Dinosaur

Un article de Vev.

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Dinosaurs were vertebrate animals that dominated terrestrial ecosystems for over 160 million years, first appearing approximately 230 million years ago. At the end of the Cretaceous Period, 65 million years ago, a catastrophic extinction event ended the dominance of dinosaurs on land. One group of dinosaurs is known to have survived to the present day: taxonomists believe modern birds are direct descendants of theropod dinosaurs.

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, 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.

Sommaire 1 What is a dinosaur? 1.1 Definition 1.1.1 Distinguishing features of dinosaurs 1.1.2 Phylogenetic definition 2 Natural history 2.1 Origins and early evolution 2.2 Classification 2.2.1 Order Saurischia 2.2.2 †Order Ornithischia 2.3 Evolution and paleobiogeography 3 Study of dinosaurs 3.1 Size 3.1.1 Largest and smallest dinosaurs 3.2 Behavior 3.3 Areas of controversy 3.3.1 Physiology 3.3.2 Soft tissue and DNA 4 Feathered dinosaurs and the origin of birds 4.1 Feathers 4.2 Skeleton 4.3 Reproductive biology 4.4 Lungs 4.5 Heart and sleeping posture 4.6 Gizzard 5 Extinction 5.1 Impact event 5.2 Deccan Traps 5.3 Possible Paleocene dinosaurs 6 History of discovery 6.1 The "dinosaur renaissance" 7 Dinosaurs in culture 8 Religious views 9 See also 10 Notes and references 11 General references 12 See also 13 External links

What is a dinosaur?

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 and modern birds). The term 'non-avian dinosaur' will be used for emphasis as needed.

Non-avian dinosaurs can be generally described as terrestrial archosaurs with limbs held erect beneath the body, that existed from the Carnian faunal stage of the Late Triassic to the Maastrichtian stage of the Late Cretaceous.<ref name=DFG97>Modèle:Cite book</ref> This excludes many prehistoric animals that are popularly conceived as dinosaurs. Examples include: marine reptiles like ichthyosaurs, mosasaurs, and plesiosaurs, which were neither terrestrial nor archosaurs; pterosaurs, which were not terrestrial; and Dimetrodon, a Permian animal more closely related to mammals.<ref name=DL90>Modèle:Cite book</ref> 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.<ref name=MM97>Modèle:Cite book</ref> One notable exception is Repenomamus giganticus, a Modèle:Kg to lb to Modèle:Kg to lb triconodont that is known to have eaten small dinosaurs like young Psittacosaurus.<ref name=huetal2005>Modèle:Cite journal</ref>

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.<ref>Modèle:Cite journal</ref> An earlier study predicted that about 3,400 dinosaur genera existed, including many which would not have been preserved in the fossil record.<ref name="russell1995">Modèle:Cite journal</ref> 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.<ref name="MacLeod"/> Despite their diversity and dominance, however, as noted, dinosaurs (with the exception of birds) did not spread into aquatic or aerial niches.

Definition

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.<ref>Owen, R. (1842). "Report on British Fossil Reptiles." Part II. Report of the British Association for the Advancement of Science, Plymouth, England.</ref> 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.<ref name=FBS97>Modèle:Cite book</ref>

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 their descendants. 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.<ref name=MJB04>Modèle:Cite book</ref>

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.<ref name=TRHJ00>Modèle:Cite book</ref> 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);<ref name=MJB04/> and an acetabulum, or hip socket, with a hole at the center of its inside surface (for example, closed in Saturnalia).<ref name=LARB99>Modèle:Cite journal</ref> Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other basal archosaurs are often poorly known and were similar in many ways; these animals have sometimes been misidentified in the literature.<ref name=NIP07>Modèle:Cite journal</ref>

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.<ref name=MJB00>Modèle:Cite book</ref> Their erect posture enabled dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that surpassed those of "sprawling" reptiles.<ref name=RC05>Modèle:Cite book</ref> Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.<ref name=TKMB07>Modèle:Cite journal</ref> 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.<ref name=TKMB07/>

Phylogenetic definition

Under phylogenetic taxonomy, dinosaurs are usually defined as all descendants of the most recent common ancestor of Triceratops and modern birds.<ref name="Irmis07">Modèle:Cite journal</ref> 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.<ref name="olshevsky2000">Olshevsky, G. (2000). "An annotated checklist of dinosaur species by continent." Mesozoic Meanderings, 3: 1–157</ref>

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 are dinosaurs.<ref name=KP04>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.</ref>

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 dinosaurs as a distinct group under the older Linnaean classification system, which accepts paraphyletic taxa that exclude some descendants of a single common ancestor. Paleontologists mostly use cladistics, which classifies birds as dinosaurs, but some biologists of the older generation do not.

