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Episode 256: Mammoths and the End of the Ice Ages

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Further reading:

Million-year-old mammoth genomes shatter record for oldest ancient DNA

Mammoth Genome Project (with pictures of cave art and ancient carvings of mammoths)

The most famous cave painting of a mammoth, from a cave in France:

Sivatherium:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

It’s the last Monday of 2021, which means the very last extinction event episode. There’ve been way more extinction events in earth’s long history than the five we’ve covered this year, and not all of the extinction events I chose to highlight were even necessarily the biggest. This one, for instance.

You may have noticed a pattern when I talk about ice age megafauna. So many animals went extinct about 11,000 years ago. That’s this week’s topic, the end-Pleistocene extinction event.

The Pleistocene is often called the ice age, or ice ages since it consisted of multiple glaciation periods separated by warmer times when the glaciers would retreat for a while. It started roughly 2.6 million years ago and is considered to have ended 11,700 years ago. Keep in mind, as always, that these dates are just a shorthand to help scientists refer to changes in earth’s history. There was no one day where the sun rose and everything had abruptly changed from one era to another. The changes took place over a long time, hundreds of thousands of years, with different parts of the world changing more quickly or slowly than others depending on local conditions.

At the beginning of the Pleistocene, the world’s continents were roughly in their present positions. Two continental plates in what is now Central America collided very slowly over millions of years, which caused the land to buckle up and magma to erupt through the earth’s crust as volcanoes. The volcanoes created islands in the Central American Seaway, a section of ocean between North and South America that connected the Atlantic and Pacific Oceans. By around 5 to 10 million years ago, the volcanoes and land continued to be pushed up, and sediment from rivers filled in between them, until finally instead of islands there was actual land that connected North and South America. That land is called the Isthmus of Panama and it allowed the great American interchange where animals from North America could cross into South America, and vice versa, but that’s a topic for another episode.

Another result of the Isthmus of Panama’s formation is that the Atlantic and Pacific Oceans were more separated. Instead of ocean currents circulating between North and South America, they were cut off and new currents formed. Ocean currents help distribute warm water to colder areas and cold water to warmer areas, which affects air and land temperatures too. Around 2.5 million years ago, the ocean current changes had changed the entire overall temperature of the earth, making it much cooler overall. That wasn’t the only cause of the ice ages, but it was a major factor.

The earth gradually became cooler and dryer, a process that had already started due to other causes and was accelerated by the ocean current changes. As the global temperature dropped, more and more water was locked up in huge glaciers called ice sheets, at first around the poles and then farther south. This meant sea levels dropped a lot. North America was connected to Asia by a stretch of grassland steppe called Beringia that had formerly been submerged.

As the temperatures dropped and the climate changed, animals and plants had to adapt. The ancestors of modern elephants had lived in Africa for millions of years, but they started migrating to other parts of the world around 3 million years ago. Because they were already big, they were good at retaining heat in their bodies and became quite successful as the climate grew cooler and cooler. They evolved long hair to stay even warmer and spread throughout much of the world, including Europe, Asia, and North America. You may know them as mammoths, which were closely related to the modern Asian elephant. The first mammoth known was the South African mammoth that lived around 5 million years ago and stood about 12 feet tall at the shoulder, or 3.7 meters.

We actually know a lot about the various species of mammoth because we have so many remains. Our own distant ancestors left cave paintings and carvings of mammoths and other animals in many parts of the world, we’ve found lots of fossilized remains, and we have lots of subfossil remains too. Because the mammoth lived so recently and sometimes in places where the climate hasn’t changed all that much in the last 10,000 years, namely very cold parts of the world with deep layers of permafrost beneath the surface, sometimes mammoth remains are found that look extremely fresh.

Before people understood extinction and related natural concepts, some people who lived in areas where dead mammoths occasionally weathered out of the permafrost thought they’d only died recently. That’s how fresh the dead animals looked. The people didn’t know what the animals were, though, and assumed that since they were only ever seen partially buried, they must be underground animals. In parts of Siberia, people thought mammoths lived underground and if they accidentally came to the surface, they died.

In February of 2021, a genetic study of mammoth DNA found in teeth was published in Nature. Nature is one of the most important scientific journals in the world and they don’t just publish any old genetic study these days, now that DNA is so much easier to sequence than it used to be. In this case, though, the DNA came from three mammoth teeth that were more than one million years old and possibly around 1.5 million years old. The teeth were found in the 1970s in different places. Before DNA was successfully found in the teeth, the oldest DNA sequenced was from a horse bone that was about 780,000 years old at the most.

