Biology:

Anatomy

The sea otter is an aquatic mammal in the family Mustelidae, the weasel family. It is the largest in its family in terms of weight. Living in the Pacific Ocean, it has the densest coat of any animal. Its hind legs have flippers for propulsion and their front feet have retractable claws, which is a unique adaptation in their taxonomic family (Kenyon, 1975). Adult females typically weigh up to 36 kilograms whereas males weigh up to 45 kg. Their bodies are long and streamlined with flat, short tails relative to their total length. Their ears are small and externally similar to those of pinnipeds (Steele, 2009).

(Image credit: © Josefine Stenudd 2003)

Fur

Sea otters have very little body fat compared to all other marine mammals. Instead of a thick layer of fat, they have dense fur. Their fur is denser than any other mammal, with 26,000 to 164,000 hairs per square inch in order to ensure their temperature stays at their set point- the ideal physiological state for homeostasis- (Cook 2018).

(Image credit: © Dylan Wyman 2006)

Sex

Sea otters are moderately sexually dimorphic. The male sea otter can weigh up to 45 kg and is 57 inches long on average. The female sea otter is much smaller, at 32 kg, and 54 inches long (Cook 2018).

(Image credit: © Ashley Murphy 2011)

Head and Torso

The axial skeleton of the sea otter - the bones of the head and torso - is typical of land mammals. Their relatively long torso contains 7 cervical, 14 thoracic, 6 lumbar, 3 sacral and 20 caudal vertebrae. (Stoskopf 1990) They do not have a clavicle, which might be an adaptation to give their pectoral girdle flexibility (Cook 2018).

(Image credit: © Robin Agarwal 2018)

Limbs

The appendicular skeleton of the sea otter -consisting of the bones of the upper limbs- and their rear limbs as well, are uniquely adapted to fully aquatic life compared to other otter species which are semi-terrestrial. Sea otters have four short femurs. Their forefeet are actually small pads with retractable claws, adapted for foraging and grooming. Their hind feet are tailored to swimming and are very flipper-like. They are not mobile on land because of their short femurs and long 5th digit, which make it hard to walk, which is additional evidence that this species has evolved for exclusively aquatic life (Cook 2018).

(Image credit: © Alan Wolf 2007)

Teeth

Sea otters have flatter molars than river otters, adapted for crushing rather than tearing food. Their incisors are chisel-shaped for scraping meat from shells, which is vital to obtaining essential nutrients- nutrients their bodies cannot synthesize on their own and must obtain through external means- and minerals. Sea otters are aged by counting the rings of their pre-molar tooth (Cook 2018).

References:

Kenyon, K. W. (1975a). The Sea Otter in the Eastern Pacific Ocean. Dover Publications.

Steele, J. H., Thorpe, S. A., & Turekian, K. K. (2010). Elements of Physical Oceanography: A derivative of the Encyclopedia of Ocean Sciences (1st ed.). Academic Press.

Cook, N. (2018). A pictorial guide to sea otter anatomy and necropsy findings. https://doi.org/10.26226/morressier.5b040f11d64f25001b0ecd19

Stoskopf, M. K., & Herbert, D. (1990). Selected Anatomical Features of the Sea Otter (Enhydra lutris). Journal of Zoo and Wildlife Medicine, 21(1), 36–47. http://www.jstor.org/stable/20095017

Stenudd, J. (2003). 20030614K Sea otters (Enhydra lutris) at Vancouver Aquarium | British Columbia, Canada. Flickr. Retrieved December 18, 2022, from https://www.flickr.com/photos/72616463@N00/2764322597/in/photolist-5dgSNr.

