Oligocene
Ruby River Formation
Ruby River Basin, Madison Co., MT, USA

0.2 inch fly in paper shale.

This is an unidentified fly of the Order Diptera which includes flies, mosquitoes, and midges.  As the name indicates, dipterans are considered two-winged forms though they also bear a pair of halteres which have been interpreted as a vestigial second pair of wings that now serve as balancing organs during flight.

Flies appeared by the Middle Triassic and diversified across the rest of the Mesozoic.  They survived the K/T extinction and diversified again during the early Cenozoic.