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For other uses, see Dinosaur (disambiguation).
| Dinosaurs Fossil range: Triassic – Cretaceous (excluding Aves) | ||||||||||||||
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 Mounted skeletons of Tyrannosaurus (left) and Apatosaurus (right) at the American Museum of Natural History. | ||||||||||||||
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Dinosaurs were the dominant vertebrate animals of the terrestrial ecosystems for over 160 million years, from the late Triassic period (about 230 million years ago) to the end of the Cretaceous period (65 million years ago). They are divided into a number of subgroups, the largest two being based on the structure of the hip. Saurischians retained the lizard-like hips of their ancestors, and included theropods like Tyrannosaurus and sauropodomorphs like Diplodocus. Ornithischians were herbivores with bird-like hips, and included such groups as armored, horned, bone-headed, and duck-billed dinosaurs. These groups evolved a variety of adaptations and occupied diverse niches as the Earth and its environments changed during the Mesozoic Era, but (with the exception of birds; see below), perished in the Cretaceous–Tertiary extinction event approximately 65 million years ago.
Research since the 1970s has changed the scientific and public understanding of dinosaurs, from slow, unintelligent cold-blooded animals, to active animals with elevated metabolisms, often with adaptations for social interactions. One important component of the renewed interest in dinosaurs is their relationship with birds; research indicates that theropod dinosaurs are the most likely ancestors of birds. In fact, most paleontologists regard birds as the only surviving dinosaurs. Crocodilians are the other surviving close relatives of dinosaurs, and both groups are members of the Archosauria, a group of reptiles that first appeared in the very late Permian and became dominant in the mid-Triassic.
Since the first dinosaur fossils were recognized in the early 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. They have been featured in best-selling books and films (notably Jurassic Park), 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 none of these were dinosaurs. In colloquial English "dinosaur" is sometimes used to to describe an obsolete or unsuccessful thing or person, despite the dinosaurs\' 160 million-year reign and the global abundance and diversity of their descendants, the birds.
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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.Owen, R. (1842). "Report on British Fossil Reptiles." Part II. Report of the British Association for the Advancement of Science, Plymouth, England. The term is derived from the Greek words δεινός (deinos meaning "terrible", "fearsome", or "formidable") and σαύρα (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 majesty.Farlow, J.O., and Brett-Surman, M.K. (1997). Preface. In: Farlow, J.O., and Brett-Surman, M.K. (eds.). The Complete Dinosaur.. Indiana University Press, ix-xi. ISBN 0-253-33349-0.
Triceratops skeleton at the American Museum of Natural History in New York City.
Under phylogenetic taxonomy, dinosaurs are usually defined as all descendants of the most recent common ancestor of Triceratops and modern birds.Irmis, Randall B. (2007). "A reappraisal of the phylogeny of early dinosaurs". The Palaeontological Association Newsletter 65: 92-94. Retrieved on 2007-11-22. It has also been suggested that Dinosauria be defined as all of 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.Olshevsky, G. (2000). "An annotated checklist of dinosaur species by continent." Mesozoic Meanderings, 3: 1–157 Both definitions result in the same set of animals being defined as dinosaurs, including theropods (mostly bipedal carnivores), sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails), ankylosaurians (armored herbivorous quadrupeds), stegosaurians (plated herbivorous quadrupeds), ceratopsians (herbivorous quadrupeds with horns and frills), and ornithopods (bipedal or quadrupedal herbivores including "duck-bills"). These definitions are written to correspond with scientific conceptions of dinosaurs that predate the modern use of phylogenetics. The continuity of meaning is intended to prevent confusion about what the term "dinosaur" means.
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 must be included in a group for that group to be natural, birds are dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.Padian, K. (2004). Basal Avialae. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (second edition). University of California Press:Berkeley, 210–231. ISBN 0-520-24209-2.
