Newfound Island Graveyard May Yield Clues to Dodo Life of Long Ago
Everyone knows about the death of the dodo, but no one knows much about its life.
The stocky flightless bird became extinct at the end of the 1600's, less than two centuries after European explorers discovered its home, the Indian Ocean island of Mauritius. Beyond passing descriptions, little evidence of the bird has survived — a preserved skin here, an isolated leg bone there.
Over the last few weeks, however, a team of scientists has been exploring a trove of dodo fossils that may be as old as 3,000 years. Along with the dodos, the scientists have found fossils of other species of birds, reptiles, bats and numerous plants.
"You name it, we've got it," Kenneth Rijsdijk, the team's leader and a physical geographer at the Geological Survey of the Netherlands, said in a phone interview. "We've found the whole ecosystem."
The scientists expect the site to offer the first clear picture of the dodo's ecological world before humans arrived. It may allow them to better understand how dodos and many other species became extinct.
The origins of the dodo are mysterious. Studies on its DNA indicate that it descended from pigeons. The dodo's closest relative was the solitaire, another extinct flightless bird that lived only on the nearby island of Rodrigues.
The dodo and the solitaire share a common ancestor that the scientists estimate lived 25 million years ago. But Mauritius formed only about eight million years ago. No one knows where the dodo's ancestors lived before then.
Once they arrived on the island, dodos followed the same evolutionary path that other birds have taken on other islands, like Madagascar and Hawaii. They became stocky and flightless as they adapted to feeding on plants. "Nature abhors a vacuum," said Dr. David A. Burney, the director of conservation at the National Tropical Botanical Garden in Hawaii and a professor at Fordham University in New York, who was not part of the dodo fossil team. "With a few million years these birds turned into the avian equivalent of pigs and goats."
Plant-eating mammals play a major role in shaping their ecosystems. Dodos may have thinned the Mauritius forests, and some plants may have come to depend on them to spread their seeds.
With almost no fossils to study, scientists had been unable to test these ideas. Now it will be possible, thanks to the discovery of the dodo graveyard. Dr. Rijsdijk and Frans Bunnik, also of the Geological Survey of the Netherlands, found it almost by accident.
They went to Mauritius in October 2005 to look for evidence of the ecology on the island when Dutch settlers established a fort there in 1638. "From the current landscape you cannot get a proper picture of what it was like in the 17th century," Dr. Rijsdijk said.
Today the forests have been replaced by sugar plantations and settlements.
Dr. Rijsdijk and Dr. Bunnik searched for deposits of deep, undisturbed soil that might have preserved centuries of pollen grains and other vegetation. "We rounded the island to find places where we could reconstruct the environmental history of Mauritius for the last thousand years," Dr. Rijsdijk said.
The scientists discovered a number of sites. Their last visit was to a sugar plantation where isolated dodo bones were found in 1865. The bones had been found in a swamp called Mare aux Songes, but their precise location was never recorded.
The manager of the plantation showed the scientists some test drilling cores that had been made in the 1990's. The scientists were excited to see that they were rich in organic matter and even contained bone fragments from an extinct giant tortoise.
Dr. Rijsdijk and Dr. Bunnik made their way to the drilling site and worked an auger by hand through a layer rock. When they finally reached mud underneath, they reached into the hole and brought up tortoise bone fragments and a large seed from an endangered tree, the tambalacoque.
The scientists then used digging equipment to bring up scoopfuls of mud. "The first scoop was completely full of seeds, bones and wood debris," Dr. Rijsdijk said. "We were completely flabbergasted."
Dr. Rijsdijk returned to the Netherlands and planned a large expedition to Mare aux Songes. In June he took a team of international scientists to the site, where they began to pull out a wealth of fossils. The seven-acre tract is packed with dodo bones, some possibly belonging to chicks. The haul includes bones from two giant tortoise species, a giant lizard called a skink, a fruit bat, an owl, a rail and many other smaller birds.
Based on the underlying geology of the site, Dr. Rijsdijk estimates that it is 3,000 years old. More precise dating based on carbon isotopes is now under way.
Dr. Rijsdijk said that the fossils appeared to have formed in a forest lake. A big storm may have washed the animals and plants into the lake, where their bones settled into a single layer.
"Think of it like a snapshot," Dr. Burney of Fordham said. "You set up a big camera and photograph the landscape at a particular instance. You've got the dodos and the other species, all captured in a moment."
The scientists are now studying the material more carefully. Some are looking for ancient DNA, while others will analyze the dodo bones to get clues to their diet. "We may be really be able to shine a light on the dodo's role in the ecosystem," Dr. Rijsdijk said. The scientists will present early findings at the University of Oxford in September and will return to Mare aux Songes in 2007.
By understanding the Mauritius ecosystem before humans arrived, they hope to find clues to the dodo's extinction. Dodos were easy to hunt, but hunting alone probably did not wipe them out. Recent research indicates that the early Dutch settlers rarely ate dodo meat. Nor did the deforestation of the island doom the dodo. Major forest clearing did not begin until after the dodo became extinct.
The mammals introduced to the island by early visitors may have been the culprits. Pigs and monkeys quickly established themselves and may have competed for food, eaten dodo eggs or somehow disrupted the environment. "A lot of the earliest changes to these little islands actually sweep ahead of the humans," Dr. Burney said.
Dr. Rijsdijk and his colleagues plan to build an ecological model of Mauritius to study how the introduction of new animals could have changed it. While the dodo is gone for good, such an ecological model may help efforts to restore native habitats to parts of Mauritius.
On the Hawaiian island of Kauai, Dr. Burney has reconstructed 10,000 years of ecological history from deposits in a single cave. The National Tropical Botanical Garden is now using the information to guide the restoration of surrounding forests.
Dr. Burney said similar projects could work on Mauritius. "It's looking to the past to restore the future," he said.