Icaronycteris is an extinct genus of microchiropteran (echolocating) bat that lived in the early Eocene, approximately , making it the earliest known definitive bat. Four exceptionally preserved specimens, among the best preserved bat fossils, are known from the Green River Formation of North America. The best known species is  I. index.
Icaronycteris is an extinct genus of microchiropteran (echolocating) bats that lived during the early Eocene epoch, approximately , and is recognized as the earliest known representative of a definitive bat lineage. Four exceptionally preserved specimens, among the most well-preserved bat fossils, are known from the Green River Formation in North America. The most notable species within this genus is I. index.