Essay: Lemurs in Madagascar—Then
The lemurs of Madagascar, the most diverse group of primates in the world, had even more members in their ranks before humans first arrived to the island two millennia ago. There wasPalaeopropithecus ingens, a lemur that hung from branches like a sloth. There was Daubentonia robusta, or an oversize version of the current-day aye-aye—a lemur with long, skeletal fingers, large eyes, and rodentlike teeth. The lumbering Archaeoindris fontoynontii weighed in at 160 kg, the size of a male gorilla. The 45–85 kg Megaladapis edwardsi had a prehensile upper lip to pluck leaves while slowly ascending trees like a koala.
These four species, all larger than current-day lemurs, are now extinct. In fact, about 16 of the perhaps 70 species of wildly diverse lemurs that existed upon human arrival aren’t around anymore. Of the species still living, four top Conservation International’s “World’s 25 Most Endangered Primates” list.
Despite the disappearances of plants and animals on Madagascar, the country remains incredibly rich biologically. Its environments vary from desert to rain forest to shrubby highlands. The country still boasts a huge variety of species, 90 percent of which are found nowhere else. How did Madagascar develop such a range of wildlife? The reasons can be traced back to when Madagascar began to be decidedly its own place, some 160 million years ago.
A Fateful Split
At that time, Madagascar (then attached to India, Australia, and Antarctica) began to split from the supercontinent Gondwanaland. Just before the start of the Late Cretaceous period, 124 million years ago, Madagascar arrived at its present position, separated from Africa by the 770 km wide Gulf of Mozambique. Now the fourth-largest island in the world, it straddles many latitudes. This helps foster its myriad climates and habitats.
This geographic seclusion from other land is one reason why Madagascar is considered a “laboratory of evolution” by researchers like University of Massachusetts paleontologist Laurie Godfrey. The country’s flora and fauna have evolved independently, with little influence from species migrating from adjacent areas. As evidenced by Charles Darwin's discovery of a unique finch for each unique island of the Galapagos chain, physical barriers to interbreeding are key to the development of new species in an area. Such evolutionary isolation of the island of Madagascar would have telling consequences for its lemur populations.
“There is some evidence that there was a single colonizing ancestor of lemurs on Madagascar, long after the island was already separated from Africa and other bodies of land,” says Godfrey. She digs and studies lemurs’ “subfossil” bones—i.e. bones buried too recently to fossilize—to learn which species lived here when. DNA analysis of present-day lemurs suggests that lemurs’ original ancestor lived nearly 70 million years ago, a few million years before the dinosaurs disappeared. No one is certain if this “proto-lemur” negotiated the surrounding waters to arrive on the island or if primates (including lemurs) evolved on the once-connected landmasses from earlier inhabitants. Several theories exist about lemur origins, but molecular studies have repeatedly shown that this ancestor diversified into eight families of lemurs: three extinct and five still alive. Scientists call this evolutionary process “adaptive radiation.” “The idea suggests that high diversity results because animals adapted to different niches, different habitats, and different foods within the same habitat,” says Godfrey.
Coping with Change
Such an ancient adaptive radiation means that the lemurs of Madagascar—both extinct and living—are quite different from one another. Every extinct lemur was larger than the largest living today, the domino-colored, bushy-eared, tailless indri, which is the size of a 7-month-old child. The tiniest lemur, the mouse lemur, is closer in size to its namesake. Some lemurs eat leaves, others fungus, and still others the soil near termite mounds. Many lemurs have odd adaptations that give them a competitive edge, such as the aye-aye’s lengthy fingers, which it uses to pluck woodboring insect larvae. Another instance is the bamboo lemur’s resistance to the cyanide naturally present in its food, bamboo shoots. This allows it to exploit a resource others avoid.
Some scientists argue that lemurs may have evolved in the many ways they did to cope with limited resources on a constantly changing island environment. "Madagascar is a great place to study both natural and human-induced changes in the environment," says Godfrey. "It's a natural experiment, so to speak. We desperately need to understand its dynamics if we are going to conserve the remaining primates not only on Madagascar but also in the rest of the world."
More on the mechanisms of evolution and adaptive radiation.
Conservation International: 25 Most Endangered Primates
Lemurs top the list.
Primate Info Net
NASA Earth Observatory: Burning in Madagascar
A satellite image of the country showing active fires.
More About This Resource...
Our innovative Science Bulletins are an online and exhibition program that offers the public a window into the excitement of scientific discovery. This essay was published in April 2006 as part of the Lemurs of Madagascar: Surviving on an Island of Change Bio Feature.
- It begins by explaining that the lemurs of Madagascar, the most diverse group of primates in the world, had even more members in their ranks before humans first arrived on the island two millennia ago.
- It then takes a look at the biological diversity of Madagascar, which still boasts a huge variety of species, 90 percent of which are found nowhere else.
- The essay concludes by stating that some scientists argue that lemurs may have evolved in the many ways they did to cope with limited resources on a constantly changing island environment.
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Ask students what they know about Madagascar. Where is the island located? What species is it known for?
- Have them read the essay (either online or a printed copy).
- Working individually or in small groups, have students research one of the four extinct species of lemurs mentioned in the article (Palaeopropithecus ingens, Daubentonia robusta, Archaeoindris fontoynontii, egaladapis edwardsi) and report their findings to the class.