Fleas are highly specialized parasitic insects, preying on mammals and birds. They are related to Flies and Scorpionflies, though this relationship is not obvious as Fleas have become physically specialized, loosing their wings, altering their body shape and evolving specialized legs and mouthparts. A number of putative fossil fleas have been described from the Jurassic and Cretaceous of Asia and Australia, but these are very different to modern fleas, leading many scientists to question if they are in fact fleas.
In a paper in the 29 February 2012 edition of the journal Nature, a team of scientists led by Diying Huang of the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology part of the Chinese Academy of Sciences, describing a number of fleas from the Middle Jurassic and Early Cretaceous of China.
Giant Fleas from the Middle Jurassic (165 million years ago) of Daohugou in Inner Mongolia. The female, left is 20 mm long, the male, right, 15 mm. From Huang et al. (2012).
These fleas lack the jumping legs of modern fleas, but are fairly flea-shaped, and do have the mouthparts of fleas. They appear to be adapted to clinging onto feathers or course hairs. Modern reptiles have thick, scaly skins, which offer protection against fleas (though some other parasites can deal with this), but many Jurassic Dinosaurs are known to have been feathery, and Pterosaurs appear to have had hairy skin. Hair and feathers are superior to scales in many ways, particularly insulation, but parasites such as fleas find it easy to get underneath them and target the soft skin beneath.
Fleas from the Early Cretaceous (125 million years ago) of Huangbanjigou in Liaoning Province. (a) Male. Scale bar 2 mm. (b) Enlargement of the mouthparts of (a). Scale bar 1 mm. (c) Enlargement of the genitalia of (a). Scale bar 1 mm. (d) Female. Scale bar 2 mm. From Huang et al. (2012).
The described fleas are very large compared to modern fleas, up to 20 mm (2 cm) in length, suggesting they may have fed on similarly large target species (the largest mammals of the time were a few centimeters long, unlikely to have been able to support such large parasites). Certainly fleas which evolved on the feathers of Dinosaurs and hair of Pterosaurs would be pre-adapted to live on the feathers of birds and fur of mammals, when these became available.
These new Fleas may also help to resolve the status of previously described species that have been disputed as Fleas, buy helping to build up an understanding of the character traits present in early members of the group.
Tarwinia australis, a putative fossil Flea from the Late Cretaceous of Australia. Like the Chinese Fleas Tarwinia lacks the jumping legs of modern species, which had caused some palaeontologists to question whether it was a true Flea. From Museum Victoria.
Strashila incredibilis, a possible Flea from the Late Jurassic of Eastern Siberia. It appears unlike either Jurassic or Modern Fleas, and may be some sort of Louse. Grimaldi & Engel (2005). Evolution of the Insects. Cambridge University Press.