Diverse transitional giant fleas from the Mesozoic era of China

The morphology of the oldest definitive fleas—from the Middle Jurassic and Early Cretaceous periods of China—suggests that they had ‘reptilian’ hosts before radiating to mammalian and avian hosts, and their stout and elongate sucking siphons suggest that they may be rooted among the scorpionflies of the Mesozoic era. Keeping dinosaurs up to scratch Fleas are familiar parasitic insects and disease vectors, but their phylogenetic affinities are obscure — not least because of their highly specialized morphology, adapted to sucking the blood of mammals and birds. Although fleas have long been suspected of being related to the Mecoptera, or scorpionflies, all fossil fleas belong to families that are alive today, so the physical transition between them and modern flies has been a mystery. The discovery of ancient fleas from the age of the dinosaurs could change that. These insects did not have jumping legs and bear traits of a scorpionfly ancestry. They were also big — more than 2 centimetres long in some cases. These giant fleas may have evolved to take advantage of the feathery coats of dinosaurs. Fleas are one of the major lineages of ectoparasitic insects and are now highly specialized for feeding on the blood of birds or mammals 1 . This has isolated them among holometabolan insect orders, although they derive from the Antliophora (scorpionflies and true flies). Like most ectoparasitic lineages, their fossil record is meagre and confined to Cenozoic-era representatives of modern families 1 , so that we lack evidence of the origins of fleas in the Mesozoic era. The origins of the first recognized Cretaceous stem-group flea, Tarwinia , remains highly controversial 1 . Here we report fossils of the oldest definitive fleas—giant forms from the Middle Jurassic and Early Cretaceous periods of China. They exhibit many defining features of fleas but retain primitive traits such as non-jumping hindlegs. More importantly, all have stout and elongate sucking siphons for piercing the hides of their hosts, implying that these fleas may be rooted among the pollinating ‘long siphonate’ scorpionflies of the Mesozoic. Their special morphology suggests that their earliest hosts were hairy or feathered ‘reptilians’, and that they radiated to mammalian and bird hosts later in the Cenozoic.