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IcaronycterisIcaronycteris is an extinct genus of microchiropteran (echolocating) bat that lived in the early Eocene, about 52.2 million years ago, in forests in the Green River Formation of North America. The only thoroughly described species of bat is I. index (1). Fragmentary material from France has been tentatively placed as a second species I. menui (2).
Icaronycteris (3) measured about 14 cm (5.5 in) long with a wingspan of 37 cm (15 in). It probably weighed a few ounces. It closely resembled modern bats, but had some primitive traits. 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. It had a full set of relatively unspecialised teeth, similar to those of a modern shrew. Its anatomy suggests that, like modern bats, Icaronycteris slept hanging upside down, holding onto a tree branch or stone ridge with its hind legs (4). Icaronycteris had a talent for echolocation; moth scales have been found in the stomach of one Icaronycterus specimen (6). Icaronycteris existed in the same time and place as another prehistoric bat that lacked the ability to echolocate, Onychonycteris (6).