Traces of blood survive 46 million years
The female mosquito's distended abdomen contained haeme, a compound found in blood (Source: PNAS)
Last meal Organic molecules from blood can survive in fossils for nearly 50 million years, say scientists.
The molecules have been found in the last meal of a mosquito that died 46 million years ago, the researchers report this week in the Proceedings of the National Academy of Sciences.
The discovery of molecules derived from haemoglobin, the chemical in blood that carries oxygen, is compelling evidence that the mosquito was sucking blood just before it perished.
The fossilisation of the blood-laden mosquito was an "extremely improbable event" say the researchers, led by Dr Ralph Harbach of the Natural History Museum in London.
"First of all the mosquito had to take a blood meal, and then die immediately afterwards - before she digested it - and then she had to fall into the right sort of water or mud and then be covered with silt quite rapidly. And there had to be just the right conditions for compression and temperature," says Harbach.
Female blood-suckers
The female mosquito (only females suck blood) lived in a warm wet environment in what is now North-Western Montana in the USA.
Her fossilised body was preserved in oil shale, and her distended abdomen could be clearly seen.
The researchers showed that there was an unusually high level of iron in her abdomen and also identified chemicals from haemoglobin using a non-destructive type of mass spectrometry.
Both findings point to the load in the abdomen being blood.
Samples from the adjacent rock and from a male mosquito from the same deposit did not show high iron or signs of haemoglobin, they say.
The type of blood could not be determined, but Harbach says the closest-related modern day species feeds on birds. "This mosquito lived in a wetland, and I think there would probably have been a lot of birds," he adds.
"The evidence is that we can detect organic molecules that have survived tens of millions of years and that opens up the possibility of finding other types of molecules," Harbach says.
Harbach and lead author Dale Greenwalt of the Smithsonian Institution in Washington, USA want to look to look for other organic molecules that may also have survived, such as pigments.
"We're thinking of looking at the eyes of this mosquito to see if we can pick up the eye pigments," he says.
Shades of Jurassic Park
The study is reminiscent of Jurassic Park, where DNA from dinosaur blood in a fossil mosquito's meal is used to create a dinosaur.
But finding DNA in this mosquito is highly unlikely, say the researchers.
"We know DNA is not preserved, nor will anyone ever find it in deep time fossils until we develop new technology," says Greenwalt.
Professor Michael Archer of University of New South Wales, who was not involved in the study, says the mosquito research has pushed back the boundary for identifying molecules important in life.
"They questioned whether or not a fossil insect 46 million years old really shouldn't have organic molecules in it. Clearly it does."
And he is more optimistic about the chances of finding preserved DNA in fossils.
He says until recently it was thought DNA could only be found in fossils 10,000 - 20,000 years old.
"Just this year a study was published about fossil bone from a horse which was 735,000 years old and they got definite readable DNA out of that bone."
"It's the synergy with the Jurassic Park movie," says Archer, "the idea of having something that's recoverable from the meal of a fossilised mosquito that makes this [study] particularly mischievously intriguing."