Genetic material breaks down relatively quickly once an animal dies, becoming more and more fragmented as the years pass by. That’s why we don’t have any dinosaur DNA—they just lived too long ago for any usable genetic material to remain. The mammoth genetic study is a big deal since it’s pushed back scientists’ ability to sequence ancient DNA, at least of some samples. In the case of both the mammoth teeth and the ancient horse bone, the remains were preserved in permafrost that slowed the fragmentation of the DNA.

The study found that one of the teeth belonged to an early woolly mammoth and the other two were from early steppe mammoths, but it’s not as simple as it sounds. The two steppe mammoth teeth looked alike but their genetic story was very different. One had genetic markers that identified it as an ancestor of woolly mammoths–but the other didn’t. The one that didn’t is called the Krestovka sample and was found in Russia. Researchers aren’t sure yet if it’s actually a new species or subspecies, but it was obviously part of a population isolated from other steppe mammoths.

But it gets even more complicated, because Columbian mammoths from North America do show that some of their ancestors were related to the Krestovka sample–and Columbian mammoths are also related to woolly mammoths. Researchers suspect that the Columbian mammoth was a species that developed from hybrids of the Krestovka steppe mammoths and woolly mammoths. Over half a million years ago, there were enough of these hybrid mammoths that they were actually numerous enough to form their own stable species. Hybrid speciation is still a relatively new concept but as genetic studies get more sophisticated, we’re getting more evidence of it happening.

Researchers are hopeful that even older genetic samples can eventually be sequenced, but there’s a hard limit to DNA found in permafrost. That limit is 2.6 million years, which is when the permafrost began forming. And that brings us back to the ice age.

Mammoths weren’t the only animals adapted to cold conditions, of course. They weren’t even the only elephant lineage that adapted to the cold. Mastodons aren’t actually that closely related to mammoths but they are an elephant relation.

The woolly rhinoceros was about the size of living rhinoceros species but was covered in thick fur. It had a massive hump on its shoulders that was made up of fat reserves and muscle, much like modern bison. It went extinct about 10,000 years ago.

A giraffe relation, Sivatherium, lived in Africa and parts of Asia during the Pleistocene. Its neck wasn’t as long as a modern giraffe’s but it was still tall, over 7 feet tall at the shoulder, or more than 2 meters, and almost 10 feet tall including the head and neck, or 3 meters. The males had two pairs of ossicones that resembled antlers, a large pair on its head and a smaller pair over its eyes. Ossicones are bony projections usually covered with skin and hair, and modern giraffes have ossicones too.

Mammals weren’t the only megafauna, though. Mega just means big, and fauna just means animal. There were megafauna birds and reptiles too, such as the Asian ostrich. It lived throughout much of Asia and the Middle East until around 8,000 years ago and was related to the modern ostrich. The wonambi was an Australian constrictor snake, not related to the snakes living in Australia now, that could grow up to 30 feet long, or 9 meters.

So what happened to cause the extinction of all these amazing animals? Surely we know more about this extinction event than we do about older ones since it happened so recently, right?

Actually, no. Although it feels significant to us now, the end-Pleistocene extinction event actually wasn’t very big compared to the others we’ve discussed this year. A lot of ice age megafauna are still around, including bears, wolves, moose, reindeer, horses, bison, elephants, giraffes, lions, tigers, camels, kangaroos, tapirs, ostriches, condors, and lots more. Even humans are ice age megafauna since we spread throughout the world during the Pleistocene.

We do have hints of what might have caused the end-Pleistocene extinction event, and one big hint comes from what happened in Australia. Like the rest of the world, Australia’s climate was cooler and dryer during the ice ages and animals that had adapted to the cold lived throughout the continent. This included diprotodon that we talked about in episode 224, along with kangaroos, wombats, koalas, and other marsupial mammals that were bigger than the ones living today. But extinctions in Australia started a lot earlier than they did in the rest of the world, around 45,000 years ago. There’s also no corresponding extinction event among marine animals. By about 40,000 years ago almost 90% of all species of Australian megafauna had gone extinct, while smaller animals and marine animals were mostly just fine.

One specific event that happened around 45,000 years ago was the colonization of Australia by humans. Humans had visited and even lived in Australia as far back as 70,000 years ago, but by 45,000 years ago they were really spreading throughout the land. The animals of Australia had never encountered smart, fast tool-users before and didn’t know what to do except try to avoid them. Humans had weapons like spears that could kill at long range, and humans worked together to kill animals that before then had no predators due to their size. Humans also drink a lot of water because we developed in a part of Africa where water is abundant. Fresh water isn’t nearly as abundant in Australia, so humans would stake out water sources and keep other animals away.