Natural history

Origins and early evolution

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.<ref>Modèle:Cite journal</ref> <ref name="TannerLucas">Modèle:Cite journal</ref> 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;<ref name="Sereno1999">Modèle:Cite journal</ref> if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.<ref name=SFRM93>Modèle:Cite journal</ref> 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.<ref name=MJB04/>

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 competition. This now appears unlikely, for several reasons. Early considerations of dinosaur evolution had dinosaurs as polyphyletic, with multiple groups of unrelated "dinosaurs" evolving due to similar pressures, but dinosaurs are now known to have formed a single group. Early conceptions also had a long, drawn-out period of competition beginning in the Middle Triassic, but more work has shown that dinosaurs did not appear that early and had a sudden diversification. 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.<ref name=MJB04/>

Classification

Main article: Dinosaur classification

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.<ref name=MJB00/> This basic form was modified by rotating the pubis backward to varying degrees in several groups (Herrerasaurus,<ref name=GSP88>Modèle:Cite book</ref> therizinosauroids,<ref name="clarketal2004">Clark, J.M., Maryanska, T., and Barsbold, R. (2004). "Therizinosauroidea", in The Dinosauria, 2nd ed. 151–164.</ref> dromaeosaurids,<ref name=MAPM04>Norell, M.A., and Makovicky, P.J. (2004). "Dromaeosauridae", in The Dinosauria, 2nd ed. 196-210.</ref> and birds<ref name=KP04/>). 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".)

Saurischian pelvis structure (left side)

Tyrannosaurus pelvis (showing saurischian structure - left side)

Ornithischian pelvis structure (left side).

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.

The dagger (†) is used to indicate taxa that are extinct.

Order Saurischia

• †Infraorder Herrerasauria
• Suborder Theropoda
  • †Superfamily Coelophysoidea
  • †Infraorder Ceratosauria
    • Family Ceratosauridae
    • Family Abelisauridae
  • Clade Tetanurae
    • †Superfamily Spinosauroidea
      • Family Megalosauridae
      • Family Spinosauridae
    • †Infraorder Carnosauria
    • Clade Coelurosauria
      • †Superfamily Tyrannosauroidea
      • †Infraorder Ornithomimosauria
      • †Infraorder Segnosauria
      • †Infraorder Oviraptorosauria
      • †Infraorder Deinonychosauria
        • Family Dromaeosauridae
        • Family Troodontidae

• †Suborder Sauropodomorpha
  • Infraorder Prosauropoda
    • Family Riojasauridae
    • Family Plateosauridae
    • Family Massospondylidae
  • Infraorder Sauropoda
    • Family Anchisauridae
    • Family Melanorosauridae
    • Family Blikanasauridae
    • Family Vulcanodontidae
    • Family Cetiosauridae
    • Family Omeisauridae
    • Clade Turiasauria
    • Clade Neosauropoda
      • Superfamily Diplodocoidea
      • Family Camarasauridae
      • Family Brachiosauridae
      • Superfamily Titanosauroidea

†Order Ornithischia

• Family Fabrosauridae
• Suborder Thyreophora
  • Family Scelidosauridae
  • Infraorder Stegosauria
  • Infraorder Ankylosauria
    • Family Nodosauridae
    • Family Ankylosauridae
• Suborder Cerapoda
  • Family Heterodontosauridae
  • Infraorder Ornithopoda
    • Family Hypsilophodontidae
    • Family Iguanodontidae
    • Superfamily Hadrosauroidea
  • Clade Marginocephalia
    • Infraorder Pachycephalosauria
    • Infraorder Ceratopsia
      • Family Psittacosauridae
      • Family Protoceratopsidae
      • Family Ceratopsidae

Evolution and paleobiogeography

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 predators and prosauropod herbivores.<ref name=HCL04>Modèle:Cite book</ref> 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.<ref name=FS04>Modèle:Cite book</ref> 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.<ref name=HCL04/> 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.<ref name=FS04/> Another notable evolutionary event of the Jurassic was the appearance of true birds, descended from maniraptoran coelurosaurians.<ref name=KP04/>

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 <ref name=HCL04/> 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.<ref name=FS04/> Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid Nigersaurus.<ref name=serenoetal07>Modèle:Cite journal</ref>

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.<ref name=HCL04/> Flowering plants were greatly radiating,<ref name=FS04/> with the first grasses appearing by the end of the Cretaceous.<ref name=PSAS05>Modèle:Cite journal</ref> 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.<ref name=FS04/>

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.<ref name=AF04>Modèle:Cite book</ref>

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.<ref name="softtissue">Modèle:Cite journal</ref><ref name="Schweitzer2005"/> 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). Two topics of particular interest and study have been dinosaur size and behavior.

