The dodo has found its place on the avian family tree at last. A new study combines genetic and geological evidence to reveal the famed bird's evolutionary history and retrace its ancestors' route from Southeast Asia, across the Indian Ocean, to islands off the coast of Africa--where humans found them and hunted them to extinction.
Although ornithologists suspected that the dodo--a rotund, flightless bird that lived on the island of Mauritius--was a kind of overgrown pigeon, its place in the evolutionary tree has been hard to pinpoint. Even less was known about the bird's geographical origins.
So Beth Shapiro, Alan Cooper, and others at the University of Oxford, United Kingdom, took DNA samples from the dodo skin mounted in Oxford's Museum of Natural History--the very same bird that inspired Lewis Carroll to include a dodo in his tale Alice in Wonderland. The researchers also sampled DNA from a solitaire, another extinct, large and flightless bird from Rodrigues, an island near Mauritius in the western Indian Ocean, as well as from 35 species of living pigeons and doves. They analyzed the DNA sequences to come up with a tree showing evolutionary relationships.
The dodo and solitaire turned out to be each other's closest relatives, and both nested smack in the middle of the pigeon and dove family tree. The two species apparently diverged from each other about 25 million years ago--long before Mauritius and Rodrigues had formed. (Geologists estimate the ages of the islands at 7 million and 1.5 million years, respectively.) Thus the birds must have diverged on another land mass before moving to the islands, the team concludes. Geological evidence shows that the island chain that now includes Mauritius and Rodrigues first rose above sea level 25 million years ago. Because the two extinct birds appear most closely related to pigeons from Southeast Asia, the authors contend that the birds' ancestors probably evolved there, emigrated to the new chain, then island-hopped through the millennia to their final destinations. The study appears in the 1 March issue of Science.
The work shows that knowing something about the way landmasses were aligned in the past is crucial to correctly inferring biological history, says Christophe Thébaud of the University of Toulouse, France, an evolutionary ecologist who works in the region. Thébaud and his student Ben Warren say they have found that other birds and plants on Mauritius and Rodrigues also appear to have Asian origins, despite the islands' greater proximity to Africa, suggesting the dodo and solitaire weren't the only ones to make the transoceanic trek.