Extinct Dodo Related to Pigeons, DNA Shows
for National Geographic News
|February 28, 2002|
Scientists have determined, through DNA analysis, that the long-extinct
dodo belongs in the dove and pigeon family.
The dodo, poster bird
for species extinction, has a pitiful reputation as a stupendously
overweight idiot of a bird that couldn't even fly. But scientific
evidence is slowly correcting that impression. Its new rep: an
evolutionary success, perfectly adapted to its living conditions, thin
and relatively fast, but still an early victim to the spread of
Dutch sailors began using the Indian Ocean island of
Mauritius as a stopover in 1598; Within 80 years, the dodo was gone.
Having evolved over millions of years to take maximum advantage of its
splendid isolation, its size and inability to flee from predators
ushered it into extinction in an evolutionary instant.
The adaptations the dodo made for island livingflightlessness and gigantismhave made understanding its evolutionary history and classifying it based on body characteristics difficult. Over the years, the dodo has been grouped with the carnivorous raptors; ratites, which include emus and ostriches; parrots; and shorebirds. Since the mid-1800s, the dodo has been classified as part of the family that includes pigeons and doves. But there has been no hard proof.
Molecular analysis of DNA retrieved from a dodo specimen at the Oxford University Museum of Natural History, England, confirms that the bird belongs firmly in the middle of the pigeon tree in evolutionary terms, reports a study published in the March 1 issue of the journal Science. Its closest living relative is the Nicobar pigeon, which lives in the Nicobar Islands and Southeast Asia, and it is part of a group of large island-dwelling birds that spend a great deal of time on the ground. Other modern representatives include the crowned pigeons of New Guinea and the tooth-billed pigeon of Samoa.
So why do scientists care whether a long-extinct dumb fat bird found on only one island in the whole world was related to a pigeon or an ostrich?
"Island taxa such as the dodo and solitaire often represent extreme examples of evolutionand if we want to examine how we, or the life around us, evolved then such animals are very educational," said Alan Cooper, a zoologist at the University of Oxford and one of the co-authors of the study. "By examining island birds we can investigate how evolution worksbecause extreme examples are often the best views of how something works."
Earlier scientists had speculated that the dodo, and its closest relative, the also-extinct solitaire, descended from migratory African pigeons that got lost and colonized the islands. The genetic evidence clearly shows that the dodo and solitaire came from southeast Asia, where all their close relatives remain.
The Oxford scientists can't tell when the dodo arrived on Mauritius, or when it became flightless. Geological evidence indicates that the island was created as a result of volcanic activity and emerged from the water about 8 million years ago. Whether the birds flew, swam or hitched a ride on floating debris like trees or clumps of seaweed, remains unknown. The DNA evidence does indicate that the dodo and the solitaire separated from a common ancestor about 25.6 million years ago. The common ancestor separated from other Southeast Asian birds around 42.6 million years ago.
Rescuing the Rep of the Dodo
Animals that evolve in isolation frequently exhibit somewhat bizarre traits, and a giant flightless bird is surely on the extreme end of avian evolution. But that doesn't make the dodo a failure. David Quammen, in his seminal book on island biogeography and extinctions The Song of the Dodo, calls the species an evolutionary success; it adapted well to local conditions.
Having reached Mauritius, the birds adapted, probably over several million years, to living on an island that had no predators and a wealth of fruit lying on the ground. They gradually traded their ability to fly for the ability to store larger amounts of fat that would carry them through times of scarcity. To store the fat, they got bigger, making it more difficult to fly. Surrendering the ability to fly, and thus to elude enemies, he says, was an easy trade-off; there were no enemies to flee.
That all ended when the Portuguese and Dutch began arriving in the 16th and 17th centuries. Having no reason to fear man, the big ground-dwelling birds were easy prey. Numerous contemporary accounts describe the birds as trusting and friendlyhardly bothering to get out of the sailors' way, never mind trying to run and hide. But that was ecological naiveté, says Quammen, not stupidity.
Although hunting certainly reduced populations, it was the animals the sailors brought with them, especially pigs, rats, and monkeys, that delivered the death blow to the species by preying upon their eggs and chicks, if not the adults.
And while the dodo was definitely a big bird, it probably wasn't nearly as fat and geeky as has been depicted. Most of what is known about what the dodo looks like is derived from paintings and caricatures from the 17th century.
Andrew Kitchener, a biologist and curator at the Royal Museum of Scotland, has shown that the dodo was probably much thinner and more lithe than has generally been depicted. Most of the sketches and paintings were copies, not based on original observations. Some may be based on birds in captivity in Europe that were unintentionally overfed, and fattened up beyond what would occur in nature.
The derogatory catch phrase "Dumb as a Dodo" has lived for more than 350 years; emerging science may slowly reshape our understanding and give the long-dead bird some respect.
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