Written and Illustrated by Talia Felgenhauer, 2023-24 Undergraduate Fellow in Communications. Originally published in LEMURS Magazine: The “Why” Issue in February 2024.
Madagascar is an island like no other. Located hundreds of miles off the southeastern coast of Africa, Madagascar has been isolated for more than 80 million years, changing and evolving independently from the rest of the world. Today, the island is famed for its extraordinary biodiversity and distinctive flora and fauna, with more than 85% of its species found nowhere else on Earth.
The island of Madagascar is a natural laboratory for evolutionary experiments. Through isolation and ecological opportunity, Madagascar has shaped the unique evolution of thousands of species. “While smaller islands tend to have more uniform ecosystems, Madagascar is big enough that it has variation,” explains Matt Borths, Ph.D., a paleontologist and Curator of the DLC’s Museum of Natural History.
The fourth largest island in the world, Madagascar stretches the length of the entire western coast of the United States. Its sheer size, plus its varied topography and four regional climates, creates such a vast array of habitats for animals and plants that Madagascar is often called the “Eighth Continent.”
“Every region of the island is different,” says Charlie Welch, who oversees the DLC’s conservation programs on the island. “You run the gamut from the spiny desert in the south, which of course is very dry, to the rainforest in the east, which gets nearly three meters of rain annually.” Because each region has its own ecological opportunities and niches to fill, species spread out and adapt to fit their very different surroundings.
“There is an explosion in biodiversity that’s triggered by the amount of variation in ecosystems across the island.” –Matt Borths, Ph.D.
“What really makes Madagascar unique is that it’s been an isolated island for so many millions of years,” says Charlie. Madagascar broke from Africa 165 million years ago and India 80 million years ago and has stood alone ever since.
Over the course of its long isolation, a small number of species made it to the island, most flying, swimming, or rafting across the Mozambique Channel from mainland Africa. For those that survived the trip, Madagascar was a whole new world. With less competition for resources, new niches to fill, and almost no genetic influx from the rest of the world, species diversified and life evolved in new directions.
It was as difficult to leave the island as it was to arrive. Species were marooned there, spending millions of years evolving their own unique characteristics. Today, more than 85% of the mammals, reptiles, amphibians, and plants of Madagascar are found nowhere else on Earth.
“You get this whole array of plants and animals that exist nowhere else in the world. That’s incredibly special.” –Charlie Welch
In addition to this extreme endemism, Madagascar has one of the highest numbers of endangered species in any country, making this biodiversity hotspot a top priority for conservation.
Because constraints on an island can be different from those of a continent, islands can push and pull evolution in new directions. “In most ecosystems you would say ‘here are the rules, here is what this animal is capable of evolving into,’” says Matt. “But on islands, animals can really break the mold.” Size is one way island animals may differ from their mainland relatives. Over time, islands may shrink a big animal lineage, or enlarge a small one.
GIANT JUMPING RAT (Critically Endangered, Hypogeomys antimena)
Giant jumping rats are the largest endemic rodents on Madagascar. With long ears and powerful back legs, they have adaptations like a rabbit’s, an animal that was absent from Madagascar before humans introduced them to the island. Jumping rats’ swiveling ears allow them to hear approaching predators, and if threatened, they can hop over three feet to evade danger.
SMALL TO BIG: Insular Gigantism
On continents, small animals use their size to hide from predators. But on islands, which are difficult for most species to reach, there may be fewer predators on the prowl. With less predation and less competition for resources, the benefits of having a larger body may outweigh the benefits of a smaller one. Over time, small species isolated on islands may evolve to be much larger than their mainland counterparts. Caption pointing to giant jumping rat: Larger bodies can store more food and lose less heat.
MALAGASY PYGMY HIPPOPOTAMUS (Extinct, Hippopotamus laloumena, H. lemerlei, H. madagascariensis)
The Malagasy pygmy hippopotamus was far smaller than its mainland African cousin, the common hippo (Hippopotamus amphibius). Whereas the common hippo can weigh 9,000 pounds and is one of Earth’s largest living mammals, the Malagasy pygmy hippo was approximately the size of a large pig. Even so, it still weighed hundreds of pounds and was one of the larger animals on the island.
Unlike common hippos that graze on open grass, Madagascar’s pygmy hippos preferred browsing on sedges and leaves in the island’s wet, forested landscapes.
Like other large animals on Madagascar, pygmy hippos went extinct within the last 1,000 years. In the subsistence shift hypothesis, paleontologist Laurie Godfrey, Ph.D., and an international team of colleagues suggest that the island’s “megafaunal crash” between 700-1,000 CE was due to people’s transition from hunting/gathering to forming permanent communities and raising domestic animals and crops. Clearing the forest to plant rice and create grazing land for herds of cattle severely modified or destroyed the animals’ habitats, and their populations crashed and never recovered.
