Although there are currently 3,524 species of mosquito (Family Culicidae), there are relatively few examples of fossil species. The most recently published discovery has increased the total number to 26 species, with the earliest coming from Cretaceous amber (much to the delight of Jurassic Park enthusiasts - as these mosquitos could have sucked the blood of dinosaurs). The new fossils are from the Eocene Epoch and have been named Culiseta kishenehn and Culiseta lemniscata. They were unearthed from the Kishenehn Basin, northwestern Montana, USA. They are not in amber, but are compression fossils - the first to be 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. (Source here)
As is so often the case, the fossils can be assigned to modern-day families and genera. Speciation within genera with time means that fossils are less frequently linked with extant species. However, in this example, similarities are apparent:
"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)".
The modern mosquito carries viruses that infect the brains of horses, causing paralysis and very often death. However, there were no horses in North America during the Eocene Epoch, so this raises questions about what blood these mosquitos drank. It appears that many living species of Culiseta feed on birds. So, says Harbach, "these ancient mosquitoes probably fed on birds too. [. . .] mosquitoes are basically opportunistic and will feed on other types of animals if their preferred hosts are unavailable."
Inevitably, discoverers of new fossils seek to locate their finds within an evolutionary context. If Culiseta shows stasis, which it does, how does this relate to other fossil mosquitos? The researchers suggest that Culiseta is "primitive" and can be interpreted as a stem group which diversified. Whilst the diversification story may be viable, we do need to be careful about the terms "primitive" and "stem group", because the Culiseta are still alive and well today!
"Extant species of Culiseta exhibit generalized features that indicate the genus is a primitive lineage of subfamily Culicinae. Culiseta may be what paleontologists refer to as a "stem group", a paraphyletic or polyphyletic assemblage of species that share features of extinct taxa."
No doubt some readers want to have more on whether mosquitos fed on dinosaur blood. This is the parting comment in the news story from the Natural History Museum:
"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 [. . .]. Harbach concludes, "If the early ancestral mosquitoes had already evolved to feed on blood, it is conceivable that they may have fed on dinosaurs"."
Two Eocene species of Culiseta (Diptera: Culicidae) from the Kishenehn Formation in Montana
Ralph E. Harbach & Dale Greenwalt
Zootaxa, 3530: 25-34 (2012)
Culiseta kishenehn, sp. n. and Cs. lemniscata, sp. n. (Diptera: Culicidae: Culisetini) are described from compression fossils from the 46 million year old Kishenehn shale deposits in Montana, USA. The new species appear to share features with extant species of subgenera Climacura and Culicella, respectively. The antiquity of Culiseta is examined and previously described Eocene fossil species are discussed. Eoaedes gen. n. and Aetheapnomyia gen. n. are established for Aedes damzeni PodÄ—nas and Ae. hoffeinsorum Szadziewski, two Eocene fossil species in Baltic amber.
New ancient mosquitoes, could there be blood? Natural History Museum News (19 November 2012)
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