From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word "dinosaur" does not include birds. Additionally, referring to dinosaurs that are not birds as "non-avian dinosaurs" is cumbersome. For clarity, this article will use "dinosaur" as a synonym for "non-avian dinosaur". The term "non-avian dinosaur" will be used for emphasis as needed. It is also technically correct to refer to dinosaurs as a distinct group under the older Linnaean classification system, which accepts paraphyletic taxa that exclude some descendants of a single common ancestor.
Stegosaurus skeleton, Field Museum, Chicago.
Using one of the above definitions, dinosaurs (aside from birds) can be generally described as terrestrial archosaurian reptiles with limbs held erect beneath the body, that existed from the Late Triassic (first appearing in the Carnian faunal stage) to the Late Cretaceous (going extinct at the end of the Maastrichtian).Glut, Donald F. (1997). Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co, 40. ISBN 0-89950-917-7. Many prehistoric animals are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and Dimetrodon, but are not classified scientifically as dinosaurs. Marine reptiles like ichthyosaurs, mosasaurs, and plesiosaurs were neither terrestrial nor archosaurs; pterosaurs were archosaurs but not terrestrial; and Dimetrodon was a Permian animal more closely related to mammals.Lambert, David; and the Diagram Group (1990). The Dinosaur Data Book. New York: Avon Books, 288. ISBN 0-380-75896-3. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a cat, and were generally rodent-sized carnivores of small prey.Morales, Michael (1997). "Nondinosaurian vertebrates of the Mesozoic", in Farlow, James O.; and Brett-Surman, Michael K. (eds.): The Complete Dinosaur. Bloomington: Indiana University Press, 607-624. ISBN 0-253-33349-0. One notable exception is Repenomamus giganticus, a triconodont weighing between 12 kilograms (26 lb) and 14 kilograms (31 lb) that is known to have eaten small dinosaurs like young Psittacosaurus.Hu Yaoming; Meng Jin; Wang Yuanqing; and Li Chuankui (2005). "Large Mesozoic mammals fed on dinosaurs". Nature 433: 149–152. doi:10.1038/nature03102.
Dinosaurs 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.Wang, S.C., and Dodson, P. (2006). "Estimating the Diversity of Dinosaurs". Proceedings of the National Academy of Sciences USA 103 (37): 13601–13605. PMID 16954187. An earlier study predicted that about 3,400 dinosaur genera existed, including many which would not have been preserved in the fossil record.Russell, Dale A. (1995). "China and the lost worlds of the dinosaurian era". Historical Biology 10: 3-12. Some were herbivorous, others carnivorous. Some dinosaurs were bipeds, some were quadrupeds, and others, such as Ammosaurus and Iguanodon, could walk just as easily on two or four legs. Many had bony armor, or cranial modifications like horns and crests. Although known for large size, many dinosaurs were human-sized or smaller. Dinosaur remains have been found on every continent on Earth, including Antarctica. Despite their diversity and dominance, however, dinosaurs (other than birds) did not spread into aquatic or aerial niches.
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 their descendants. Such common features 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.Benton, Michael J. (2004). "Origin and relationships of Dinosauria", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 7-19. ISBN 0-520-24209-2.
Edmontonia was an "armored dinosaur" of the group Ankylosauria.
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. For example, as diapsid reptiles, dinosaurs ancestrally had two pairs of temporal fenestrae (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the snout and lower jaw.Holtz, Jr., T.R. (2000). Classification and evolution of the dinosaur groups. In: Paul, G.S. (ed.). The Scientific American Book of Dinosaurs.. St. Martin\'s Press, 140–168. ISBN 0-312-26226-4. Additionally, several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs, or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups. These include an elongated scapula, or shoulder blade; a sacrum composed of three or more fused vertebrae (three are found in some other archosaurs, but only two in are found in Herrerasaurus); and an acetabulum, or hip socket, with a hole at the center of its inside surface (closed in Saturnalia, for example).Langer, M.C., Abdala, F., Richter, M., and Benton, M.J. (1999). "A sauropodomorph dinosaur from the Upper Triassic (Carnian) of southern Brazil". Comptes Rendus de l\'Academie des Sciences, Paris: Sciences de la terre et des planètes 329: 511–517. Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the Late Triassic are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.Nesbitt, Sterling J.; Irmis, Randall B.; and Parker, William G. (2007). "A critical re-evaluation of the Late Triassic dinosaur taxa of North America". Journal of Systematic Palaeontology 5 (2): 209-243.