Size

Main article: Dinosaur size

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 Modèle:Kg to lb and over Modèle:M to ft in length.<ref name=Cosewic> 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. </ref>

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.<ref name="Sereno1999"/> Theropod dinosaurs, when sorted by estimated weight into categories based on order of magnitude, most often fall into the 100 to 1,000 kg (500 to 4,500 lb) category, whereas recent predatory carnivorans peak in the 10 to 100 kg (50 to 450 lb) category.<ref name=JF93>Modèle:Cite book</ref> A rough estimate for average dinosaur weight is about Modèle:Kg to 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 kg (5 to 10 lb).<ref name=NMNH> Anatomy and evolution

. National Museum of Natural History  
 

 

. Retrieved on 2007-11-21. </ref>

Largest and smallest dinosaurs

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.

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;<ref name=EC68>Colbert, E.H. (196Image:Cool.gif. Men and Dinosaurs: The Search in Field and Laboratory. E. P. Dutton & Company:New York, vii + 283 p. ISBN 0140212884.</ref> this mount is Modèle:M to ft tall and Modèle:M to ft long, and would have belonged to an animal that weighed between 30,000 and 60,000 kg (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 100,00 kg (90 to 110 short tons); the longest, the Modèle:M to ft long Supersaurus; and the tallest, the Modèle:M to 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 Modèle:M to ft long and weighed over Modèle:Kg to lb,<ref name=KC06>Modèle:Cite book</ref> heavier than all known dinosaurs except possibly the poorly known Bruhathkayosaurus, which could have weighed 175,000 to 220,000 kg (400,000 to 500,000 lb). The largest known carnivorous dinosaur was Spinosaurus, reaching a length of 16 to 18 m (50 to 60 ft), and weighing in at Modèle:Kg to lb.<ref name=SMBM06>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.</ref> 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 meter (2 ft) in length.

Behavior

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.<ref>Modèle:Cite journal</ref> 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,<ref>Modèle:Cite journal</ref> 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.<ref name=LG93>Modèle:Cite book</ref><ref name="maxwell&ostrom1995">Modèle:Cite journal(abstract)</ref> However, this lifestyle is not found among the modern relatives of dinosaurs (crocodiles and other reptiles, and birds), 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.<ref name=RB07>Modèle:Cite journal</ref>

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.<ref name=HM79>Modèle:Cite journal</ref> There is also evidence that other Cretaceous-era dinosaurs, like Patagonian titanosaurian sauropods (1997 discovery), had similar nesting behaviors,<ref name=CCDJCF98>Modèle:Cite journal</ref> 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.<ref>Oviraptor nesting Oviraptor nests or Protoceratops?</ref> Parental care is also implied by the fossilized remains of a grouping of Psittacosaurus consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting.<ref name=mengetal2004>Modèle:Cite journal</ref> Trackways have also confirmed parental behavior among sauropods and ornithopods from the Isle of Skye in northwestern Scotland.<ref>Dinosaur family tracks Footprints show maternal instinct after leaving the nest.</ref> Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, in a manner similar to modern birds and crocodiles.

The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile to be used for active defense, so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.<ref name=PC98>Modèle:Cite journal</ref> The nature of dinosaur communication also remains enigmatic, and is an active area of research. For example, recent studies suggest that the hollow crests of the lambeosaurines may have functioned as resonance chambers used for a wide range of vocalizations.<ref name=JAH75>Modèle:Cite journal</ref><ref name=DW98>Modèle:Cite journal</ref>

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the Gobi Desert in 1971. It included a Velociraptor attacking a Protoceratops,<ref> The Fighting Dinosaurs

. American Museum of Natural History  
 

 

. Retrieved on 2007-12-05. </ref> providing evidence that dinosaurs did indeed attack each other.<ref name=carpenter1998>Modèle:Cite journal</ref> Additional evidence for attacking live prey is the partially-healed tail of an Edmontosaurus, a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived.<ref name=carpenter1998/> Cannibalism amongst some species of dinosaurs was confirmed by tooth marks found in Madagascar in 2003, involving the theropod Majungasaurus.<ref name=rogersetal2003>Modèle:Cite journal</ref>

