For the first time, scientists have sequenced the mitochondrial (mt) genome of an extinct animal. The success "is a landmark technologically," says ancient DNA expert Hendrik Poinar of the Max Planck Institute for Evolutionary Anthropology in Leipzig. "It moves the ancient DNA field into the genomics era."
DNA is rarely preserved in fossils, because it breaks down easily when subjected to heat, acidic water, and other forces. Luckily, the bones of moas--a group of large flightless birds that lived in New Zealand until they were hunted to extinction 400 years ago--can be found in cold, alpine caves. Because the caves are made of limestone, the water that trickles through is buffered and does less damage to the DNA.
Working with bones from two kinds of moa, biologist Alan Cooper of Oxford University in the U.K. and colleagues were able to extract fragments of mtDNA from three samples and assemble their entire sequences--each consisted of almost 17,000 base pairs. They report the genomes in the 8 February issue of Nature. A second team, ornithologists Allan Baker and Oliver Haddrath of the Royal Ontario Museum in Toronto, analyzed two genera of moa (including one different from Cooper's) to reconstruct two mtDNA genomes; their results are in press at the Proceedings of the Royal Society.
The moa studies illustrate that different evolutionary trees can be drawn depending on whether the animals are classified according to their genes or their physical appearance, notes Joel Cracraft of the American Museum of Natural History in New York City. Morphological analysis of flightless birds, or ratites, groups the kiwi and the moa. But the mtDNA findings are consistent with a gene-based family tree that distances the kiwi, clumping it instead with the more recently derived emu and the cassowary. What's more, the two mtDNA studies themselves part company on which ratite came first, the moa or South America's rhea. "Obviously, these DNA trees will be debated," Baker says.
Despite these uncertainties, the potential of DNA sequences from extinct species is that they can "significantly improve the picture of ... evolution," notes David Mindell, who directs the Genomic Diversity Laboratory at the University of Michigan, Ann Arbor. "It is a bit like discovering a lost relative and using their information to get a better understanding of your family tree."