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What's New! The Evolution of Pacific Harbour SealsSite constructed by: Robby Chen and
Jeffery Low  http://www.photolib.noaa.gov/historic/cgs/theb3714.htm Pacific Harbour seals, Phoca vitulina richerdsi, are currently flourishing in the waters off the Northwestern coast of North America. These seals have a very large population of 300,000 animals (1979). In comparision to other seals, they are quite small in size. Males are approximately 1.62m in length and weigh 73kg. Females are slightly smaller in size, measuring 1.5m in length and 50kg in weight. The majority of harbour seals are two toned, with lighter spots on darker fur. Pacific Harbour seals are classifed as followed:
The origin of Pacific Harbour seals is very controversial because it is not known if they are monophyletic or biphyletic. Most scientists believe seals and sea lions evolved from the same ancestor because their genes are fairly similar. Using fossils and comparative morphology, scientists believe that both seals and sea lions, under the family name Pinnipeds, originated from an otterlike carnivore found in the North Atlantic during the Miocene.  A Monophyletic Cladiogram of Pinniped evolution with Ursids as
their closest releative.
Modern day Pacific Harbour seals have adapted to fit their life in the marine environment. They have evolved to excel in their aquatic habitat, however, the price they pay to specialize in the water is that they have lost the ability to live on land safely. The body structure of Pacific Harbour seals allows them to move quickly in the ocean, but their hind limbs are connected to their pelvic bone in such a way that it is impossible to rotate their hind limbs 360 degrees. As a result, Pacific Harbour seals cannot run or walk on solid ground. Their front limbs have evolved into flippers, which allow seals to swim quickly and change directions with ease.
The cold waters of the North Pacific have forced the seals to develop an insulation system of blubber and fur which enables them to withstand the low temperatures. Aside from acting as an insulator, the blubber also acts as an energy reserve. Due to the need for food deep underneath the ocean's surface, the respiratory systems of seals have had to adapt to the requirements of deep sea diving. The lungs of the seals are collapsable to allow them to maintain even pressure in the body when diving. When the pressure in the body is equal, the seals are able to dive deeply and surface quickly without suffering from decompression sickness. Futhermore, the seals can conserve their oxygen by shunting blood to their vital organs. Their metabolic rate and temperature decrease to slow their heart beat to as little as one-tenth the normal rate. The seals also have more hemoglobin and a component in their blood called myoglobin in large quantities which enables them to tolerate large quantites of caron dioxide in their bloodstream. Finally, the seals have a very high tolerance for lactic acid buildup in their muscles, which enables them to sustain their muscle activity.  http://www.photolib.noaa.gov/coastline/line1722.htm ReferencesBerta, Annalisa and Sumich, James L. "Marine Mammals: Evolutionary Biology" Academic Press, London. 1999. King, Judith E. "Seals of the world" Comstock Publishing Associates, New York. 1983. Riedman, Marianne. "The Pinnipeds" University of California Press, California. 1990. Questions and answers about seals |
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