Pinnipedia is a broadly distributed and varied group of semi-aquatic sea mammals. It consists of three families that include Otariidae (eared seals), Odobenidae (extant walruses) and the Phocidae (Earless seals) (Harrison & King 102).
Pinnipeds were first spotted in the middle Miocene having been tremendously specialized for an aquatic survival. It has been proposed that the pinnipedia may have had a two fold origin and a monophyletic foundation.
Pinnipeds are polygamous with the males being larger than the females. Towards the breeding season, the males choose the breeding sites and establish harems on the arrival of the females. This depends on the species. The males assertively defend groups of particular females while others protect the reproductive terrain. Males compete for females.
Breeding occurs especially during the late spring and summer. A single pup is normally produced yearly but twins’ occasionally occur. After giving birth, the females wean their young ones for an uneven period of time. The females possess a postpartum estrus that permits them to breed soon after reproduction (Harrison & King 102).
Pinnipeds constitute slightly more than 28% of the diversity of marine mammal species with 33-37 living species being spread all through the world. Of these species, 18 belong to the family Phocidae, and the remaining 14-18 species belong to the Otariidae and the Odobenidae family.
Shapes/ Sizes and Color
Pinnipeds are smooth bodied and have a barrel shape. This makes them to be well adapted to their marine habitats. The large size of Pinnipeds in comparison with most earth carnivores helps them to preserve warmth in their bodies. Their sizes differ with the smallest Pinniped being 1.3 m when fully grown and the largest being 4m long.
Color patterns in Pinnipeds occur almost entirely among the family Phocidae. Others show dark and disruptive color patterns (Nowak 1458). Some Pinnipeds have a homogeneous coloration and this permits them to intermingle well with their icy surroundings.
Pinnipeds have a typical behavior of going back to land to reproduce. They are polygynous with triumphant males mating with quite a number of females throughout the breeding period. The males compete for females and the females reach sexual maturity before the males.
Pinnipeds are carnivorous. They feed on sea creatures including fish, crustaceans and sea birds. Most are general feeders while a few concentrate on some foods only. Pinniped eyes are well adapted to darkness hence they do most of their feeding at night (Henry 110).
Role of Pinnipeds in the food chain
Pinnipeds play a major role in the food chain. They feed on crustaceans, echinoderms, fish and young whales. They are themselves eaten by orcas, bears and human beings. Walruses for instance have been chased by natives due to their flesh, hide and tusk.
Pinnipeds have tusks that grow up to a length of one meter. Males have larger tusks compared to the females. They use these tasks for fighting and sparring their enemies. Pinnipeds also have bristles all over their mouths for defense.
Pinnipeds are adapted for movement both on land and on water. They have wing like flippers on the front and on the back. Both pairs assist them while walking on land. During swimming in water, the hind limbs are turned backwards and are kept parallel with the vertebral column. Their feet act as sufficient propellers. Some Pinnipeds are however belly walkers with rising and falling movements of the abdomen. Pinnipeds movement in water is thus graceful and they frequently engage themselves in water sports.
They spend almost all their life in water, beaches or ice floes. Pinnipeds are good divers being able to fight back ache and fatigue associated with lactic acid build up during spinning. They produce sounds while in water or on land. These sounds are associated with breeding and other social interactions (Henry 110).
Harrison, Richard & King, Judith. Marine mammals .London: Hutchinson University Library, 2006. Print.
Henry, William. Antarctic Pinnipedia .Washington, D.C: American Geophysical Union, 1971. Print.
Nowak, Ronald. Walker’s Mammals of the World. London: John Hopkins University Press, 1999. Print.