Bats, a collective term for mammals in the order Pterodactyla, are mammals with the ability to fly. The forelimbs of bats are extremely slender except for the first finger, with thin and hairless wing membranes between the fingers and between the forelimbs and hind limbs, and usually also between the hind limbs; Bats are divided into two categories, big bats and small bats. The name Pterodactyls is derived from the characteristic of their forelimbs or hands degenerating into wings. Beneficial to humans due to the large predation of insects, it plays an important role in agricultural and forestry ecosystems, and the feces in caves are excellent phosphate fertilizers. Some bats are also carriers or hosts of pathogens, which can pose a threat to fruit trees.

The Yishen bat is about 14 centimeters long, with wings spread up to 37 centimeters. It looks a lot like bats today, but has some primitive features. Its tail is long and not connected to its hind limbs. The first wing finger has claws and the body is relatively flexible. The Izumi bat, like many modern bats, sleeps upside down from trees or rocks. The Yishen bat is an extinct bat belonging to the suborder Pterodactyla, which lived in the early Eocene about 52.5 million years ago. Its fossils were discovered in North America. There is only one species under it, called the index finger bat.