A 46-million-year-old mosquito with an abdomen so full of blood it is at bursting point has been discovered in Montana.
The mosquito was unearthed in shale sediments while its belly still contained large traces of iron and the organic molecule porphyrin, which are found in vertebrate blood.
In a discovery reminiscent of Jurassic Park, scientists from the US National Museum of Natural History in Washington said the fossil was rare because of the undigested blood.
A number of fossilised mosquitos have been found in the past, but mostly their feeding habits have been examined through their anatomy or the presence of parasites in their guts, Nature scientific journal reports.
Study leader Dale Greenwalt said the chances of the blood remaining intact in the mosquito over many years were near impossible: "The abdomen of a blood-engorged mosquito is like a balloon ready to burst. It is very fragile.
"The chances that it wouldn't have disintegrated prior to fossilization were infinitesimally small."
Published in the Proceedings of the National Academy of Sciences, the authors wrote: "Fossils, in addition to documenting the existence of extinct species, can often provide information on the behaviour of ancient organisms.
"The present study describes the fossil of a blood-engorged mosquito in oil shale from northwestern Montana. The existence of this rare specimen extends the existence of blood-feeding behaviour in this family of insects 46 million years into the past."
They said that while the DNA of the creature the mosquito fed on did not survive fossilisation, other organic molecules did stay intact to provide information about the period.
George Poinar, who studies fossilized insects at Oregon State University, said: "This shows that details of a blood-sucking mosquito can be nicely preserved in a medium other than amber."
Speaking about the similarities with the Michael Crichton book Jurassic Park, no dinosaurs will result from the find as the mosquito lived long after they had gone extinct and the DNA did not survive. The researchers believe the blood is probably from a bird.
"It's following Crichton's script in that we're using a blood-engorged fossil mosquito and in this case we're using the direct descendent of the dinosaurs, given that we're 20 million years late," Greenwalt said.