(Image credit: © J. Stephen Conn, 2009)
Sea otters are relative newcomers to the ranks of marine mammals, having only evolved 5 million years ago. Their ancestors, members of the Mustelidae family, experienced adaptive radiation, which is when one species radiates out to form several other species. In fact, there are 13 kinds of otters and several terrestrial mustelids, like the badger and weasel. The sea otter, unlike the others, evolved to have a host of adaptations, like its extremely thick fur, suited to the harsh conditions of their sea environments. Because they were nearly hunted to extinction, they faced a magnified form of genetic drift (which is the effect of chance on a population’s gene pool) (Fowler et al., 2017) known as the bottleneck effect, which is explained in depth on the conservation page. This can cause genetic issues and scientists are currently observing how the otter population responds (Smithsonian’s National Zoo & Conservation Biology Institute, 2019).
Sea otters are in the family Mustelidae, which is a diverse group of nearly 70 carnivorous land and aquatic mammals. They are varied but usually have long bodies, short legs, and thick fur. These animals are the result of divergent evolution from a common ancestor, possibly the Corumictis wolsani (Koepfli, 2008).
Sea otters belong to the genus Enhydra. The only other two species in the genus are extinct otters. These otters have/had non-blade carnassials, which are the upper premolar and the first lower molar found in carnivorous mammals; adapted for shearing flesh (Solé & Ladevèze, 2017). Through speciation, Enhydra lutris, commonly known as the sea otter, evolved to be fully adapted to its environment. It is the only mustelid that does not have an anal scent gland and does not burrow (Koepfli, 2008).
Another interesting adaptation sea otters have is amphibious vision. Amphibious vision is vision that is adapted to both terresrial and aquatic environments. Humans have very poor vision underwater, fish have very poor vision out of water. Organisms with amphibious vision are well-suited to both and this feature is typically found in species that spend a good portion of their lives both above and below water (Strobel et al., 2020).
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Subfamily: Lutrinae
Genus: Enhydra
Species: E. lutris
Smithsonian’s National Zoo & Conservation Biology Institute. (2019, June 21). Evolution Fast Track: Otter Genetic History Provides Clues for Future Recovery. Smithsonian’s National Zoo. https://nationalzoo.si.edu/center-for-conservation-genomics/news/evolution-fast-track-otter-genetic-history-provides-clues-for
Koepfli, K. (2008, February 14). Multigene phylogeny of the Mustelidae: Resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation - BMC Biology. BioMed Central. https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-6-10
Solé, F., & Ladevèze, S. (2017). Evolution of the hypercarnivorous dentition in mammals (metatheria, eutheria) and its bearing on the development of tribosphenic molars. Evolution & Development, 19(2), 56–68. https://doi.org/10.1111/ede.12219
Fowler, S., Roush, R., & Wise, J. (2017). Concepts of Biology. OpenStax College, Rice University.
Strobel, S. M. K., Moore, B. A., Freeman, K. S., Murray, M. J., & Reichmuth, C. (2020). Adaptations for amphibious vision in Sea Otters (enhydra lutris): Structural and functional observations. Journal of Comparative Physiology A, 206(5), 767–782. https://doi.org/10.1007/s00359-020-01436-4
Conn, J. S. (2009). Sea otter pair. Flickr. Retrieved December 19, 2022, from https://www.flickr.com/photos/jstephenconn/5336255344/in/photolist-98xGNu-dfu9ny-5Yy8Hx-6TKJqT-6ThQtZ-54m9Yb-6Epffs-3bncGz-7dd8uA-e2oDHX-p7VTX6-R5WcDi-GnQgZs-AFq25-4dh8FA-Edv1-DP18W2-39E2vP-rdLxDc-fkWDaS-bJoBdX-dyU3Bk-9rbCp7-e2oEmZ-f42RBP-75sHsM-9gSWbQ-oXXPhi-4DM7FX-5nF2iM-69qjRR-o9w7xy-FXobgf-rb7JWb-hLyJaQ-x4QDsT-owJEVD-dFbAXb-89qcNS-hLxVKN-otFxLz-e4URMo-6rmjzb-oNdmwP-jwWF4H-qTCc6A-hLyzuJ-2ibX2t-Snk7j-3brFKy.