The North American river otter (Lontra canadensis) is a member of Mustelidae (Carnivora), the clade that also includes badgers, minks and weasels. Mustelids are caniform carnivorans, meaning that they are more closely related to dogs and bears than to cats and hyenas. Within Mustelidae, Lutrinae, which includes both river and sea otters, is most closely related to Mephitinae, the skunks (Wyss and Flynn, 1993). The current distribution of the North American river otter extends from New England to the Great Lakes states, the Atlantic coast and Gulf of Mexico, much of Canada and Alaska, and the Pacific northwest of the United States (Lerivière and Walton, 1998). Although the fossil record of Lutrinae in North America extends to the Lower and Upper Pliocene, evidence suggests that otters originated in Eurasia. The first record of Lontra canadensis is from the Irvingtonian (Lerivière and Walton, 1998).
The North American river otter is often placed within the genus Lutra (e.g., Nowak, 1991), which includes Old World river otters. However, many researchers accept Lontra as a valid genus (Kellnhauser, 1983) because morphological data clearly separate Lontra from Lutra (van Zyll de Jong, 1972, 1987). In fact, Lontra is more closely related to the clawless otters (Aonyx and Amblonyx) than to Lutra.
Four species of Lontra are currently recognized: L. canadensis, L. felina, L. longicaudus and L. provocax (Lerivière and Walton, 1998). Lontra canadensis can be distinguished from these other species by its small size relative to L. felina (a marine species) and fur on the ventral surface of its feet. Additional diagnostic features include fully webbed feet, a long and tapered tail that contributes over 1/3 of the total length of the animal, and short, dark, glossy fur. North American River otters lack much subcutaneous and abdominal fat, and the pelage provides the primary means of insulation (Batichman and Kollias, 2000). The fur is very dense, and is concentrated to roughly 57,800 hairs per cm2 (Lerivière and Walton, 1998).
The dental formula of Lontra canadensis is 3/3, 1/1, 4/3, 1/2. Internally, North American river otters have a liver with 6 lobes, a large spleen (similar to that in Lutra lutra), and multilobate (reniculate) kidneys (Baitchman and Kollias, 2000). Such kidneys are observed in other otters, but this condition is unique among mustelids. Furthermore, the kidneys of otters are not retroperitoneal, but rather suspended in mesenchyme within the abdominal cavity.
Female Lontra canadensis are polygynous, and breeding occurs from December to April (Lerivière and Walton, 1998). True gestation lasts 61-63 days, but there is delayed implantation of the egg in the uterus, which may last up to 8 months. Because of this, young typically are born between February and April. Litter sizes are generally 1-3 kits, but a litter of 5 is not unknown. Weaning occurs at 12 weeks after birth, and maximum weight of both males and females is acheieved at 3-4 years (Lerivière and Walton, 1998). Wild L. canadensis live up to 10 years, but individuals may live up to 23 years in captivity (Baitchman and Kollias, 2000).
North American river otters are active year round, and they are nocturnal to crepuscular (Lerivière and Walton, 1998). Among mustelids, L. canadensis is one of the more social. Both small groups and solitary individuals have been observed in the wild. There is no apparent correlation between kinship and sociality, nor is there a correlation between age or body size and solitary behavior in male L. canadensis (Blundell et al., 2004).
Additional Information on the Skull
Click on the thumbnails below for labeled images of the skull in standard anatomical views.
Baitchman, E. J. and G. V. Kollias. 2000. Clinical anatomy of the North American river otter (Lontra canadensis). Journal of Zoo and Wildlife Medicine 31:473-483.
Blundell, G. M., M. Ben-David, P. Groves, R. T. Bowyer, and E. Geffen. 2004. Kinship and sociality in coastal river otters: are they related? Behavioral Ecology 15:705-714.
Kellnhauser, J. T. 1983. The acceptance of Lontra Gray for the New World river otters. Canadian Journal of Zoology 61:278-279.
Lerivière, S. and L. R. Walton. 1998. Lonta canadensis. Mammalian Species 587:1-8.
Nowak, R. M. 1991. Walker’s Mammals of the World, Fifth Edition. Volume II. The Johns Hopkins University Press, Baltimore. 1629 pp.
van Zyll de Jong, C. G. 1972. A systematic review of the Nearctic and Neotropical river otters (genus Lutra, Mustelidae, Carnivora). Life Sciences Contributions of the Royal Ontario Museum 80:1-104.
van Zyll de Jong, C. G. 1987. A phylogenetic study of the Lutrinae (Carnivora; Mustelidae) using morphological data. Canadian Journal of Zoology 65:2536-2544.
Wyss, A. R. and J. J. Flynn. 1993. A phylogenetic analysis and definition of the Carnivora. pp. 32-52 IN Szalay, F. S., M J. Novacek, and M. C. McKenna, eds. Mammal Phylogeny: Placentals. Springer-Verlag, New York.
Lontra canadensis page on the Animal Diversity Web (University of Michigan Museum of Zoology)
L. canadensis page on the Discover Life's Encyclopedia
L. canadensis page on the Lioncrusher's Domain