 "Icaronycteris", "Archaeonycteris", "Hassianycetris", and "Palaeochiropteryx", unlike most other fossil bats, have not been referred to any extant family or superfamily.These Eocene taxa are known from exceptionally well-preserved fossils, and they have long formed a basis for reconstructing the early evolutionary history of Chiroptera.Smith (1977) suggested that these taxa represent an extinct clade of early microchiropterans which he dubbed Palaeochiropterygoidea.