Scientists have identified 2 new mosquitoes that are 46 million years old. Ancient species of mosquitoes are incredibly rare and the total number identified is now 26. In comparison, scientists know of 100s of species of dinosaur.The fossils of species Culiseta kishenehn and Culiseta lemniscata were unearthed from the Kishenehn Basin, northwestern Montana, USA, and they are the first compression fossils identified from the genus Culiseta.
Ancient mosquito species, Culiseta kishenehn, is very similar to a species living today that spreads a deadly virus affecting horses.
The Natural History Museum's Ralph Harbach and the National Museum of Natural History's Dale Greenwalt were able to spot minute details that distinguish one mosquito species from another, such as wing veins from 0.5 to 1.5mm 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 (58-34 million years ago) could also contain blood?
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.
New ancient mosquito, Culiseta kishenehn, abdomen and right wing (about 3mm long). The veins on the wings are clearly visible.
And it was in another amber fossil that the oldest fossil mosquito, Burmaculex antiquus, was found - the Burmese amber was from the mid-Cretaceous (99.6-89.3 million years ago).
The new ancient mosquitoes are compression fossils. 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.
'Compression fossils are generally less informative morphologically than specimens preserved in amber,' says Harbach. 'It is probably less likely for blood to be detected in compression fossils, but it should be possible.'
Dr Harbach was surprised to see so much detail in the fossils, including the incredible detail of the minute scales and setae (hair-like structures) on veins on a mosquito wing.
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. Harbach explains, '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,' says Harbach.
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, says Harbach. '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? Harbach says it's possible. Evidence suggests mosquitoes evolved in the Jurassic Period (200-146 million years ago). Harbach concludes, 'If the early ancestral mosquitoes had already evolved to feed on blood, it is conceivable that they may have fed on dinosaurs.'
Harbach, R.E. & Greenwalt's Two new genera and two new species of fossil Culicidae (Diptera) from Eocene deposits of the Kishenehn Formation in Montana research paper is published in Zootaxa.