2/16/2012

what are Dinosaurs ?

what are Dinosaurs ?
Dinosaur:
Millions of years, long before humans were dinosaurs. Dinosaurs were one of several types of dinosaurs during the Mesozoic Era, lived the "Age of Reptiles."

Dinosaurs are a diverse group of animals of the clade Dinosauria and superiority. It appeared during the Triassic Period, about 230 million years, and became the dominant terrestrial vertebrates 135 million years, from the early Jurassic period (about 200 million years) to late Cretaceous (65 5 million years), if the extinction of the Cretaceous-Paleogene extinction of the dinosaurs, most groups in the late Mesozoic done. The fossil record indicates that birds evolved from theropod dinosaurs in Jurassic developed and therefore considered a type of dinosaur in the modern systems of classification. Some birds have the extinction event that occurred there survived 65 million years, and continue the line of dinosaurs to the present.

Dinosaurs are a diverse group of animal taxonomy, morphology and ecology. Birds are over 9,000 species living in the most diverse group of vertebrates, in addition perciforme fish. With fossils paleontologists have evidence of more than 500 different species and identified over 1000 different types of non-avian dinosaurs. Sunrise on every continent of the two species are represented remains.Some herbivores, carnivores fossils. Most bipedal dinosaurs had disappeared, although many groups, including four-legged friends, and some were conducted between these attitudes. Many species have developed public structures such as horns or crests, and some prehistoric groups developed skeletal abnormalities such as bony armor and spines. The birds were the dominant vertebrates on our planet since the extinction of pterosaurs flying, and it seems that building the nest and spawning a common feature of all dinosaurs. Many dinosaurs were large prehistoric animals - the largest sauropods could reach a length of nearly 60 meters (200 feet) and was multi-stage - and while many were quite large extinct theropods, most have changed very little in size especially of birds and other progressive groups.

Although the word dinosaur means "terrible lizard," the name is somewhat misleading, because the dinosaurs are not lizards. On the contrary, are a special group of reptiles with an upright posture is not separately in lizards. In the first half of the 20th century, before the birds are known for dinosaurs, most of the scientific community believed dinosaurs slowly and calmly. Most research since the 1970s, however, said that the old dinosaurs were carnivores, especially the active groups of animals with a high metabolism and numerous adaptations for social interaction.

Since the first dinosaur fossils from the early 19th century were found, mounted dinosaur skeletons and fossil replicas of the main attractions of museums around the world were, and the dinosaurs became part of world culture. Their diversity has attracted the largest sizes of groups, and nature seems monstrous and fantastic interest and the public's imagination for over a century. They appeared in films and bestsellers such as Jurassic Park, and new discoveries are regularly in the media.


Definition:
In phylogenetic taxonomy, dinosaurs are usually regarded as the group of "Triceratops, Neornithes [modern birds], the most recent common ancestor and all its descendants" is defined. A also suggested that dinosaurs are defined with respect to the common ancestor of Megalosaurus and Iguanodon last, because they were two of the three types of Richard Owen in quotes, as acknowledged by the Dinosauria. Both definitions lead to the same group of animals, defined as a dinosaur, "ornithischian dinosaurs = + Saurischia" carnivorous theropods (bipedal and mostly including birds) ankylosaurians (armored herbivorous quadrupeds), the stegosaurians (plated herbivorous quadrupeds), ceratopsians (herbivorous quadrupeds with horns and frills), ornithopods ( herbivorous bipeds or four, as the "duck" Treasury bills), and perhaps sauropodomorphs (most large herbivorous quadrupeds with long necks and tails).

Paleontologists many consider the point at which sauropodomorphs and theropods, sauropodomorphs interval, the definition of two dinosaurs and saurischians prohibited. To avoid instability, dinosaurs defined conservative compared to four anchor nodes: Triceratops horridus, and loricatus Saltasaurus Passer domesticus, their most recent common ancestor and all its descendants. "Safer" can be defined as "dinosaurs = + + sauropodomorphs ornithischians theropods" he said.

There is broad consensus among paleontologists that birds descended from theropod dinosaurs. With the strict definition of phylogenetic nomenclature that are all descended from a common ancestor in a group for this group, of course, include, birds can be seen as dinosaurs and dinosaurs are, therefore, does not have any off. Birds are classified by most paleontologists as belonging coelurosaurs Maniraptora subgroups, which are theropods, which saurischians, are dinosaurs. From the perspective of cladistic so the birds are dinosaurs, although they belong to ordinary language, the word "dinosaur" is not generally refers to birds.