The Australian extinctions were probably a combination of climate change, humans hunting large animals that reproduced slowly, and humans outcompeting animals for water sources. The same causes probably led to extinctions in other parts of the world, but because humans took longer to spread to continents like the Americas that are far away from Africa, those extinctions mostly took place later than in Australia. It’s also important to note that Africa showed almost no extinctions at the end of the Pleistocene. Researchers think this is because the animals of Africa evolved alongside humans and knew how to deal with us.

Natural climate change was definitely a contributing cause to the extinctions, though. Ice sheets melted, glaciers retreated, and the world warmed over the course of just a few thousand years. Animals that were well adapted to the cold had to move to places where it was still cold, but those places didn’t always have the right foods or enough food. The sea levels rose too, cutting off access to parts of the world. Beringia became covered with ocean again, for instance, where it remains today, separating Asia from North America.

Humans probably finished off the mammoths by hunting the last ones to extinction, but some populations survived much later than the 10- to 12,000 years ago commonly given as their extinction date. There were still mammoths alive in the world only 4,000 years ago and maybe only 3,700 years ago—but only on an island where humans didn’t live.

Wrangel Island is located in the Arctic Ocean near western Siberia, more than 85 miles from the nearest coast, or 140 km. It has low mountains and sea cliffs and is cold and dry most of the year, which is the kind of climate mammoths preferred.

The woolly mammoths that lived on Wrangel Island were probably cut off from the mainland when sea levels rose and flooded Beringia. They lived on for thousands of years after their mainland relations had gone extinct. Gradually the mammoths became more and more inbred, leading to genetic defects at a much higher rate than in a healthy population. Even so, the mammoths might have managed to survive even longer except for one thing. Around 1700 BCE, humans arrived on the island. Shortly afterwards, the mammoth was extinct.

Wrangel Island is a nature sanctuary these days and home to lots of animals, including polar bears, walruses, Arctic foxes, seals, reindeer, musk ox, and wolves. All of these are considered ice age megafauna, so although the mammoths are gone, other megafauna remain.

While we don’t know for sure that humans played a big part in the end-Pleistocene extinction event, we sure didn’t help. We can’t blame our ancient ancestors for their actions but we can learn from their mistakes. We’re in the middle of another extinction event right now, often called the Holocene extinction or Anthropocene extinction, directly due to our actions. Habitat loss, pollution, overhunting, and human-caused climate change are driving more species of animal and plant to extinction every year.

It can feel overwhelming, but there are lots of small things you can do to help. Just picking up trash and putting it in the waste bin or remembering to take your reusable bags to the grocery store can make a difference. No one person can fix all the world’s problems, but if everyone does a little bit to help, the big problems get smaller and more manageable. If everyone pitches in, we can make the world a cleaner, better place for animals and for people.

Happy new year! Let’s make it a great one!

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or Podchaser, or just tell a friend. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 050: Tallest Animals

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We’re discovering which animals are the tallest this week! This episode includes our first dinosaur!

Sauroposeidon proteles:

Giraffes:

Bop bop bop have at thee!

Paraceratherium (I couldn’t find one that I liked so I drew one, along with a giraffe and ostrich to scale):

Ostrich running:

I SAID DON’T @ ME

A fine day at the ostrich races. I could not make this stuff up if I tried:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re looking at tall animals. Is the giraffe the tallest mammal that’s ever lived? Is the ostrich the tallest bird? And what about tall dinosaurs?

I don’t talk about dinosaurs much in this podcast because there are so many good podcasts devoted specifically to dinosaurs. I recommend I Know Dino. It’s family friendly and goes over the latest dinosaur news without talking down to listeners or dumbing down the information.

Four-footed animals are usually measured at the shoulder, since some animals hold their heads low, like bison, while others hold their heads high, like horses. But we’re talking about tall animals today, and that includes animals with long necks. So the measurements here are all from head to toe, with the head and neck held in its natural standing position.

Let’s start with the real biggie, the tallest dinosaur ever found.

In 1994 a guy named Bobby Cross noticed some fossils weathering out of the ground at the Oklahoma correctional facility where he worked as a dog trainer. As he always did when he found fossils, he called the Oklahoma Museum of Natural History. They sent a team to take a look. The team found four vertebrae, but they were just so big—around four feet long each, or 120 cm—that at first they thought they must be fossilized tree trunks.

