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: research about dinosaurs

  1. #1
      Maria Isa
    Apr 2012
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    402

    research about dinosaurs

    research about dinosaurs

    From 230 million to 65 million years ago, reptiles called dinosaurs lived on the Earth. They varied tremendously in size and shape. Some were about the size of a dog but others were huge, weighing many tons. The largest species ate plants, but others were flesh eaters. Most were four-legged, but many walked and ran on their hind legs only. Dinosaur fossils have been discovered nearly worldwide, and major new finds are continually reported. These fossils include bones, eggs, footprints, and even traces of feathers. Based on their study of fossils, scientists have been able to classify dinosaurs into two main groups, the Saurischia ("lizard hips") and the Ornithischia ("bird hips"). Also using fossils as a guide, scientists have created life-size models that show how different events in a dinosaur's life may have occurred. But many mysteries remain. One of the biggest concerns the disappearance of the dinosaurs. Scientists have proposed various theories to account for the extinction of these fascinating animals, but none have been conclusively proven














    Dinosaur (Greek for "terrible lizard") is the term given to various kinds of extinct reptiles of the Mesozoic Era, from 230 to 65 million years ago. During the era these often (but not always) very large reptiles were the dominant land animals on Earth. The term was proposed as a formal zoologic name in 1842 by the British anatomist Sir Richard Owen, in reference to large fossil bones unearthed in southern England, but it is used today only in an informal sense. The animals are classified in two formal categories, the orders Saurischia and Ornithischia, within the reptile subclass Archosauria.

    Thousands of dinosaur remains have been found nearly worldwide. The earliest discoveries were for many years attributed to two Englishmen. The first, Gideon Mantell, a doctor, made his find in Sussex, England, in 1822 and called it Iguanodon ("iguana tooth"). The second, the Rev. Willam Buckland, made his find near Oxford, England, and called it Megalosaurus ("great lizard"). In fact, fossil remains had already been discovered in 1818 at Windsor, Conn., by Solomon Ellsworth, Jr. The remains, reported as human by Nathan Smith in the 1820 issue of the American Journal of Sciences and Arts, were only recently recognized as pertaining to the Late Triassic/Early Jurassic prosauropod Anchisaurus.
    Dinosaurs varied greatly in form and size and were adapted for diverse habitats and lifestyles. They ranged in weight from 2 to 3 kg (4 to 6 lb), in the case of Compsognathus, up to 73 metric tons (160,000 lb), in the case of Brachiosaurus. Most known dinosaurs were large, weighing more than 500 kg (1,100 lb), and few weighed less than 45 kg (100 lb). Most were herbivores, but saurischians such as the theropods were carnivorous. Most dinosaurs were also four-legged, but some were obligatory bipeds, unable to adopt a four-legged posture. Others were facultative bipeds, able to walk occasionally on their hind legs.
    Dinosaurs have always been classified as reptiles, because they all have anatomical features found in living reptiles and not in mammals or amphibians. For that reason they traditionally have been assumed to have been like reptiles in physiology, as well: that is, cold-blooded (ectothermic), or dependent on external heat sources. In recent years, however, different lines of evidence have been interpreted as indicating that dinosaurs may have been warm-blooded, with rates of metabolism comparable to those of mammals and birds. Such evidence includes their upright posture and carriage, mammallike microscopic structure of bones, skeletal features suggestive of high activity, specialized food-processing dentitions, and the low ratios of dinosaurian predators to prey animals, suggesting large food requirements. In addition, what appears to be a fossilized heart was found in the chest cavity of a dinosaur fossil from the late Cretaceous, and computerized imaging of the organ in 2000 suggested that it had a birdlike or even mammalian structure with four chambers. All such evidence requires further study and is not conclusive, however, and all the facts can be alternatively explained. The reasonable possibility remains that some dinosaurs may have been endothermic, maintaining body temperature and heat production by means of internal metabolic






  2. #2
      Maria Isa
    Apr 2012
    -
    402

    : research about dinosaurs

    Dinosaur Research




    For more than a century, paleontologists have been collecting abundant, often spectacular dinosaur fossils from the Western Interior of North America. The bulk of these remains occur in rocks dating to the final stages of the Cretaceous Period, the end of the age of dinosaurs. Only recently have we begun to appreciate that most of these dinosaursamong them horned, duck-billed, dome-headed, and armored plant-eaters, as well as giant tyrannosaur meat-eaters and smaller raptor-like predatorsexisted on a lost continent known as Laramidia. About 100 million years ago, exceptionally high sea levels flooded central North America, resulting in a north-south oriented seaway extending from the Arctic Ocean to the Gulf of Mexico. This shallow sea isolated life-forms on the eastern and western landmasses for most the next 30 million years. We know little of what happened on the eastern landmass (known as Appalachia), but its western counterpart, Laramidia, witnessed a tremendous florescence of dinosaurs and other Cretaceous life-forms.
    Surprisingly, despite the giant sizes of many of the dinosaurs and the small size of Laramidia (less than one-fifth the size of present day North America), several investigators have suggested that entirely different species co-existed in the northern and southern regions, at least during certain intervals. Dinosaur fossils recovered from up in Alberta and Montana were found to represent the same major groups but distinct species compared to their supposedly coeval counterparts down in New Mexico, and Texas. If this hypothesis proved to be true, it would force paleontologists to answer some very difficult questions. In particular, how were so many giant animals able to co-exist on such a diminutive chunk of land? Was there more plant food around at that time? Or did dinosaurs not require as much food as big-bodied mammals of the present day? One of the major obstacles that prevented adequate testing of this hypothesis was a dearth of dinosaurs from the American southwest; the vast majority of Laramidian dinosaurs were known only from north.