Dinosaurs stood erect in a manner similar to most modern mammals, but distinct from most other reptiles, whose limbs sprawl out to either side. Their posture was due to the development of a laterally-facing recess in the pelvis (usually an open socket) and a corresponding inwardly-facing distinct head on the femur.Benton, M.J. (2004). Vertebrate Paleontology. Blackwell Publishers, xii-452. ISBN 0-632-05614-2. Their erect posture enabled dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles.Cowen, Richard. "Dinosaurs", History of Life, 4th edition, Blackwell Publishing, 151-175. ISBN 1405117567. Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.Kubo; and Benton, M.J. (2007). "Evolution of hindlimb posture in archosaurs: limb stresses in extinct vertebrates". Palaeontology 50 (6): 1519-1529. Some non-dinosaurian archosaurs, including rauisuchians, also had erect limbs but achieved this by a "pillar erect" configuration of the hip joint, where instead of having a projection from the femur insert on a socket on the hip, the upper pelvic bone was rotated to form an overhanging shelf.
For a long time many scientists thought dinosaurs were polyphyletic with multiple groups of unrelated "dinosaurs" evolving due to similar pressures,Seeley, H.G. (1887). "On the classification of the fossil animals commonly named Dinosauria". Proc R Soc London 43: 165-171. Royal Society. Romer, A.S. (1956). Osteology of the Reptiles. University of Chicago. but dinosaurs are now known to have formed a single group. (1974) "Dinosaur monophyly and a new class of vertebrates". Nature 248: 168-172. doi:10.1038/248168a0.
Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago during the Middle to Late Triassic period, roughly 20 million years after the Permian-Triassic extinction event wiped out an estimated 95% of all life on Earth.Kump LR, Pavlov A & Arthur MA (2005). "Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia". Geology 33 (5): 397-400. doi:10.1130/G21295.1. Tanner LH, Lucas SG & Chapman MG (2004). "Assessing the record and causes of Late Triassic extinctions". Earth-Science Reviews 65 (1-2): 103-139. doi:10.1016/S0012-8252(03)00082-5. Retrieved on 2007-10-22. Radiometric dating of the rock formation that contained fossils from the early dinosaur genus Eoraptor establishes its presence in the fossil record at this time. Paleontologists believe Eoraptor resembles the common ancestor of all dinosaurs;Sereno PC (1999). "The evolution of dinosaurs". Science 284 (5423): 2137-2147. doi:10.1126/science.284.5423.2137. if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.Sereno, P.C.; Forster, C.A.; Rogers, R.R.; and Monetta, A.M. (1993). "Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria". Nature 361: 64–66. doi:10.1038/361064a0. The discovery of primitive, dinosaur-like ornithodirans such as Marasuchus and Lagerpeton in Argentinian Middle Triassic strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators.
When dinosaurs appeared, terrestrial habitats were occupied by various types of basal archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchias, and rhynchosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the Carnian and Norian faunal stages (about 215 million years ago), dicynodonts and a variety of basal archosauromorphs, including the prolacertiforms and rynchosaurs, became extinct. This was followed by the Triassic-Jurassic extinction event (about 200 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles.
