An international team of paleontologists has identified two ancient species of mosquitoes from so-called compression fossils found in the Kishenehn Basin, northwestern Montana, the United States.

Ancient mosquitoes are very rare and the total number of species identified is now 26.

The newly identified species, called Culiseta kishenehn and Culiseta lemniscata, lived on Earth during the Eocene epoch about 46 million years ago. They are the first compression fossils identified from the genus Culiseta. They are produced in rock that is compressed over time, often creating animal fossils that are distorted, unlike the body fossils you get with amber where the whole body is often nicely preserved.

The team was able to spot minute details that distinguish one mosquito species from another, such as wing veins from 0.5 to 1.5 mm long, to minuscule setae, the hair-like structures near the base of the wing.

But is it possible that these fossil mosquitoes from the time of the Eocene epoch could also contain blood?

“Compression fossils are generally less informative morphologically than specimens preserved in amber,” said Dr Ralph Harbach of the Natural History Museum in London, lead author of a paper reporting the new species in the journal Zootaxa. “It is probably less likely for blood to be detected in compression fossils, but it should be possible.”

Blood has already been found in fossil mosquitoes of a similar age to the new finds. A species in the genus Culex preserved in 45-15 million-year-old Dominican amber had blood that contained bird malaria parasites. Some scientists think that human malarial parasites, which are transmitted by the Anopheles mosquitoes, arose by transfer from birds to humans.

And it was in another amber fossil that the oldest fossil mosquito, Burmaculex antiquus, was found – the Burmese amber was from the mid-Cretaceous.

So, what kind of viruses might the new ancient mosquitoes have carried?

“Although 46 million years old, they look very similar to some living species of the same genus Culiseta,” Dr Harbach said. “Culiseta kishenehn bears close resemblance to the living North American Culiseta melanura, which is a vector of Eastern and Western equine encephalitis viruses (EEE and WEE).”

“These viruses quickly infect the brains of horses and cause paralysis and very often death. EEE can infect amphibians, reptiles, birds and mammals, including humans. And there is currently no cure for the human form which is sometimes fatal,” Dr Harbach said.

“There were no horses or humans during the Eocene epoch and many living species of Culiseta feed on birds. So these ancient mosquitoes probably fed on birds too,” he said. “However, mosquitoes are basically opportunistic and will feed on other types of animals if their preferred hosts are unavailable.”

“Since some of today’s mosquitoes also feed on reptiles, could the more ancient mosquitoes have sucked from a dinosaur?” Dr Harbach said: “it’s possible. Evidence suggests mosquitoes evolved in the Jurassic Period (200-146 million years ago). If the early ancestral mosquitoes had already evolved to feed on blood, it is conceivable that they may have fed on dinosaurs.”

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Bibliographic information: Harbach RE et al. 2012. Two new genera and two new species of fossil Culicidae (Diptera) from Eocene deposits of the Kishenehn Formation in Montana. Zootaxa 3530: 25–34