Post by DinosaurMichael on Feb 27, 2012 20:18:13 GMT -5
Woolly Mammoth - Mammuthus primigenius
The woolly mammoth (Mammuthus primigenius), 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. They are perhaps the most well known species of mammoth. This mammoth species was first recorded in (possibly 150,000 years old) deposits of the second last glaciation in Eurasia. It was derived from the steppe mammoth (Mammuthus armeniacus). It disappeared from most of its range at the end of the Pleistocene (10,000 years ago), with an isolated population still living on Wrangel Island until roughly 1700 BC. Woolly mammoths are common in the fossil record. Unlike most other prehistoric animals, their remains are often not literally fossilised - that is, turned into stone - but rather are preserved in their organic state. This is due in part to the frozen climate of their habitats, and to their massive size. Woolly mammoths are therefore among the best-understood prehistoric vertebrates known to science in terms of anatomy. Woolly mammoths lived in two groups which are speculated to be divergent enough to be characterised as subspecies. One group stayed in the middle of the high Arctic, while the other group had a much wider range. The Bering Land Bridge likely played an important role in structuring woolly mammoth populations, acting as an ecological barrier. Recent stable isotope studies of Siberian and New World mammoths has shown there were also differences in climatic conditions on either side of the Bering Land Bridge, with Siberia being more uniformly colder and drier throughout the Late Pleistocene. Woolly mammoths were not noticeably larger than present-day African elephants. Fully grown mammoth bulls reached heights between 2.8 m (9.2 ft) and 3.0 m (9.8 ft) while the dwarf varieties reached between 1.8 m (5.9 ft) and 2.3 m (7.5 ft). Woolly mammoths had a number of adaptations to the cold, most famously the thick layer of shaggy hair, up to 1 meter in length, with a fine underwool, for which the woolly mammoth is named. The coats were similar to those of muskoxen, and it is likely mammoths moulted in summer. They also had far smaller ears than modern elephants; the largest mammoth ear found so far was only 30 cm (12 in) long, compared to 180 cm (71 in) for an African elephant. Their skin was no thicker than that of present-day elephants, but unlike elephants, they had numerous sebaceous glands in their skin which secreted greasy fat into their hair, improving its insulating qualities. They had a layer of fat up to 8 cm (3.1 in) thick under the skin which, like the blubber of whales, helped to keep them warm. Similar to reindeer and musk oxen, their haemoglobin was adapted to the cold, with three genetic mutations to improve oxygen delivery around the body and prevent freezing. Other characteristic features included a high, peaked head that appears knob-like in many cave paintings, and a high shoulder hump resulting from long spinous processes on the neck vertebrae that probably carried fat deposits. Another feature at times found in cave paintings was confirmed by the discovery of the nearly intact remains of a baby mammoth named Dima. Unlike the trunk lobes of living elephants, Dima's upper lip at the tip of the trunk had a broad lobe feature, while the lower lip had a broad, squarish flap. Their teeth were also adapted to their diet of coarse tundra grasses, with more plates and a higher crown than their southern relatives. Woolly mammoths had extremely long tusks — up to 5 m (16 ft) long — which were markedly curved, to a much greater extent than those of elephants. It is not clear whether the tusks were a specific adaptation to their environment; mammoths may have used their tusks as shovels to clear snow from the ground and reach the vegetation buried below. This is evidenced by flat sections on the ventral surface of some tusks. It has also been observed in many specimens that there may be an amount of wear on top of the tusk that would suggest some animals had a preference as to which tusk on which they rested their trunks.
