字幕列表 影片播放 列印英文字幕 Thanks to LEGO.com and the LEGO Store—presenting the LEGO Ideas Tree House—for 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 is … kinda 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 genus “Ursus,” 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 they’re 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 might’ve 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 might’ve 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, we’ve 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 we’ve 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 they’re 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 they’ve 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 bears’ poop 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 pandas’ diet 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 ancestors’ first 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 Store— presenting the LEGO Ideas Tree House —for their support of PBS. The LEGO Ideas Tree House set aims to celebrate the seasons of the natural world with an interchangeable set of leaves – green 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.