Rodriguez said. [Baby Panda Photos: See a Cub Growing Up]

Surprisingly, a lacrosse stick did the trick. The panda team covered the lacrosse-stick net with brown paper (so the cub’s feet wouldn’t get stuck in the netting) and held it out to Mei Xiang, so she could see the crying cub. Then, a member of the panda team stuck a hand into a hole in the den’s wall, felt around for Mom’s right armpit (where she usually tucked the cubs) and removed the other twin.

It was an unnerving situation.

“Your arm is in there with the bear,” Rodriguez said.

Luckily, in her post-pregnancy haze, Mei Xiang was largely oblivious to the outside world, focusing most of her attention on the cub. Even so, each swap required three to four people, each of whom received training, Murphy said.

The lacrosse-stick method helped the swaps proceed, allowing the team to continue switching the cubs between the incubator and Mom, Rodriguez said.

Last days

Until the panda team developed the lacrosse-stick method, they couldn’t always switch the twins on time. During one long stint in the incubator on Aug. 24, the little panda twin needed fluids and nutrients. So, the panda team fed it with a handheld bottle holding formula made from water, and human and puppy formula, Neiffer said.

“We noticed that he was having some trouble with the nipples, a little bit of troubling swallowing. The milk was pooling up in his throat,” Neiffer said. “And we worry about aspiration of that material into the lungs. It’s one of our biggest concerns.”

Feeding baby animals is as challenging as it is gratifying, and usually involves two to three people, he said.

“With small mammals and birds, you can be the most talented and excellent bottle feeder, and you can have these [aspirations] occur,” Neiffer said. “If the baby is literally sucking a drop of milk from a bottle and decides it’s going to squirm or vocalize, and that drop falls into the trachea, even a small amount can start a pretty significant reaction.”

To be cautious, the caretakers started the cub on antibiotics that target respiratory tissue. Neiffer described it as a catch-22 situation: “We’re trying to get enough calories into cub to survive, but at the same time don’t want to cause any problems,” he said.

They attempted another twin swap that night, but it was not successful. On the way back to the incubator, the little cub regurgitated, and formula came out of his mouth, again raising concerns about aspiration.

Finally, at about 2 p.m. on Aug. 25, the zookeepers successfully swapped the cubs again. The little cub stayed with Mom until the next morning — its last day living on Earth. [Butter Balls: Photos of Playful Pandas]

The end

The panda team quickly realized the little twin had not increased in weight, appeared weaker and less vocal, and had possible respiratory issues.

The zookeepers placed the cub in the incubator, but “all through the morning until the baby died, we had a lot of challenges with keeping the baby’s body temperature at a level that we felt was compatible with life,” Neiffer said.

The treatment ramped up immediately: They gave the cub fluids (to prevent dehydration), a sugar called dextrose (to prevent low blood sugar), antibiotics (to target possible lung infections) and a drug that helps pull fluid off the chest. The caretakers used the incubator’s nebulizer (which atomizes fluids into a breathable steam) to give the cub a saline solution that kept the animal’s respiratory membranes moist, and a drug that helps break up mucus.

Sometimes the cub appeared to be improving, but it stopped breathing at about 1:50 p.m. Zoo staff began resuscitation efforts, but to no avail: The cub died at 2:05 p.m. on Aug. 26.

A postmortem X-ray showed that at least 70 percent of the cub’s lung tissue was inflamed. Neiffer said he suspects the damage from the aspiration pneumonia happened quickly, probably within 24 to 48 hours of the aspiration event.

Aspiration pneumonia could technically happen to a cub while nursing on its mother, but Neiffer said he has never seen that happen in his career of about 20 years. A cub with a cleft palate might have a greater risk of aspirating its mother’s milk, but the condition is typically associated with hand-raised babies, Neiffer said.

To avoid future deaths like this, the zoo plans to modify the nipple sizes and holes on the handheld bottles, and copy nipple designs that have been used by other institutions, Neiffer said.

The twin who lived

The larger, surviving twin is “doing gangbusters” Neiffer said. This cub now spends all of its time with its mother, unless she leaves to drink, defecate or urinate outside her den. In those rare moments, zookeepers sometimes sneak in and weigh the cub to make sure it’s growing.

And it is. The little guy’s waistline is widening, and it’s now able to push itself up on all fours. It’s moved from screaming vocalizations to grunting, as expected, Neiffer said. The black saddle patch on the cub’s back is coming in, and admirers can catch a glimpse of the cute cub on the panda cam.

The other pandas at the zoo, Tian Tian and Bao Bao, haven’t met the twin, but seemed to sense something was up after the birth, the zookeepers said. The animals stopped vocalizing as much, providing quiet to Mei Xiang as she nursed her young, the panda team said.

“We are very happy that the other baby seems to be doing great,” Neiffer said. “And Mei Xiang is a great mother. We are hoping that we just get to watch him grow.”

Editor’s Note: This story was updated to better reflect when the surviving panda cub will be named. It may be named this autumn before it is 100 days old, according to the zoo.