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By Phil Myers
This family includes 14 species in 7 genera. Their distribution is complex. In the Pacific, they are found along the North and South American coasts, the coasts of central and northern Asia, and on New Zealand and several other islands, including the Galapagos. In the South Atlantic, otariids can be found along the South American coast and on a number of islands. In the Indian Ocean, they are found only along the coast of SW Australia and on islands.
Sea lions are large, ranging from around 150 kg to over 1000 kg, and males tend to be much larger than females. Their bodies are slender and elongate. Small, cartilaginous external ears are present. All otariids have fur. In the sea lions, relatively coarse hairs predominate, while in the fur seals, dense underfur is also present. Colors are generally shades of brown, without stripes or other contrasting markings. The fore flippers of otariids are long and paddle-like, more than 1/4 of the length of the body. The surfaces of the fore flippers are naked and leathery, and claws are present but small. The hind flippers are also large. They differ from those of true seals ( phocids) in that they can be rotated under the animal when it is on land, partially supporting the body and helping in locomotion. Otariids also have a small but distinct tail. Males have a baculum.
The 
skulls of otariids is bear-like. An alisphenoid canal is present, as are postorbital and supraorbital processes. The occipital condyles are located high on the back of the cranium. The bony part of the eustachian tube is not enlarged. The dental formula is 3/2, 1/1, 4/4, 1-3/1 = 34-38. Postcanine teeth are homodont and generally conical in shape. The first two incisors have a distinctive transverse groove that divides them into two cusps, while the third is canine-like. The canines are large, concial, and curved.
Otariids tend to be highly social, forming large herds during the breeding season. Within these herds, individual males maintain harems. Males arrive on the breeding grounds before females and set up territories, which they defend aggressively. Females arrive and segregate into harems of 3 - 40 indidivuals, depending on the size and strength of the male. Soon after they arrive, females give birth to pups from the previous year's breeding season, and within a few days, enter estrous. Mating takes place on land. A period of delayed implantation insures that the young will be born in a year, when the breeding herds again form.
These animals feed on fish, cephalopods, and crustaceans.
Otariids are known from as early as the Early Miocene. Their phylogenetic relationships are discussed in the description of the order Carnivora.
Literature and references cited
Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. 1999. Mammalogy. Adaptation, Diversity, and Ecology. WCB McGraw-Hill, Boston. xii+563pp.
Paradiso, J. L. 1975. Walker's Mammals of the World, Third Edition. Johns Hopkins University Press, Baltimore.
Savage, R. J. G. and M. R. Long. 1986. Mammal Evolution, an Illustrated Guide. Facts of File Publications, New York. 259 pp.
Stains, H. J. 1984. Carnivores. Pp. 491-521 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.
Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.
Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mammalogy. Fourth Edition. Saunders College Publishing, Philadelphia. vii+565pp.
Wilson, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.
Contributors
Phil Myers (author), Museum of Zoology, University of Michigan.
