Dinosaur

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Dinosaur
The dinosaurs (Dinosauria in latin) are vertebrates that have prevailed on terrestrial ecosystems for over 160 million years. They appeared on Earth in the first half of the Triassic (about -251 to -199.6 million years), there are over 230 million years. The supercontinent of Pangaea not yet fragmented, dinosaurs were able to colonize every continent on foot dry. At the end of the Cretaceous, there are about 65 million years, a disaster caused the extinction of dinosaurs and ended their reign on terrestrial wildlife. A group of dinosaurs, however, survived the disaster, indeed, taxonomists consider birds today as the descendants of dinosaurs theropods.

Since the first dinosaur fossils were found in the early nineteenth century, the reconstructed skeletons and exhibitions have become major attractions in museums worldwide. The dinosaurs have become an integral part of popular culture, appearing in books and films to success, and new discoveries are regularly reported in the media.

The term dinosaur is sometimes used informally to describe other prehistoric reptiles that were not dinosaurs. The most famous are the pelycosauriens (including the Dimetrodon and Edaphosaurus), the flying reptiles group ptérosaures and many marine reptiles such as ichthyosaurs, plésiosaures, mosasaures or nothosaures. None of them was a dinosaur.


Definition History
The taxon Dinosauria was introduced by the English paleontologist Richard Owen in 1842 to bring together a "tribe or suborder separate Sauropsidés". The term derives from the Greek δεινός (deinos: "tremendous, terrible") and σαύρα (will "lizard" or "reptile"). Owen has chosen this title by reference to the fear that could inspire their size, their teeth and claws often impressive. Indeed, many dinosaurs could be of considerable size (more than fifteen meters long), which earned them a success. However, these animals could also have a very small size (a few centimeters). Recent discoveries have made it more difficult to distinguish clearly between different dinosaurs, but found fossil skeletons seem almost all have points in common with those of Archosauriens. The post dinosaurs have characteristics slightly modified.

The synapomorphies dinosaurs include, for example, a ridge oval on the humerus, a skull diapside.


Definition modern
According to the phylogenetic taxonomy, dinosaurs are usually defined as all descendants of more recent common ancestor of Triceratops and modern birds. It was also suggested that the dinosaurs are defined as all descendants of more recent common ancestor and deMegalosaurus the Iguanodon, because these are two of the three species cited by Richard Owen when he recognized the dinosaurs. The two definitions give the same set of animals regarded as dinosaurs, including the theropods (mostly carnivores bipèdesl ), Sauropodomorphes (mostly four-legged herbivores with a long neck and a long tail), ankylosauriens and stégosauriens (four-legged herbivores covered with bony plates), ceratopsias (four-legged herbivores horned), and ornithopodes (or herbivores bipèdes quadrupeds including "duck beak"). These definitions are written to correspond with the scientific conceptions of dinosaurs which historically above the modern use of phylogenetic. This continuity is used to avoid confusion with what the term means dinosaur.

There is an almost total consensus among palaeontologists that birds are descendants of dinosaurs theropods. Using the definition strictly cladistic that all descendants of a single common ancestor must be included in a group so this group is natural, birds "are" dinosaurs and dinosaurs did not disappeared. The birds are classified by most paleontologists as belonging to the subgroup of maniraptors, which are coelurosaures, which are theropods, which are saurischiens, which are dinosaurs.

From the viewpoint of cladistic, birds are dinosaurs, but in plain language the word "dinosaur" does not include birds. For the sake of clarity, this article uses the word "dinosaur" as a synonym for "non-avian dinosaur." The term "non-avian dinosaur" will be used to enhance when necessary. It is also technically correct to refer to dinosaurs as a distinct group with the oldest system of scientific classification of species, which accepts taxa Paraphyliques which exclude some descendants of a single common ancestor.


Size
Relying on fossil discovered, it is certain that dinosauriens were a group of large animals while their average size has varied during the Triassic, Jurassic and Cretaceous. According to paleontologist Bill Erickson, weight median fluctuates between 9 kg and 5 tons, a recent study on 63 kinds of dinosaurs gave an average weight of 850 kg (comparable to that of a grizzly) and a median weight of nearly two tons, or as much as a giraffe . In comparison, the average weight of mammals east of 863 grams, or that of a large rodent. The smallest of dinosaurs discovered was greater than two-thirds of mammals today. The majority of the dinosaurs was greater than 98% of existing mammals.


More large and smaller dinosaurs
Only a small fraction of dead animals become fossils, and only a few specimens discovered fossils are complete, and impressions of skin and soft tissues are rare. The reconstruction of a skeleton of a species by comparing the size and morphology of the bones with those of another similar case better known is an inexact art, and the recomposition of muscles and other organs of a specimen is scientifically difficult. There will never be really sure of the size of the largest and smallest dinosaurs.

Among the dinosaurs, sauropodes were huge, the biggest was an order of magnitude more massive that all animals which have been available on Earth. The prehistoric mammals as Indricotherium and the Colombian mammoth were dwarves compared to sauropodes. Only a handful of aquatic animals contemporary approach or exceed in size, such as the blue whale, which weighs 180 tons and reached 31 meters long at most.

The largest and heaviest dinosaur known from almost complete skeletons is the Brachiosaurus brancai (also known as Giraffatitan). It measured 12 meters high, 22.5 m long, and would have weighed between 30 and 60 tons (for memory an elephant savanna in Africa, the largest land animal in the world, weighs on average 7.7 tonnes). The longest dinosaur fossil from a complete is the Diplodocus which was 27 meters (Pittsburgh, Carnegie Natural History Museum, 1907).

