Fossils unearthed at two sites in China reveal that fleas, up to 10 times as large as modern fleas, drank the blood of dinosaurs and pterosaurs.

(These Jurassic fleas are believed to be 165 million years old. They had claws on each of their six legs, with tiny teeth on the claws that helped the insects cling to hair shafts, and feathers.

I do hope no-one gets the idea of cloning these wee beasties.)
Source and icky picture.