The first few lines of primitive dinosaurs diversified through the Carnian and Norian stages of the Triassic, most likely by occupying the niches of groups that became extinct. Traditionally, dinosaurs were thought to have replaced the variety of other Triassic land animals by proving superior through a long period of competition. This now appears unlikely, for several reasons. Dinosaurs do not show a pattern of steadily increasing in diversity and numbers, as would be predicted if they were competitively replacing other groups; instead, they were very rare through the Carnian, making up only 1-2% of individuals present in faunas. In the Norian, however, after the extinction of several other groups, they became significant components of faunas, representing 50-90% of individuals. Also, what had been viewed as a key adaptation of dinosaurs, their erect stance, is now known to have present in several contemporaneous groups that were not as successful (aetosaurs, ornithosuchids, rauisuchians, and some groups of crocodylomorphs). Finally, the Late Triassic itself was a time of great upheaval in life, with shifts in plant life, marine life, and climate.
Dinosaurs (including birds) are archosaurs, like modern crocodilians. Archosaurs\' diapsid skulls have two holes, called temporal fenestrae, located where the jaw muscles attach, and an additional antorbital fenestra in front of the eyes. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Anatomically, dinosaurs share many other archosaur characteristics, including teeth that grow from sockets rather than as direct extensions of the jawbones. 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 crocodylians sprawl out to either side.
Collectively, dinosaurs are usually regarded as a superorder or an unranked clade. They are divided into two orders, Saurischia and Ornithischia, depending upon pelvic structure. 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. Saurischians (\'lizard-hipped\', from the Greek sauros (σαυρος) meaning \'lizard\' and ischion (ισχιον) meaning \'hip joint\') retained the hip structure of their ancestors, with a pubis bone directed cranially, or forward. This basic form was modified by rotating the pubis backward to varying degrees in several groups (Herrerasaurus,Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster, 248-250. therizinosauroids,Clark, J.M., Maryanska, T., and Barsbold, R. (2004). "Therizinosauroidea", in The Dinosauria, 2nd ed. 151–164. dromaeosaurids,Norell, M.A., and Makovicky, P.J. (2004). "Dromaeosauridae", in The Dinosauria, 2nd ed. 196-210. and birds). Saurischia includes the theropods (bipedal and mostly carnivores, except for birds) and sauropodomorphs (long-necked quadrupedal herbivores).
By contrast, ornithischians (\'bird-hipped\', from the Greek ornitheios (ορνιθειος) meaning \'of a bird\' and ischion (ισχιον) meaning \'hip joint\') had a pelvis that superficially resembled a bird\'s pelvis: the pubis bone was oriented caudally (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of herbivores. (NB: the terms "lizard hip" and "bird-hip" are misnomers — birds evolved from dinosaurs with "lizard hips".)
Saurischia.png
Saurischian pelvis structure (left side) |
Tyrannosaurus pelvis left.jpg
Tyrannosaurus pelvis (showing saurischian structure - left side) |
Ornithischia.png
Ornithischian pelvis structure (left side). |
Edmontosaurus pelvis left.jpg
Edmontosaurus pelvis (showing ornithischian structure - left side) |
The following is a simplified classification of dinosaur families. A more detailed version can be found at List of dinosaur classifications.
Struthiomimus, an ostrich-like theropod dinosaur.
Brachiosaurus is an example of a sauropod dinosaur.
Various ornithopod dinosaurs and one heterodontosaurid. Far left: Camptosaurus, left: Iguanodon, center background: Shantungosaurus, center foreground: Dryosaurus, right: Corythosaurus, far right (small): Heterodontosaurus, far right (large) Tenontosaurus.
