Diprotodons free essay sample

Introduction Diprotodon, meaning two forward teeth,  sometimes known as the  Giant Wombat  or the  Rhinoceros Wombat, was the largest known  marsupial that ever lived and the last of the extinct, herbivorous Diprotodontids. Diprotodon was the first fossil mammal named from Australia and one of the most well-known of the mega fauna. It was widespread across Australia when the first indigenous people arrived, co-existing with them for thousands of years before becoming extinct about 25,000 years ago. Distribution and Abundance Diprotodon is known from many sites across Australia, including the Darling Downs in southeastern Queensland: Wellington Caves, Tambar Springs and Cuddie Springs in New South Wales; Bacchus Marsh in Victoria; Lake Callabonna, Naracoorte Caves and Burra in South Australia. It is believed that Diprotodons could be found in all parts of Australia except in Tasmania. Until recently it was unknown how many species of  Diprotodon  had existed. Sir Richard Owen, a well- known palaeolontologist, studied them and gave the genus the name, Diprotodon in 1938. Wikipedia Reports 4 species : Diprotodon optatum, Diprotodon minor, Diprotodon laden, Diprotodon annextans. Timeline Evolution of the Flora The past 2 million years have been characterized by marked instability of the vegetation caused by dramatic cyclical fluctuations in climate. The remaining evergreen rainforest was further stressed. Evidence from southeastern Australia indicates that rainforest and Sclerophyll vegetation had very restricted distributions within a predominantly steppe vegetation during the cold dry periods of the ice ages. These colder conditions would have also made it easier for cold-adapted herbaceous plants from overseas to colonize Australia. By around 750,000 years ago, the vegetation had become adapted to the climatic changes. This pattern was broken within the last glacial cycle, possibly 140,000 years ago, with substantial replacement of the remaining rainforest and fire-sensitive sclerophyll vegetation by fire-tolerant communities, especially those dominated by eucalypts. This change was accompanied by significant increases in charcoal due to an increase in burning, perhaps the result of Aboriginal activities. Effects of this increase were probably greatest during the height of the last ice age, between about 20, 000 and 10,000 years ago. Today’s plant distributions have developed only within the past 10,000 years under higher temperatures and rainfall levels and have been affected by frequent fires. The Historical Development of Fauna The development of contemporary climatic patterns in Australia – of monsoonal rains across the north, Mediterranean winter rains across the south, year-rain only on the mountain ranges of the coast, and low erratic rain inland – has had the effect of zoning the flora and fauna. Fauna Today Within the concentric faunal zones, the climatic fluctuations of the past several million years created cyclic make-and-break connections around the fringe of the continent. During cold, dry spells, the regional faunas were split and compressed into refugia and the fauna specied into isolation. When conditions ameliorated during the warmer, wetter periods between the ice ages, the isolated stocks expanded with their habitat and remet, to overlap or, if the speciation had not been completed to interbreed. In this way, rings of species formed around the periphery of the continent. Many of the refugia are self-evident from the number of endemic forms now present there. Evolution of Climate In â€Å"Pleistocene Climate Variation† compline by J. Richerson from the University of California, Richerson states that, using a variety of proxy measures of past temperature, rainfall, ice volume mostly from cores of ocean sediments, and ice caps, paleoclimatologists have constructed an increasingly detailed picture of the climate deterioration over the last few million years, culminating in the Pleistocene ice ages. The trend of deteriorating began in the mid-Miocene, about 14 million years ago. By the Pleistocene, the Earth’s temperature had dropped several degrees and the amplitude of climate variation increased. Continental ice sheets began in the middle Pleistocene about 900,000 years ago. Pleistocene environments varied gently in complex ways that presented organisms with major adaptive challenges. The glacial environments were not only colder but drier and had lower carbon dioxide content. Hence, the overall plant productivity was lower. According to time series analysts, the climate record of the past few million years is highly non-stationary. Physical features of the Diprotodon compared with the wombat Like many large living herbivores, Diprotodon was heavily built, large-bellied quadruped. It is up to 3. 