Rodents make up the largest order of mammals, with over 40% of mammalian species. They have two
incisors in the upper and lower jaw which grow continually and must be kept short by gnawing.
The lagomorphs comprise two families,
Leporidae (
hares and
rabbits), and Ochotonidae (
pikas). Though they can resemble
rodents, and were classified as a
superfamily in that order until the early 20th century, they have since been considered a separate order. They differ from rodents in a number of physical characteristics, such as having four incisors in the upper jaw rather than two.
The order Erinaceomorpha contains a single family, Erinaceidae, which comprise the
hedgehogs and
gymnures. The hedgehogs are easily recognised by their spines while gymnures look more like large rats.
The bats' most distinguishing feature is that their forelimbs are developed as wings, making them the only mammals capable of flight. Bat species account for about 20% of all mammals.
The even-toed ungulates are
ungulates whose weight is borne about equally by the third and fourth toes, rather than mostly or entirely by the third as in
perissodactyls. There are about 220 artiodactyl species, including many that are of great economic importance to humans.
^Banaszek, A.; Bogomolov, P.; Feoktistova, N.; La Haye, M.; Monecke, S.; Reiners, T. E.; Rusin, M.; Surov, A.; Weinhold, U. & Ziomek, J. (2020).
"Cricetus cricetus". IUCN Red List of Threatened Species. 2020: e.T5529A111875852.
^Batsaikhan, N.; Henttonen, H.; Meinig, H.; Shenbrot, G.; Bukhnikashvili, A.; Hutterer, R.; Kryštufek, B.; Yigit, N.; Mitsain, G. & Palomo, L. (2016).
"Arvicola amphibius". IUCN Red List of Threatened Species. 2016: e.T2149A115060819.
^McDonald, R. A.; Abramov, A. V.; Stubbe, M.; Herrero, J.; Maran, T.; Tikhonov, A.; Cavallini, P.; Kranz, A.; Giannatos, G.; Kryštufek, B. & Reid, F. (2019).
"Mustela nivalis". IUCN Red List of Threatened Species. 2019: e.T70207409A147993366.
^Skumatov, D.; Abramov, A.V.; Herrero, J.; Kitchener, A.; Maran, T.; Kranz, A.; Sándor, A.; Stubbe, M.; Saveljev, A.; Savour-Soubelet, A.; Guinot-Ghestem, M.; Zuberogoitia, I.; Birks, J.D.S.; Weber, A.; Melisch, R. & Ruette, S. (2016).
"Mustela putorius". IUCN Red List of Threatened Species. 2016: e.T41658A45214384.