Based on current fossil evidence from dinosaurs such as Oryctodromeus, some herbivorous species seem to have led a partially fossorial (burrowing) lifestyle,<ref name=VMK07>Modèle:Cite journal</ref> and some bird-like species may have been arboreal (tree-climbing), most notably primitive dromaeosaurids such as Microraptor<ref name="chatterjee2007">Modèle:Cite journal</ref> and the enigmatic scansoriopterygids.<ref name="zhang2002">Modèle:Cite journal</ref> However, most dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, in particular, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run,<ref>Modèle:Cite journal</ref> whether diplodocids could create sonic booms via whip-like tail snapping,<ref>Modèle:Cite journal</ref> and whether sauropods could float.<ref>Modèle:Cite journal</ref>

Areas of controversy

Physiology

Main article: Physiology of dinosaurs

A vigorous debate on the subject of temperature regulation in dinosaurs has been ongoing since the 1960s. Originally, scientists broadly disagreed as to whether dinosaurs were capable of regulating their body temperatures at all. More recently, dinosaur endothermy has become the consensus view, and debate has focused on the mechanisms of temperature regulation.

After dinosaurs were discovered, paleontologists first posited that they were ectothermic creatures: "terrible lizards" as their name suggests. This supposed cold-bloodedness implied that dinosaurs were relatively slow, sluggish organisms, comparable to modern reptiles, which need external sources of heat in order to regulate their body temperature. Dinosaur ectothermy remained a prevalent view until Robert T. "Bob" Bakker, an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968.

Modern evidence indicates that dinosaurs thrived in cooler temperate climates, and that at least some dinosaur species must have regulated their body temperature by internal biological means (perhaps aided by the animals' bulk). Evidence of endothermism in dinosaurs includes the discovery of polar dinosaurs in Australia and Antarctica (where they would have experienced a cold, dark six-month winter), the discovery of dinosaurs whose feathers may have provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone. Skeletal structures suggest that theropods and other dinosaurs had active lifestyles better suited to an endothermic cardiovascular system, while sauropods exhibit fewer endothermic characteristics. It is certainly possible that some dinosaurs were endothermic while others were not. Scientific debate over the specifics continues.<ref>Parsons, K.M. (2001). Drawing Out Leviathan. Indiana University Press. 22–48. ISBN 0-253-33937-5.</ref>

Complicating the debate is the fact that warm-bloodedness can emerge based on more than one mechanism. Most discussions of dinosaur endothermy tend to compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess insulation, such as fat, fur, or feathers, which slows down heat loss. However, large mammals, such as elephants, face a different problem because of their relatively small ratio of surface area to volume (Haldane's principle). This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they are hairless, and have large ears which increase their surface area, and have behavioral adaptations as well (such as using the trunk to spray water on themselves and mud wallowing). These behaviors increase cooling through evaporation.

Large dinosaurs would presumably have had to deal with similar issues; their body size suggest they lost heat relatively slowly to the surrounding air, and so could have been what are called inertial homeotherms, animals that are warmer than their environments through sheer size rather than through special adaptations like those of birds or mammals. However, so far this theory fails to account for the vast number of dog- and goat-sized dinosaur species which made up the bulk of the ecosystem during the Mesozoic Era.

Soft tissue and DNA

One of the best examples of soft tissue impressions in a fossil dinosaur was discovered in Petraroia, Italy. The discovery was reported in 1998, and described the specimen of a small, very young coelurosaur, Scipionyx samniticus. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur.<ref name="softtissue" />

In the March 2005 issue of Science, Dr. Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana. After recovery, the tissue was rehydrated by the science team.<ref name="Schweitzer2005"/>

When the fossilized bone was treated over several weeks to remove mineral content from the fossilized bone marrow cavity (a process called demineralization), Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). Scrutiny under the microscope further revealed that the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. The exact nature and composition of this material, and the implications of Dr. Schweitzer's discovery, are not yet clear; study and interpretation of the material is ongoing.<ref name="Schweitzer2005">Modèle:Cite journal</ref>

The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but upon further inspection and peer review, neither of these reports could be confirmed.<ref>Modèle:Cite journal</ref> However, a functional visual peptide of a theoretical dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of related modern species such as reptiles and birds.<ref>Modèle:Cite journal</ref> In addition, several proteins have putatively been detected in dinosaur fossils,<ref>Modèle:Cite journal</ref> including hemoglobin.<ref>Modèle:Cite journal</ref>

Even if dinosaur DNA could be reconstructed, it would be exceedingly difficult to clone and "grow" dinosaurs using current technology since no closely related species exist to provide zygotes or a suitable environment for embryonic development.

