Smith (1977) suggested that these taxa represent an extinct clade of early microchiropterans which he dubbed Palaeochiropterygoidea. In contrast, Van Valen (1979) argued that these fossil forms are representatives of Eochiroptera, a primitive grade ancestral to both Megachiroptera and Microchiroptera; modern researchers, however, consider this clade to be obsolete. Novacek (1987) reanalyzed morphology of "Icaronycteris" and "Palaeochiropteryx" and concluded that they are more closely related to Microchroptera than to Megachiroptera. Most recently, Simmons and Geisler (1998) found that "Icaronycteris", "Archaeonycteris", "Hassianycteris", and "Palaeochiropteryx" represent a series of consecutive sister-taxa to extant microchiropteran bats.