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The Living Edens Madagascar-A World Apart Eden Evolution




Isolation and Biodiversity
By Dr. Laurie Godfrey

About 300 miles east of southern Africa, across the Mozambique Channel, lies the island of Madagascar. Best known for its lemurs (primitive relatives of monkeys, apes, and humans), colorful chameleons, stunning orchids, and towering baobab trees, Madagascar is home to some of the world's most unique flora and fauna. Almost all of Madagascar's reptile and amphibian species, half of its birds, and all of its lemurs are endemic to the island; meaning they can be found nowhere else on earth.

4 images: lemur, chameleon, orchid and palm treeMadagascar is unusual not only for its endemic species, but also for the species that are conspicuously absent. Because of Madagascar's geographic isolation, many groups of plants and animals are entirely absent from the island. Some groups are represented only by species very recently introduced by humans. Missing on the island are the many species of large mammals — antelopes, elephants, zebras, camels, giraffes, hyenas, lions and cheetahs — that roam continental Africa today. The only large African mammal that “made it” to Madagascar prior to the arrival of humans several thousand years ago was the hippopotamus. Hippos, similar to those that occupy the Nile River basin today, apparently swam to Madagascar sometime during the Tertiary era. Their descendants underwent dwarfing and evolved into species unique to the island.

This distinctive biodiversity is a result of Madagascar's geographic isolation. Geologists believe that 165 million years ago Madagascar was connected to Africa, but began to drift away from the continent sometime during the next 15 million years. Paleontologists exploring Madagascar's Mesozoic era deposits have found the bones of dinosaurs, early birds and mammals. However, most of the groups of mammals and other terrestrial fauna that are well represented on Madagascar today had not evolved when Madagascar first split from continental Africa.

It is believed that the ancestors of these animals (including at least one species of primitive primates) arrived on this great island after having crossed large expanses of ocean by rafting on floating logs or matted vegetation. The subsequent adaptive radiation of these taxonomic groups is what makes Madagascar so special. The animal and plant life of this great island is largely the result of a natural experiment in evolution on a land apart, but very much “like our own.”

The Arrival of Humans

Majestic Madagascar landscapePeople first came to Madagascar in boats about 2000 years ago. The oldest human-modified bones of extinct species appear in the fossil record at this time. Charcoal “signals,” found in lake sediments, increased dramatically during this period -- indicating an increase in fires. Pollen profiles, read from lake sediment cores, reveal the arrival of introduced plants, including marijuana. Archaeologists believe that Madagascar may have been an important stopping point along a trade route that ran from southeast Asia to east Africa.

The cultural practices of the Malagasy people reflect their mixed Asiatic and African roots. These dual roots are evident in the ceremony of exhuming, rewrapping, and reburying the skeletal remains of revered ancestors; rice paddy agriculture; cattle husbandry; and the Malagasy language itself—spoken by people who live in the interior of Borneo.

Evolving into Oblivion

When humans first arrived on Madagascar, there were at least 50 lemur species living on the island, the largest of which rivaled the body mass of a male gorilla or orangutan. Not one of the 33 lemur species that still survive on the island is as large as the smallest of the lemurs that disappeared from Madagascar during the past several millennia. Along with the giant lemurs, Madagascar was populated by other megafauna that have also since vanished. There were huge tortoises, giant predatory raptors, and pygmy hippopotamuses. There were gigantic flightless birds called elephant birds. These birds were larger than any other birds - living or extinct. They were heavier than the famous 10-foot-tall moas of New Zealand. The eggs of elephant birds could hold the fluid contents of about 180 chicken eggs! There were no cats or Standing lemur with arms spread widedogs on Madagascar; rather there were strange primitive carnivores (mongooses, civets, and cryptoprocts), including one that weighed more than 10 kilograms.

Over the past 2000 years, all of Madagascar's large endemic animals became extinct, and it is estimated that less than 3% of what was once a huge expanse of western deciduous forest exists today.

