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 twentieth 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 order Cetacea includes whales, dolphins and porpoises. They are the mammals most fully adapted to aquatic life with a spindle-shaped nearly hairless body, protected by a thick layer of blubber, and forelimbs and tail modified to provide propulsion underwater.
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.
Baraniak E., Kubasik W., Pałka K. (1998). "Smużka stepowa Sicista subtilis (Pallas, 1773) (Rodentia: Zapodidae) – nowy gatunek ssaka w faunie Polski". Przegląd Zoologiczny. 42 (2): 241–243.
Bogdanowicz W., Ruprecht A. L. (1987). "Przypadki stwierdzeń szopa pracza Procoyon lotor (Linnaeus, 1758) w Polsce". Przegląd Zoologiczny. 31 (3): 375–383
Carleton M., Musser G., Pavlinov I. (2003). "Myodes Pallas, 1811, is the valid name for the genus of red-backed voles. W: A. O. Averianov, N. I. Abramson (red.) Systematics, Phylogeny and Paleontology of Small Mammals. An International Conference Devoted to the 90th Anniversary of Prof. I. M. Gromov". Proceedings of the Zoological Institute, Saint Petersburg: 96–98.
Mitchell-Jones A. J., Amori G., Bogdanowicz W., Kryštufek B., Reinjders P. J. H., Spitzenberger F., Stubbe M., Thissen J. B. M., Vohralik V., Zima J. (1999). The Atlas of European Mammals. Academic Press, London.
Niermann I., Biedermann M., Bogdanowicz W., Brinkmann R., Le Bris Y., Ciechanowski M., Dietz C., Dietz I., Estók P., Helversen O. v., Le Houédec A., Paksuz S., Petrov B. P., Özkan B., Piksa K., Rachwald A., Roué S. Y., Sachanowicz K., Schorcht W., Tereba A., Mayer F. (2007). "Biogeography of the recently described Myotis alcathoe von Helversen and Heller, 2001". Acta Chiropterologica. 9: 361–378.
Pucek Z. (1981). Key to Vertebrates of Poland: Mammals. Polish Scientific Publishers, Warszawa.