Post by DinosaurMichael on Aug 4, 2012 5:20:00 GMT -5
Pleistocene Polar Bear - Ursus maritimus tyrannus
Ursus maritimus tyrannus was a very large fossil subspecies of polar bear, descended from an Arctic population of brown bears. Its name in Latin means tyrant sea bear. Ranging up to an estimated mass of 1,200 kg (2,600 lb), it was rather larger than any living bear race and was one of the largest mammalian terrestrial carnivores ever to exist. The species is mentioned by Björn Kurtén, who assigned it to a polar bear subspecies, U. m. tyrannus. Its bones have been found in England. 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.
Majungasaurus - Majungsaurus crenatissimus
Majungasaurus ( /məˌdʒʌŋɡəˈsɔrəs/ mah-JUNG-gə-SOR-əs; "Mahajanga lizard") is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 65.5 million years ago, at the end of the Cretaceous Period. Only one species (M. crenatissimus) has been identified. This dinosaur was briefly called Majungatholus, a name which is now considered a junior synonym of Majungasaurus. Like other abelisaurids, Majungasaurus was a bipedal predator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids. Known from several well-preserved skulls and abundant skeletal material, Majungasaurus has recently become one of the best-studied theropod dinosaurs from the Southern Hemisphere. It appears to be most closely related to abelisaurids from India rather than South America or continental Africa, a fact which has important biogeographical implications. Majungasaurus was the apex predator in its ecosystem, mainly preying on sauropods like Rapetosaurus, and is also one of the few dinosaurs for which there is direct evidence of cannibalism. was a medium-sized theropod that typically measured 6–7 meters (20–23 ft) in length, including its tail. Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26 ft). Scientists estimate that an average adult Majungasaurus weighed more than 1100 kilograms (2400 lb), although the largest animals would have weighed more. Its 8–9 meter (26–30 ft) relative Carnotaurus has been estimated to weigh 1500 kilograms (3300 lb).
Ursus maritimus tyrannus was a very large fossil subspecies of polar bear, descended from an Arctic population of brown bears. Its name in Latin means tyrant sea bear. Ranging up to an estimated mass of 1,200 kg (2,600 lb), it was rather larger than any living bear race and was one of the largest mammalian terrestrial carnivores ever to exist. The species is mentioned by Björn Kurtén, who assigned it to a polar bear subspecies, U. m. tyrannus. Its bones have been found in England. 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.
Majungasaurus - Majungsaurus crenatissimus
Majungasaurus ( /məˌdʒʌŋɡəˈsɔrəs/ mah-JUNG-gə-SOR-əs; "Mahajanga lizard") is a genus of abelisaurid theropod dinosaur that lived in Madagascar from 70 to 65.5 million years ago, at the end of the Cretaceous Period. Only one species (M. crenatissimus) has been identified. This dinosaur was briefly called Majungatholus, a name which is now considered a junior synonym of Majungasaurus. Like other abelisaurids, Majungasaurus was a bipedal predator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids. Known from several well-preserved skulls and abundant skeletal material, Majungasaurus has recently become one of the best-studied theropod dinosaurs from the Southern Hemisphere. It appears to be most closely related to abelisaurids from India rather than South America or continental Africa, a fact which has important biogeographical implications. Majungasaurus was the apex predator in its ecosystem, mainly preying on sauropods like Rapetosaurus, and is also one of the few dinosaurs for which there is direct evidence of cannibalism. was a medium-sized theropod that typically measured 6–7 meters (20–23 ft) in length, including its tail. Fragmentary remains of larger individuals indicate that some adults reached lengths of more than 8 meters (26 ft). Scientists estimate that an average adult Majungasaurus weighed more than 1100 kilograms (2400 lb), although the largest animals would have weighed more. Its 8–9 meter (26–30 ft) relative Carnotaurus has been estimated to weigh 1500 kilograms (3300 lb).
