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Just a few thousand years ago, the island
of Madagascar was inhabited by giants.
Giant … lemurs.
These remarkable primates lived only on Madagascar,
and they were part of an evolutionary event
that continues to this day - a radiation that
saw primates adapt to fill the ecological
niches that, in other places, were occupied
by totally different animals -- like sloths,
monkeys, and even woodpeckers.
There were the so-called monkey lemurs, named
for their skeletal similarities to baboons.
There were three species of koala lemurs,
which of course were not koalas, but they
specialized in eating leaves and had grasping,
pincer-like feet that kept their large bodies
in the trees.
But maybe the weirdest of these extinct giants
were the sloth lemurs.
This family included Archaeoindris, the biggest
lemur that ever lived, and most of its members
seemed to have adaptations for hanging from
tree branches, like sloths do today.
What all these strange creatures had in common
was their large body size: they likely ranged
from the size of a large terrier to almost
as big as an adult male gorilla.
But today, they’re all gone.
Their largest living relative is the modestly
sized indri.
So what happened here?
How did such a diverse group of primates evolve
in the first place, and how did they help
shape the unique environments of Madagascar?
And how did they get winnowed down, leaving
only their smaller relatives behind?
As far as that last question goes, the answer
might lie in the arrival of another, different
type of primate on the island: us.
Madagascar has been separated from all other
land masses since the Late Cretaceous Period,
about 85 million years ago.
And the fossils that date to the time after
its split from the Indian subcontinent include
some very cool dinosaurs, like Majungasaurus,
and weird early mammals, like the cute little
Vintana.
But the fossil record of Madagascar stops
abruptly at the beginning of the Cenozoic
Era, about 66 million years ago.
There are almost no fossils on Madagascar
from that whole stretch of time, until about
26,000 years ago, which makes the early evolution
of the few mammal groups that got to the island
kind of mysterious.
But, based on genetic studies, we’re pretty
sure that the ancestors of modern lemurs made
it there after it had already become an island.
The most widely-accepted estimate says that
lemurs arrived on Madagascar between 50 million
and 60 million years ago.
So, how did those first lemurs get there?
Experts think they probably ... floated.
That’s right!
Some paleontologists have suggested the lemurs
rafted over on large mats of vegetation or
maybe inside hollow trees that washed out
across the Mozambique Channel - a distance
today of more than 400 kilometers.
This kind of movement is called a “sweepstakes
dispersal” - a rare or chance event where
an animal is able to cross a pretty extreme
barrier.
And we’ve talked about this phenomenon before!
Most scientists think rodents got from Africa
to South America by way of a similar ocean
crossing.
Those seafaring lemur ancestors were probably
very small, like modern mouse and dwarf lemurs,
and they might’ve behaved like them, too
- sleeping the day away in small groups inside
hollow trees.
And it’s also been suggested that they could’ve
been able to enter a state of torpor or hibernation,
again like modern mouse and dwarf lemurs do.
This would’ve helped them survive a long-distance
trip and emerge ready to colonize Madagascar.
At least, that’s how the most widely-accepted
explanation for how lemurs got to the island.
But some experts think that lemurs might actually
have taken two trips.
This is based on the study of two fossil species,
one from Kenya and one from Egypt, that date
to well after the earliest lemurs were supposed
to have made it to Madagascar.
And these two fossils bear some resemblance
to the aye-aye, the weirdest and earliest
branch off the family tree of all living lemurs.
So maybe aye-ayes took a separate trip to
Madagascar from all the other lemurs.
We just don’t know enough yet to be sure.
However lemurs got to the island, once they
landed there, they took over in what’s called
an adaptive radiation.
Over the last 50 to 60 million years, they
diversified into eight different families,
five of which still have living members, and
they filled a huge variety of ecological niches.
For example, take the aye-aye.
Today, it’s the only species left in its
family, and it fills the same basic ecological
role as … a woodpecker!
It uses its extra-long, extra-creepy third
finger to tap on trees to find insect larvae.
Then it chews a hole into the bark with its
rodent-like incisors, sticks that skinny finger
into the hole and pull out grubs.
But in the past there was a giant aye-aye.
It weighed up to seven times more than the
modern aye-aye.
And it lived in the dry forests of southwestern
Madagascar, where it likely used the same
kind of foraging behavior, tapping tree trunks
in search of insects, much like a woodpecker.
And while lemurs have managed to fill the
many vacant niches on the island, they also
shaped its ecosystems.
Living ruffed lemurs specialize in eating
fruit.
So they play an important ecological role
as seed dispersers.
They help plants move their seeds from place
to place by eating their fruits and dropping
the seeds in new places as they move through
the forest.
