Editing Mammal (section)

====Aquatic====
{{Main|Aquatic locomotion|Marine mammal|Aquatic mammal}}
[[File:Living-on-the-Edge-Settlement-Patterns-by-the-Symbiotic-Barnacle-Xenobalanus-globicipitis-on-Small-pone.0127367.s001.ogv|thumb|A pod of [[short-beaked common dolphin]]s swimming]]
Fully aquatic mammals, the cetaceans and [[sirenia]]ns, have lost their legs and have a tail fin to propel themselves through the water. [[Flipper (anatomy)|Flipper]] movement is continuous. Whales swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Their skeletal anatomy allows them to be fast swimmers. Most species have a [[dorsal fin]] to prevent themselves from turning upside-down in the water.<ref>{{cite journal | vauthors = Perry DA |year=1949 |title=The anatomical basis of swimming in Whales |journal=Journal of Zoology |volume=119 |issue=1 |pages=49–60 |doi=10.1111/j.1096-3642.1949.tb00866.x}}</ref><ref>{{cite journal | vauthors = Fish FE, Hui CA |year=1991 |title=Dolphin swimming – a review |journal=Mammal Review |volume=21 |issue=4 |pages=181–195 |url=https://darwin.wcupa.edu/~biology/fish/pubs/pdf/1991MRDolphinswimming.pdf |archive-url=https://web.archive.org/web/20060829000617/http://darwin.wcupa.edu/~biology/fish/pubs/pdf/1991MRDolphinswimming.pdf |url-status=dead |archive-date=29 August 2006 |doi=10.1111/j.1365-2907.1991.tb00292.x }}</ref> The flukes of sirenians are raised up and down in long strokes to move the animal forward, and can be twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing.<ref>{{cite book| vauthors = Marsh H |chapter-url= https://www.environment.gov.au/biodiversity/abrs/publications/fauna-of-australia/pubs/volume1b/57-ind.pdf |chapter=Chapter 57: Dugongidae |title=Fauna of Australia |volume=1 |publisher=Australian Government Publications |isbn=978-0-644-06056-1 |location=Canberra |year=1989 |oclc=27492815 |url-status=dead |archive-url=https://web.archive.org/web/20130511221756/http://www.environment.gov.au/biodiversity/abrs/publications/fauna-of-australia/pubs/volume1b/57-ind.pdf |archive-date=11 May 2013 }}</ref>

[[Semi-aquatic]] mammals, like pinnipeds, have two pairs of flippers on the front and back, the fore-flippers and hind-flippers. The elbows and ankles are enclosed within the body.<ref name=Berta63>{{cite book | vauthors = Berta A | title = Return to the Sea: The Life and Evolutionary Times of Marine Mammals | chapter = Pinniped Diversity: Evolution and Adaptations | publisher = University of California Press | date = 2012 | isbn = 978-0-520-27057-2 | pages = 62–64}}</ref><ref name="Fish 2003">{{cite journal | vauthors = Fish FE, Hurley J, Costa DP | title = Maneuverability by the sea lion Zalophus californianus: turning performance of an unstable body design | journal = The Journal of Experimental Biology | volume = 206 | issue = Pt 4 | pages = 667–674 | date = February 2003 | pmid = 12517984 | doi = 10.1242/jeb.00144 | doi-access = free | bibcode = 2003JExpB.206..667F }}</ref> Pinnipeds have several adaptions for reducing [[Drag (physics)|drag]]. In addition to their streamlined bodies, they have smooth networks of [[Muscle fascicle|muscle bundles]] in their skin that may increase [[laminar flow]] and make it easier for them to slip through water. They also lack [[Arrector pili muscle|arrector pili]], so their fur can be streamlined as they swim.<ref name=Riedman3/> They rely on their fore-flippers for locomotion in a wing-like manner similar to [[penguin]]s and [[sea turtles]].<ref name="Fish1996">{{Cite journal | vauthors = Fish FE |title=Transitions from drag-based to lift-based propulsion in mammalian swimming |doi=10.1093/icb/36.6.628 |journal=Integrative and Comparative Biology |volume=36 |issue=6 |pages=628–641 |year=1996|doi-access=free }}</ref> Fore-flipper movement is not continuous, and the animal glides between each stroke.<ref name="Fish 2003"/> Compared to terrestrial carnivorans, the fore-limbs are reduced in length, which gives the locomotor muscles at the shoulder and elbow joints greater mechanical advantage;<ref name=Berta63/> the hind-flippers serve as stabilizers.<ref name=Riedman3>{{cite book| vauthors = Riedman M |year=1990|title=The Pinnipeds: Seals, Sea Lions, and Walruses| url = https://archive.org/details/pinnipedssealsse0000ried | url-access = registration |publisher=University of California Press|isbn=978-0-520-06497-3|oclc=19511610}}</ref> Other semi-aquatic mammals include beavers, [[hippopotamus]]es, [[otter]]s and platypuses.<ref>{{cite journal | vauthors = Fish FE | title = Biomechanics and energetics in aquatic and semiaquatic mammals: platypus to whale | journal = Physiological and Biochemical Zoology | volume = 73 | issue = 6 | pages = 683–698 | year = 2000 | pmid = 11121343 | doi = 10.1086/318108 | url = https://darwin.wcupa.edu/~biology/fish/pubs/pdf/2000PBZ-PlatToWhale.pdf | url-status = dead | citeseerx = 10.1.1.734.1217 | s2cid = 49732160 | archive-url = https://web.archive.org/web/20160804111726/http://darwin.wcupa.edu/~biology/fish/pubs/pdf/2000PBZ-PlatToWhale.pdf | archive-date = 4 August 2016 }}</ref> Hippos are very large semi-aquatic mammals, and their barrel-shaped bodies have [[wikt:graviportal|graviportal]] skeletal structures,<ref>{{cite book | vauthors = Eltringham SK |year=1999|title=The Hippos|chapter=Anatomy and Physiology|location= London|publisher=T & AD Poyser Ltd|page=8|isbn=978-0-85661-131-5|oclc=42274422}}</ref> adapted to carrying their enormous weight, and their [[specific gravity]] allows them to sink and move along the bottom of a river.<ref>{{cite magazine|title=Hippopotamus ''Hippopotamus amphibius''|magazine=National Geographic|access-date= 30 April 2016|url= https://animals.nationalgeographic.com/animals/mammals/hippopotamus/|archive-url= https://web.archive.org/web/20141125041546/http://animals.nationalgeographic.com/animals/mammals/hippopotamus/|archive-date= 25 November 2014|url-status=dead}}</ref>