Greek and Roman mythology is full of stories
about exotic islands that were home to weird and fearsome monsters — like one-eyed ogres,
seductive sirens, and man-eating giants. And I’m here to tell you: Back in the late
Miocene epoch, there was in fact an island–or maybe a group of islands– in the Mediterranean
Sea that was populated with fantastic giant beasts. But, these giants were actually … pretty
small. Some of them you might even consider cute. There were enormous hamsters. And big, fat waterbirds that could neither
fly nor swim. And animal like hedgehogs that were as big
as house cats. These organisms were only giants compared
to their ancestors, which had lived on the European mainland. But once they became isolated on these Mediterranean
islands, some of these little critters attained massive body sizes. That’s because geographic isolation is a
powerful force in evolution. Sometimes, when a population of animals gets
cut off from many of its normal predators or competitors, it gives rise to new species
of unusual sizes. Sometimes, they turn out to be miniaturized
versions of their ancestors. Other times, giants! The tale of these Mediterranean island beasts
of the Miocene is no myth. It’s a lesson in the very strange, but very
real, powers of natural selection. In 1969, a group of Dutch paleontologists
were working in Gargano, a region on the eastern coast of Italy, when they discovered deep
fissures, or cracks, in the limestone quarries and road cuts there. And these cracks turned out to be full of
fossils! For millions of years, it seemed, animals
had been stumbling into these fissures, like natural traps, starting about 8 million years
ago. The result was an amazingly rich fossil deposit,
a snapshot of life in this place in the Late Miocene Epoch. But a few things about the Gargano fossils
turned out to be really … odd. For one thing, scientists were confused about
the fossils they didn’t find. Elsewhere in Europe, deposits from the late
Miocene tend to contain a lot of large mammals — like extinct elephants, cats, and perissodactyls,
the group of hoofed mammals that includes horses. But at Gargano, none of those animals were
anywhere to be found. Instead, researchers uncovered an eclectic
and bizarre bestiary, including fossils of smaller animals that seemed … overgrown. There were extra-large owls, alarmingly big
hamsters, and supersized hedgehogs. This strange assortment of animals came to
be known as the Mikrotia fauna. And for decades, the Gargano Peninsula –along
with a handful of nearby towns — were the only places on the planet where these creatures
were known. Then in the 1990s, fossils of some of those
same, peculiar animals turned up at Miocene sites near Scontrone, a town in central Italy. So, what exactly were these animals? Why were the Miocene animals of Gargano and
Scontrone so different from their counterparts in the rest of Europe? For paleontologists, the most likely explanation
was that these areas must’ve been cut off — geographically separated — from the rest
of Europe. Specifically, they were probably islands — or
maybe parts of the same island. This would explain not only why these animals
appear just at those sites; it would also account for the strange body sizes of animals
that were ordinarily quite small. I’ve talked before about how, in island
environments, large-bodied animals often get smaller over time. In the case of Columbian mammoths on the Channel
Islands of California, for example, the absence of large predators, combined with limited
food, led natural selection to favor smaller body sizes. So, after thousands of years, some of the
giant Columbian mammoths had developed into what scientists consider a new, separate and
smaller species: the Pygmy mammoth! This phenomenon is known as insular dwarfism. But it’s only part of the story about how
island environments can tinker with animals’ body plans. The flip-side is what happened to some of
the animals of Gargano and Scotrone: Insular Gigantism. Both processes are part of what’s known
as Foster’s Rule, identified by biologist J. Bristol Foster in 1964. Essentially, Foster’s Rule says that in
isolated environments, large animals frequently get smaller — and tiny animals often become
larger. And this is what happened to many animals
in the Mikrotia fauna. And it happened because their habitat allowed
it to happen. Much like the modern Channel Islands, the
regions of Gargano and Scontrone in the deep past were higher in elevation than the surrounding
areas. So as sea levels rose and fell over millions
of years due to changes in climate, these places became isolated from the rest of Europe,
and then reconnected, many times. And it may have been during one of these periods
of low sea levels when some ancestors of the island giants first made their way to Gargano
and Scontrone. Researchers think that, about 30 million years
ago, in the Oligocene Epoch, a global cooling trend lowered sea levels in the Mediterranean
and elsewhere, forming a land bridge between the mainland and these two spots. But then, about 15 million years ago, the
climate warmed again and sea levels rose, turning those high spots into islands and
severing their connection to the mainland. So, maybe the ancestors of the Mikrotia fauna
simply walked across the land bridge before it became submerged. But other scientists have proposed that most
of them arrived much more recently — just around 8 million years ago — when the island
or islands were properly isolated. In that case, it’s thought that the animals
might have rafted on piles of floating debris–like logs, branches, and palm leaves — much in
the same way that the ancestors of South America’s rodents are thought to have migrated from
Africa! Either way, once they’d reached their new
island habitats, many of the animals started to follow different evolutionary paths. Some stayed small, and some may have actually
shrunk. But others responded to their new environment
by getting downright huge. Just look at Deinogalerix, a shrew-like member
of the hedgehog family that’s found only in these Mikrotia fossil deposits. Early species of this genus were about 30
to 45 centimeters long, making them only slightly bigger than a modern European hedgehog. But over time, bigger and badder Deinogalerix
started to evolve alongside them. The largest species–found only in the most
recent deposits–was some 60-centimeters long! And even though it was a member of the hedgehog
family, Deinogalerix had teeth that were more like those of cats and dogs. Using its long, pointy incisors and crushing
