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  • Thanks to LEGO.com and the LEGO Storepresenting the LEGO Ideas Tree Housefor their support

  • of PBS.

  • The mountain forests of China are the last home of a very peculiar bear indeed: the giant

  • panda.

  • It’s one of the most recognizable mammals in the world, with its distinctive black-and-white

  • coat and its adorably round physique.

  • And it’s been confusing researchers ever since it was first described by Western scientists

  • in the 1800s.

  • For one thing, the giant panda is mostly a committed herbivore that specializes in eating

  • bamboo, which is not very bear-like behavior.

  • It also shares its name, its diet, part of its habitat, and an enlarged wrist bone that

  • functions like a thumb with the more common red panda.

  • But it turns out, the two pandas are actually not that closely related!

  • And while it used to range over much of East Asia, today it’s found only in a few pockets

  • of mountain habitat in central China.

  • But oddly enough, its earliest relatives actually lived in Europe, their fossils having been

  • found in Hungary and Spain.

  • Everything we discover about the giant panda just seems to lead to more questions.

  • Like why isn’t it more closely related to the red panda, if they have so much in common?

  • And how does a bear -- which is a member of the order Carnivora -- evolve into an herbivore?

  • How can it survive on bamboo, if it evolved from omnivores?

  • Like, how do pandas even work?

  • Despite how it looks, nothing about the history of the giant panda is black and white.

  • But it iskinda fuzzy.

  • Now, because the giant panda is so odd in so many ways -- from its very picky diet to

  • its weird, extra-thumb thing -- scientists for a long time wondered: Are pandas even

  • bears?

  • And it wasn’t until the late 20th century that we finally got an answer -- that’s

  • how weird these animals are.

  • The giant panda saga started in 1869, when it was given its first scientific name by

  • a French missionary and naturalist based in China.

  • He called it Ursus melanoleucus -- literally, the black and white bear.

  • So, we know he thought it was a bear, because he put it in the genusUrsus,” with most

  • of the other living bears.

  • But only a year later, another researcher examined a giant panda skeleton and decided

  • it was more like a red panda than a bear!

  • So he changed its scientific name to Ailuropoda melanoleuca, which is what it’s still called

  • today.

  • But the controversy over the panda’s bearishness continued for more than 100 years.

  • The experts who thought it was a bear pointed to a ton of similarities between giant pandas

  • and other bears, found throughout their entire bodies - in their teeth, skeletons, muscles,

  • and organ systems.

  • But the scientists who thought it was closer to red pandas focused on their similarities

  • in feeding behavior and their shared habitat.

  • Giant pandas and red pandas live in the same places and eat the same thing: bamboo.

  • It wasn’t until the early 1980s that the first genetic analysis of giant pandas was

  • done.

  • It looked at the number of different mutations per gene in pandas and other carnivores.

  • The more differences per gene there are, the longer those two species have been separated

  • reproductively, which means theyre more distantly related.

  • These early DNA studies suggested that the giant panda was only a distant relative of

  • the red panda.

  • And it found that the red panda lineage actually branched off somewhere between two different

  • families - the one that contains skunks, and the one that includes raccoons and their relatives.

  • So, sorry no!

  • Scientifically speaking, it’s not super accurate to describe a raccoon as a trash

  • panda.

  • But there is a relationship there, at least with red pandas!

  • It wasn’t until studies were done in the late 2000s of the giant panda’s whole genome

  • that it was confirmed that the giant panda was indeed a bear.

  • And it turned out that its closest living relative isn’t the red panda; it’s the

  • South American spectacled bear, which belongs to the second-oldest branch on the bear family

  • tree.

  • And the oldest branch of the bear family?

  • That’s where the pandas came from.

  • According to molecular clock studies of the genomes of the bear family, the giant panda

  • lineage originated around 20 million years ago, in the early Miocene Epoch, when its

  • branch split off from all of the other living bears.

  • But, we don’t know where this happened exactly.

  • Since pandas today are found only in China, for a long time it was thought that they originated

  • in East Asia.

  • But based on fossils from several different sites, it looks like they mightve actually

  • evolved in...

  • Europe.

  • Or, at the very least, pandas had some close European cousins, with whom they shared a

  • common ancestor.

  • The oldest, most basal member of the giant panda lineage comes from deposits in northern

  • Spain dating back 11.6 million years.

  • There, scientists have discovered the remains of a bear known as Kretzoiarctos

  • Its fossils consist of only teeth and jaws, but its premolars have some features, like

  • additional little cusps, that researchers think are adaptations to a more herbivorous

  • diet.

  • So it seems that the giant panda’s taste for plants goes pretty far back in its evolutionary

  • history.

  • Just a little younger than Kretzoiarctos is another European panda known as Miomaci pannonicum,

  • and it comes from deposits dating back about 10 million years in both Hungary and Spain.

  • It too is only known from teeth and jaws, but the teeth of Miomaci have microscopic

  • pits and scratches in them that are kinda like the patterns seen on the teeth of modern

  • giant pandas.

  • So some researchers think it mightve had a similar diet and lifestyle as the giant

  • panda.

  • And a third European genus is known from scrappy remains from France, Germany, and Hungary

  • that overlap in time with the other two panda ancestors.

  • So for a few million years, weve got panda relatives living throughout central and western

  • Europe.

  • But then, something strange and frustrating happens.

  • There seems to be a panda hiatus in the fossil record.