8m long from head to tail and 1. 7m at the shoulder. While wombats are short-legged, muscular  quadrupeds, approximately 1m in length with a  tail  that is a mere nubbin. Diprotodons had an oversized skull, like those of other Diprotodontids, was lightweight and filled with numerous air spaces while Wombats have the most developed brain of any marsupial The skull contained four molars in  each jaw, three pairs of  upper incisors, and one pair of lower incisors. From this dentition, we can deduce that the diprotodons were herbivorous like wombats. The Diprotodons were probably browsers, rather than grazers, as their incisors enabled them to strip vegetation from branches. The molars, with their ? at surfaces, ground the food before it was swallowed. The limbs of  the Diprotodon  were sturdy and pillar-like. The upper limb bones were longer than the lower limb bones. The distinctive feet of  Diprotodon  were remarkably small for its size, and were in turned, as in wombats. At just under 4 metres in length and up to 2800 kilograms in weight, the  Diprotodon, although massive, was smaller than either a hippopotamus or rhinoceros, to which it is often compared. Unlike the Diprotdon, all four limbs of the wombat are short and powerful, the forelegs being the strongest. They also have powerful shoulders which help them dig. The hind legs are longer than the front; this can best be seen by examining a wombats skeleton. Both the front paws and the rear feet are wide and each have five digits. All digits are armed with broad claws except the first toe which is shorter than the others. The claws are long, strong, and well-designed for digging. Like all marsupials, diprotodons had a pouch. There are even bones of adult female diprotodons that are accompanied by the tiny skeletons of their joeys, which were in the pouch when their mothers died. Marsupial babies are born at a very early stage of development. Little more than embryos, they struggle through their mother’s fur to the pouch and latch onto one of the teats inside. The teat expands in their mouth, and they’re locked in place for the next few months, feeding on their mother’s milk. When the diprotodon baby outgrew the pouch, it ventured out into the wide world, keeping close to its mother and retreating to its furry refuge at the ? rst sign of danger, in much the same way as a kangaroo joey. In the case of the wombats, the pouch on the female wombat opens to the rear. This not only prevents it from filling with dirt and debris when the mother digs, it also provides greater protection to the young when the mother walks or runs as wombats have minimal ground clearance. Climate in the Pleistocene epoch and the current Climate in Australia The Pleistocene dates from 2. 88 million to 12,000 years ago before present, the era in which the Diprotodons lived. The overall climate of the Pleistocene could be characterized as continuous El Nino. Prolonged differences in Pacific Ocean surface temperatures compared with the average value define El Nino. Repeated glaciations occurred during the Pleistocnee with 30% of the earth’s surface being covered by ice at maximum glacial extent. During glacials plant productivity was lower but a high percentage of plants being tundra, shrub desert and steppe which favour herbivores like the Diprotodon. Huge volumes of water in continental ice sheets about 1500 to 3000 metres thich resulted in temporary sea levels drop of approximately 100 metres over the entire surface of the earth including Australia. Australia today experiences a relatively harsh and variable climate. Temperature ranges from above 50 degrees Celsius to well below zero unlike in the Pleistocene era. Due to the lack of mountains and the influence of surrounding oceans minimum temperatures are moderated. Rainfall patterns in Australia are highly seasonal. More than three quarters of the continent receive less than 600 mm of rainfall and less than 300 mm of rainfall is experienced in half of the continent. Northern Australia however, has heavy monsoonal rains in Summer and occasionally destructive tropical cyclones. Southern Australia enjoys a generally mild but still highly variable climate with predominantly winter rains and frequent spring and summer bushfires in the south eastern states. Australia’s tropical/ subtropical location and cold waters off the western coast make most of Western Australia a hot desert. These cold water produce moisture needed on the mainland. A 2005 study by Australia and American researchers investigated the desertification of the interior, maintain that regular burning by early settlers could have prevented monsoons from reaching interior Australia. ` Extinction Diprotodonts, along with a wide range of other