Mouthpart homologies and life habits of Mesozoic long-proboscid scorpionflies.

Mesozoic long-proboscid scorpionflies (Mesopsychoidea) provide important clues to ancient plant-pollinator interactions. Among them, the family Aneuretopsychidae is especially important because its mouthparts are vital to deciphering the early evolution of Mesopsychoidea and putatively the origin of fleas (Siphonaptera). However, the identification of mouthpart homologs among Aneuretopsychidae remains controversial because of the lack of three-dimensional anatomical data. Here, we report the first Aneuretopsychidae from Late Cretaceous Burmese amber, which have short maxillary palpi and elongate mouthpart elements consisting of one pair of galeae and one hypopharynx. Their mouthparts are identical to those of Pseudopolycentropodidae (= Dualulidae, new synonym) but are not homologous to those of Siphonaptera. Our phylogenetic analysis provides robust evidence for the debated monophyly of Mesopsychoidea. Our results suggest that the long-proboscid condition has most likely evolved once in Mesopsychoidea, independently from fleas, and further reveal the variety and complexity of mid-Cretaceous pollinating insects.

Diverse transitional giant fleas from the Mesozoic era of China.

Fleas are one of the major lineages of ectoparasitic insects and are now highly specialized for feeding on the blood of birds or mammals. 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, 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. 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.