cheek teeth, the largest of this genus probably behaved like a badger or raccoon, hunting
much bigger prey than its ancestors ever could. And it did, simply because it could! Back on the mainland, the ancestors of Deinogalerix
needed to stay small in order to avoid all the large predators. But in this island environment, there were
very few large, terrestrial carnivores. So without the selective pressure to remain
small, Deinogalerix was free to expand in size and take advantage of new niches. Its ancestors probably specialized in eating
insects, but this animal could’ve also hunted other, larger prey, like vertebrates. In the process, it emerged as one of the area’s
biggest land-dwelling hunters. This was Foster’s Rule in action! But a big old hedgehog-like thing still had
some competitors–and natural enemies. Because, these islands were also home to some
unusually large birds of prey. Take the giant owl known as Tyto gigantea,
which appeared on Gargano in the Late Miocene. We don’t know for sure which species it
evolved from, but we do know that there was nothing near its size on the mainland. Based on its fossils, scientists think Tyto
gigantea may have had a wingspan of two meters or more — twice the size of a living barn
owl. Likewise, the islands were also home to a
bird of prey known as Garganoaetus, which included two species. The larger one probably rivaled today’s
golden eagle in size, and it’s only found in more recent deposits. So this suggests that Garganoaetus, like the
giant owl, developed a bigger body size over time. But here’s a question: On an island with
few other predators, why would these birds of prey get so large? Wouldn’t that just mean they’d need more
food? Well, some researchers think that on these
islands of giants, both predators and prey were engaged in a sort of evolutionary arms
race. Research has shown that the modern barn owl
can’t swallow any rodents whose heads are longer than 17 millimeters. But by being bigger, these birds would’ve
had an easier time hunting–and gulping down–the local rodents, which were also getting quite
hefty. For example, there’s the burrowing rodent
Mikrotia, the Gargano native that gave this whole group its name. One species of Mikrotia had a skull that was
twice the size of a modern rat’s head, suggesting the rest of the animal was pretty big too. There was also a giant species of dormouse
— which are usually tiny and adorable — but this one weighed about a kilogram….Which
still sounds pretty cute to me! And then there was Gargano’s strange, giant
hamster Hattomys gargantua. It was three times heavier than today’s
common hamster and much bigger than the any species that lived on the mainland at the
time. Mind you, not all of these island animals
expanded in size over time. Small and normal-sized birds and rodents coexisted
with giant species. But some rodents definitely got bigger, either
because they simply could or because it let them expand into new dietary niches. And as they grew, the birds of prey also evolved
larger sizes in order to hunt and eat them. This same phenomenon occurred among other
kinds of birds, too. Take the case of Garganornis, first reported
in 2013. Garganornis belonged to the same family of
birds as ducks and geese. But it weighed between 15 and 22 kilograms,
up to twice as much as a large Canada goose. Unlike modern geese and ducks, its toes and
lower leg bones were really short, suggesting that it spent most of its time walking on
land and not paddling in the water. And judging by the bones in its wings, it
probably couldn’t fly, either. So, researchers think that Garganornis adapted
to take advantage of its island’s lack of big, herbivorous mammals. By growing bigger and staying on land, it
may have been able to broaden its niche and forage on a wider range of terrestrial plants,
while its size could’ve helped it fend off some of those birds of prey. And size adaptations seemed to have benefitted
some larger mammals on the island, too. One herbivore known exclusively from Mikrotia
deposits was the truly strange Hoplitomeryx, a genus of hoofed mammals with saber-like
fangs and five horns on their heads. Five! And there were lots of different species of
this so-called “prongdeer” that varied a lot in size. By one estimate, the smallest only weighed
around 5 to 6 kilograms, while the biggest may have tipped the scales at 113 kilograms. And species of different sizes seem to have
lived at the same time, which kind of makes sense. DIfferent sizes would make different food
sources available to each species. This would’ve not only kept the “prongdeer”
from competing with each other, it could also have prevented from from overgrazing their
little island. But there was a change on the horizon that
none of the weird and beautiful Mikrotia fauna could adapt their way out of. About 5.3 million years ago, a massive amount
of Atlantic water passed through the Strait of Gibraltar–which had once been lifted above
sea level. This flooded the Mediterranean. Rising water levels dramatically shrank the
little giants’ island habitat, which is probably what drove them to extinction. Just a few million years later, in the early
Pleistocene, some areas of central and southern Italy went through a period of tectonic uplift. That reunited Gargano and Scontrone with the
rest of the mainland, where they remain today. So, competition, food availability, predator/prey
relationships, and niche expansion: any or all of these things can, very gradually, make
either pygmies or giants out of animals that are isolated on islands. It’s not mythology! It’s natural history! And we have their fascinating fossil remains
to remind us of the odd little giants that once roamed those ancient Mediterranean islands. Thanks for watching! We want to let you know about a new show from
PBS Digital Studios: Sound Field is a new music education show
from that explores the music theory, production, history and culture behind our favorite songs
and musical styles. Pop, classical, rap, jazz, electronic, folk,
country and more — Sound Field covers it all. Hosted by two supremely talented musicians,
Arthur “LA” Buckner and Nahre Sol, every episode is one part video essay and one part
musical performance. So go subscribe to Sound Field! Link in the description below. Thanks for joining me today in the newly named
Konstantin Haase studio! And extra big thanks to our current Eontologists,
Jake Hart, Jon Ivy, John Davison Ng and STEVE! If you’d like to join them and our other
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Author Since: Mar 11, 2019

