 The dinosaurs (Dinosauria in Latin) are vertebrates ruling 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 Pangea was not fragmented, the 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 the dinosaurs and ended their reign on terrestrial wildlife. A group of dinosaurs, however, has survived the disaster, because taxonomists consider birds today as the descendants of dinosaurs theropods.
Since the first dinosaur fossils were found in the early nineteenth century, the reconstructed skeleton and exhibitions have become major attractions in museums around the world. Dinosaurs have become part of popular culture, appearing in books and movies success, and new discoveries are regularly reported in the media.
The term dinosaur is sometimes used informally to describe other prehistoric reptiles were not dinosaurs. The best known examples are the pelycosauriens (which include Dimétrodon and the Édaphosaure), the flying reptiles of the group of pterosaurs and many marine reptiles such as ichthyosaurs, the plesiosaurs, the Mosasaurs or nothosaurs. 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 (saura "lizard" or "reptile"). Owen has chosen this name with 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 won them some success. However, these animals could also have a very small (a few centimeters). Recent discoveries have made it more difficult to distinguish between different dinosaurs, but found fossil skeletons seem almost all have in common with those of Archosauriens. Dinosaurs post slightly characteristics have changed.
The synapomorphies dinosaurs include, for example, an oval crest on the humerus, a skull diapside.
Modern Definition
Skeleton Triceratops at the American Museum of Natural History in New York.
According to the phylogenetic classification, dinosaurs are usually defined as all descendants of the most recent common ancestor of Triceratops and birds modern It was also suggested that the dinosaurs are defined as all descendants of the most recent common ancestor of Megalosaurus and the Iguanodon, because these are two of the three species cited by Richard Owen when he recognized the dinosaurs Both definitions give the same set of animals as dinosaurs, including theropods (mostly bipedal carnivores), the sauropodomorphes (mostly herbivorous quadrupeds with a long neck and a long tail), the ankylosauriens and stégosauriens (herbivores quadrupeds covered with bony plates), the ceratopsians (four-legged herbivores horns) and ornithopodes (or bipedal herbivorous quadrupeds including "duck-bills"). These definitions are written to correspond with scientific conceptions of dinosaurs that historically precede the modern use of phylogenetics. This continuity is used to avoid confusion with what the term means dinosaur.
There is an almost total consensus among paleontologists that birds are descendants of dinosaurs theropods. Using the strict definition cladistic that all descendants of a single common ancestor must be included in the same group for this group to be valid, the birds are "dinosaurs and dinosaurs have not disappeared. The birds are classified by most paleontologists as belonging to subgroup maniraptors, which are coelurosaures, which are theropods, which are saurischiens, which are dinosaurs
From the point of view of cladistics, birds are dinosaurs, but in everyday language the word "dinosaur" does not include birds. For clarity, this article uses the word "dinosaur" as a synonym for "non-avian dinosaur." The term "non-avian dinosaur 'will be used to strengthen when necessary. It is also technically correct to refer to dinosaurs as a distinct group with the old system of scientific classification of species, which accepts taxons paraphylétiques excluding some descendants of a single common ancestor.
|
