When Giant Lemurs Ruled Madagascar

I'm so excited to be the person to announce this... Eons Enamel Pins are now available! Get yours at DFTBA.com!! Just a few thousand years ago, the island of Madagascar was inhabited by

giant

s. Giants…

lemurs

. These extraordinary primates lived only in Madagascar and were part of an evolutionary event that continues to this day: a radiation that saw primates adapt to fill ecological niches that, elsewhere, were occupied by totally different animals, such as sloths, monkeys and even woodpeckers. There were 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 specialized in eating leaves and had grasping, pincer-like legs that kept their large bodies in trees.

But perhaps the strangest of these extinct

giant

s were the sloth lemurs. This family included Archaeoindris, the largest lemur that ever lived, and most of its members appeared to have adaptations for hanging from tree branches, as sloths do today. What all of these strange creatures had in common was their large body size: they probably ranged from the size of a large terrier to almost the size of an adult male gorilla. But today everyone is gone. Its 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 Madagascar's unique environments?

And how were they eliminated, leaving behind only their smaller relatives? As for this last question, the answer could lie in the arrival of a different type of primate to the island: us. Madagascar has been separated from all other land masses since the Late Cretaceous period, about 85 million years ago. And fossils dating from the time after it separated from the Indian subcontinent include some cool dinosaurs, like Majungasaurus, and strange early mammals, like the cute little Vintana. But Madagascar's fossil record stops abruptly at the beginning of the Cenozoic Era, about 66 million years ago. There are almost no fossils in Madagascar from that entire time period, up to about 26,000 years ago, making the early evolution of the few groups of mammals that arrived on the island somewhat mysterious.

But, based on genetic studies, we're pretty sure that the ancestors of modern lemurs arrived there after it had already become an island. The most accepted estimate says that lemurs arrived in Madagascar between 50 and 60 million years ago. So how did those first lemurs get there? Experts think they probably... floated. That's how it is! Some paleontologists have suggested that lemurs navigated rafts on large mats of vegetation or perhaps inside hollow trees that were washed across the Mozambique Channel, a current distance of more than 400 kilometers. This type of movement is called a “draw dispersal,” a rare or chance event in which an animal is able to cross a fairly extreme barrier.

And we've talked about this phenomenon before! Most scientists believe that rodents came from Africa to South America through a similar ocean crossing. Those ancestors of seafaring lemurs were probably very small, like modern mice and dwarf lemurs, and may have also behaved like them: sleeping all day in small groups inside hollow trees. And it has also been suggested that they might have entered a state of torpor or hibernation, as modern mice and dwarf lemurs do. This would have helped them survive a long-distance journey and be ready to colonize Madagascar. At least, that is the most accepted explanation for how the lemurs arrived on the island.

But some experts believe the lemurs could have made two trips. This is based on the study of two fossil species, one from Kenya and one from Egypt, dating back to long after the first lemurs were supposed to have arrived in Madagascar. And these two fossils bear some resemblance to the aye-aye, the strangest and oldest branch of the family tree of all living lemurs. So perhaps aye-ayes made a trip to Madagascar separate from that of all the other lemurs. We just don't know enough yet to know for sure. Regardless of how the lemurs got to the island, once they landed there, they took over in what is called adaptive radiation.

Over the last 50 to 60 million years, they diversified into eight different families, five of which still have living members, and filled an enormous variety of ecological niches. For example, let's take the aye-aye. Today, it is the only remaining species in its family and serves the same basic ecological function as... a woodpecker! It uses its extra-long, creepy third finger to tap trees and find insect larvae. It then chews a hole in the bark with its rodent-like incisors, sticks its thin finger into the hole, and pulls out the larvae. 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 probably used the same type of foraging behavior, tapping on tree trunks in search of insects, much like a woodpecker. And while the lemurs managed to fill the many vacant niches on the island, they also shaped its ecosystems. Living ruffed lemurs specialize in eating fruits. That is why they play an important ecological role as seed dispersers. They help plants move their seeds from one place to another by eating their fruits and dropping the seeds in new places as they move through the forest. And gorged lemurs can swallow seeds more than 30 millimeters in diameter, larger than a US quarter!