  • The next time they show up is in China, millions of years later.

  • There weve found two species belonging to the genus known as Ailurarctos.

  • They date to between 6 million and 8 million years ago, and both are only known, again,

  • from teeth.

  • And those teeth suggest that those bears were smaller than the modern giant panda and were

  • probably more omnivorous.

  • They had broad lower molar crowns, like living bears, but with a wrinkled pattern to their

  • enamel, which is what the giant panda has.

  • So their teeth look like a transitional step between those of more typical bears and those

  • of the highly specialized panda.

  • Then!

  • About 2 million years ago, we finally find the earliest known fossils of bears that truly

  • belong to the same genus as the modern giant panda, the genus Ailuropoda.

  • These fossils come from cave sites in southern China, and the most complete of them is a

  • skull that has a lot of similarities to the skulls of living pandas.

  • This fossil panda was smaller than its modern relatives and maybe had a less powerful bite.

  • But it also had extra-cuspy teeth that were specialized for breaking down fibrous foods.

  • But experts aren’t sure about when pandas adopted the habit theyre most famous for:

  • relying on bamboo as their main source of food.

  • One recent study compared the isotopes of carbon and oxygen preserved in the tooth enamel

  • of modern and ancient pandas.

  • Carbon can tell you about an animal’s diet, while oxygen can tell you about the climate

  • it lived in.

  • And the carbon values suggested that ancient pandas were herbivores by at least 2.5 million

  • years ago -- but the chemistry wasn’t a perfect match with modern, bamboo-eating pandas.

  • The teeth also had a much wider range of oxygen values, which means they probably lived in

  • a lot more different kinds of environments than pandas do today.

  • So it looks like ancient pandas had broader diets and were more ecologically flexible

  • than their living descendants.

  • But modern pandas are definitely all about that bamboo - which again, for a bear, is

  • just really weird.

  • See, the giant panda has the GI tract, the digestive enzymes, and the gut microbes of

  • a carnivore.

  • It doesn’t have the multi-chambered stomach of cattle or produce the enzymes that other

  • herbivores use to break down cellulose, which is the key ingredient in bamboo and other

  • plants.

  • So, for a long time, the panda’s diet was considered a sort of evolutionary riddle.

  • But a paper published in 2019 seems to have figured out how theyve been able to survive

  • on a mostly bamboo diet.

  • Researchers sampled the shoots and leaves of the different kinds of bamboo plants that

  • a select group of pandas was eating throughout the year.

  • Then they sampled the bearspoop for a before-and-after picture of the nutrients

  • that they were taking in and putting out.

  • And the researchers found that, at the molecular level, the pandasdiet looked more like

  • a carnivore’s than like a herbivore’s.

  • Specifically, their ratio of macronutrients -- like proteins, carbs, and lipids - resembled

  • those of meat eaters.

  • It turns out that pandas switch which type of bamboo and which parts of the plant they

  • eat throughout the year, to maximize protein and minimize fiber!

  • So the percentage of energy that they get from protein is actually equivalent to the

  • diet of WOLVES.

  • Pandas are basically vegan gym bros.

  • So maybe the transition from an omnivorous, bear-like ancestor to the gentle bamboo eaters

  • we know today wasn’t such a stretch for the giant panda, after all.

  • From its Early Miocene origins near the base of the bear lineage, the giant panda has come

  • a long way.

  • Taxonomically, it went from a red panda relative to a true bear.

  • Geographically, it went from its ancestorsfirst appearance in Europe, all the way to

  • the mountains of China, where it survives today.

  • Physically, it went from a dog-sized omnivore to a, well, bear-sized herbivore that still

  • packs in the protein, in an very unexpected way.

  • If the evolutionary history of the giant panda

  • remains kind of fuzzy, its future isn’t very clear either.

  • It was once considered to be on the brink of extinction, but in 2014 there were more

  • than 1800 counted in the wild -- a viable, but still vulnerable, number.

  • Those false-thumbed, bamboo-eating mammals of Central China are the last remaining characters

  • in the story of the world’s most un-bear-like bear.

  • Thanks to LEGO.com and the LEGO Storepresenting

  • the LEGO Ideas Tree Housefor their support of PBS.

  • The LEGO Ideas Tree House set aims to celebrate the seasons of the natural world with an interchangeable

  • set of leavesgreen for summer and yellow/ brown for fall.

  • The 3,036 piece set is designed for ambitious builders and includes removable treetop and

  • cabin roofs, a wind-up crane feature, and a landscape base with a picnic table and bonfire.

  • There’s even a bathtub!

  • As part of the LEGO Group’s commitment to make products using sustainable material by

  • 2030, the 180 tree foliage elements are made from plant-based polyethylene plastic using

  • sustainably sourced sugarcane.

  • Click the link in the description to learn more.

  • Weird extra thumbs up to this month’s Eontologists: Patrick Seifert, Jake Hart, Jon Davison Ng,

  • Sean Dennis, Hollis, and Steve!

  • To join them and become an Eonite go to patreon.com/eons and pledge your support!

  • And thank you for joining me in the Konstantin Haase Studio.

  • Be sure to subscribe at youtube.com/eons.

Thanks to LEGO.com and the LEGO Storepresenting the LEGO Ideas Tree Housefor their support

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大熊猫的模糊起源(The Fuzzy Origins of the Giant Panda)

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    joey joey 發佈於 2021 年 05 月 03 日
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