Triceratops - Triceratops horridus
Triceratops ( /traɪˈsɛrətɒps/ try-SERR-ə-tops) is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago (Mya) in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene extinction event. The term Triceratops, which literally means "three-horned face," is derived from the Greek τρί- (tri-) meaning "three", κέρας (kéras) meaning "horn", and ὤψ (ops) meaning "face". Bearing a large bony frill and three horns on its large four-legged body, and conjuring similarities with the modern rhinoceros, Triceratops is one of the most recognizable of all dinosaurs and the best known ceratopsid. It shared the landscape with and was preyed upon by the fearsome Tyrannosaurus, though it is less certain that the two did battle in the manner often depicted in traditional museum displays and popular images. The exact placement of the Triceratops genus within the ceratopsid group has been debated by paleontologists. Two species, T. horridus and T. prorsus, are considered valid although many other species have been named. Recent research suggests that the contemporaneous Torosaurus, a ceratopsid long regarded as a separate genus, actually represents Triceratops in its mature form. Triceratops has been documented by numerous remains collected since the genus was first described in 1889, including at least one complete individual skeleton. Paleontologist John Scannella observed: "It is hard to walk out into the Hell Creek Formation and not stumble upon a Triceratops weathering out of a hillside." Forty-seven complete or partial skulls were discovered in just that area during the decade 2000–2010. Specimens representing life stages from hatchling to adult have been found. The function of the frills and three distinctive facial horns has long inspired debate. Traditionally these have been viewed as defensive weapons against predators. More recent theories, noting the presence of blood vessels in the skull bones of ceratopsids, find it more probable that these features were primarily used in identification, courtship and dominance displays, much like the antlers and horns of modern reindeer, mountain goats, or rhinoceros beetles. The theory finds additional support if Torosaurus represents the mature form of Triceratops, as this would mean the frill also developed holes (fenestrae) as individuals reached maturity, rendering the structure more useful for display than defense. Individual Triceratops are estimated to have reached about 7.9 to 9.0 m (26.0–29.5 ft) in length, 2.9 to 3.0 m (9.5–9.8 ft) in height, and 6.1–12.0 tonnes (13,000–26,000 lb) in weight. The most distinctive feature is their large skull, among the largest of all land animals. The largest known skull (specimen BYU 12183) is estimated to have been 2.5 metres (8.2 ft) in length when complete, and could reach almost a third of the length of the entire animal. It bore a single horn on the snout, above the nostrils, and a pair of horns approximately 1 m (3 ft) long, with one above each eye. To the rear of the skull was a relatively short, bony frill, adorned with epoccipitals in some specimens. Most other ceratopsids had large fenestrae in their frills, while those of Triceratops were noticeably solid. The skin of Triceratops was unusual compared to other dinosaurs. Skin impressions from an as-yet undescribed specimen show that some species may have been covered in bristle-like structures, similar to the more primitive ceratopsian Psittacosaurus.
The woolly mammoth (Mammuthus primigenius), 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. They are perhaps the most well known species of mammoth. This mammoth species was first recorded in (possibly 150,000 years old) deposits of the second last glaciation in Eurasia. It was derived from the steppe mammoth (Mammuthus armeniacus). It disappeared from most of its range at the end of the Pleistocene (10,000 years ago), with an isolated population still living on Wrangel Island until roughly 1700 BC. Woolly mammoths are common in the fossil record. Unlike most other prehistoric animals, their remains are often not literally fossilised - that is, turned into stone - but rather are preserved in their organic state. This is due in part to the frozen climate of their habitats, and to their massive size. Woolly mammoths are therefore among the best-understood prehistoric vertebrates known to science in terms of anatomy. Woolly mammoths lived in two groups which are speculated to be divergent enough to be characterised as subspecies. One group stayed in the middle of the high Arctic, while the other group had a much wider range. The Bering Land Bridge likely played an important role in structuring woolly mammoth populations, acting as an ecological barrier. Recent stable isotope studies of Siberian and New World mammoths has shown there were also differences in climatic conditions on either side of the Bering Land Bridge, with Siberia being more uniformly colder and drier throughout the Late Pleistocene. Woolly mammoths were not noticeably larger than present-day African elephants. Fully grown mammoth bulls reached heights between 2.8 m (9.2 ft) and 3.0 m (9.8 ft) while the dwarf varieties reached between 1.8 m (5.9 ft) and 2.3 m (7.5 ft). Woolly mammoths had a number of adaptations to the cold, most famously the thick layer of shaggy hair, up to 1 meter in length, with a fine underwool, for which the woolly mammoth is named. The coats were similar to those of muskoxen, and