Sauroposeidon proteles was probably closely related to Brachiosaurus, but was even bigger and taller. Sauroposeidon stood 60 feet tall, or 18 meters, and its neck alone was 39 feet long, or 12 meters. Its body and legs were relatively short and stocky. We don’t have a complete skeleton, just the four vertebrae found in southeastern Oklahoma, and a few vertebrae from two other individuals found in Montana and Texas. A trail of giant footprints in Texas may be a Sauroposeidon track too. But for sauropods, neck vertebrae are the most valuable fossils because they tell so much about the animal.

Sauroposeidon’s neck bones were massive, but they were lighter than they look due to tiny air sacs in the bones, like those in bird bones. The air sacs in bird bones actually contain air that flows through the lungs, called pneumatic bones, which provides the bird with more oxygen. A CT scan of the Sauroposeidon fossils—at least the portions of the fossils that would actually fit in the CT scanner—revealed that sauroposeidon’s vertebrae were constructed in the same way that bird bones are. We know that pterosaurs and theropods had pneumatic bones, so it’s not too surprising that at least some sauropods did too.

Sauroposeidon lived around 110 million years ago, during the Mesozoic era, specifically during the early to mid Cretaceous. The sea level was much higher then than it is now, so Sauroposeidon lived near the coast. It ate plants, and like many birds, it also swallowed stones to help it digest those plants, called gastroliths. Paleontologists have found lots of sauropod gastroliths associated with fossil animals. Unlike mammals, which chew their food before swallowing, sauropods swallowed it whole and the plant material was broken up in a stomach or gizzard-like structure. That’s why its head is so small relative to its body, and how it could eat enough plants to keep such an enormous body going. It probably ate literally a ton of food every single day.

We know a lot about sauropods, and since sauroposeidon appears to be structurally typical of other sauropods, just really big, it’s a safe bet to assume it was like other sauropods in many ways. It probably nested in groups and laid about two dozen eggs at a time in big nests on the ground. We don’t have any sauroposeidon eggs, but they probably wouldn’t have been all that big, maybe about the size of a football. Babies would have grown rapidly and were full grown in ten to twenty years. Sauroposeidon migrated in herds throughout the year, traveling from nesting grounds to new grazing grounds. While it lived near the ocean, it would have had to be careful about walking on soft ground. An animal that tall and heavy can get mired in mud easily. Paleontologists have actually found fossils of sauropods that died standing up, unable to climb out of a muddy hole after sinking in soft ground.

Giraffes are the tallest living animals today, with the tallest recorded giraffe, a male, measuring 19.3 feet, or 5.88 meters. That’s pretty darn tall, about 1/3 the height of sauroposeidon. Giraffes are related to deer and cattle, and live in the savannahs and forests of Africa, where they eat tree leaves that are much too high off the ground for other animals to reach. Female giraffes and their young make up loose groups, while males form groups of their own. While giraffes can kick hard enough to kill lions, when males fight over females, they use their necks. A male will swing its head at another male, and the two will tussle back and forth bopping necks together. As a result, male giraffes have thicker, stronger necks than females. Males are also usually taller than females.

The giraffe not only has a long neck and long legs, it has a long tongue that it uses to grab leaves that are juuuust too far away. The tongue is about 18 inches long, or 45 cm. A giraffe at Knoxville Zoo licked my hair once. The giraffe’s upper lip is also prehensile, and is hairy as a protection from thorns. Because of all the thorns it encounters, giraffe skin is surprisingly tough. The giraffe has large eyes that give it good vision, and it also has keen hearing and smell. It can close its nostrils to protect them from dust, sand, insects, and—you guessed it—thorns. So many thorns. And giraffe fur contains natural parasite repellents, which also makes giraffes smell funny.

All this is pretty awesome, but we’re not done with giraffe awesomeness. Giraffes have skin-covered horns called ossicones. Females and males both have ossicones, although males also have a median lump at the front of the skull that’s not exactly an ossicone but is sort of like one. Some females also have this median lump. Ossicones are made of cartilage that has ossified, or turned boney, and they’re covered in skin and hair, although since males use their ossicones in necking fights, they tend to rub all the hair off and have bald ossicones.

