Ursus Maritimus Tyrannus - Evolution and Classification

Evolution and Classification

U. m. tyrannus was the first polar bear and evolved sometime in the Middle Pleistocene. While the oldest fossil is 70,000 years old, the species is thought to have evolved between 100,000 and 250,000 years ago from a population of brown bear likely isolated by glaciation. That population is believed to have diminished in numbers quickly into a much smaller population, with selection pressures favouring those individuals who adapted better to the changed environment. Over time, subject to intense selective pressures, the small population evolved the characteristics of the first polar bears.

Initially the isolated brown bears displayed the same traits as brown bears of that time period. Because litters of cubs can show significant variations in hair color and hair thickness, this gave certain individuals a survival advantage passed on with each generation. Eventually skull changes and even changes in dentition occurred, leading to the smooth and rather quick evolution of U. m. tyrannus.