Feathered dinosaurs and the origin of birds

Main article: Feathered dinosaurs

Main article: Origin of birds

Birds and non-avian dinosaurs share many features. Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are generally accepted to have been their closest ancient relatives.<ref>Modèle:Cite journal</ref>

Feathers

Archaeopteryx, the first good example of a "feathered dinosaur", was discovered in 1861. The initial specimen was found in the Solnhofen limestone in southern Germany, which is a lagerstätte, a rare and remarkable geological formation known for its superbly detailed fossils. Archaeopteryx is a transitional fossil, with features clearly intermediate between those of modern reptiles and birds. Brought to light just two years after Darwin's seminal The Origin of Species, its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for Compsognathus.<ref name=PW88>Modèle:Cite journal</ref>

Since the 1990s, a number of additional feathered dinosaurs have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. Most of these specimens were unearthed in Liaoning province, northeastern China, which was part of an island continent during the Cretaceous period. Though feathers have been found only in the lagerstätte of the Yixian Formation and a few other places, it is possible that non-avian dinosaurs elsewhere in the world were also feathered. The lack of widespread fossil evidence for feathered non-avian dinosaurs may be due to the fact that delicate features like skin and feathers are not often preserved by fossilization and thus are absent from the fossil record.

A recent development in the debate centers around the discovery of impressions of "protofeathers" surrounding many dinosaur fossils. Said protofeathers suggest that the tyrannosauroids may have been feathered.<ref>Modèle:Cite journal</ref> However, others claim that these protofeathers are simply the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument.<ref>Modèle:Cite journal</ref>

The feathered dinosaurs discovered so far include Beipiaosaurus, Caudipteryx, Dilong, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, Sinosauropteryx, and Jinfengopteryx. Dinosaur-like birds like Confuciusornis, which are anatomically closer to modern avians, have also been discovered. All of these specimens come from the same formation in northern China. The dromaeosauridae family in particular seems to have been heavily feathered, and at least one dromaeosaurid, Cryptovolans, may have been capable of flight.

Skeleton

Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent the more important link for paleontologists. Furthermore, it is increasingly clear that the relationship between birds and dinosaurs, and the evolution of flight, are more complex topics than previously realized. For example, while it was once believed that birds evolved from dinosaurs in one linear progression, some scientists, most notably Gregory S. Paul, conclude that dinosaurs such as the dromaeosaurs may have evolved from birds, losing the power of flight while keeping their feathers in a manner similar to the modern ostrich and other ratites.

Comparison of bird and dinosaur skeletons, as well as cladistic analysis, strengthens the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include the neck, pubis, wrist (semi-lunate carpal), arm and pectoral girdle, shoulder blade, clavicle and breast bone.

Reproductive biology

A discovery of features in a Tyrannosaurus rex skeleton recently provided even more evidence that dinosaurs and birds evolved from a common ancestor and, for the first time, allowed paleontologists to establish the sex of a dinosaur. When laying eggs, female birds grow a special type of bone in their limbs. This medullary bone, which is rich in calcium, forms a layer inside the hard outer bone that is used to make eggshells. The presence of endosteally-derived bone tissues lining the interior marrow cavities of portions of the Tyrannosaurus rex specimen's hind limb suggested that T. rex used similar reproductive strategies, and revealed the specimen to be female.<ref name="schweitzeretal2005">Modèle:Cite journal</ref>

A dinosaur embryo (pertaining to the prosauropod Massospondylus) was found without teeth, indicating that some parental care was required to feed the young dinosaur.<ref name="Reiszetal05">Modèle:Cite journal</ref> It is also possible that the adult dinosaurs regurgitated into a young dinosaur's mouth to provide sustenance, a behavior that is also characteristic of numerous modern bird species.

Lungs

Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to an investigation which was led by Patrick O'Connor of Ohio University. The lungs of theropod dinosaurs (carnivores that walked on two legs and had birdlike feet) likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said. The study was funded in part by the National Science Foundation.<ref>Modèle:Cite journal</ref>

Heart and sleeping posture

Modern computerized tomography (CT) scans of a dinosaur chest cavity (conducted in 2000) found the apparent remnants of complex four-chambered hearts, much like those found in today's mammals and birds.<ref>Modèle:Cite journal</ref> The idea is controversial within the scientific community, coming under fire for bad anatomical science<ref>Modèle:Cite journal</ref> or simply wishful thinking.<ref>Modèle:Cite journal</ref> A recently discovered troodont fossil demonstrates that the dinosaurs slept like certain modern birds, with their heads tucked under their arms.<ref>Modèle:Cite journal</ref> This behavior, which may have helped to keep the head warm, is also characteristic of modern birds.

