Sair [ays_quiz id="24"][1] Dinosaurs first appeared 231.4 million years ago, during the Triassic period. They throughout the Jurassic period (201 million years ago) until the end of the Cretaceous period (66 million years ago). At that point, an extinction event occurred, but their descendants still include birds and reptiles today.[2] Paleontologists have narrowed down 500 specific genera and more than 1,000 different species of non-avian dinosaurs on every continent, based on their studies of fossil evidence. Dinosaurs were both biped and quadrupedal, both meat-eating and plant- eating. Some had bony armor, spines, horns, and crests.[3] Some dinosaurs were as high as 9.25 meters and as long as 58 meters, although the majority of them were quite small. Dinosaurs were a group of reptiles and neornithes (birds). Birds are now noted as the only surviving group of theropod dinosaurs. Dinosaurs are classed as archosaurs with limbs held straight under the body. These animals were the dominant land vertebrates of the Jurassic, Cretaceous and Mesozoic periods. Until now, 500 non-avian dinosaurs and 1047 species are considered to have existed. Some of these dinosaurs were seed-eaters, fish-eaters, insect-eating and omnivores. Some non-avian dinosaurs, such as Microraptor, could fly or glide, and others had semi-aquatic habits.[4] Dromaeosaurs stood on their hind legs, with their tails rigidly extended. Their bodies were covered in fine feathers. Paleontologists have interpreted their bodies with fossil evidence to create precise images and models of dinosaurs, now on display in museums. As individual dinosaurs of the same species are similar, scientists can estimate their features even with skeletons that have missing bones. Investigations of the dinosaur body indicate that living animals with the same construction hold their bodies in the same way. Therefore, scientists can model the reconstruction of these living animals. However, scientists don’t rely only on bones for information. Fossil bones frequently have muscle attachment scars that give clues about the location and size of the muscle. Once again, scientists compare this information with living animals to create model images.[5] When reconstructing dinosaur models, scientists and artists add more muscle to the skeleton and add armor and feathers, depending on the species. They then add color and finally, the skin is added, along with armor or feathers if the species is known to have them. In some cases, sediment around fossils has given impressions of the skin of the dinosaur. So, scientists can estimate a smooth or scaly skin on the dinosaur.[6] Ankylosaurs were known for their armoured bodies. They had hard plates, spines, and knobs on their skin. Scientists have a clear understanding of the look of these dinosaurs. Discovery of theropod fossils in Liaoning, in northeastern China, indicates that many species of predatory dinosaurs had feathers. These dinosaurs were covered with hair-like or downy feathers; others had long, pinnate feathers on their arms and tails, like birds. Fossils discovered at other locations also provide indirect evidence of feathers. Based on the quill knob fossils noted, scientists assume that these dinosaurs had feathers. At the same location in China, a well-preserved theropod fossil called Sinosauropteryx was discovered. The feathers contain melanosomes, pigment-making organelles that add colour to the skin, hair, and feathers in modern animals. From this information, scientists were able to conclude that this predator had an orange-and-brown striped tail. However, the colour of most dinosaur skin continues to be a mystery.[7] Regarding behaviour, it is believed that herding or flocking was common to dinosaur groups, as noted among bird groups too. Multiple trackways suggest that dinosaurs were social animals and moved in large herds, similar to the behaviour of American bison or the African springbok. There is some evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurs, ornithopods, and ceratopsians, formed aggregations of immature individuals. A site in Inner Mongolia has revealed remains of over 20 Sinornithomimus, from one to seven years old. This collection is considered to have been a social group that became trapped in mud. It is also believed that theropods were pack hunters working together to attack prey. This behaviour, however, is uncommon among modern birds, crocodiles, and other reptiles which suggests that this mammal- like pack hunting and aggressive behaviour were more common among theropods.
