Scientists led by Dr Ralph Harbach of Natural History Museum in London have reported a stunning discovery: a well-preserved 46-million-year-old female mosquito full of blood.

The unique fossil was found in the Middle Eocene Kishenehn Formation in northwestern Montana.

“The preservation of fossil female mosquito was an extremely improbable event,” Dr Harbach with co-authors wrote in a paper published in the Proceedings of the National Academy of Sciences.

“The insect had to take a blood meal, be blown to the water’s surface, and sink to the bottom of a pond or similar lacustrine structure to be quickly embedded in fine anaerobic sediment, all without disruption of its fragile distended blood-filled abdomen.”

The fossil was identified as an ancient species of Culiseta, a small mosquito genus that includes 37 extant species.

“This fossil has provided a unique opportunity to ask whether or not a portion of the hemoglobin molecule could be preserved after tens of millions of years.”

Using nondestructive mass-spectrometry analysis, Dr Harbach’s team detected organic molecules of heme (the oxygen-carrying group of blood component hemoglobin) in the abdomen of the mosquito.

“The abdomen of the fossil mosquito is shown to contain very high levels of iron, and time-of-flight secondary ion mass spectrometry data provide unequivocal identification of porphyrin molecules. The combination of these two determinations indicates that the porphyrins are derived from the oxygen-carrying heme moiety of hemoglobin,” the researchers explained.

Their findings show that although large and fragile molecules such as DNA cannot survive fossilization, other complex organic molecules such as iron-stabilized heme can survive intact.

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Bibliographic information: Dale E. Greenwalt et al. 2013. Hemoglobin-derived porphyrins preserved in a Middle Eocene blood-engorged mosquito. PNAS, published online October 14, 2013; doi: 10.1073/pnas.1310885110