Post by DinosaurMichael on Sept 24, 2013 0:46:41 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. 
Steppe Rhinoceros - Elasmotherium sibiricum
Elasmotherium ("Thin Plate Beast") is an extinct genus of giant rhinoceros endemic to Eurasia during the Late Pliocene through the Pleistocene, documented from 2.6 mya to as late as 50,000 years ago, possibly later, in the Late Pleistocene, an approximate span of slightly less than 2.6 million years. Three species are recognised. The best known, E. sibiricum was the size of a mammoth and is thought to have borne a large, thick horn on its forehead which was used for defense, attracting mates, driving away competitors, sweeping snow from the grass in winter and digging for water and plant roots. Like all rhinoceroses, elasmotheres were herbivorous. Unlike any others, its high-crowned molars were ever-growing. Its legs were longer than those of other rhinos and were designed for galloping, giving it a horse-like gait. The Russian paleontologists of the 19th century who discovered and named the initial fossils were influenced by ancient legends of a huge unicorn roaming the steppes of Siberia. To date no evidence either contradicts or confirms the possibility that Elasmotherium survived into legendary times. The most reconstructed species is perhaps E. sibiricum by generations of scientists working at the Paleontological Museum in Moscow and elsewhere in Russia. The majority of the fossils fall or have fallen within their national jurisdiction. The dimensions and morphology of the various reconstructions vary considerably. They are for the most part estimating the gross details from the minutiae. However, they all agree on the general order of magnitude, that sibiricum was comparable to a Mammoth and was rather larger than the contemporary Woolly Rhinoceros. E. sibiricum had a measured shoulder height of approximately 2 metres (6.6 ft). To it, however, must be added the height of a massive hump anchored on the fin-like transverse processes extending from the top of the cervical vertebrae, a maximum of 53 centimetres (1.74 ft). The total height then was in excess of 253 centimetres (8.30 ft). The measured length of sibiricum (from a nearly complete skeleton found at Gaevskaya) is 4.5 metres (15 ft). Extrapolation from the greater size of caucasicum molars obtains a length of 5 metres (16 ft)—5.2 metres (17 ft) for caucasicum. According to Legendre's formula, E. sibiricum had a mass of over 4,000 kilograms (3.9 long tons; 4.4 short tons); E. caucasicum, 5,000 kilograms (4.9 long tons; 5.5 short tons). These weights place Elasmotherium in the "really huge" category of all Rhinocerotidae and therefore the animal was "strongly brachyopodial;" that is, they required feet of large contact area to prevent sinking into the soil. The feet were unguligrade, the front larger than the rear: purely tridactyl on Digits II-IV in the rear, but with an extra vestigial digit, I, in the front.