BIG TO SMALL: Insular Dwarfism
By definition, islands are smaller than continents and thus have fewer resources. A large animal needs a large amount of resources to sustain a healthy population, and islands are not always big enough to provide that. When a large species is marooned on a smaller land mass, it can be beneficial to evolve a smaller body size that better fits the constraints of the island’s resources.
Caption pointing to pygmy hippo: Smaller bodies need less space and fewer resources.
BOXED FEATURE: What Is a Subfossil?
Subfossils are animal remains that are less than 10,000 years old. This means they often represent species that went extinct very recently. There are even subfossils of species that are still around today. In Madagascar, much of what we know about the biodiversity of the island is represented by subfossils. Older fossils (remains of life over 10,000 years old) are mostly from much more ancient time periods.
Subfossils are often found in caves. “Caves act as time capsules, and even though they contain only relatively recent material, we find some really spectacular animals,” Matt says. “We find everything from giant lemurs to pygmy hippos.”
Because the animals found went extinct so recently, they are especially interesting for conservation reasons. “The factors that led to extinction in Madagascar are acting all over the world. With subfossils, we can learn about extinctions of the past to prevent extinctions of the future,” says Matt.
Between 55 and 25 million years ago, the ancestor of aye-ayes and the ancestor of all other lemurs were blown out to sea, likely in two distinct colonization events, drifting across the Mozambique Channel from mainland Africa and eventually landing on the island of Madagascar. When these ancestors arrived, Madagascar had no other tree-dwelling mammals.
“Very few mammal species initially made it to Madagascar, so there was more time for the lucky few that did arrive to fill ecological roles that wouldn’t ordinarily belong to them,” says Matt.
Lemurs were part of this “lucky few.” As some of the first mammals to arrive on the island (it’s possible that tenrecs and some bat lineages were present first), these early primates had few predators and little competition for resources. They diversified and spread across Madagascar, developing different strategies for survival based on geographic region, available resources, and competition.
“Because of the pressures and opportunities of the island, the primates that managed to get to Madagascar are completely different than those left on the African continent,” says Charlie. “This teaches us what evolution is capable of.”
“Ancestral lemurs had an extremely basic body plan, and from that plan you can get all sorts of creatures,” Matt adds.
From the gorilla-sized Megaladapis to the 1.2-ounce Madame Berthe’s mouse lemur, species evolved to fill a staggering variety of ecological niches. Currently there are more than 100 different species of lemur, in addition to at least 17 species that have already gone extinct.
Today, lemurs are the most endangered group of vertebrates on Earth. They also constitute one-fifth of the world’s primate species, giving Madagascar the highest primate diversity in the world for its size. These factors make Madagascar and its lemurs urgent priorities for research and conservation.
Rafting Graphic:
1. A raft of vegetation breaks away from the coast of Africa, likely dislodged by a severe storm.
2. Lemur ancestors are carried across the Mozambique Channel, possibly surviving the journey by hibernating.
3. The raft arrives on the coast of Madagascar, where the “shipwrecked” primates evolve into today’s lemurs.
GOLDEN BAMBOO LEMUR (Critically Endangered, Hapalemur aureus)
Golden bamboo lemurs are specially adapted to eat the cyanide-rich shoots of giant bamboo (Cathariostachys madagascariensis), which comprises as much as 90% of their diet. By evolving to eat toxic bamboo that few other animals can eat, these lemurs reduced competition and gained an abundant food source.
Lemurs did not stop specializing there: Even amongst the bamboo lemurs, different species eat different parts of the bamboo plant. The greater bamboo lemur (Prolemur simus) uses its powerful bite to rip through the woody husks of mature bamboo stalks, whereas the golden bamboo lemur eats the tender shoots, which have a higher concentration of cyanide than mature stalks do.
While these extremely specialized diets help bamboo lemurs avoid competition, they are also limiting. Bamboo lemurs occupy such specialized niches that it is difficult for them to survive in a changing environment, making them one of the more critically endangered genera of lemurs.
AYE-AYE (Endangered, Daubentonia madagascariensis; Extinct, Daubentonia robusta)
There are no woodpeckers on Madagascar; instead, the aye-aye exploits this grub-eating niche. This bizarre-looking nocturnal primate has developed a series of adaptations, unique among lemurs, that makes it a gold medal-worthy percussive forager.
HOW DOES THE AYE-AYE HUNT?
1. The aye-aye, with the largest ear-to-body-size ratio of any primate, cups its ears downward toward a tree branch or rotting log.
