Around 200 million years ago, the most diverse group of reptiles, the Dinosaurs existed which got extinct with time. The first dinosaur was seen in Triassic Period between 233 to 243 million years ago. Their dominance continued throughout the Jurassic and Cretaceous periods. There were two varieties of dinosaurs in past. According to paleontologists, there are almost 500 varieties of avian dinosaurs and 1000 varieties of non-avian dinosaurs. Dinosaurs are represented on every continent by both extinct species and fossil remains. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to have been sluggish and cold blooded. As the first dinosaur was seen in 19th century, the fossils of dinosaurs attract the tourist and are kept in many museums around the world. In almost every country, dinosaurs were found in earlier 19th century.The large sizes of some dinosaur groups, as well as their seemingly monstrous and fantastic nature. Amongst bestsellers such as Jurassic Park dinosaurs are mentioned. Paleontologists make continuous new discovers regularly about dinosaurs.
20 million years ago, Dinosaurs diverged from their archosaur ancestors during the Middle to Late Triassic epochs. According to Paleontologists Eoraptor are known to be the ancestors of dinosaurs.When dinosaurs appeared, they were not the dominant terrestrial animals. The terrestrial habitats were occupied by various types of archosauromorphs and therapisds, like cynodonts and rhynchosaurs. Their main competitors were the pseudosuchia, such as aetosaurs, ornithosuchids and rauisuchians, which were more successful than the dinosaurs.Dinosaur evolution after the Triassic follows changes in vegetation and the location of continents. In the Late Triassic and Early Jurassic, the continents were connected as the single landmass Pangaea, and there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and early sauropodomorph herbivores.
Dinosaurs belong to a group known as archosaurs, which also includes modern crocodilians. Within the archosaur group, dinosaurs are differentiated most noticeably by their gait. Dinosaur legs extend directly beneath the body, whereas the legs of lizards and crocodilians sprawl out to either side.Collectively, dinosaurs as a clade are divided into two primary branches, Saurischia and Ornithischia. Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia, while Ornithischia includes all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their pelvic structure.
Scientists will probably never be certain of the largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork.
The behavior of dinosaurs are common among the birds and some are common with crocodiles.The first potential evidence for herding or flocking as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31 lguanodon bernissartenis, ornithischians that were then thought to have perished together in Bernissart, Belgium after they fell into a deep, flooded sinkhole and drowned.The type of collagen an animal has in its bones varies according to its DNA and, in both cases, this collagen was of the same type found in modern chickens and ostriches.
In 2015, researchers reported finding structures similar to blood cells and collagen fibers, preserved in the bone fossils of six Cretaceous dinosaur specimens, which are approximately 75 million years old. Dinosaurs are the extinct species which has many mysteries found by scientist.
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