Even extinction and the passing of millennia are no barriers to clever geneticists. In the past few years, scientists have managed to sequence the complete genome of a prehistoric human and produced “first drafts” of the mammoth and Neanderthal genomes. More controversially, some groups have even recovered DNA from dinosaurs. Now, a variety of extinct birds join the ancient DNA club including the largest that ever lived – Aepyornis, the elephant bird.
In a first for palaeontology, Charlotte Oskam from Murdoch University, Perth, extracted DNA from 18 fossil eggshells, either directly excavated or taken from museum collections. Some came from long-deceased members of living species including the emu, an owl and a duck. Others belonged to extinct species including Madagascar’s 3-metre tall elephant bird and the giants moas of New Zealand. A few of these specimens are just a few centuries old, but the oldest came from an emu that lived 19,000 years ago.
It turns out that bird eggshells are an excellent source of ancient DNA. They’re made of a protein matrix that is loaded with DNA and surrounded by crystals of calcium carbonate. The structure shelters the DNA and acts as a barrier to oxygen and water, two of the major contributors to DNA damage. Eggshells also stop microbes from growing and it seems that ancient ones still do the same. Oskam found that the fossil shells had around 125 times less bacterial DNA than bones of the same species did.
This is important – bacteria are a major problem for attempts to extract ancient DNA and they force scientists to search for uncontaminated sources, like frozen hair. Eggshells, it seems, provide similarly bacteria-free samples. Still, Oskam’s team took every precaution to prevent contamination. They used clean rooms and many control samples. Many of their sequences, like those of Aepyornis, were checked by two independent laboratories.
The Aepyornis sequences are particularly encouraging because many scientists have previously tried to extract DNA from the bones of this giant and failed. Eggshells seem like a more promising source and it certainly helps that the eggs of many of these giant species were massive and thick. But Oskam did also recover DNA from a fossil duck egg, which suggests that it should be possible to sequence the genes of even small extinct birds, like the dodo.