The only other animal alive today that has ossicones is the okapi, a close relative of the giraffe, but giraffe ancestors once had all kinds of weird ossicones. Xenokeryx amidalae, for instance, which lived about 16 million years ago in what is now Spain, had two ossicones over its eyes, and a third sticking up from the back of its head that was T-shaped. The name amidalae comes from the character Padme Amidala in Star Wars: The Phantom Menace, if you remember that weirdly shaped headdress she wore.

Because giraffes are so tall, they have some physical adaptations that are unique among mammals living today. A giraffe has the same number of neck bones as all other mammals except sloths and manatees, which are weird, but the vertebrae are much longer than in other mammals, almost a foot long, or 28 cm. The giraffe can also tilt its head right back until it’s just about in line with the back of the neck. I’m picturing everyone listening tilting their heads back right now, and hopefully you notice how the back of your neck curves when you look up. Also, please don’t wreck your car because you’re looking up while driving. The giraffe’s circulatory system is really unusual. Its heart is enormous and beats around 150 times per minute. The jugular veins, which are the big veins that carry blood up the neck to the brain, have valves that keep blood from running backwards when a giraffe lowers its head to drink.

Giraffes can walk, and giraffes can run, but they don’t have any other gaits. They can’t trot or canter, for instance. Even humans have more than two gaits, because we can skip. Despite its height, a giraffe can really move. It can run over 30 miles per hour, or about 50 km per hour, and keep it up for several miles. It has cloven hooves. Because a giraffe’s body is so heavy and its legs so long and thin, it has specialized ligament structures in its legs that keep them from collapsing. Horses also have this structure, which also helps the animal sleep while standing.

Oh, and the giraffe doesn’t eat leaves all the time. It spends a lot of the day just standing around chewing its cud.

There used to be a mammal that stood almost as tall as the giraffe at the shoulder. Paraceratherium orgosensis went extinct around 23 million years ago, and it’s not even related to the giraffe. It’s a member of the rhinoceros family. Like sauroposeidon, we don’t have a complete skeleton of paraceratherium, so its size is an estimate based on the proportions of closely related animals whose sizes we do know. It probably stood 18 feet high at the shoulder, or 5.5 meters, and while its neck was probably around 7 feet long, or a little over 2 meters, it probably held it forward like a rhino instead of up like a giraffe, so it didn’t add much to the animal’s overall height.

In episode 32 we learned about the giant moa, a flightless bird that once lived in New Zealand. It was probably the tallest bird that ever lived, with big females 12 feet tall, or 3.6 meters. But the tallest living bird is the ostrich. It also lives in Africa and is famous for being flightless and for being able to run really fast. In fact, it’s not only the tallest bird alive, it’s the fastest. It can run over 40 miles per hour, or about 70 km per hour, and it uses its large wings as rudders and even to help it brake. With its head raised, a big ostrich can be nine feet tall, or 2.8 meters.

There are a lot of differences between ostriches and most other birds. Most birds have four toes, for instance. The ostrich has two, one large toe with a hoof-like nail, and a smaller outer toe with no nail at all. All other living birds secrete urine and feces together, but the ostrich secretes them separately the way mammals do. And while most male birds don’t have a penis, the male ostrich does. And the ostrich has a double kneecap. Not only is that unique to birds, it’s unique to everything. No other animal known, living or extinct, has a double kneecap. Researchers have no idea what it’s for, although one hypothesis is that it allows a running ostrich to extend its legs farther, and another hypothesis is that it might protect tendons in the bird’s leg.

The ostrich eats plants, seeds, and sometimes insects. Like Sauroposeidon and many other dinosaurs and birds, the ostrich swallows small rocks and pebbles to help digest its food in its gizzard. The gizzard contracts, smashing the gastroliths and plants together to help break up the plant material the way mammals would chew it.

Ostrich eggs are the biggest laid by any living bird, about six inches long, or 15 cm. Females lay their eggs in a communal nest.

Ostriches are farmed like big chickens, for their feathers, meat, and skin for leather. Ostriches are also sometimes ridden and raced with special saddles and bridles. But ostriches aren’t easy birds to manage. They can be aggressive, and they can kill a human with one kick.

To wrap things back around to dinosaurs, some researchers think many fast-running dinosaurs used their feathered forelimbs the way ostriches use their wings, to help maneuver and possibly to help keep unfeathered portions of the body warm at night. During the day, when it’s hot, ostriches keep their wings raised so that their unfeathered upper legs can release heat into the atmosphere, but at night they cover their upper legs to retain heat. It’s just another link between birds and their long-distant ancestors, the dinosaurs.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or whatever platform you listen on. We also have a Patreon if you’d like to support us that way.

Thanks for listening!