Gizzard

Another piece of evidence that birds and dinosaurs are closely related is the use of gizzard stones. These stones are swallowed by animals to aid digestion and break down food and hard fibres once they enter the stomach. When found in association with fossils, gizzard stones are called gastroliths.<ref>Modèle:Cite journal</ref>

Extinction

Main article: Cretaceous–Tertiary extinction event

Main article: K–T boundary

Non-avian dinosaurs suddenly became extinct approximately 65 million years ago. Many other groups of animals also became extinct at this time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most birds, and many groups of mammals.<ref name="MacLeod">Modèle:Cite journal</ref> This mass extinction is known as the Cretaceous–Tertiary extinction event. The nature of the event that caused this mass extinction has been extensively studied since the 1970s; at present, several related theories are supported by paleontologists. Though the general consensus is that an impact event was the primary cause of dinosaur extinction, some scientists cite other possible causes, or support the idea that a confluence of several factors was responsible for the sudden disappearance of dinosaurs from the fossil record.

At the peak of the dinosaur era, there were no polar ice caps, and sea levels are estimated to have been from 100 to 250 m (300 to 800 ft) higher than they are today. The planet's temperature was also much more uniform, with only 25 °C (45 °F) separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C (90 °F) warmer than today.<ref name="pmid16311326">Modèle:Cite journal</ref><ref>Modèle:Cite journal</ref>

The atmosphere's composition during the dinosaur era was vastly different as well. Carbon dioxide levels were up to 12 times higher than today's levels, and oxygen formed 32 to 35% of the atmosphere, as compared to 21% today. However, by the late Cretaceous, the environment was changing dramatically. Volcanic activity was decreasing, which led to a cooling trend as levels of atmospheric carbon dioxide dropped. Oxygen levels in the atmosphere also started to fluctuate and would ultimately fall considerably. Some scientists hypothesize that climate change, combined with lower oxygen levels, might have led directly to the demise of many species. If the dinosaurs had respiratory systems similar to those commonly found in modern birds, it may have been particularly difficult for them to cope with reduced respiratory efficiency, given the enormous oxygen demands of their very large bodies.<ref name="MacLeod"/>

Impact event

The asteroid collision theory, which was first proposed by Walter Alvarez in the late 1970s, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez proposed that a sudden increase in iridium levels, recorded around the world in the period's rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5 to 15 kilometer (3 to 9 mi) wide bolide hit in the vicinity of the Yucatán Peninsula, creating the Modèle:Km to mi wide Chicxulub Crater and triggering the mass extinction. Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth's atmospheric temperature, while others claim that it would have instead created an unusual heat wave.

Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).

In September of 2007, U.S. researchers led by William Bottke of the Southwest Research Institute in Boulder, Colorado, and Czech scientists used computer simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that a giant asteroid named Baptistina, approximately Modèle:Km to mi in diameter, orbiting in the asteroid belt which lies between Mars and Jupiter, was struck by a smaller unnamed asteroid about 55 kilometers (35 mi) in diameter about 160 million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the Baptistina family. Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the Modèle:Km to mi wide meteorite which struck Mexico's Yucatan peninsula 65 million years ago, creating the Chicxulub crater (Modèle:Km to mi).

While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that "passages of the solar companion star Nemesis through the Oort comet cloud would trigger comet showers."<ref name="Koeberl">Modèle:Cite book</ref> One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.<ref name="Koeberl"/>

Deccan Traps

Main article: Deccan Traps

Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 mya and lasted for over 2 million years. However, there is evidence that two-thirds of the Deccan Traps were created in 1 million years about 65.5 mya, so these eruptions would have caused a fairly rapid extinction, possibly a period of thousands of years, but still a longer period than what would be expected from a single impact event.<ref>Modèle:Cite journal</ref><ref name="Duncan">Modèle:Cite journal</ref>

The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reducing photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere.<ref name="Duncan"/> Before the mass extinction of the dinosaurs, the release of volcanic gasses during the formation of the Deccan traps "contributed to an apparently massive global warming. Some data point to an average rise in temperature of 8 °C (14 °F) in the last half million years before the impact [at Chicxulub]."<ref>Modèle:Cite journal</ref><ref name="Duncan"/>

In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez (who died in 198Image:Cool.gif replied that paleontologists were being misled by sparse data. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.<ref>Modèle:Cite book</ref>

