[4] I. sigei is based on well-preserved fragments of dentaries and lower teeth found in Western India.

[5] In 2023, the species I. gunnelli also from the Green River Formation was distinguished from I. index, and I. menui and I. sigei were proposed to be removed from the genus due to them not being closely related.

The tail was much longer and not connected to the hind legs with a skin membrane, the first wing finger bore a claw and the body was more flexible.

Its anatomy suggests that, like modern bats, Icaronycteris slept while hanging upside down, holding onto a tree branch or stone ridge with its hind legs.

[6] According to Simmons & Geisler 1998,[7] Icaronycteris is the first genus, followed by Archaeonycteris, Hassianycetris, and Palaeochiropteryx, in a series leading to extant microchiropteran bats.