Post by grrraaahhh on Nov 10, 2010 20:01:11 GMT -9
Ursus maritimus tyrannus (The Tyrannt Sea Bear)
Ursus maritimus tyrannus was a very large fossil subspecies of the modern Polar bears that descended from an Arctic population of Brown bears. Its name in Latin means The Tyrannt Sea Bear. The species is mentioned by Björn Kurtén (1964), who assigned it to a Polar bear subspecies, Ursus maritimus tyrannus. Its bones have been found in contemporary England.
Ursus maritimus tyrannus was the first Polar bear and evolved sometime in the mid-Pleistocene. While the oldest fossil is 100,000 years old, the species is thought to have evolved between 100,000 and 250,000 years ago from a population of brown bears 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 were 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. maritimus tyrannus.