2. The aye-aye drums its skinny “tapping finger” rapidly against the wood, listening for hollow spots that may indicate the presence of insect tunnels below.
3. Once a hollow spot is located, the aye-aye uses its rodent-like front teeth to gnaw a small hole into the wood.
4. The aye-aye inserts its hyper-mobile tapping finger into the hole, searching for insect larvae.
5. The aye-aye hooks a larva with its claw, extracts it from the hole, and enjoys a juicy snack!
PALAEOPROPITHECUS (Extinct, Palaeopropithecus ingens, P. maximus, P. kelyus)
Palaeopropithecus, which survived until ~ 550 years ago and could weigh more than 100 pounds, was a lemur built for life upside down. With long limbs and hook-like hands, it was probably awkward on the forest floor and instead lived suspended in the trees. These adaptations and lifestyle are similar to those of arboreal sloths, earning them the nickname “sloth lemurs.”
Madagascar’s giants, including sloth lemurs, played a key role in seed dispersal. Plant seeds are often covered in sweet-tasting pulp, enticing lemurs and other seed dispersers to seek and gulp them down. As giant lemurs roamed through the forest, they passed the large seeds of their favorite fruits with their feces, germinating future generations of fruiting trees. Large burs (prickly seed pods) also embedded in their fur.
“Big animals can carry big seeds in their guts or on their fur and not be bothered by them,” says Matt. “A small animal, on the other hand, will eat around large seeds and therefore not transport them very far from the parent plant. Or if a big bur latches on, a small creature will notice and brush it off quickly. So the extinct giants of Madagascar probably helped move seeds all over the landscape, diversifying the forest for other creatures.”
MEGALADAPIS (Extinct, Megaladapis edwardsi, M. grandidieri, M. madagascariensis)
Megaladapis was a gigantic, gorilla-sized lemur that specialized in eating leaves. Folivores (animals that feed on leaves) are able to exploit one of the most abundant resources in the forest. With the help of their specialized teeth and digestive systems, these lemurs unlock nutrients that are difficult for other animals to access.
Megaladapis may have had a leaf-eating adaptation that is not seen in living lemurs: a prehensile snout. This flexible nose and upper lip may have helped Megaladapis grasp the large quantity of leaves required to fuel such a large-bodied animal.
Megaladapis and the other giant lemurs are extinct, but just barely. “As far as we can tell, Megaladapis only went extinct in the past 800 years,” says Matt. “There were people building castles in Europe as Megaladapis stomped around Madagascar.”
INDRI (Critically Endangered, Indri indri)
Today, the 20-pound indris the largest surviving species of lemur. The indri is found in only a small sliver of eastern rainforest, where its unearthly, wailing song can be heard for over a mile. As primatologist Allison Jolly said, “Indri sing the song of the forest as whales sing the song of the sea.”
Like many lemur species, the indri is unable to survive within human care. Once the indri is gone from Madagascar’s forests, it is gone forever.
ELEPHANT BIRDS (Extinct, Aepyornis hildebrandti, A. maximus, Mullerornis modestus)
Madagascar was once home to the largest birds ever known. The island harbored several species of ratites called elephant birds until they became extinct around 1,000 years ago. The largest, Aepyornis maximus, stood 10 feet tall and weighed nearly a ton.
Ratites are big, flightless birds with powerful legs and no keel on their breastbone. (The keel is a raised area where wing muscles would normally attach.) All ratites probably trace their ancestry back to a flying relative, with each lineage independently losing the ability to fly.
The name “elephant bird” was inspired by Marco Polo’s stories of a bird so large it could prey on an elephant. The myth of the roc, the colossal bird that swooped up Sinbad the Sailor, may also have originated with elephant birds and their giant eggs.
Like other ratites, elephant birds were incapable of flight. “Lots of people wish they could fly like a bird, but, given the chance, birds love to lose their wings so they can just walk on the ground,” says Matt. “This is probably because maintaining all that flying muscle and specialized feathers takes a lot of energy. If birds don’t need to fly, natural selection reduces those structures.”
On islands, plenty of food and a relative lack of predators can eliminate a bird’s need for flight. “Flightlessness is especially common on islands where there are fewer creatures raiding nests,” Matt explains. “Dodos were giant flightless pigeons. Hawaii once had a giant flightless duck. And Madagascar had its elephant birds.”
Caption: One elephant bird egg could contain two gallons of liquid, the equivalent of 160 chicken eggs! Unlike chickens, however, an elephant bird probably laid only one or two eggs per year.
FOSSA (Vulnerable, Cryptoprocta ferox; Extinct, Cryptoprocta spelea)
The fossa (pronounced “foo-sa” or “foosh”) is Madagascar’s largest carnivorous mammal.