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, there was a worldwide dinosaur fauna mostly composed of coelophysoid carnivores and prosauropod herbivores.Holtz, Thomas R., Jr.; Chapman, Ralph E.; and Lamanna, Matthew C. (2004). "Mesozoic biogeography of Dinosauria", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 627-642. ISBN 0-520-24209-2. Gymnosperm plants (particularly conifers), a potential food source, radiated in the Late Triassic. Prosauropods did not have sophisticated mechanisms for processing food in the mouth, so must have employed other means of breaking down food farther along the digestive tract.Fastovsky, David E.; and Smith, Joshua B. (2004). "Dinosaur paleoecology", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 614-626. ISBN 0-520-24209-2. The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ceratosaurians, spinosauroids, and carnosaurians, and herbivores consisting of stegosaurian ornithischians and large sauropods. Examples of this include the Morrison Formation of North America and Tendaguru Beds of Tanzania. Dinosaurs in China show some differences, with specialized sinraptorid theropods and unusual, long-necked sauropods like Mamenchisaurus. Ankylosaurians and ornithopods were also becoming more common, but prosauropods had become extinct. Conifers and pteridophytes were the most common plants. Sauropods, like the earlier prosauropods, were not oral processors, but ornithischians were evolving various means of dealing with food in the mouth, including potential cheek-like organs to keep food in the mouth, and jaw motions to grind food. Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians.
By the Early Cretaceous and the ongoing breakup of Pangaea, dinosaurs were becoming strongly differentiated by landmass. The earliest part of this time saw the spread of ankylosaurians, iguanodontians, and brachiosaurids through Europe, North America, and northern Africa. These were later supplemented or replaced in Africa by large spinosaurid and carcharodontosaurid theropods, and rebbachisaurid and titanosaurian sauropods, also found in South America. In Asia, maniraptoran coelurosaurians like dromaeosaurids, troodontids, and oviraptorosaurians became the common theropods, and ankylosaurids and early ceratopsians like Psittacosaurus became important herbivores. Meanwhile, Australia was home to a fauna of basal ankylosaurians, hypsilophodonts, and iguanodontians The stegosaurians appear to have gone extinct at some point in the late Early Cretaceous or early Late Cretaceous. A major change in the Early Cretaceous, which would be amplified in the Late Cretaceous, was the evolution of flowering plants. At the same time, several groups of dinosaurian herbivores evolved more sophisticated ways to orally process food. Ceratopsians developed a method of slicing with teeth stacked on each other in batteries, and iguanodontians refined a method of grinding with tooth batteries, taken to its extreme in hadrosaurids. Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid Nigersaurus.Sereno, P.C.; Wilson, J.A.; Witmer, L.M.; Whitlock, J.A.; Maga, A.; Ide, O.; and Rowe, T.A. (2007). "Structural extremes in a Cretaceous dinosaur". PLoS ONE 2 (11): e1230. doi:10.1371/journal.pone.0001230.
There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were tyrannosaurids and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and pachycephalosaurians. In the southern continents that had made up the now-splitting Gondwana, abelisaurids were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, rhabdodontid iguanodontians, nodosaurid ankylosaurians, and titanosaurian sauropods were prevalent. Flowering plants were greatly radiating, with the first grasses appearing by the end of the Cretaceous.Prasad, V.; Strömberg, C.A.E.; Alimohammadian, H; and Sahni, A. (2005). "Dinosaur coprolites and the early evolution of grasses and grazers". Science 310 (5751): 1170-1180. doi:10.1126/science.1118806. Grinding hadrosaurids and shearing ceratopsians became extremely diverse across North America and Asia. Theropods were also radiating as herbivores or omnivores, with therizinosaurians and ornithomimosaurians becoming common.
The Cretaceous–Tertiary extinction event, which occurred approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaurs except for the line that had already given rise to the first birds. Some other diapsid groups, such as crocodylians, lizards, snakes, sphenodontians, and choristoderans, also survived the event.Archibald, J. David; and Fastovsky, David E. (2004). "Dinosaur Extinction", in Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, 672–684. ISBN 0-520-24209-2.
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.Dal Sasso, C. and Signore, M. (1998)). "Exceptional soft-tissue preservation in a theropod dinosaur from Italy". Nature 292 (6674): 383–387. doi:10.1038/32884. Many fields of study contribute to our understanding of dinosaurs, including physics (especially biomechanics), chemistry, biology, and the earth sciences (of which paleontology is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior.
Comparative size of Diplodocus; human figures provide scale.