General description:
With the above definitions, the dinosaur archosaurs generally described as held by members in the body. Many groups of prehistoric animals are popularly conceived as the dinosaurs, such as ichthyosaurs, plesiosaurs, pterosaurs and Dimetrodon, but are not scientifically classified as a dinosaur, and none had the characteristic attitude of the right branch of real dinosaurs. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic period, the Jurassic and Cretaceous, especially time. Other groups of animals were limited in size and niches, mammals, for example, is rarely the size of a cat, rodents and carnivores were generally the size of small prey. A notable exception is Repenomamus giganticus, a triconodont weighing between 12 kg (26 lb) and 14 kg (31 lb), which is known to have eaten small dinosaurs like young Psittacosaurus.

Dinosaurs have always been a diverse group of animals, according to a 2006 study, more than 500 dinosaur genera avialan not positively identified to date and the total number of species preserved in the fossil is estimated to be approximately 1850 75% still to be discovered. [5] An earlier study found that about 3,400 dinosaur genera, many of which were not preserved in fossils. With the September 17, 2008 was appointed in 1047 different kinds of dinosaurs. [6] Some are herbivores, carnivores. Although most dinosaurs were bipeds, some prehistoric species of quadrupeds, and others like Ammosaurus and Iguanodon, could walk on two legs or four. Cranial modifications like horns and crests among the dinosaurs together, and some extinct species had bony armor. Although best known for its size, many Mesozoic dinosaurs man-sized or smaller, and modern birds are generally very low. Dinosaurs live on every continent today, and fossils show that achieved global sales of at least the early Jurassic period. [7] Modern birds live most of the available habitat from land to sea, and there is evidence that some dinosaurs avialan (eg Microraptor) could not fly, or at least reduce, and others, as was Spinosauridae style semi-aquatic life.

Distinguishing anatomical features
Despite recent discoveries have made ​​it difficult to present a list of general acceptance of the characteristics of dinosaurs, nearly all dinosaurs discovered so far share certain modifications in the backbone of ancestral archosaurian. While some groups of dinosaurs featured further modified versions later, these properties because they are usually about dinosaurs, the first dinosaurs, and have passed to their offspring. These common features of a taxonomic group are called synapomorphies.

A detailed assessment of the relationship is confirmed S. archosaurs and Nesbitt found the following unambiguous synapomorphies 12, some already known:

  • in the skull, is a timeless trench (excavation) being processed by the supratemporal fenestra.
  • epipophyses present (excluding atlas and axis) in the anterior cervical. 
  • top of the deltopectoral crest (a projection in which the muscles join deltopectoral) is located, or with more than 30% over the entire length of the humerus (arm bone). 
  • a radius less than 80% of the length of the humerus. 
  • fourth trochanter (projection, when the muscle attaches caudofemoralis) in the femur (thighbone) is a strong flange. 
  • fourth trochanter asymmetrical, with distal edge forming a steeper angle to the shaft. 
  • in the talus and the calcaneus to the proximal articular surface of the fibula takes less than 30% of the transverse width of the element. 
  • exocciptials (in the backbone of the skull) does not meet along the center line in the bottom of the cavity endocranial. 
  • proximal articular surfaces of the legs of the seat with the pubic bone and iliac separated by a concave surface. 
  • cnemial peak to the tibia (shin bone) is anterolateral. 
  • This rib partitioned proximodistally aligned with the rear surface of the distal tibia.
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The evolutionary history:
Origin and early evolution
Dinosaurs diverged from their ancestor Archosauria about 230 million years during the period at the eastern end of the Triassic period, about 20 million years after the Permian-Triassic extinction of about 95% of all life on earth destroyed. Radiometric dating of rock formations, dinosaur fossils as early Eoraptor puts his presence in the fossil record at that time contained. Paleontologists believe Eoraptor resembles the common ancestor of all dinosaurs, if this is true, its traits suggest that early bipedal dinosaurs are predators of small size. The discovery of primitive dinosaurs ornithodirans Marasuchus Lagerpeton in Argentina and the Middle Triassic strata supports this view, the analysis of recovered fossils suggests that these animals were really small predators, bipeds.

When dinosaurs appeared, terrestrial habitats were occupied by different types of archosaurs and therapsids, cynodonts as aetosaurs and dicynodonts and ornithosuchids and rhynchosaurs rauisuchians. Most of these animals disappeared during the Triassic, in one of two events. First, at the boundary between the Carnian and Norian stages of wildlife (about 215 million years) died, dicynodonts and a variety of basal archosauromorphs including prolacertiforms and rhynchosaurs. It was developed by the extinction event Triassic-Jurassic (about 200 million years), which saw the end of most other groups of early archosaurs, like aetosaur ornithosuchids and continued phytosaurs rauisuchians. These losses left behind a land fauna of crocodiles, dinosaurs, mammals, turtles and pterosaurians. The first lines of the first dinosaurs through the steps and Norian Carnian Triassic, more broadly diversified by occupying the niches of groups that have disappeared.