“On mainland Africa, the ancestors of the fossa would have been mid-tier carnivores,” says Matt. “They would’ve been outranked by, or competing with, hyaenodonts and the ancient relatives of modern dogs, cats, and hyenas.” But when the fossa’s ancestors arrived on Madagascar 20 million years ago, there were no other large carnivores on the island; so fossas evolved to become the island’s apex predators.
Although it looks like a wild cat, the fossa is most closely related to mongooses. It is a superb hunter, with retractable claws and swiveling ankle joints that enable it to run and leap nimbly through branches—even race down tree trunks headfirst! Meanwhile, the fossa’s three-foot-long tail acts as a counterweight, keeping the animal balanced even in the most precarious positions.
Fossas are opportunistic hunters, and their diet consists of 500+ vertebrate species found in the humid forests where the fossa makes its home. But the fossa specializes in hunting lemurs, which comprise 50% of its diet. When giant lemurs roamed Madagascar, the giant fossa was there to prey on them.
Although both fossa species looked nearly identical, C. spelea was larger and more powerful than C. ferox and may have weighed as much as 44 pounds. The giant fossa most likely went extinct due to habitat loss, and the decline of the giant lemurs it preyed on. The 11- to 22-pound C. ferox continues to face the same troubles today.
Caption: Although many of the fossa’s characteristics appear cat-like, fossas are not related to cat species at all. This is a perfect example of convergent evolution, in which similar traits evolve in unrelated species based on environmental pressures.
PATTERNS OF EXTINCTION
It takes a lot to sustain large animals. They need more food, water, and shelter. Because of the space needed to find enough food or meet mates, large animals also require more space and have larger home ranges than most small animals do.
Large animals often face the additional challenge of subsistence hunting. With big, slower-moving bodies, they make easier targets and can feed more people.
Many of Madagascar’s giants have already gone extinct. The largest surviving lemur, the indri, is critically endangered due to the same pressures faced by its extinct or endangered kin: habitat loss due to deforestation and climate change, and hunting pressure from humans.
TENRECS (30+ species within the family Tenrecidae. Conservation status ranges from Least Concern to Endangered)
This is no hedgehog! Although both have spines and can roll into spiky balls, these animals evolved completely independently. In fact, hedgehog tenrecs are more closely related to elephants than to hedgehogs! So why do they look alike? Sharp spines are an effective defense against predators—so effective, in fact, that they have evolved multiple times on unrelated animals. This is called convergent evolution.
For some tenrecs, spines serve an additional purpose. The lowland streaked tenrec can rub its spines together to produce high-pitched squeaks used to communicate with other tenrecs. This is called stridulation, and tenrecs are the only mammals known to be capable of it.
When tenrecs made landfall on Madagascar between 42 and 25 million years ago, they left behind the packed ecosystems of Africa. In their new world of reduced competition and predation, they diversified into more than 30 species.
Like lemurs, tenrecs are a superb example of adaptive radiation. “It’s probably the most classic adaptive radiation I’ve seen in my life,” says tenrec researcher PJ Stephenson, Ph.D., quoted in David Quammen’s The Song of the Dodo. “You’ve got ancestral stock, it arrives on the island, finds all the niches available. Evolution takes its course. And it adapts to fill all the niches… You’ve got shrews, you’ve got hedgehogs, you’ve got moles. You’ve got things you can’t possibly describe. It’s unbelievable.”
“THE PREDICTED ONE”
IN 1862, Charles Darwin received a specimen from a colleague. It was a white, star-shaped flower from Madagascar that would later be named “Darwin’s orchid” (Angraecum sesquipedale). The orchid had an unusual adaptation: a nectar tube measuring almost 12 inches long. Darwin exclaimed to a friend, “Good heavens, what insect can suck this!” He then hypothesized the existence of a moth with a tongue so long that it could suck nectar from the very bottom of the tube.
Fellow naturalist Alfred Russel Wallace agreed. He was so sure of the moth’s existence that he wrote, “Naturalists who visit that island (Madagascar) should search for it with as much confidence as astronomers searched for the planet Neptune—and they will be equally successful.”
Darwin and Wallace were proven right with the discovery of Wallace’s sphinx moth, christened Xanthopan praedicta (“the predicted one”). At nearly one foot in length, the proboscis of Wallace’s sphinx moth is the longest of any insect.
Darwin, although he did not live to see the moth discovered, believed that the moth and the orchid had evolved together over time in a process now known as escalatory coevolution. As generations of the orchid evolved longer nectar tubes, the moths would evolve longer tongues. The moth had less competition for food as no other pollinators could reach the orchid’s nectar, and the orchid had a higher chance of pollination because the moth was likely to visit more of the same species.
