Saurophthirus laevigatus: A new species of Flea from the Early Cretaceous Yixian Formation of Liaoning Province, China.
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Siphonaptera, commonly known as Fleas, are one of the widely known blood-sucking ectoparasitic Insects, comprising more than 2500 described species in 16 extant families. Up to now, the fossil Siphonaptera contain 16 species in five families from Cainozoic amber and Mesozoic compression fossils. All Cainozoic Fleas have been placed in two families, the Ctenophthalmidae and Pulicidae, while all Mesozoic Fleas, grouped in three families, the Pseudopulicidae, Saurophthiridae, and Tarwiniidae, which together form an extinct superfamily, the Saurophthiroidea, comprising nine species within five genera. Saurophthirus longipes, an unusual insect from the Early Cretaceous Zaza Formation of Baissa in Siberia, was described by Arnold Ponomarenko in 1976. He reported that its similarities with Fleas are piercing-sucking proboscis and soft distensible abdomen. A family of Saurophthiridae was established by Ponomarenko ten years later in 1986, including only this species. Another species of this family, Saurophthirus exquisitus, was described in 2013, based on three specimens, from the Early Cretaceous Yixian Formation of Liaoning Province, China, and it was suggested that the Saurophthiridae represent a transitional group from basal to extant Fleas. These fossil Fleas display some features seen in crown Fleas but are still considerably different from extant Fleas in many morphological characters, e.g., the absence of pronotal and genal ctenidia (comblike structures) on the body, the lack of the uniquely modified jumping hind legs, distinct ctenidia on the tibiae, more developed eyes, antennae with more than 15 segments, absence of laterally compressed abdomen, presence of medium body size, swollen hind coxae and partially extended male genitalia. These features indicate that Saurophthirus is more closely related to modern Fleas than to the Cretaceous genera Pseudopulex and Tarwinia.