Possible Paleocene dinosaurs

Nonavian dinosaur remains are occasionally found above the K-T boundary In 2002, paleontologists Zielinski and Budahn reported the discovery of a single hadrosaur leg bone fossil in the San Juan Basin, New Mexico and described it as evidence of Paleocene dinosaurs. The formation in which the bone was discovered has been dated to the early Paleocene epoch approximately 64.5 million years ago. If the bone was not re-deposited into that stratum by weathering action, it would provide evidence that some dinosaur populations may have survived at least a half million years into the Cenozoic Era.<ref name="Fassett">Modèle:Cite journal</ref> Other evidence includes the finding of dinosaur remains in the Hell Creek Formation up to 1.3 meters (51 in) above (40,000 years later than) the K-T boundary. Similar reports have come from other parts of the world, including China.<ref name="Sloan">Modèle:Cite journal</ref> Many scientists, however, dismiss the "Paleocene dinosaurs" as re-worked, i.e. washed out of their original locations and then re-buried in much later sediments,<ref name=FS05>Modèle:Cite journal</ref><ref>Modèle:Cite journal</ref> or find that, if correct, the presence of a handful of dinosaurs in the early Paleocene would not change the underlying facts of the extinction.<ref name=FS05/>

History of discovery

Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese, whose modern word for dinosaur is konglong (恐龍, or "terrible dragon"), considered them to be dragon bones and documented them as such. For example, Hua Yang Guo Zhi, a book written by Zhang Qu during the Western Jin Dynasty, reported the discovery of dragon bones at Wucheng in Sichuan Province.<ref>Modèle:Cite book</ref> Villagers in central China have been digging up dinosaur bones for decades, thinking they were from dragons, to make traditional medicine.<ref> Dinosaur bones 'used as medicine'

. BBC News 
 
 (2007)
   

. Retrieved on 2007-07-06. </ref> In Europe, dinosaur fossils were generally believed to be the remains of giants and other creatures killed by the Great Flood.

Megalosaurus was the first dinosaur to be formally described, in 1677, when part of a bone was recovered from a limestone quarry at Cornwell near Oxford, England. This bone fragment was identified correctly as the lower extremity of the femur of an animal larger than anything living in modern times. The second dinosaur genus to be identified, Iguanodon, was discovered in 1822 by the English geologist Gideon Mantell, who recognized similarities between his fossils and the bones of modern iguanas. Two years later, the Rev William Buckland, a professor of geology at Oxford University, unearthed more fossilized bones of Megalosaurus and became the first person to describe dinosaurs in a scientific journal.

The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur". He recognized that the remains that had been found so far, Iguanodon, Megalosaurus and Hylaeosaurus, shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of Prince Albert of Saxe-Coburg-Gotha, the husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other biological and geological exhibits.

In 1858, the first known American dinosaur was discovered, in marl pits in the small town of Haddonfield, New Jersey (although fossils had been found before, their nature had not been correctly discerned). The creature was named Hadrosaurus foulkii. It was an extremely important find; Hadrosaurus was the first nearly complete dinosaur skeleton found and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards. Foulke's discoveries sparked a wave of dinosaur mania in the United States.

Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh, both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars. The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an Elasmosaurus skeleton was flawed; Cope had inadvertently placed the plesiosaur's head at what should have been the animal's tail end. The fight between the two scientists lasted for over 30 years, ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt. Marsh 'won' the contest primarily because he was better funded through a relationship with the US Geological Survey. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods; for example, their diggers often used dynamite to unearth bones (a method modern paleontologists would find appalling). Despite their unrefined methods, the contributions of Cope and Marsh to paleontology were vast; Marsh unearthed 86 new species of dinosaur and Cope discovered 56, for a total of 142 new species. Cope's collection is now at the American Museum of Natural History in New York, while Marsh's is on display at the Peabody Museum of Natural History at Yale University.<ref>Modèle:Cite book</ref>

Since 1897, the search for dinosaur fossils has extended to every continent, including Antarctica. The first Antarctic dinosaur to be discovered, the ankylosaurid Antarctopelta oliveroi, was found on Ross Island in 1986, although it was 1994 before an Antarctic species, the theropod Cryolophosaurus ellioti, was formally named and described in a scientific journal.

Current dinosaur "hot spots" include southern South America (especially Argentina) and China. China in particular has produced many exceptional feathered dinosaur specimens due to the unique geology of its dinosaur beds, as well as an ancient arid climate particularly conducive to fossilization.

The "dinosaur renaissance"

Main article: Dinosaur renaissance

The field of dinosaur research has enjoyed a surge in activity that began in the 1970s and is ongoing. This was triggered, in part, by John Ostrom's discovery of Deinonychus, an active, vicious predator that may have been warm-blooded, in marked contrast to the then-prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology, arguably the primary scientific discipline involved in dinosaur research, has become a global science. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India, South America, Madagascar, Antarctica, and most significantly in China (the amazingly well-preserved feathered dinosaurs in China have further consolidated the link between dinosaurs and their conjectured living descendants, modern birds). The widespread application of cladistics, which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record.