While the evidence is incomplete, it is clear that, as a group, dinosaurs were large. Even by dinosaur standards, the sauropods were gigantic. 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 the Indricotherium and the Columbian mammoth were dwarfed by the giant sauropods, and only a handful of modern aquatic animals approach or surpass them in size — most notably the blue whale, which reaches up to 173,000 kilograms (381,000 lb) and over 30 meters (100 ft) in length.Assessment and Update Status Report on the Blue Whale Balaenoptera musculus. Committee on the Status of Endangered Wildlife in Canada (2002). Retrieved on 2007-12-05.
Most dinosaurs, however, were much smaller than the giant sauropods. Current evidence suggests that dinosaur average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods. Theropod dinosaurs, when sorted by estimated weight into categories based on order of magnitude, most often fall into the 100 to 1,000 kilogram (500 to 4,500 lb) category, whereas recent predatory carnivorans peak in the 10 to 100 kilogram (50 to 450 lb) category.Farlow, James A. (1993). "On the rareness of big, fierce animals: speculations about the body sizes, population densities, and geographic ranges of predatory mammals and large, carnivorous dinosaurs", Functional Morphology and Evolution, American Journal of Science, Special Volume 293-A, 167-199. A rough estimate for average dinosaur weight is about 100 kilograms (200 lb). This contrasts sharply with the size of Cenozoic mammals, estimated by the same source (the National Museum of Natural History) as about 2 to 5 kilograms (5 to 10 lb).Anatomy and evolution. National Museum of Natural History. Retrieved on 2007-11-21.
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. As a result, scientists will probably never be certain of the largest and smallest dinosaurs.
Comparative size of Brachiosaurus.
.png/58px-Human-eoraptor size comparison(v2).png)
Comparative size of Eoraptor.
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;Colbert, E.H. (1968). Men and Dinosaurs: The Search in Field and Laboratory. E. P. Dutton & Company:New York, vii + 283 p. ISBN 0140212884. this mount is 12 meters (39 ft) tall and 22.5 meters (74 ft) long, and would have belonged to an animal that weighed between 30,000 and 60,000 kilograms (70,000 and 130,000 lb). 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.
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 80,000 to 100,000 kilograms (90 to 110 short tons); the longest, the 40 meters (130 ft) long Supersaurus; and the tallest, the 18 meters (59 ft) Sauroposeidon, which could have reached a sixth-floor window. The 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 120,000 kilograms (260,000 lb),Carpenter, Kenneth (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus", Paleontology and Geology of the Upper Jurassic Morrison Formation (pdf), New Mexico Museum of Natural History and Science Bulletin, 36, Albuquerque, New Mexico: New Mexico Museum of Natural History and Science, 131-138. heavier than all known dinosaurs except possibly the poorly known Bruhathkayosaurus, which could have weighed 175,000 to 220,000 kilograms (400,000 to 500,000 lb). The largest known carnivorous dinosaur was Spinosaurus, reaching a length of 16 to 18 meters (50 to 60 ft), and weighing in at 8,150 kilograms (18,000 lb).dal Sasso, C., Maganuco, S., Buffetaut, E., and Mendez, M.A. (2006). New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities. Journal of Vertebrate Paleontology 25(4):888–896. Other large meat-eaters included Giganotosaurus, Mapusaurus, Tyrannosaurus rex and Carcharodontosaurus.
Not including modern birds, the smallest dinosaurs known were about the size of a crow or a chicken. The theropods Microraptor and Parvicursor were both under 0.6 meters (2 ft) in length.
A nesting ground of Maiasaura was discovered in 1978.
Interpretations of dinosaur behavior are generally based on the pose of body fossils and their habitat, computer simulations of their biomechanics, and comparisons with modern animals in similar ecological niches. As such, the current understanding of dinosaur behavior relies on speculation, and will likely remain controversial for the foreseeable future. However, there is general agreement that some behaviors which are common in crocodiles and birds, dinosaurs\' closest living relatives, were also common among dinosaurs.