Wyman, D. (2006). Sea otter. Flickr. Retrieved December 18, 2022, from https://www.flickr.com/photos/dwyman/209635003/in/photolist-jwrbB-86MQKr-e3YbNQ-vUNywv-qeSz8B-54m9QJ-rbJkhp-aeK28X-aPoNQp-aPoNG8-CZEwEJ-djjCeK-yo1Fq3-4oTrW5-JWQEih-2Cdmtd-aJ7Yvz-7mFJyU-PC5fPw-y6tVfa-q7RuM-4gSQLL-91EC4x-4phZKx-wzb8pk-QKUCgG-KLTxj6-a145aP-6SECcM-aAoqYS-3cid2g-bvtP6s-djU5hp-vZwzW-vUNhcX-6Epeqo-51mcSB-4si5Bf-nh5cMG-yKKW25-3cicYp-smjwNV-yKKnWW-dfu9vN-Dx6c5B-3buDqC-pzZKRV-bvtLt1-4uNZKX-q5d1xL.

Murphy, A. (2011). Sea otter. Flickr. Retrieved December 18, 2022, from https://www.flickr.com/photos/ashleymurphy/6062719001/in/photolist-aeK28X-aPoNQp-aPoNG8-CZEwEJ-djjCeK-yo1Fq3-4oTrW5-JWQEih-2Cdmtd-aJ7Yvz-7mFJyU-PC5fPw-y6tVfa-q7RuM-4gSQLL-91EC4x-4phZKx-wzb8pk-QKUCgG-KLTxj6-a145aP-6SECcM-aAoqYS-3cid2g-bvtP6s-djU5hp-vZwzW-vUNhcX-6Epeqo-51mcSB-4si5Bf-nh5cMG-yKKW25-3cicYp-smjwNV-yKKnWW-dfu9vN-Dx6c5B-3buDqC-pzZKRV-bvtLt1-4uNZKX-q5d1xL-4q9MYp-JXhiT1-89qc1m-4qdReJ-4DvpL2-5FHa41-6EgzhF.

Agarwal, R. G. (2018). Sea otter feet. Flickr. Retrieved December 18, 2022, from https://www.flickr.com/photos/30314434@N06/40171751175/in/photolist-24cQJ4z-8EryPj-2mhQfgk-azs38M-wrtwyC-xJq6A6-yLGpeK-xrUYpR-x4e5Mu-x6NNSc-x6Rhxi-5NPGTU-tjMt81-4wMcJK-xbyuXL-wNSJDw-oyfKRV-cJYEsj-owucVB-sDoHG7-e7xiGw-x6Rb96-71pSdx-oyVEse-wMxrrn-of25Ai-w9C7YJ-w9JcRX-x6EaQH-x4kR9d-xXRTFt-yg1pGV-tnnjQR-oyf5r2-71pSmv-wofWq7-wYS4ph-w9EbiW-71tUfh-71pV5x-x74KGa-71tRm1-wjFt5i-xrp4V7-rqK7pG-ou2Dbw-cJYEHN-cJYEKU-ow3Vnn-xrhGHQ.

Wolf, A. (2007). Do I have any clam stuck in my teeth? Flickr. Retrieved December 18, 2022, from https://www.flickr.com/photos/alumroot/823856613/in/photolist-2fNtSn-4U4Cwy-7WXTKm-4LBzEz-6CpVyw-2XRzB4-7WXTYs-qUbpT-7WXU5q-nho2bN-xd2zX5-xtuDoy-w9C7YJ-deoSPK-sr1f1s-24WB1bn-y5pDmh-nwPEKu-DrSbH-w9Wn3Z-wPer2f-6pWy4n-owsrpb-xuJdPZ-y7HjkJ-wPcTts-x1G8qT-qij2RB-wM4T6p-ouHSHD-otcGPM-xnbbig-oxC8Dg-owKXxV-wmjWw2-ov3DvF-wd34ae-xmoWBA-y5w4hk-ot9KHP-xrvJar-wiSc6Z-xGQwcv-nho1Y5-xAyxcZ-xiQQ8M-wYeZ5D-xq7jt1-xDnx4g-xvPcke.

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