But there are trees in Madagascar that produce fruits with even larger seeds. And in the past, there was a giant relative of ruffed lemurs called Pachylemur that might have helped disperse those seeds. We know it was a fruit specialist, like its living relatives, from the wear pattern of its teeth. And at about three or four times the size of living ruffed lemurs, it could have easily acquired those really big seeds. But there were also less friendly interactions between the plants and animals of Madagascar that have left their mark on the island's plant life to this day.

In the south and southwest of Madagascar, there is an incredibly unique ecoregion called the thorn forest. The vast majority of plants are only found on the island and are adapted to warm temperatures and short rainy seasons. They are also, as their name suggests, completely covered in thick, sharp thorns. Which is strange, because their relatives on the African continent don't have thorns. Therefore, researchers have hypothesized that the thorns of these tree species are an adaptation to defend their leaves from climbing and leaf-eating animals not found on the continent, namely lemurs. To test this hypothesis, the researchers compared the levels of carbon and nitrogen isotopes in the bones of extinct lemurs with the levels observed in thorn forest plants.

This method is based on the idea that you are what you eat: the elements found in the foods you eat are incorporated into your tissues. And they discovered that those isotope levels matched! It seems that one of the extinct monkey lemurs and one of the extinct sloth lemurs probably ate many thorn forest plants! But since most living lemurs generally no longer eat those plants, it seems those spines have become an evolutionary anachronism, a trait that co-evolved with species that no longer exist. So what happened to all the giant primates? After thriving in Madagascar for millions of years, what ended his reign?

Well, in the late Pleistocene, the climate was changing rapidly and becoming more variable. From about 9,000 to 5,000 years ago, the island's climate ranged between being much wetter than Madagascar is today and also much drier, with droughts sometimes lasting up to 300 years. Between 4,000 and 2,500 years ago, the climate continued to become drier, changing vegetation and ecosystems across Madagascar. And then, perhaps about 2,300 years ago, a new primate arrived on the island that would change everything: humans. There is some controversy over

when

exactly that happened, because the initial archaeological record of the island is incomplete. But the giant lemurs were still alive

when

people appeared.

And it looks 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 appear to be around 2,000 years old. But those bones were collected in the early 20th century 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 were also found in the early 20th century, and were rediscovered in a museum collection in the 1980s. They cannot be radiometrically dated, but there is no doubt that humans modified these teeth.

We just don't know when. What we do know is that many of the giant lemurs became extinct about 1,000 years ago, along with other island megafauna such as pygmy hippos and elephant birds. It seems that lemurs were able to coexist with the first human inhabitants of Madagascar, at least for a time. This is also when we start to see an increase in carbon in the island's sediment record. That charcoal suggests a greater human impact on the landscape, as people started fires to clear the land and promote the growth of grass for livestock to feed on. The last known remains of a giant lemur, one of the sloth lemurs, date back to just 500 years ago.

While we can't definitively say that human hunting was responsible for their extinction, it is clear that the extinction was selective: all the large animals in lemurs are gone. It could also be because they were easier to hunt than their smaller relatives. It could be because larger animals need more space, making them more vulnerable to habitat loss and fragmentation. Or it could be because they tend to reproduce more slowly than smaller species. It was probably a combination of all of these. Investigators are still working to find out exactly what happened. They are finding new remains, including some from underwater caves.

They are rediscovering ancient material in museums. And they are examining the DNA of ancient, living lemurs to try to piece together the end of the story. And although the giants are gone, the ecosystems they shaped (and the lemurs we still find today) are reminders of that time when the giants

ruled

Madagascar. A big shout out to this month's eontologists: Patrick Seifert, Jake Hart, Jon Davison Ng, and Steve. To become Eonite, pledge your support at patreon.com/eons! And thanks for joining me at the Konstantin Haase Studio. If you like what we do here, subscribe at youtube.com/eons.