And ruffed lemurs can swallow seeds that are
more than 30 millimeters around -- bigger
than an American quarter!
But there are trees on Madagascar that produce
fruits with even bigger seeds.
And in the past, there was a giant relative
of the ruffed lemurs called Pachylemur that
might’ve helped disperse those seeds.
We know it was a fruit-specialist, like its
living relatives, because of the pattern of
wear on its teeth.
And at about three or four times the size
of living ruffed lemurs, it could’ve easily
taken on those really big seeds.
But there were also less-friendly interactions
taking place between Madagascar’s plants
and animals that have left their mark on the
island’s plant life to this day.
In southern and southwestern Madagascar, there’s
an incredibly unique ecoregion called the
spiny forest.
The vast majority of the plants there are
only found on the island, and they’re adapted
to hot temperatures and short rainy seasons.
They’re also, as the name suggests, totally
covered in sharp, thick thorns.
Which is strange, because their relatives
on the African mainland don’t have thorns.
So researchers have hypothesized that the
thorns of these tree species are an adaptation
for defending its leaves from climbing, leaf-eating
animals that aren’t found on the mainland
- namely, lemurs.
To test this hypothesis, researchers have
compared carbon and nitrogen isotope levels
from the bones of extinct lemurs to the levels
seen in the plants of the spiny forest.
This method is based on the idea that you
are what you eat - the elements found in the
food you eat are incorporated into your tissues.
And they found that those isotope levels matched!
So it looks like one of the extinct monkey
lemurs and one of the extinct sloth lemurs
probably ate a lot of the plants of the spiny
forest!
But since most living lemurs generally don’t
eat those plants anymore, it seems that those
thorns have become an evolutionary anachronism
- a trait that coevolved with species that
no longer exist.
So, what happened to all the giant primates?
After thriving on Madagascar for millions
of years, what put an end to their reign?
Well, in the Late Pleistocene Epoch, the climate
was changing rapidly and becoming more variable.
From around 9000 to 5000 years ago, the island’s
climate swung back and forth between being
much wetter than Madagascar is today and also
much drier, with droughts sometimes lasting
up to 300 years.
Between 4000 and 2500 years ago, the climate
continued to become drier, changing vegetation
and ecosystems throughout Madagascar.
And then, maybe around 2300 years ago, a new
primate arrived on the island that would change
everything: humans.
There’s some controversy about when exactly
that happened, because the early archaeological
record of the island is incomplete.
But the giant lemurs were still alive when
people showed up.
And it seems like we might have hunted them.
There are cut-marked bones of two species
of extinct giant lemur from two sites in southwestern
Madagascar that seem to be around 2000 years
old.
But those bones were collected in the early
1900s, and we don’t have a very good record
of their context, so some researchers have
argued against this as evidence of butchery.
However!
Some incisors of a giant aye-aye with holes
drilled through them were also found in the
early 1900s, and were rediscovered in a museum
collection in the 1980s.
They can’t be radiometrically dated, but
there’s no question that humans modified
these teeth.
We just don’t know when.
What we do know is that many of the giant
lemurs went extinct around 1000 years ago,
along with other megafauna on the island,
like pygmy hippos and elephant birds.
So it seems the lemurs were able to coexist
with the early human inhabitants of Madagascar,
at least for a while.
This is also when we start to see an increase
in charcoal in the sediment record of the
island.
That charcoal suggests a greater human impact
on the landscape, as people started fires
to clear land and promote the growth of grass
for cattle to feed on.
The last known remains of a giant lemur - one
of the sloth lemurs - date back just 500ish years
ago
While we can’t definitively say that human
hunting was responsible for their extinction,
it’s clear that the extinction was selective:
all the large-bodied lemurs are gone.
It might also be because they were more easily
hunted than their smaller relatives.
It might be because larger animals need more
space, so they’re more vulnerable to habitat
loss and fragmentation.
Or it might be because they tend to reproduce
more slowly than smaller species.
It was probably some combination of all of
these.
Researchers are still working on figuring
out exactly what happened.
They’re finding new remains, including some
from underwater caves.
They’re rediscovering old material in museums.
And they’re examining DNA from both ancient
and living lemurs to try to piece together
the end of the story.
And while the giants are gone, the ecosystems
that they shaped -- and the lemurs that we
still find today -- are reminders of that
time when giants ruled Madagascar.
Big high fives to this month’s Eontologists:
Patrick Seifert, Jake Hart, Jon Davison Ng,
and Steve!
To become an Eonite, go pledge your support
patreon.com/eons!
And thanks for joining me in the Konstantin
Haase Studio.
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