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| {{Automatic taxobox | |||
| |name = Dinosaurs | |||
| |fossil_range = ]—Present, {{fossilrange|231.4|0|earliest=243}} | |||
| |image = Various dinosaurs.png | |||
| |image_width = 285px | |||
| |image_caption = Mounted skeletons of various non-avian dinosaurs, each from a different group. Clockwise from top-left are skeletons of: a predatory ] ('']''), a large ] ('']''), a duck-billed ] ('']''), a bird-like ] ('']''), an early ] ('']''), and a plated ]n ('']''). | |||
| |authority = ], 1842 | |||
| |subdivision_ranks = Major groups | |||
| |subdivision = | |||
| * {{extinct}}''']''' | |||
| ** {{extinct}}] | |||
| ** {{extinct}}] | |||
| ** {{extinct}}] | |||
| ** {{extinct}}] | |||
| * ''']''' | |||
| ** {{extinct}}] | |||
| ** ] | |||
| }} | |||
| '''Dinosaurs''' are a diverse group of animals of the ] '''Dinosauria'''. They first appeared during the ] period, approximately 230 million years ago, and were the dominant terrestrial ]s for 135 million years, from the beginning of the ] (about 200 million years ago) until the end of the ] (65.5 million years ago), when the ] led to the extinction of most dinosaur groups at the close of the ]. The ] record indicates that ]s evolved from ] dinosaurs during the Jurassic Period, and consequently they are considered a subgroup of dinosaurs in modern classification systems.<ref name=GauthQuer/><ref name=Zhou2004/> Some birds survived the extinction event that occurred 65 million years ago, and their descendants continue the dinosaur lineage to the present day. | |||
| Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 9,000 living species, are the most diverse group of vertebrates besides ] fish.<ref name=Alfaroetal2009/> Using fossil evidence, ]s have identified over 500 distinct ]<ref name=Wang&Dodson/> and more than 1,000 different species of non-avian dinosaurs.<ref name=AmosBBC/> Dinosaurs are represented on every continent by both ] species and fossil remains.<ref name=MacLeod/> Some are herbivorous, others carnivorous. Most dinosaurs have been ], though many extinct groups included ] species, and some were able to shift between these body postures. Many species possess elaborate display structures such as horns or crests, and some prehistoric groups developed skeletal modifications such as ] and ]. Birds have been the planet's dominant flying vertebrate since the extinction of the ]s, and evidence suggests that egg laying and nest building is a trait shared by all dinosaurs. While many prehistoric dinosaurs were large animals—the largest ]s could reach lengths of almost 60 meters (200 feet) and were several stories tall—the idea that non-avian dinosaurs were uniformly gigantic is a misconception; many ancient species were nearly as small as birds are today. | |||
| Although the word ''dinosaur'' means "terrible lizard", the name is somewhat misleading, as dinosaurs are not ]s. Rather, they represent a separate group of reptiles with a distinct upright posture not found in lizards, and many extinct forms did not exhibit traditional reptilian characteristics. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the scientific community believed dinosaurs to be sluggish and ]. Most ], however, has indicated that ancient dinosaurs, particularly the carnivorous groups, were active animals with elevated ]s and numerous adaptations for social interaction. | |||
| Since the first dinosaur ]s were recognized in the early 19th century, mounted fossil dinosaur skeletons have been major attractions at museums around the world, and dinosaurs have become an enduring part of world culture. The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs' regular appearance in best-selling books and films such as '']''. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, and new discoveries are regularly covered by the media. | |||
| ==Etymology== | |||
| The ] '''Dinosauria''' was formally named in 1842 by ] Sir ], 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 name=Owen1842/>{{rp|103}} The term is derived from the ] words ] (''deinos'', meaning "terrible," "potent," or "fearfully great") and ] (''sauros'', meaning "lizard" or "reptile").<ref name=Owen1842/>{{rp|103}}<ref name=LSJ/> 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/> | |||
| ==Definition== | |||
| ]'' skeleton, ]]] | |||
| Under phylogenetic taxonomy, dinosaurs are usually defined as the group consisting of '']'', ] , their ], and all descendants".<ref name=MJB04dino/> It has also been suggested that Dinosauria be defined with respect to the ] of '']'' and '']'', because these were two of the three genera cited by Richard Owen when he recognized the Dinosauria.<ref name=olshevsky2000/> Both definitions result in the same set of animals being defined as dinosaurs: "Dinosauria = ] + ]", encompassing ] (mostly ] ]s and ]s), ]ns (armored herbivorous quadrupeds), ]ns (plated herbivorous quadrupeds), ]ns (herbivorous quadrupeds with horns and frills), ] (bipedal or quadrupedal herbivores including "duck-bills"), and, perhaps, ] (mostly large ] ]s with long necks and tails). | |||
