THE SOUND OF CRICKETS IN THE EOCENE NIGHT: FOSSIL INSECT EARS FROM THE GREEN RIVER FORMATION
Previously documented fossil insect ears have all been poorly preserved foreleg tympana of crickets and katydids (Orthoptera, Ensifera). The Department of Paleobiology of the National Museum of Natural History houses a large collection of insects from the Eocene Green River Formation of Colorado and Utah, most of which have not as yet been identified. These collections were surveyed for orthopterans and members of other groups that preserved evidence for tympana. Among the some 400 specimens of Orthopteran, most have lost the distal articles of the forelimbs. Nine, however, show excellent preservation of the tympanum on the foreleg tibia. Of these, all but one belong to the Family Gryllidae, the true crickets. The other specimen belongs to the Superfamily Tettigonioidea, the katydids and bush-crickets (Gwynne, 2001). As can be seen by comparison with modern forms, the morphology of the foreleg tympanum in crickets and katydids is essentially unchanged since Green River times. Since the Green River biota also contains the oldest microchiropteran bats, this is a key data point in documenting the evolution of insect hearing.