Since the first dinosaur fossils were recognized in the nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world.Dinosaurs have become a part of world culture and remain consistently popular among children and adults alike. They have been featured in best-selling books and films, and new discoveries are regularly covered by the media.
The term dinosaur is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although technically none of these weredinosaurs.
The taxon Dinosauria was formally named in 1842 by English palaeontologist Richard Owen, who used it to refer to the "distinct tribe or sub-order of Saurian Reptiles" that were then being recognized in England and around the world. The term is derived from the Greek words deinos meaning "terrible", "fearsome", or "formidable") and [/Fσαύρα saura meaning "lizard" or "reptile"). Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majestyDinosaurs were an extremely varied group of animals; according to a 2006 study, over 500 dinosaur genera have been identified with certainty so far, and the total number of genera preserved in the fossil record has been estimated at around 1,850, nearly 75% of which remain to be discovered. An earlier study predicted that about 3,400 dinosaur genera existed, including many which would not have been preserved in the fossil record. Some were herbivorous, others carnivorous. Somedinosaurs were bipeds, some were quadrupeds, and others, such as Ammosaurus and Iguanodon could walk just as easily on two or four legs. Regardless of body type, nearly all known dinosaurs were well-adapted for a predominantly terrestrial, rather than aquatic or aerial, habitat.
Distinguishing features of dinosaurs
While recent discoveries have made it more difficult to present a universally agreed-upon list of dinosaurs' distinguishing features, nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton. Although some later groups of dinosaurs featured further modified versions of these traits, they are considered typical across Dinosauria; the earliest dinosaurs had them and passed them on to all theirdescendants. Such common structures across a taxonomic group are called synapomorphies.
Dinosaur synapomorphies include an elongated crest on the humerus, or upper arm bone, to accommodate the attachment of deltopectoral muscles; a shelf at the rear of the ilium, or main hip bone; a tibia, or shin bone, featuring a broad lower edge and a flange pointing out and to the rear; and an ascending projection on the astragalus, one of the ankle bones, which secures it to the tibia
A variety of other skeletal features were shared by many dinosaurs. However, because they were either common to other groups of archosaurs or were not present in all early dinosaurs, these features are not considered to be synapomorphies. Such shared features include a diapsid skull bearing two pairs of holes in the temporal region; holes in the snout and lower jaw (two characteristics shared by other archosaurs); loss of the skull's postfrontal bone; a long neck incorporating an S-shaped curve; an elongated scapula, or shoulder blade; forelimbs shorter and lighter than hind limbs, coupled to asymmetrical hands; a sacrum composed of three or more fused vertebrae; and an acetabulum, or hip socket, with a hole at the center of its inside surface
The open, or "perforate", hip joint described above had significant implications for dinosaur movement and behavior. Most notably, it allowed dinosaur hind limbs to be "underslung", or situated directly beneath the animals' bodies; this, in turn, alloweddinosaurs to stand ***** in a manner similar to modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. Vertical limb configuration also enableddinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles. Edmontonia was an "armored dinosaur" of the group Ankylosauria
Phylogenetic definition
Under phylogenetic taxonomy, dinosaurs are usually defined as all descendants of the most recent common ancestor of Triceratops and modern birds..It has also been suggested that Dinosauria be defined as all the descendants of the most recent common ancestor of Megalosaurus and Iguanodon, because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.] They are divided into Ornithischia (bird-hipped) and Saurischia (lizard-hipped), depending upon pelvic structure. Ornithischiandinosaurs had a four-pronged pelvic configuration, incorporating a caudally-directed (rear-pointing) pubis bone with (most commonly) a forward-pointing process. By contrast, the pelvic structure of saurischiandinosaurs was three-pronged, and featured a pubis bone directed cranially, or forwards, only. Ornithischia includes all taxa sharing a more recent common ancestor with Triceratops than with Saurischia, while Saurischia includes those taxa sharing a more recent common ancestor with birds than with Ornithischia.
There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct. Modern birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which aredinosaurs.
However, referring to birds as 'avian dinosaurs' and to all other dinosaurs as 'non-avian dinosaurs' is cumbersome. Birds are still referred to as birds, at least in popular usage and among ornithologists. It is also technically correct to refer to birds as a distinct group under the older Linnaean classification system, which accepts paraphyletic taxa that exclude somedescendants of a single common ancestor. Paleontologists mostly use cladistics, which classifies birds as dinosaurs, but some biologists of the older generation do not.
For clarity, this article will use 'dinosaur' as a synonym for 'non-avian dinosaur', and 'bird' as a synonym for 'avian dinosaur' (meaning any animal that evolved from the common ancestor of Archaeopteryx andmodern birds). The term 'non-avian dinosaur' will be used for emphasis as needed.
Study of dinosaurs
Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues.Many fields of study contribute to our understanding of dinosaurs, including physics, chemistry, biology, and the earth sciences (of which paleontology is a sub-discipline).
Dinosaur remains have been found on every continent on Earth, including Antarctica. Numerous fossils of identical and closely related dinosaur species have been found on different continents, in accordance with the generally-accepted theory that all land masses were once connected in a super-continent called Pangaea
The "Dinosaur renaissance"was a small-scale scientific revolution started in the late 1960s, which led to renewed academic and popular interest in dinosaurs. It was sparked by new discoveries and research indicating that dinosaurs may have been active and warm-blooded animals, rather than cold-blooded and sluggish as had been the prevailing view during the first half of the twentieth century.
The new view of dinosaurs was championed by John Ostrom, who argued that birds evolved from coelurosaurian dinosaurs, and particularly Robert Bakker who argued passionately that dinosaurs were warm-blooded in a way similar to modern mammals and birds. Bakker frequently portrayed his ideas as a renaissance of those popular in the late nineteenth century, referring to the period in between the wars as "the dinosaur doldrums".
The dinosaur renaissance led to a profound shift in thinking on nearly all aspects of dinosaur biology, including physiology, evolution, behaviour, ecology and extinction. It has also lead to multiple depictions of dinosaurs in popular culture.
The tallest and heaviest dinosaur known from good skeletons is Brachiosaurus brancai (also known as Giraffatitan. Its remains were discovered in Tanzania between 1907–12. Bones from multiple similarly-sized individuals were incorporated into the skeleton now mounted and on display at the Humboldt Museum of Berlin; this mount is 12 m (38 ft) tall, 22.5 m (74 ft) long, and would have belonged to an animal that weighed between 30,000–60,000 kg (33–66 short tons). The longest complete dinosaur is the 27 m (89 ft) long Diplodocus which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907.]
Comparative size of Eoraptor
Comparative size of Eoraptor
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