Dinosaurs in culture

Main article: Cultural depictions of dinosaurs

By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the public imagination and become an enduring part of human culture. Only three decades after the first scientific descriptions of dinosaur remains, the famous dinosaur sculptures were erected in Crystal Palace Park in London. These sculptures excited the public so strongly that smaller replicas were sold, one of the first examples of tie-in merchandising. Since Crystal Palace, dinosaur exhibitions have opened at parks and museums around the world, both catering to, and reinforcing, the public interest.<ref name="torrens1993">Modèle:Cite journal</ref> Dinosaur popularity has long had a reciprocal effect on dinosaur science, as well. The competition between museums for public attention led directly to the Bone Wars waged between Marsh and Cope, each striving to return with more spectacular fossil remains than the other, and the resulting contribution to dinosaur science was enormous.<ref name="breithaupt1997">Modèle:Cite book</ref>

Dinosaurs hold an integral place in modern culture. The word "dinosaur" itself has entered the English lexicon as an expression describing anything that is impractically large, slow-moving, or obsolete, bound for extinction.<ref name="m-w">"Definition of dinosaur" Merriam-Webster's Online Dictionary. Accessed 26 May 2007.</ref> The public preoccupation with dinosaurs led to their inevitable entrance into worldwide popular culture. Beginning with a passing mention of Megalosaurus in the first paragraph of Charles Dickens' Bleak House in 1852,<ref name="bleakhouse">"London. Michaelmas term lately over, and the Lord Chancellor sitting in Lincoln's Inn Hall. Implacable November weather. As much mud in the streets, as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborne Hill." From page 1 of Dickens, Charles J.H. (1852). Bleak House. London: Bradbury & Evans.</ref> dinosaurs have been featured in a broad array of fictional works. Sir Arthur Conan Doyle's 1912 book The Lost World, the iconic 1933 film King Kong, the 1954 introduction of Godzilla and its many subsequent sequels, the best-selling 1990 novel Jurassic Park by Michael Crichton and its 1993 film version, briefly the highest-grossing film of all time, are just a few prominent examples of the long tradition of dinosaurs in fiction. Non-fiction authors, including some prominent paleontologists, have also sought to take advantage of dinosaur popularity, especially among children, to educate readers about dinosaurs in particular and science in general. Dinosaurs are ubiquitous in advertising, with numerous companies seeking to utilize dinosaurs to sell their own products or to characterize their rivals as slow-moving or obsolete.<ref name=DFGlut1997>Modèle:Cite book</ref>

Religious views

Main article: Young Earth Creationism#Palaeontology and dinosaurs

Various religious groups have views about dinosaurs that differ from those held by scientists, usually due to conflicts with creation stories in their scriptures. However, the scientific community rejects these religiously-inspired interpretations of dinosaurs.<ref name="Kitcher">Modèle:Cite book</ref><ref name="Dawkins">Modèle:Cite book</ref>

See also

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• Dinosaur classification
• Fossils
• List of dinosaurs
• List of fossil sites (with link directory)
• Prehistoric life
• Prehistoric reptiles

Notes and references

General references

See also

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External links

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For children

• Zoom Dinosaurs (www.enchantedlearning.com) From Enchanted Learning. Kid's site, info pages, theories, history.

Images

• The Art Gallery of The Dinosauricon, hosting over 2000 images from many different artists working in different styles.
• The Grave Yard, featuring skeletal restorations of a variety of prehistoric animals.
• Skeletal Drawing Professional restorations of numerous dinosaurs, and discussions of dinosaur anatomy.

Popular

• Dinosaurs & other extinct creatures: From the Natural History Museum, a well illustrated dinosaur directory.
• Dinosaurnews (www.dinosaurnews.org) The dinosaur-related headlines from around the world. Recent news on dinosaurs, including finds and discoveries, and many links.
• Dinosauria From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu.
• LiveScience.com All about dinosaurs, with current featured articles.
• Dino Russ's Lair hosts a large collection of dinosaur-related links.

Technical

• Palaeontologia Electronica From Coquina Press. Online technical journal.
• Dinobase A searchable dinosaur database, from the University of Bristol, with dinosaur lists, classification, pictures, and more.
• DinoData (www.dinodata.org) Technical site, essays, classification, anatomy.
• Dinosauria On-Line (www.dinosauria.com) Technical site, essays, pronunciation, dictionary.
• The Dinosauricon By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
• Thescelosaurus! By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species.
• Dinosauromorpha Cladogram From Palaeos. A detailed amateur site about all things paleo.
• The Dinosaur Encyclopaedia, an extensive overview of genera-based dinosaur information from 1999 and before.

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