DNA has been extracted for the first time from the fossilised eggshells of birds such as emu and moa, providing a purer source of ancient DNA than bone, say scientists.
Dr Michael Bunce, head of the Ancient DNA Research Laboratory at Murdoch University in Perth and colleagues report their findings today in the Proceedings of the Royal Society B.
"Eggshell has got a number of good characteristics about it that make it interesting to study in both an archaeological and palaeontological context," says Bunce.
He says eggshell does not exchange air with its outside environment.
"It's a sealed environment. So it's very good for dating."
Bunce says eggshell also provides stable isotopes that give scientists information about the diet of the animal that lay the egg.
He believes this is the first published report of eggshell yielding ancient DNA, and the findings could be very useful in providing definitive species identification for birds such as the moa.
Bunce and team, which included graduate student, Charlotte Oskam, analysed fragments of eggshell from extinct moa and ducks from New Zealand, extinct elephant birds from Madagascar and emu and owl from Australia.
Elephant birds have the largest known eggs, 150 times bigger than a chicken egg.
The oldest DNA they extracted was 19,000 years old, from a fragment of Australian emu eggshell.
Advantage over bone
Bunce says the most common source of ancient DNA used for phylogenetic studies is bone.
But this is often contaminated by DNA from bacteria and fungi, making it difficult to use new generation genetic sequencing techniques.
Bunce and colleagues have found that eggshell has much less bacterial DNA than bone.
"When we compare moa eggshell to moa bone of similar age, we've got 125 times less bacterial contamination, which is significant if you're going to do genomic level studies," says Bunce.
"It's more pure, if you like."
Bunce says the team was particularly excited to get ancient DNA from Australian emu eggshells.
"Australia is not a place conducive to long-term DNA preservation due to the heat," says Bunce.
He says the fact they found preserved DNA in Pleistocene eggshells from Australia and Holocene deposits from Madagascar suggests eggshell could be a good substrate for long-term preservation of DNA in warmer climates.
The researchers tried but failed to obtain DNA from a 50,000-year-old Genyornis eggshell.
"So there are limits to DNA survival in Australia," says Bunce.
Dr Jeremy Austin of the Australian Centre for Ancient DNA at University of Adelaide welcomes the study.
"It's another good new piece of ancient DNA research," he says.
"They've certainly covered a lot of different material from different species - important ones like the elephant bird from Madagascar."
He says the use of DNA from eggshell may be useful in phylogenetic studies where existing methods are inadequate.