it is likely mammoths moulted in summer. They also had far smaller ears than modern elephants; the largest mammoth ear found so far was only 30 cm (12 in) long, compared to 180 cm (71 in) for an African elephant. Their skin was no thicker than that of present-day elephants, but unlike elephants, they had numerous sebaceous glands in their skin which secreted greasy fat into their hair, improving its insulating qualities. They had a layer of fat up to 8 cm (3.1 in) thick under the skin which, like the blubber of whales, helped to keep them warm. Similar to reindeer and musk oxen, their haemoglobin was adapted to the cold, with three genetic mutations to improve oxygen delivery around the body and prevent freezing. Other characteristic features included a high, peaked head that appears knob-like in many cave paintings, and a high shoulder hump resulting from long spinous processes on the neck vertebrae that probably carried fat deposits. Another feature at times found in cave paintings was confirmed by the discovery of the nearly intact remains of a baby mammoth named Dima. Unlike the trunk lobes of living elephants, Dima's upper lip at the tip of the trunk had a broad lobe feature, while the lower lip had a broad, squarish flap. Their teeth were also adapted to their diet of coarse tundra grasses, with more plates and a higher crown than their southern relatives. Woolly mammoths had extremely long tusks — up to 5 m (16 ft) long — which were markedly curved, to a much greater extent than those of elephants. It is not clear whether the tusks were a specific adaptation to their environment; mammoths may have used their tusks as shovels to clear snow from the ground and reach the vegetation buried below. This is evidenced by flat sections on the ventral surface of some tusks. It has also been observed in many specimens that there may be an amount of wear on top of the tusk that would suggest some animals had a preference as to which tusk on which they rested their trunks.
Triceratops - Triceratops horridus
Triceratops ( /traɪˈsɛrətɒps/ try-SERR-ə-tops) is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago (Mya) in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene extinction event. The term Triceratops, which literally means "three-horned face," is derived from the Greek τρί- (tri-) meaning "three", κέρας (kéras) meaning "horn", and ὤψ (ops) meaning "face". Bearing a large bony frill and three horns on its large four-legged body, and conjuring similarities with the modern rhinoceros, Triceratops is one of the most recognizable of all dinosaurs and the best known ceratopsid. It shared the landscape with and was preyed upon by the fearsome Tyrannosaurus, though it is less certain that the two did battle in the manner often depicted in traditional museum displays and popular images. The exact placement of the Triceratops genus within the ceratopsid group has been debated by paleontologists. Two species, T. horridus and T. prorsus, are considered valid although many other species have been named. Recent research suggests that the contemporaneous Torosaurus, a ceratopsid long regarded as a separate genus, actually represents Triceratops in its mature form. Triceratops has been documented by numerous remains collected since the genus was first described in 1889, including at least one complete individual skeleton. Paleontologist John Scannella observed: "It is hard to walk out into the Hell Creek Formation and not stumble upon a Triceratops weathering out of a hillside." Forty-seven complete or partial skulls were discovered in just that area during the decade 2000–2010. Specimens representing life stages from hatchling to adult have been found. The function of the frills and three distinctive facial horns has long inspired debate. Traditionally these have been viewed as defensive weapons against predators. More recent theories, noting the presence of blood vessels in the skull bones of ceratopsids, find it more probable that these features were primarily used in identification, courtship and dominance displays, much like the antlers and horns of modern reindeer, mountain goats, or rhinoceros beetles. The theory finds additional support if Torosaurus represents the mature form of Triceratops, as this would mean the frill also developed holes (fenestrae) as individuals reached maturity, rendering the structure more useful for display than defense. Individual Triceratops are estimated to have reached about 7.9 to 9.0 m (26.0–29.5 ft) in length, 2.9 to 3.0 m (9.5–9.8 ft) in height, and 6.1–12.0 tonnes (13,000–26,000 lb) in weight. The most distinctive feature is their large skull, among the largest of all land animals. The largest known skull (specimen BYU 12183) is estimated to have been 2.5 metres (8.2 ft) in length when complete, and could reach almost a third of the length of the entire animal. It bore a single horn on the snout, above the nostrils, and a pair of horns approximately 1 m (3 ft) long, with one above each eye. To the rear of the skull was a relatively short, bony frill, adorned with epoccipitals in some specimens. Most other ceratopsids had large fenestrae in their frills, while those of Triceratops were noticeably solid. The skin of Triceratops was unusual compared to other dinosaurs. Skin impressions from an as-yet undescribed specimen show that some species may have been covered in bristle-like structures, similar to the more primitive ceratopsian Psittacosaurus.