| ] (''Passer domesticus'') is often used to represent modern birds in definitions of the group Dinosauria]] | |||
| Many paleontologists note that the point at which sauropodomorphs and theropods diverged may omit sauropodomorphs from the definition for both saurischians and dinosaurs. To avoid instability, Dinosauria can be more conservatively defined with respect to four anchoring nodes: ''Triceratops horridus'', '']'', and '']'', their most recent common ancestor, and all descendants. This "safer" definition can be expressed as "Dinosauria = Ornithischia + ] + ]".<ref name=Sereno2005/> | |||
| There is near universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. In traditional taxonomy, birds were considered a separate "]" which had ''evolved from'' dinosaurs. However, a majority of modern paleontologists reject the traditional style of classification in favor of ], which requires that all descendants of a single common ancestor must be included in a group for that group to be natural. Birds are thus considered by most modern scientists to ''be'' dinosaurs and dinosaurs are, therefore, not extinct. Birds are classified by most paleontologists as belonging to the subgroup ], which are ], which are theropods, which are ]ns, which are dinosaurs.<ref name=KP04/> | |||
| {{clear}} | |||
| ===General description=== | |||
| Using one of the above definitions, dinosaurs can be generally described as ]s with ].<ref name=DFG97/> Many prehistoric animal groups are popularly conceived of as dinosaurs, such as ]s, ]s, ]s, ]s, and '']'', but are not classified scientifically as dinosaurs, and none had the erect limb posture characteristic of true dinosaurs.<ref name=DL90/> Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the ] and ] periods. 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/> One notable exception is '']'', a ] weighing between {{convert|12|kg|lb}} and {{convert|14|kg|lb}} that is known to have eaten small dinosaurs like young '']''.<ref name=huetal2005/> | |||
| ]'' skeleton, ]]] | |||
| Dinosaurs have always been an extremely varied group of animals; according to a 2006 study, over 500 non-avialan 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 1850, nearly 75% of which remain to be discovered.<ref name=Wang&Dodson/> An earlier study predicted that about 3400 dinosaur genera existed, including many which would not have been preserved in the fossil record.<ref name=russell1995/> By September 17, 2008, 1047 different species of dinosaurs had been named.<ref name=AmosBBC/> Some are herbivorous, others carnivorous. While most dinosaurs have been bipeds, some prehistoric species were quadrupeds, and others, such as '']'' and '']'', could walk just as easily on two or four legs. Cranial modifications like horns and crests are common among dinosaurs, and some extinct species had ]. Although known for large size, many Mesozoic dinosaurs were human-sized or smaller, and modern birds are generally very small in size. Dinosaurs today inhabit every continents, and fossils show that they had achieved global distribution by at least the early Jurassic period.<ref name=MacLeod/> Modern birds inhabit most available habitats, from terrestrial to marine, and there is evidence that some non-avialan dinosaurs (such as '']'') could fly or at least glide, and others, such as ], had semi-aquatic habits.<ref name=RMetal10/> | |||
| ===Distinguishing anatomical features=== | |||
| 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 ]ian 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 ]. | |||
| A detailed assessment of archosaur interrelations by S. Nesbitt<ref name=nesbitt2011/> confirmed or found the following 12 unambiguous synapomorphies, some previously known: | |||
| * in the skull, a supratemporal fossa (excavation) is present in front of the supratemporal ] | |||
| * epipophyses present in anterior neck vertebrae (except atlas and axis) | |||
| * apex of deltopectoral crest (a projection on which the ] muscles attach) located at or more than 30% down the length of the ] (upper arm bone) | |||
| * ] shorter than 80% of humerus length | |||
| * fourth trochanter (projection where the ] attaches) on the ] (thigh bone) is a sharp flange | |||
| * fourth trochanter asymmetrical, with distal margin forming a steeper angle to the shaft | |||
| * on the ] and ] the proximal articular facet for ] occupies less than 30% of the transverse width of the element | |||
| * exocciptials (bones at the back of the skull) do not meet along the midline on the floor of the endocranial cavity | |||
