The fossil record of female sexual ornamentation in Empididae (Diptera: Empidoidea), with description of four new species

Abstract

Females of the subfamily Empidinae (Diptera: Empididae s.s.) often exhibit sexual ornamentation, an adaptation that, within the animal world at large, is most often associated with males, especially in vertebrates. Ornaments of female Empidinae include: 1) legs with rows of relatively large pennate scales, 2) enlarged and/or darkly pigmented wings and 3) inflated abdominal sacs. Ornamentation makes the females appear larger, a characteristic that may make them appear, albeit deceptively, more fecund, and therefore more attractive to potential mates. Given the rarity of female sexual ornamentation, these flies, particularly those of the tribe Empidini, have become a model system for study of this phenomenon. The family’s fossil record consists of 111 known occurrences including several genera from the middle Jurassic. This fossil record however is dominated by two genera, Empis and Rhamphomyia, which account for nearly 60% of all fossil occurrences. Unfortunately, there has been no fossil record of empidine sexual ornamentation other than pennate leg scales. Herein, we review this fossil record and describe the first empidine fossils, all from the Middle Eocene Kishenehn Formation, with enlarged and/or darkly pigmented wings, Rhamphomyia kitadai sp. nov. and R. brunnipennis sp. nov., and two new species of Rhamphomyia which display pennate leg scales, R. decens sp. nov. and R. pennipes sp. nov. Rhamphomyia enena Cockerell, 1921, the oldest known fossil that exhibits pennate leg scales, is redescribed.