    Skull of Gryposaurus monumentensis, a giant duck-billed dinosaur recently discovered in Grand Staircase-Escalante National Monument, southern Utah.

    In 1999, shortly after accepting a joint curator-faculty position at the University of Utah, I initiated the Kaiparowits Basin Project, a field-based project focused in Grand Staircase-Escalante National Monument (GSENM), southern Utah. From the beginning, one of the major aims was to investigate the radical idea of dinosaur provincialism. GSENM is a rugged, wild and remote place, the last major region in lower 48 states to be formally mapped. In 1999, this spectacular 1.9 million acre monument, traversed even today only by a handful of dirt roads, represented arguably the last major unexplored dinosaur bone yard in the United States. Over the past decade, crews from the Utah Museum of Natural History exploring the GSENM badlandsin particular units of sedimentary rock known as the Kaiparowits and Wahweap Formationshave discovered dozens of partial dinosaur skeletons, many of them with skulls. Duck-billed dinosaurs, horned dinosaurs, armored dinosaurs, dome-headed dinosaurs, tyrannosaurs, and many others have come to light. These ancient skeletal remains often preserve skin impressions, providing even more intimate insights into the look of these animals.
    As of today, every identifiable dinosaur species from the Late Cretaceous of GSENM appears to be new to science, distinct from varieties found further to the north. Examples include the giant duck-billed dinosaur, Gryposaurus monumentensis, with its oversized nose, and the feathered, raptor-like theropod dinosaur Hagyryphus giganteus. Recently discovered animals still under study include three new horned dinosaurs, all distant relatives of Triceratops, and an armored dinosaur with horns. The top predator here was a tyrannosaura smaller, more ancient cousin of T. rex. Together, all of these animals (bolstered by new and improved evidence of the age of the rocks in Utah and elsewhere on Laramidia) provide by far the strongest evidence to date of the presence of isolated dinosaur provinces on Laramidia around 75 million years ago. So we are now faced with answering those sticky questions about cramming so many giant animals onto a small landmass.
    In addition to dinosaurs, the Kaiparowits Basin Project has sought to understand ancient environments by studying the rocks and recovering fossils of plants and non-dinosaur animals that lived in this portion of Laramidia during a brief interval of the Late Cretaceous. The panoply of remains includes fishes, amphibians, lizards, turtles, crocodiles, pterosaurs, and mammals, as well as insects, clams, and dozens of plant varieties. This research has required an interdisciplinary, multi-institutional effort involving more than a dozen experts spanning multiple disciplines. Principle investigators on the project include Mark Loewen, Randy Irmis, Mike Getty, and myself from the University of Utah, Eric Roberts of Southern Utah University, Patrick OConnor of Ohio University, and Kirk Johnson and Ian Miller of the Denver Museum of Nature and Science. Only now, more than a decade later, are we beginning to get a meaningful sense of these ancient ecosystems, with plenty of exciting discoveries still to come.

    Reconstruction of a feathered theropod dinosaur closely allied with Hagryphus giganteus. Hagryphyus is one of several newly discovered dinosaurs from southern Utah. Artwork by Michael Skrepnick.

    The emerging picture is one of a rich diversity of life inhabiting a swampy, subtropical coastal plain setting dominated by a bounty of flowering plants. Tyrannosaurs hunted horned and duck-billed dinosaurs, while gargantuan crocodiles waited submerged for any large animal to stray too close to the water. Many smaller animals familiar to us todayamong them birds, snakes, small mammals, lizards, turtles and fisheswalked, flew, slithered, swam, or scurried amongst the these giants. On a larger scale, this diverse community was but a single strand in the larger web of life that comprised Laramidia, a narrow strip of land that fluctuated in size periodically with the rise and fall of sea levels. Although the same major groupings of dinosaurs co-occurred in the north and south, northerners and southerners represent distinct species. Despite body sizes that generally exceeded those of big-bodied mammals, Laramidian dinosaurs apparently possessed small species ranges (although individual animals and herds still had plenty of room to roam). Given that most northern and southern dinosaur species within a given group appear closely similar, they may well have played similar ecological roles. For example, the long-frilled horned dinosaurs (chasmosaurines) in the north and south, although distinct species, may well have consumed very similar kinds of plants. If so, the ecological niches filled by dinosaurs might have changed very little for millions of years during the Late Cretaceous. Behind this apparent ecological stasis, however, a variety of factorsperhaps including seaway migrations and other environmental changesresulted in rapid evolutionary turnover of species. Like a long-running Broadway show, the players changed while the same story played out endlessly.


  3. #3

    Feb 2012
    633

    : research about dinosaurs

    thanxxxxxx


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      Eiman
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