| * proximal articular surfaces of the ] with the ] and the ] separated by a large concave surface | |||
| * cnemial crest on the ] (shinbone) arcs anterolaterally | |||
| * distinct proximodistally oriented ridge present on the posterior face of the distal end of the tibia | |||
| Nesbitt found a number of further potential synapomorphies, and discounted a number of synapomorphies previously suggested. Some of these are also present in ], which Nesbitt recovered as a sister group to Dinosauria, including a large anterior trochanter, metatarsals II and IV of subequal length, reduced contact between ischium and pubis, the presence of a cenmial crest on the tibia and of an ascending process on the astragalus,<ref name=MJB04dino/> and many others. | |||
| ] | |||
| ]ns (right)]] | |||
| A variety of other skeletal features are shared by dinosaurs. However, because they are either common to other groups of ] or were not present in all early dinosaurs, these features are not considered to be synapomorphies. For example, as ]s, dinosaurs ancestrally had two pairs of ]e (openings in the skull behind the eyes), and as members of the diapsid group Archosauria, had additional openings in the ] and lower jaw.<ref name=TRHJ00/> 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 ], or shoulder blade; a ] composed of three or more fused ]e (three are found in some other archosaurs, but only two are found in '']'');<ref name=MJB04dino/> and an ], or hip socket, with a hole at the center of its inside surface (closed in '']'', for example).<ref name=LARB99/> 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.<ref name=NIP07/> | |||
| Dinosaurs stand erect in a manner similar to ], but distinct from most other reptiles, whose limbs sprawl out to either side.<ref name=Holland1909>This was recognized not later than 1909: {{cite web |title=Dr. Holland and the Sprawling Sauropods |url=http://www.hmnh.org/library/diplodocus/holland1910.html }} The arguments and many of the images are also presented in {{cite book |title=Hot Blooded Dinosaurs |first=A. |last=Desmond |authorlink=Desmond |publisher=DoubleDay |year=1976 |isbn=0-385-27063-1}}</ref> This posture is 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/> Their erect posture enabled early dinosaurs to breathe easily while moving, which likely permitted stamina and activity levels that ].<ref name=RC05/> Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.<ref name=TKMB07/> Some non-dinosaurian archosaurs, including ]ns, 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 ] was rotated to form an overhanging shelf.<ref name=TKMB07/> | |||
| ==Evolutionary history== | |||
| {{Main|Evolution of dinosaurs}} | |||
| ===Origins and early evolution=== | |||
| ]]] | |||
| ]'' (large), '']'' (small) and a '']'' skull]] | |||
| Dinosaurs diverged from their ] ancestors approximately 230 million years ago during the Middle to Late ] period, roughly 20 million years after the ] wiped out an estimated 95% of all ].<ref name=KPA/><ref name=TannerLucas/> ] of the ] that contained fossils from the early dinosaur ] '']'' establishes its presence in the fossil record at this time. Paleontologists think that ''Eoraptor'' resembles the ] of all dinosaurs;<ref name=Sereno1999/> if this is true, its traits suggest that the first dinosaurs were small, bipedal ].<ref name=SFRM93/> The discovery of primitive, dinosaur-like ]s such as '']'' and '']'' in ] ] strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators. Dinosaurs may have appeared as early as 243 million years ago, as evidenced by remains of the genus '']'' from that period, though known fossils of these animals are too fragmentary to tell if they are dinosaurs or very close dinosaurian relatives.<ref name=nyasasaurus>Nesbitt, S. J., Barrett, P. M., Werning, S., Sidor, C. A., and A. J. Charig. (2012). "The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania." ''Biology Letters''.</ref> | |||
| When dinosaurs appeared, terrestrial habitats were occupied by various types of archosaurs and ], such as ]s, ]s, ]s, ], ]ns, and ]s. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the ] and ] ]s (about 215 million years ago), dicynodonts and a variety of basal ], including the ] and rhynchosaurs, became extinct. This was followed by the ] (about 200 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, ]s, and rauisuchians. These losses left behind a land fauna of ], dinosaurs, ]s, ]ns, and ]s.<ref name=MJB04dino/> The first few lines of early dinosaurs ] through the ] and ] ] of the Triassic, most likely by occupying the niches of the groups that became extinct. | |||
