Ursus maritimus tyrannus
Encyclopedia
Ursus maritimus tyrannus was a very large fossil subspecies of polar bear
, descended from an Arctic
population of brown bear
s. Its name in Latin
means tyrant sea bear. The species is mentioned by Björn Kurtén
, who assigned it to a Polar bear subspecies, U. m. tyrannus. Its bones have been found in contemporary England
.
The few bones that have been found of U. m. tyrannus are very similar to the brown bear bones, but considerably larger in dimensions. If everything is scaled out correctly from its remains, it would have been 1.83 metre at the shoulders, 3.7 metre long, and about 4 metre on the hind legs and with an average weight of 1.2 tonnes or more. Although being less massive than Arctotherium angustidens
, U. m. tyrannus was still one of the largest bear
s known and one of the largest mammalian carnivore
s to ever hunt on land.
. 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 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.
much of Europe
, including England, was covered with ice sheet
s, and large herbivore
s such as the woolly mammoth
would have been abundant. The prevalence of these prey species, and the general lack of plant
material in its environment, might have forced U. m. tyrannus to adopt a more carnivorous diet. The similarity of U. m. tyrannuss build to that of modern brown and polar bears, and its distinctness from species like Arctodus simus, would have made the animal much more suitable for taking on very large prey species, using its massive forelimb
s to grab and wrestle down prey. Modern polar bears have been observed to wrestle down and kill animals much heavier than themselves, such as bull walrus
es.
Polar Bear
The polar bear is a bear native largely within the Arctic Circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak Bear, which is approximately the same size...
, descended from an Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
population of brown bear
Brown Bear
The brown bear is a large bear distributed across much of northern Eurasia and North America. It can weigh from and its largest subspecies, the Kodiak Bear, rivals the polar bear as the largest member of the bear family and as the largest land-based predator.There are several recognized...
s. Its name in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
means tyrant sea bear. The species is mentioned by Björn Kurtén
Björn Kurtén
Björn Olof Lennartson Kurtén was a distinguished vertebrate paleontologist. He belonged to the Swedish-speaking minority in Finland. He was a professor in paleontology at the University of Helsinki from 1972 up to his death in 1988...
, who assigned it to a Polar bear subspecies, U. m. tyrannus. Its bones have been found in contemporary England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
.
The few bones that have been found of U. m. tyrannus are very similar to the brown bear bones, but considerably larger in dimensions. If everything is scaled out correctly from its remains, it would have been 1.83 metre at the shoulders, 3.7 metre long, and about 4 metre on the hind legs and with an average weight of 1.2 tonnes or more. Although being less massive than Arctotherium angustidens
Arctotherium
Arctotherium is an extinct genus of South American short-faced bears within Ursidae of the late Pliocene through the end of the Pleistocene. Their ancestors migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama. They...
, U. m. tyrannus was still one of the largest bear
Bear
Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives. Although there are only eight living species of bear, they are widespread, appearing in a wide variety of habitats throughout the Northern...
s known and one of the largest mammalian carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s to ever hunt on land.
Evolution
U. m. tyrannus was the first polar bear and evolved sometime in the Middle PleistoceneMiddle Pleistocene
The Middle Pleistocene, more specifically referred to as the Ionian stage, is a period of geologic time from ca. 781 to 126 thousand years ago....
. 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 bear
Brown Bear
The brown bear is a large bear distributed across much of northern Eurasia and North America. It can weigh from and its largest subspecies, the Kodiak Bear, rivals the polar bear as the largest member of the bear family and as the largest land-based predator.There are several recognized...
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.
Hunting and diet
The diet and hunting behaviour of U. m. tyrannus are virtually unknown, though the similarity of its anatomy to that of the brown bears may suggest that its diet and hunting behaviour were more like those of brown bears than polar bears. The development of the dentition displayed by modern polar bears began as late as 10,000 years ago, as polar bears' diets became more specialized and carnivorous; the process may have started with U. m. tyrannus. In the PleistocenePleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
much of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, including England, was covered with ice sheet
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
s, and large herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s such as the woolly mammoth
Woolly mammoth
The woolly mammoth , also called the tundra mammoth, is a species of mammoth. This animal is known from bones and frozen carcasses from northern North America and northern Eurasia with the best preserved carcasses in Siberia...
would have been abundant. The prevalence of these prey species, and the general lack of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
material in its environment, might have forced U. m. tyrannus to adopt a more carnivorous diet. The similarity of U. m. tyrannuss build to that of modern brown and polar bears, and its distinctness from species like Arctodus simus, would have made the animal much more suitable for taking on very large prey species, using its massive forelimb
Forelimb
A forelimb is an anterior limb on an animal's body. When referring to quadrupeds , the term foreleg is often instead used....
s to grab and wrestle down prey. Modern polar bears have been observed to wrestle down and kill animals much heavier than themselves, such as bull walrus
Walrus
The walrus is a large flippered marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and sub-Arctic seas of the Northern Hemisphere. The walrus is the only living species in the Odobenidae family and Odobenus genus. It is subdivided into three subspecies: the Atlantic...
es.