Australian  megafauna, became extinct shortly after humans arrived in Australia about 50,000 years ago. Three theories have been advanced to explain the mass extinction. They are : a) Climate change Australia has undergone a very long process of gradual aridification since it split off from  Gondwanaland  about 40 million years ago. The recent  ice ages  produced no significant glaciation in mainland Australia but long periods of cold and very dry weather. This dry weather during the last ice age may have killed off all the large Diprotodons. Critics point out a number of problems with this theory. First, large Diprotodons had already survived a long series of similar ice ages, and there does not seem to be any particular reason why the most recent one should have achieved what all the previous ice ages had failed to do. Also, climate change apparently peaked 25,000 years  after  the extinctions. Finally, even during climatic extremes, some parts of the continent always remain relatively exempt: for example, the tropical north stays fairly warm and wet in all climatic circumstances; alpine valleys are less affected by drought, and so on. b) Human hunting The blitzkrieg  theory is that human hunters killed and ate the diprotodons, making them extinct. The extinctions appear to have coincided with the arrival of humans on the continent, and in broad terms,  Diprotodon  was the largest species that died out.. Recent finds of  Diprotodon  bones which appear to display butchering marks lend support to this theory. But critics of this theory regard it as simplistic, arguing that there is little direct evidence of hunting, and that the dates are too uncertain to be relied on. c) Human land management The third theory says that humans indirectly caused the extinction of diprotodonts, by destroying the  ecosystem  on which they depended. In particular, early Aborigines are thought to have been  fire-stick farmers  using fire regularly and persistently to drive game, open up dense thickets of vegetation, and create fresh green regrowth for both humans and game animals to eat. Evidence for the fire hypothesis is the sudden increase in widespread ash deposits at the time that people arrived in Australia, as well as land-management and hunting practices of modern  Aboriginal  people as recorded by the earliest European settlers before Aboriginal society was devastated by European contact and  disease. Evidence against the hypothesis is the fact that humans appear to have eliminated the megafauna of  Tasmania without using fire to modify the environment there. Although they are hotly and sometimes acrimoniously debated by specialists, few would argue that it is necessary to choose one single explanation for the extinction of many different animals in a wide range of different environments, from tropical to temperate, from desert to rainforest. The Giant Beaver Castoroides ohioensis  was a species of  the Giant beaver,  huge members  of the  family  Castoridae  (Rodentia), endemic to  North America  during the Pleistocene  epoch (1. 8  MYA—11,000 years ago) It was also the period the Diprotodons existed on the face of the Earth. However, the Diprotodons lived in parts of Australia. The Giant beaver is the largest rodent in North America and second largest in the world while the Diprotodon was the largest marsupial in the world during that time. Castoroides  ranged from Florida to the Yukon, and from New York State to Nebraska, but it has not been found outside of North America like how the Diprotodons not sighted outside of Australia. The giant wombat and the giant beaver, both lived in the Ice Age existed in the Ice Age started in the Pleistocene Period. Giant beavers seem to have preferred lakes and ponds bordered by swamps as their habitat, because their remains have been found in ancient swamp deposits so often. While Diprotodon  preferred semi-arid plains, savannahs and open woodlands, and is generally absent from hilly, forested coastal regions. These giant Ice Age beavers had a length up to 8 feet and an estimated weight of 130-220 pounds; while the giant wombats were 10 feet tall and weighed about 6000 pounds. The teeth of the giant beaver are bigger and broader, prominently ridged outer surfaces and blunt, rounded tipped incisors. Generally, the teeth were well adapted to grinding up the plants that made up the animals diet. Conversely, the giant wombats possessed four pairs of  incisors   which continued to grow throughout its life. Each of its four  molars  was high-crowned, meaning that it ate harsh types of foods. In addition, the giant beaver has short hind legs and it is assumed that its feet were also webbed. However, the giant wombat’s legs were sturdy and pillar-like; the feet were small and turned in