In a real-life effort reminiscent of Hollywood's imagination, scientists have for the first time extracted the DNA of several extinct bird species from fossilized eggshells.
Included among the species for which researchers have DNA is a giant African ratite, or flightless bird, that stood 10 feet high and weighed as much as half a ton and a 19,000-year old Australian emu.
Other long-extinct animals for which DNA was found include moas and ducks from New Zealand and an owl from Australia.
The researchers removed DNA from the long-dry inner membranes of fossilized eggshells found in those countries and Madagascar.
Their success culminated efforts pursued over many years. Earlier attempts to obtain the DNA of extinct birds failed because scientists incorrectly believed that bone was the best source for the compound.
“Researchers have tried unsuccessfully to isolate DNA from fossil eggshell for years," Charlotte Oskam, the lead author of the study and a doctoral student at Australia's Murdoch University, said in a statement. "It just turned out that they were using a method designed for bone that was not suitable for fossil eggshell.”
DNA can be obtained from the fossilized bones of avian embryos only if scientists are able to remove the calcium within the bones. That presumes the availability of complete embryos or, at a minimum, fossilized bones that have not been broken down by bacteria.
The first possibility is not likely.
"We have not come across an intact egg with a fossilized embryo within it," Oskam said.
As for bacteria-caused decay in fossilized bones, the DNA integrated within those bones would disappear, too.
The structure of a fossilized eggshell is less likely to be degraded over time.
"Because eggshell is about 97 percent calcite, it's a resilient substrate and therefore is commonly found in various fossil deposits," Oskam said.
The resilience of eggshells might allow scientists to extract DNA from species that have been gone from the planet for periods even longer than the subjects of Oskam's and her colleagues' work. However, there does appear to be a limit, at least for the techniques employed by the Australian scientists.
Oskam emphasized that while the methods described in the study could be used to study the DNA of any bird, perhaps even species that existed farther back in time than the 19,000 year-old specimen described in the study, they are not useful if the goal is the extraction of DNA from the fossilized remains of non-avian dinosaurs.
"Although it would be extremely exciting to extract DNA from a dinosaur egg, I am convinced that DNA cannot be isolated from fossils that are completely mineralized," Oskam said. "In our study we report that we failed to obtain DNA from eggshells of the extinct Australian megafaunal bird, Genyornis, dated up to 50,000 years. Since the last [non-avian] dinosaurs died out 65 million years ago it is safe to say we are nowhere near approaching these sorts of ages."
The challenge when dealing with fossils of such antiquity is that there is no longer any DNA to be recovered from them because they are entirely rock.
"Because there are no organic components left [in a mineralized fossil], it would be quite impossible to isolate any DNA from the substrate," Oskam said. "Given that studies have isolated DNA from ice core sediments dating back hundreds of thousands of years, it may be possible to isolate DNA of much greater antiquity than we report in this study. Because the DNA is encapsulated in the eggshell matrix we speculate that the DNA might survive longer than in bone. But this is untested."
The researchers hope the discovery helps them understand how the long-disappeared bird species interacted with the surrounding ecosystem. They also think the discovery will illuminate their place in the evolutionary history of birds.
"Because DNA has never been isolated from Aepyornis, if we could sequence enough mitochondrial DNA we could investigate the evolutionary history of this species," Oskam said. "From our study, we can now try to obtain larger DNA fragments to build a better picture of how different species fit in the bird phylogeny."
Oskam referred to the scientific name of the elephant bird, which was the largest bird that ever lived.
Aepyornis was native to Madagascar until disappearing at some time before the end of the 17th century. The elephant bird's egg was known to have a circumference of up to 3 feet and a length of up to 13 inches long. It's volume was 160 times greater than a chicken egg.
Another of the animals for which DNA was recovered, the moa, died out about 600 years ago.
Reaching a height of up to 12 feet and weighing about 500 pounds as adults, they were hunted only by a species of eagle before the Maori arrived in New Zealand sometime before the 14th century began. Within 300 years of the Maori's settlement in Polynesia the moa were extinct.
The study was recently published in the Proceedings of the Royal Society B.
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