Dinosaurs

Main article: Dinosaur size Scale diagram comparing the average human to the largest known dinosaurs in five major clades: Sauropoda (Argentinosaurus huinculensis), Ornithopoda (Shantungosaurus giganteus), Theropoda (Spinosaurus aegyptiacus), Thyreophora (Stegosaurus armatus) and Marginocephalia (Triceratops prorsus) Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods.[34] Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the 100 to 1000 kilogram (220 to 2200 lb) category when sorted by estimated weight into categories based on order of magnitude, whereas recent predatory carnivoran mammals peak in the 10 to 100 kilogram (22 to 220 lb) category.[57] The mode of Mesozoic dinosaur body masses is between one and ten metric tonnes.[58] This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about 2 to 5 kilograms (5 to 10 lb).[59] The sauropods were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has since walked the Earth. Giant prehistoric mammals such as Paraceratherium (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size.[60] There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.[8] Largest and smallest 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 ever fossilize, 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.[61] Comparative size of Giraffatitan to the average human The tallest and heaviest dinosaur known from good skeletons is Giraffatitan brancai (previously classified as a species of Brachiosaurus). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the Museum für Naturkunde Berlin;[62] this mount is 12 meters (39 ft) tall and 21.8–22.5 meters (72–74 ft) long,[63][64] and would have belonged to an animal that weighed between 30000 and 60000 kilograms (70000 and 130000 lb). The longest complete dinosaur is the 27-meter (89 ft) long Diplodocus, which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907.[65] Comparative size of Eoraptor to the average human There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were all discovered in the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80000 to 100000 kilograms (90 to 110 short tons); some of the longest were the 33.5 meters (110 ft) long Diplodocus hallorum[8] (formerly Seismosaurus) and the 33 meters (108 ft) long Supersaurus;[66] and the tallest, the 18 meters (59 ft) tall Sauroposeidon, which could have reached a sixth-floor window. The heaviest and longest of them all may have been Amphicoelias fragillimus, known only from a now lost partial vertebral neural arch described in 1878. Extrapolating from the illustration of this bone, the animal may have been 58 meters (190 ft) long and weighed over 120000 kg (260000 lb).[8] The largest known carnivorous dinosaur was Spinosaurus, reaching a length of 16 to 18 meters (52 to 60 ft), and weighing in at 8150 kg (18000 lb).[67] Other large carnivorous theropods included Giganotosaurus, Carcharodontosaurus and Tyrannosaurus.[68] Therizinosaurus and Deinocheirus were among the tallest of the theropods. The smallest dinosaur known is the bee hummingbird,[69] with length of only 5 cm (2 in) and mass of around 1.8 g (0.06 oz).[70] Not including birds (Avialae), the smallest known dinosaurs were about the size of pigeons.[71] The smallest non-avialan dinosaurs were those theropods most closely related to birds. Anchiornis huxleyi, for example, had a total skeletal length of under 35 centimeters (1.1 ft).[71][72] A. huxleyi is currently the smallest non-avialan dinosaur described from an adult specimen, with an estimated weight of 110 grams.[72] The smallest herbivorous non-avialan dinosaurs included Microceratus and Wannanosaurus, at about 60 cm (2.0 ft) long each.[2][73]