The first direct evidence of herding behavior was the 1878 discovery of 31 Iguanodon dinosaurs which were thought to have perished together in Bernissart, Belgium, after they fell into a deep, flooded sinkhole and drowned.Yans J, Dejax J, Pons D, Dupuis C & Taquet P (2005). "Implications paléontologiques et géodynamiques de la datation palynologique des sédiments à faciès wealdien de Bernissart (bassin de Mons, Belgique)" (in French). Comptes Rendus Palevol 4 (1-2): 135–150. doi:10.1016/j.crpv.2004.12.003. Other mass death sites have been subsequently discovered. Those, along with multiple trackways, suggest that herd or pack behavior was common in many dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in Oxford, England,Day, J.J.; and Upchurch, P. (2002). "Sauropod trackways, evolution, and behavior". Science 296: 1659. doi:10.1126/science.107016. and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, Texas. Dinosaurs may have congregated in herds for defense, for migratory purposes, or to provide protection for their young. The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as pack hunters working together to bring down large prey.Lessem, Don; and Glut, Donald F. (1993). "Allosaurus", The Dinosaur Society\'s Dinosaur Encyclopedia. Random House, 19–20. ISBN 0-679-41770-2. Maxwell, W. D.; Ostrom, J.H. (1995). "Taphonomy and paleobiological implications of Tenontosaurus-Deinonychus associations". Journal of Vertebrate Paleontology 15 (4): 707-712. (abstract) However, this lifestyle is uncommon among the modern relatives of dinosaurs (crocodiles and other reptiles, and birds - Harris\'s Hawk is a well-documented exception), and the taphonomic evidence suggesting pack hunting in such theropods as Deinonychus and Allosaurus can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators.Roach, Brian T.; and Brinkman, Daniel L. (2007). "A reevaluation of cooperative pack hunting and gregariousness in Deinonychus antirrhopus and other nonavian theropod dinosaurs". Bulletin of the Peabody Museum of Natural History 48 (1): 103–138.
Fossilized egg of the oviraptorid Citipati, American Museum of Natural History.
Jack Horner\'s 1978 discovery of a Maiasaura ("good mother dinosaur") nesting ground in Montana demonstrated that parental care continued long after birth among the ornithopods.Horner, J.R.; and Makela, R. (1979). "Nest of juveniles provides evidence of family-structure among dinosaurs". Nature 282 (5736): 296–298. There is also evidence that other Cretaceous-era dinosaurs, like Patagonian titanosaurian sauropods (1997 discovery), had similar nesting behaviors,Chiappe, L.M.; Coria, R.A.; Dingus, L.; Jackson, F.; Chinsamy, A.; and Fox, M. (1998). "Sauropod dinosaur embryos from the Late Cretaceous of Patagonia". Nature 396: 258-261. and that the animals congregated in huge nesting colonies like those of penguins. The Mongolian oviraptorid Citipati was discovered in a chicken-like brooding position in 1993, which may mean it was covered with an insulating layer of feathers that kept the eggs warm.Oviraptor nesting Oviraptor nests or Protoceratops? Parental care is also implied by other finds. For example, the fossilized remains of a grouping of Psittacosaurus has been found, consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting.Meng Qingjin; Liu Jinyuan; Varricchio, David J.; Huang, Timothy; and Gao Chunling (2004). "Parental care in an ornithischian dinosaur". Nature 431: 145–146. Additionally, a dinosaur embryo (pertaining to the prosauropod Massospondylus) was found without teeth, indicating that some parental care was required to feed the young dinosaur.Reisz RR, Scott, D Sues, H-D, Evans, DC & Raath, MA (2005). "Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance". Science 309: 761–764. doi:10.1126/science.1114942. Retrieved on 2007-10-24. Trackways have also confirmed parental behavior among sauropods and ornithopods from the Isle of Skye in northwestern Scotland.Dinosaur family tracks Footprints show maternal instinct af