  1. busts through wall Country music you say?
    Also for some reason when she said a dormouse weighing a kg, a dormouse the size of a full grown golden retriever popped into my head and now im scared

  2. Foster's Rule or the Island Rule has many exceptions like Sri Lanka elephants and Kodiak bears. Many scientists like Shai Meiri doubt the generality of the Island Rule.

  3. Hoplitomeryx looks like a monster from a fantasy game. Evolution is so weird and fascinating.

  4. They always say, "Strange and bizarre animals or species of that distant past." That's silly. They're only strange and bizarre TO US. Millions of years from now, lions and tigers and giraffes and anteaters and owls and sloths will be "strange and bizarre" to whatever intelligent species may succeed us.

  5. How about if you're going to do this you convert some of your kilograms to pounds and ounces that way old people can keep up

  6. I know it’s cool to use metric but at least half your audience has no clue and I’m not learning now.

  7. This proves adaptation, not evolution. No new information was being added to its dna, instead it was decreased or altered so the animal could survive in it's new environment.

  8. I would love to see this lady host more videos. Her clear pronunciations and tone are so pleasant to listen to 💖

  9. so when animal become giant, its natural environment evolution but when human become giant, it's nephilim? kinda discrimination here.. hmmmmmmm.. ^^

  10. Double the wingspan does not equal "twice the size". If body proportions are the same, double the wing-span means that they're considerably larger than twice the size.

  11. Well I'm not surprised that animals both big and small coexisted there. If there's an enviroment that can support a lot of life, and few predators to pressure the animals, of course they'd diversify as much as they can, filling as much niches as possible.

  12. One island makes you larger. One island makes you small. And the one where you spent your summers doesn't do anything at all. Thanks! 😉 𝓡𝓲𝓴𝓴𝓲 𝓣𝓲𝓴𝓴𝓲.

  13. Evolution's basic rule: Adapt or die. I don't care how.     And you end up cool species like these. It apparently worked for them for some reason, at least for a while anyway.

  14. Even now you can find a Great horned owl which can get to 180cm in wingspan 😀 I've seen one on the road a few years ago which was easily way over 1m and it was huge even tho it wasn't the biggest owl there was in near forests.

  15. Ive watched this video dozens of times, and will probably keep coming back. Videos like this are amazing at explaining evolutionary phenomena like radial adaptation or foster's rule. Thank you for these videos

  16. How about this… all those species were actually that size and only the bigger fossils are found on islands because they are… wait for it… isolated… there can’t be an evolutionary trait to get bigger on an island with less food… that would mean they would adapt to get smaller not the other way around. They need to stop with theories without all the pieces and just focus on logical explanations

  17. There is a great video on "Island biology" by "Trey the explainer" if anyone is interested in a deeper dive into this subject

  18. I am impressed at how well you put these videos together. Also, the detailed research you share in every video!
    Thank you 😊 😎👍

  19. Do mountain lions have nightmares? Because herds of 250lb deer with 5 horns and fangs sounds pretty much like it'd fit the bill.

  20. "Can tinker with animals body plans"💕 I'd like to make some plans to animalisticly tinker with her body☺

  21. Five-horned deer with fangs, waterfowl than can't fly or swim, Owls the size of a hatchback. Go home, Mother Nature, you're drunk.