There were larger dinosaurs known, but the data are estimated on a few fragmentary fossils. Most are herbivores discovered in the years 1970 or after, including the huge argentinosaurus, which could have weighed between 80 and 100 tonnes, the longest of all, the Supersaurus of 40 meters and the largest of the Sauroposeidon 18 meters, which would have been able to achieve a 6th floor window.

An even larger dinosaur, Amphicoelias fragillimus, known only a few vertebrae discovered in 1878, could have reached 58 meters long and weighing 120 tons. The heaviest could have been the little known and even discussed Bruhathkayosaurus, which could have reached 175 to 220 tonnes.

The largest carnivore was the Spinosaurus, which reached a size of 16 to 18 metres long and weighed 9 tons. Other large carnivores included Giganotosaurus, Mapusaurus, Tyrannosaurus rex and Carcharodontosaurus.

Without birds include contemporary bird-like flies, the smallest dinosaurs were the size of a crow or a chicken. The theropods Microraptor and Parvicursor were less than 60 cm long.

Behavior
The interpretation of the behavior of dinosaurs is usually established on the provision of fossils discovered, their habitat, computer simulations of their biomechanical, and comparisons with animals present in the same ecological niche. As such, the current understanding of the behavior of dinosaurs based on speculation, some of which are likely to remain controversial for a long time. However, there is a consensus that some currents that are common among crocodiles and birds (species closest to the dinosaurs) are also common among dinosaurs.

Herds
The first evidence of herds of dinosaurs was discovered in 1878 in Belgium Bernissart. 31 Iguanodons all seemed to have perished after falling into a deep doline and flooded. Despite the discovery that these skeletons were from three separate events, other sites of mass deaths were discovered. These, with many trace fossils suggested that the flocks where the hordes were common in many species. The tracks hundreds, even thousands of herbivores, indicated that the dinosaurs beaked duck could travel in large flocks, as the buffalo or springbok. Traces of sauropodes allowed to see that these animals traveled in groups composed of several different species, and others kept the young in the middle of the herd to protect them from the traces at Davenport Ranch in Texas.

Nests
The discovery in 1978 by Jack Horner of the nest of Maiasaura ( "good mother dinosaur") in Montana showed that parental care lasted long after the outbreak among ornithopodes. There is also evidence that other dinosaurs of the Cretaceous as sauropode Saltasaurus (discovered in 1997 in Patagonia) had similar behaviour, and that these animals are clustered in vast colonies nidificatrices like those penguins. The Oviraptor of Mongolia has been discovered (1993) in a position like that of breeding chickens, which means it was covered with a layer of insulating feathers who was guarding the egg warm. Tracks Fossils have also confirmed maternal behavior among sauropodes and ornithopodes of the Isle of Skye. Nests and eggs have been found for most major groups of dinosaurs, and it appears probable that dinosaurs communicated with their Small in a manner similar to birds and crocodiles today.


Coupling and communication
The crests of some dinosaurs, like marginocephalians, theropods and hadrosauridaees may have been too fragile for an active defense and therefore would probably have been used for parades sexual or for purposes of intimidation, although there is little elements on territorialism and mating of dinosaurs.

The nature of communications between dinosaurs also remains enigmatic, but recent findings suggest that the crest digs lambeosaurines could have functioned as a sounding board used for a wide variety of vocalizations.

Hunting
From a behavioral point of view, one of the most important fossil dinosaur has been discovered in the Gobi desert in 1971. It included a Velociraptor attacking a Protoceratops, proving that dinosaurs physically attacking and eating them. Although cannibalism among the theropods is not a surprise, it was confirmed by traces of teeth on a fossil from Madagascar in 2003.

Displacement
Based on existing fossil evidence, there was no kind of dinosaur fouisseur and little dinosaurs climbers. Since the expansion of the Cenozoic mammals saw the emergence of many species fouisseuses and climbing, the lack of evidence for species of dinosaurs similar is somewhat surprising.

A good understanding of how dinosaurs moved is the key models of behavior of species. The biomechanics in particular has provided many elements such as determining the speed race of dinosaurs according to the study of forces exerted by their muscles and gravity on the structure of their skeleton, whether diplodocides could create a supersonic bang by scanning the air with their tail-shaped whip, whether the theropods giants should slow down when they were pursuing their prey to avoid fatal injuries, and if sauropodes could float.

Anatomy

* Presence of air sacs and a respiratory system similar to that of birds.
* Skull diapside
* Presence of feathers for some lines.


Metabolism
A French study on the isotopic composition of oxygen in teeth and bones of 80 dinosaurs of the Cretaceous (theropods, sauropodes, ornithopodes and ceratopsians) from deposits in North America, Europe, Africa and Asia , Showed that they should be homéothermes. The report 18O/16O - which depends on the internal temperature of the animal alive - is identical to that of mammals and birds, homéothermes, and differs significantly from that of reptiles current ectothermes and chelonians and crocodilian fossils of the Cretaceous.

The presence of structures Havers (micro-channels surrounded by a layer of bone in concentric skeletons) in the fossilized bones would also be an element for character endotherme.

A team of Florida found that the temperature was proportional to the mass and growth rates, ranging from 25 ° C for small dinosaurs up to 41 ° C for the biggest. They applied a numerical model, to estimate the body temperature depending on the size and pace of growth, eight species of psittacosaure (Psittacosaurus mongoliensis, 12 kg) in apatosaure (Apatosaurus excelsus, 26 000 kg) . According to this team, the internal temperature of Sauroposeidon proteles, the heaviest known dinosaurs (60 tons), should reach 48 ° C. This model therefore tend to prove that large dinosaurs were heated by "homéothermie inertial."

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