Name: The Island of Shrinking Mammoths
Uploaded: 2021-05-02T01:48:32.000Z
Duration: 12 min 15 s
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In 1873, a geologist named Robert Stearns reported a rather odd find on the Channel

Islands off the coast of southern California.

He had discovered a single tooth from an animal that wasn't known to have lived on the islands:

The tooth was was a bit on the small side, but it was obviously from a mammoth.

And it was enough for Stearns to conclude that the Channel Islands must have once been

Otherwise, he thought, how could the mammoth have gotten there?

Well, Stearns' hypothesis turned out to be wrong; the islands weren't ever part

But that tooth would eventually be recognized as evidence for something even more unexpected.

By 1928, enough mammoth fossils had been found on the Channel Islands that paleontologists

realized that many of them were unusually small, around 2 meters tall at the shoulder.

The mammoths were so small that they came to be seen as their own species, commonly

known as the Channel Islands Pygmy Mammoth.

These animals aren't known anywhere else in the world.

Which means that they must have evolved in place on the Channel Islands.

But they're also extremely similar to the mammoths that lived just a few dozen kilometers

away, on the California mainland: the 4 meter tall Columbian Mammoth, one of the largest

So if the islands were never connected to the mainland, then how did these little mammoths

Were they related to the giant Columbian mammoths?

And how -- and why -- were they so small?

The answers can be found in the way species respond to isolated environments with limited

It's a phenomenon that's been observed all over the world.

And the evolutionary forces that drive it are slow and gradual, but powerful.

The oldest mammoth fossil ever found on the Channel Islands is a tusk found on Santa Rosa

Uranium-series dating of nearby corals showed it to be about 80,000 years old, from the

And even though the tusk was discovered more than 140 years after Stearns found that first

tooth, both fossils raise the same question:

How did mammoths manage to get to these islands, some of which are more than 40 kilometers

To solve that puzzle, researchers began by studying what southern California was like

Back then, coastal California was often cooler and drier than it is today.

And southern California was covered with grasses and conifer trees, which fed herds of enormous

Columbian mammoths, as well as horses, and giant ground sloths.

And in turn, these herbivores were stalked by skilled predators like saber-tooth cats

But the Pleistocene was a time of tumultuous change.

The planet cooled, then warmed, then cooled again, over and over.

And those changes dramatically altered the coastline of California, as well as the size

During warmer spells, as nearby glaciers retreated, portions of the Earth's crust underneath

But every time the climate turned colder, sea levels dropped, as more water became locked

So as the seas dropped, more of the islands' land was exposed, making them bigger and bigger

until some of them eventually became connected.

The four northernmost islands were joined together into a single island that geologists

And during these times, the surface of Santarosae was much closer to the mainland than than

Sometimes, when the sea level was really low, it was just over 7 kilometers away.

So, that's a shorter distance; but it still doesn't explain how mammoths crossed the

Well, the thinking among paleontologists is: They swam!

Believe it or not, swimming comes easily to elephants.

They're strong, buoyant, and their trunks can act like snorkels.

In rare instances, African elephants have been known to swim as much as 48 kilometers,

so it seems at least plausible that a Columbian mammoth could paddle less than a quarter of

that distance to Santarosae when sea levels were low.

And even though the oldest definitive mammoth fossil on the island is 80,000 years old,

some experts think that the first mammoths made their historic journey as much 150,000

or even either 250,000 years ago, when sea levels were especially low.

But the next question you might be wondering is: Why would these animals even want to swim

I mean, southern California is nice, right?

Well, for much of the Pleistocene, mainland California was an ideal habitat for Columbian

mammoths, but in some ways, the islands were even better.

Pollen samples from the Late Pleistocene show us that Santarosae was covered with vegetation,

And although they mostly ate grasses and sedges, mammoths also sometimes ate woody plants.

Additionally some researchers think that Columbian mammoths knew that food was there, because

not only could they see this nice, lush island, they may have even been able to smell it.

Research in 2014 found that modern elephants have twice as many genes dedicated to smell

as dogs do, and they can smell food and water from considerable distances.

No matter what drew them to the island, once they got there, the mammoths found another

benefit to their new home: there were no big predators.

There's no fossil evidence of saber-toothed cats, dire wolves or any other large carnivores

It's not clear why; maybe they just didn't want to get their feet wet.

But even in the absence of predators, those pioneering Columbian mammoths eventually ran

Because, the same climate changes that made the glaciers grow also sometimes made them

shrink, dumping fresh water into the ocean and rising sea levels worldwide.

This happened a lot in the Pleistocene; the most recent period of rising sea levels began

And when the seas rose, much of the terrain flooded, including some of the grasslands

When seas were at their highest, only Santarosae's highest points were above water, and in fact

those high points form the four northern islands that we see today.

This new island environment was totally different from the one the mammoths experienced when