查了查，bats多么神奇，翅膀小到十几厘米，大到170cm:

Bat Temporal range: Eocene–Present  Pre? ? O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Clade:	Scrotifera
Order:	Chiroptera Blumenbach, 1779
Suborders
(traditional): Megachiroptera Microchiroptera (present): Yinpterochiroptera Yangochiroptera
Worldwide distribution of bat species

Bats are mammals of the order Chiroptera.^[a] With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out digits covered with a thin membrane or patagium. The smallest bat, and arguably the smallest extant mammal, is Kitti's hog-nosed bat, which is 29–34 millimetres (1+1⁄8–1+3⁄8inches) in length, 150 mm (6 in) across the wings and 2–2.6 g (1⁄16–3⁄32 oz) in mass. The largest bats are the flying foxes, with the giant golden-crowned flying fox, Acerodon jubatus, reaching a weight of 1.6 kg (3+1⁄2 lb) and having a wingspan of 1.7 m (5 ft 7 in).