Evolution and paleobiogeography:
The evolution of dinosaurs of the Triassic, after following the development of vegetation and location of continents. In the Triassic and Early Jurassic, the continents were connected into a single mass of Pangaea, and there was a carnivorous dinosaur fauna coelophysoid worldwide and herbivores, made early sauropodomorphs. Gymnosperms (conifers particularly), a potential source of irradiated food in the Late Triassic. First sauropodomorphs unsophisticated mechanisms for the production of food in the mouth, and should have used other means to further reduce the food along the digestive tract. The homogeneity of dinosaur faunas continued into the Middle East and Upper Jurassic, where most localities had predators, and the compounds of the general carnosaurians ceratosaurians spinosauroids and made herbivorous sauropods and ornithischians large stegosaurian. Examples include the Morrison Formation of North America and Tendaguru beds of Tanzania. Dinosaurs in China show some differences sinraptorid specialized theropods and unusual, long-necked sauropod Mamenchisaurus. Ankylosaurians and ornithopods were also becoming increasingly common, but prosauropods had disappeared. Conifers and ferns were the most common plants. Sauropods, like its predecessors, processors prosauropods not orally, but ornithischians were developed various means to address the food in the mouth, including potential plays like organs to keep food on the movements of the mouth and the jaw for grinding food. Another milestone in the development of the Jurassic was the appearance of true birds, descended from the coelurosaurians maniraptoran.

The Lower Cretaceous and the breakup of Pangaea continues, the dinosaurs were still very distinct from the mass of the earth. The first part of this period saw the spread of iguanodontids brachiosaurids ankylosaurians and throughout Europe, North America and North Africa. They were later supplemented or replaced in Africa by large theropods and sauropods and spinosaurs carcharodontosaurid titanosaur rebbachisaurid and also in South America. In Asia, as coelurosaurians dromaeosaurids troodontids maniraptoran, oviraptorosaurians and became the common theropods and ceratopsians like Psittacosaurus ankylosaurids and became the first large herbivores. Meanwhile, Australia was home to a wildlife ankylosaurians hypsilophodonts basal iguanodontids. The stegosaurians appear sometime in the late Cretaceous or early Cretaceous disappeared. A significant change in the Cretaceous period, which could be improved in the Late Cretaceous was the evolution of flowering plants. Meanwhile, several groups of herbivorous dinosaurs more sophisticated forms of food processing developed by mouth. Ceratopsians developed a method for cutting teeth and stacked in piles with iguanodontids method refines the cell edge for hadrosaurid molars. Some sauropods also batteries of teeth, developed best illustrated by the rebbachisaurid Nigersaurus.

There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, large tyrannosaurids theropods and different types of small theropods are maniraptoran, with a mixture of mainly herbivorous ornithischian hadrosaur, ceratopsian and ankylosaurids pachycephalosaurians. In the southern continents that are now the division of Gondwana was abelisaurids common theropods, sauropods and herbivores titanosaurids communities. Finally, in Europe, were dromaeosaurids, and the iguanodontids rhabdodontid titanosaurids spread ankylosaurians nodosaurid sauropods. Flowering plants were greatly radiating, with the emergence of weeds for the first time in the Late Cretaceous. Grinding and cutting hadrosaur ceratopsians became extremely diverse in North America and Asia. Theropods were released as herbivores or omnivores, and become habitual therizinosaurians ornithomimosaurians.

The case of the Cretaceous-Paleogene extinction, which took place about 65 million years until the end of the Cretaceous, which caused the extinction of dinosaurs of all groups, except neornithine birds. Some other groups, such as crocodiles, sebecosuchians diapsid, turtles, lizards, snakes, and sphenodontians choristoderans, also survived the event.

The lines of the surviving birds neornithine, including the ancestors of today ratites, ducks and chickens, and a variety of waterfowl, diversified rapidly in the early Paleogene period, admission hesperornithine ecological niches by published extinction groups of Mesozoic dinosaurs enantiornithines as trees, waterways and even the largest terrestrial theropods (like Gastornis and mihirungs and "terror birds"). However, mammals also rapidly diversifying during this period, and the outside the competition for control of land neornithines niches.


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