like the wombat’s feet. The main difference between the two megafauna is that the Giant wombat had a pouch but the beaver does not due to the fact that the giant beaver is a rodent and the giant wombat a marsupial. The Giant Beaver family can be seen at its favorite haunt—around a pond where cattails and sphagnum moss grow in abundance. Unlike the beavers of today, these giants were not capable of chopping down trees as their teeth tapered to a blunt point. Their diet consisted of water plants such as cattails. However, Diprotodon  was probably a browser, feeding on shrubs and forbs. One skeleton from Lake Callabonna had the remains of saltbush in its abdominal region. Diprotodon  may have eaten as much as100 to150 kilograms of vegetation daily. Its chisel-like incisors used to root out vegetation. The giant beaver played an important role in the ecosystem perhaps by altering the soil structure and micro topography, nutrient cycling and water flows over local or regional areas. It also had dramatic effects on the growth and species composition of plant communities. The Giant Beaver impoundments affect nutrient cycles and water flow, and consequently the species richness of aquatic invertebrates, fish and riparian vegetation at local and catchment scales. Similarly, the giant wombats were important in maintaining ecosystem productivity, as native grazers and ecosystem engineers, they increase soil turnover thus impacting soil nutrition. Mechanism of evolution of Australian Animals Both  geologic  and climatic events helped to make Australias fauna unique. Australia is home to many unusual animals, bugs and creatures that are found nowhere else in the world. Australia was once part of the southern supercontinent  Gondwana, which also included South America, Africa, India and Antarctica. Gondwana began to break up 140  million years ago (MYA); 50 MYA Australia separated from Antarctica and was relatively isolated until the collision of the  Indo-Australian Plate  with Asia in the  Miocene  era 5. 3 MYA. The establishment and  evolution  of the present-day fauna was apparently shaped by the unique climate and the geology of the continent. As Australia  drifted, it was, to some extent, isolated from the effects of global climate change. The unique fauna that originated in Gondwana, such as the marsupials, survived and  adapted  in Australia. After the  Miocene, fauna of Asian origin were able to establish themselves in Australia. The  Wallace Line—the hypothetical line separating the zoogeographical  regions of Asia and Australasia—marks the tectonic boundary between the  Eurasian  and Indo-Australian plates. This continental boundary prevented the formation of land bridges and resulted in a distinct zoological distribution, with limited overlap, of most Asian and Australian fauna, with the exception of birds. Following the emergence of the circumpolar current in the mid-Oligocene  era (some 15 MYA), the Australian climate became increasingly  arid, giving rise to a diverse group of arid-specialized organisms, just as the wet tropical and seasonally wet areas gave rise to their own uniquely adapted species. Therefore, being situated a long distance from other parts of the world, and having many climatic changes throughout each part of the country, Australian animals have had to adapt to this. This has led Australia into being one continental country that boasts many unusual types of species, land and sea dwelling. Distributional patterns differ according to whether the fauna which already belonged to the Australian landmass or a fauna that immigrated. Much of the old endemic component of the fauna, dates from the time when the Australian landmass was still joined to the super-continent Gondwana. Old endemic groups show marked evolutionary diversification into different environments with numerous species and genera ranged about all corners of Australia. New immigrants show little evolutionary diversification. Most are represented by only one or two itinerant species of genera that are diverse in Eurasia. Most of the species are wide-spread in Australia or limited to the tropical north, the region in which they are arrived from Eurasia. Another distributional characteristic of the new immigrants is their common occurrence in habitats that also are recent developments in Australia. Australia was home to many giant species of animals, but evolution and hunting by the indigenous people wiped out many of the larger or giant species of kangaroo and wombats. Today we still have smaller versions of these creatures, but they are still unique to this land and habitat. Many of these strange animals cannot be found anywhere else in the world, although certain characteristics of each can be seen in animals that may be extinct