Madagascar's unusual endemism makes it one of the world's top conservation priorities. But its endemic plants and animals continue to suffer from practices such as slash-and-burn agriculture and the harvesting of woody plants for charcoal and timber. Grasses are often deliberately burned to stimulate the growth of fresh blades to feed the cattle. Wild animals are sometimes also hunted. Because of the tremendous endemicity and wealth of plant and animal species on Madagascar, conservationists believe that forest destruction here may have a greater negative impact on global biodiversity than anywhere else on earth.

Subfossil Finds

Cave, marsh, and stream sites have yielded the bones of animals that lived on the great island prior to colonization by humans and during the past two millennia. These subfossil sites, so-called because the bones are too fresh to have become fossilized, provide some direct evidence of the history of the long and slow decimation of Madagascar's wildlife following the arrival of humans.

Recent explorations of some of these subfossil sites by a team from Duke University (North Carolina) and associated scientists (from the University of Massachusetts, Amherst; the State University of New York at Stony Brook, and the University of Madagascar in Antananarivo) have added enormously to our knowledge of the anatomy and adaptations of Madagascar's paleofauna. These scientists have explored, among other sites, the 110 kilometers of caves at the Ankarana mountains in northern Madagascar, and a pit called Ankilitelo that descends almost 500 feet deep in southwestern Madagascar. The subfossil sites contain the bones of elephant birds, pygmy hippopotamuses, giant tortoises and at least 17 species of extinct lemurs. The oldest radiocarbon-dated bones of extinct lemurs are about 12,000-26,000 years old. The most recent are only 1000-500 years old -- proof that giant lemurs survived human occupation of the island by at least 1,500 years. There is also some circumstantial evidence that pygmy hippos may have been alive as recently as 100 years ago.

Extinct Giants

Fossil studies have concluded that the giant extinct lemurs of Madagascar were an extraordinarily diverse group. There was a giant aye-aye, a relative of the living aye-aye, but three to five times as heavy. Both living and extinct aye-ayes possess an elongated third digit and enormous rodent-like incisors — adaptations for extracting grubs and insect larvae from tunnels in dead wood. The robust extinct aye-aye is the only extinct lemur that clearly belongs to a non-extinct genus.

Lemur exposing teethMegaladapis was an orangutan-sized lemur with teeth very like those of the living sportive lemur (Lepilemur). Unlike the Lepilemur, however, Megaladapis had a long muzzle and widely separated eyes --very uncharacteristic of primates! Its feet were enormous pincer-like grasping devices. Its forelimbs were long and robust. Paleontologists believe that it climbed trees like koalas and subsisted almost entirely on a diet of leaves.

The “Sloth” lemurs, so named because of its remarkable convergences with tree-dwelling sloth of South and Central America, had crania and teeth that suggest a close relationship with some living lemurs (indris, sifakas, and avahis). The largest of the sloth lemurs was the gorilla-sized Archaeoindris, which probably spent a large amount of time on the ground. The most specialized was Palaeopropithecus, a chimpanzee-sized lemur with teeth like those of the sifaka, but bodies like those of arboreal sloths. These upside-down animals had long forelimbs and short hindlimbs, and enormous, hook-like hands and feet.

Advancing the Research

Thanks to the development of the Polymerase Chain Reaction (PCR) techniques, it is now possible to extract ancient DNA from the bones of subfossil lemurs. DNA samples are currently being analyzed in a laboratory at Northwestern University in Chicago. These methods will be used to test hypotheses of evolutionary relationship that were derived from the analysis of the skeletal morphology of extant and extinct lemurs.

Dr. Laurie Godfrey has been involved with paleontological fieldwork in Madagascar since the mid-1980's. She received her PhD in biological anthropology at Harvard University in 1977, and currently teaches anthropology at the University of Massachesetts in Amherst.

 



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