| ===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 ], and there was a worldwide dinosaur fauna mostly composed of ] ]s and early ] ]s.<ref name=HCL04/> ] plants (particularly ]s), a potential food source, radiated in the Late Triassic. Early sauropodomorphs did not have sophisticated mechanisms for processing food in the mouth, and so must have employed other means of breaking down food farther along the digestive tract.<ref name=FS04/> The general homogeneity of dinosaurian faunas continued into the Middle and Late Jurassic, where most localities had predators consisting of ]ns, ], and ]ns, and herbivores consisting of ]n ornithischians and large sauropods. Examples of this include the ] of North America and ] of Tanzania. Dinosaurs in China show some differences, with specialized ] theropods and unusual, long-necked sauropods like '']''.<ref name=HCL04/> ]ns and ] were also becoming more common, but prosauropods had become extinct. Conifers and ]s 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 ]-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 ]n ]ns.<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, ]ns, and ] through Europe, North America, and northern Africa. These were later supplemented or replaced in Africa by large ] and ] theropods, and ] and ]n sauropods, also found in South America. In Asia, ]n ]ns like ], ], and ]ns became the common theropods, and ] and early ]ns like ''Psittacosaurus'' became important herbivores. Meanwhile, Australia was home to a fauna of basal ankylosaurians, ]s, 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 ]. 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 ]s.<ref name=FS04/> Some sauropods also evolved tooth batteries, best exemplified by the rebbachisaurid '']''.<ref name=serenoetal07/> | |||
| There were three general dinosaur faunas in the Late Cretaceous. In the northern continents of North America and Asia, the major theropods were ] and various types of smaller maniraptoran theropods, with a predominantly ornithischian herbivore assemblage of hadrosaurids, ceratopsians, ankylosaurids, and ]ns. In the southern continents that had made up the now-splitting ], ] were the common theropods, and titanosaurian sauropods the common herbivores. Finally, in Europe, dromaeosaurids, ] iguanodontians, ] 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/> Grinding hadrosaurids and shearing ceratopsians became extremely diverse across North America and Asia. Theropods were also radiating as ]s or ]s, with ]ians and ]ns becoming common.<ref name=FS04/> | |||
| The ], which occurred approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaur groups except for the ] birds. Some other ] groups, such as crocodilians, ]ns, ]s, ]s, ]s, ]ns, and ]ns, also survived the event.<ref name=AF04/> | |||
| The surviving lineages of neornithine birds, including the ancestors of modern ]s, ], and a variety of ], diversified rapidly at the beginning of the ] period, entering ecological niches left vacant by the extinction of Mesozoic dinosaur groups such as the arboreal ]s, aquatic ]s, and even the larger terrestrial theropods (in the form of '']'', ]s, and "]s"). However, mammals were also rapidly diversifying during this time, and out-competed the neornithines for dominance of most terrestrial niches.<ref name=lindow>Lindow, B.E.K. (2011). "Bird Evolution Across the K–Pg Boundary and the Basal Neornithine Diversification." In Dyke, G. and Kaiser, G. (eds.)''Living Dinosaurs: The Evolutionary History of Modern Birds'', John Wiley & Sons, Ltd, Chichester, UK. {{doi|10.1002/9781119990475.ch14}}</ref> | |||
| ==Classification== | |||
| {{Main|Dinosaur classification}} | |||
| Dinosaurs are ]s, like modern ]ns. 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 crocodilians sprawl out to either side. | |||
| Collectively, dinosaurs as a ] are divided into two primary branches, ] and ]. Saurischia includes those taxa sharing a more recent common ancestor with birds than with ], while Ornithischia includes all ] sharing a more recent common ancestor with '']'' than with Saurischia. Anatomically, these two groups can be distinguished most noticeably by their ] structure. Early saurischians—"lizard-hipped", from the ] ''sauros'' (σαῦρος) meaning "lizard" and ''ischion'' (ἰσχίον) meaning "hip joint—retained the hip structure of their ancestors, with a ] bone directed ], or forward.<ref name=MJB00/> This basic form was modified by rotating the pubis backward to varying degrees in several groups ('']'',<ref name=GSP88/> ]oids,<ref name=clarketal2004/> ],<ref name=MAPM04/> and ]s<ref name=KP04/>). Saurischia includes the ] (exclusively bipedal and with a wide variety of diets) and ] (long-necked ]s which include advanced, quadrupedal groups). | |||
| By contrast, ornithischians—"bird-hipped", from the ] ''ornitheios'' (ὀρνίθειος) meaning "of a bird" and ''ischion'' (ἰσχίον) meaning "hip joint"—had a pelvis that superficially resembled a bird's pelvis: the ] bone was oriented ] (rear-pointing). Unlike birds, the ornithischian pubis also usually had an additional forward-pointing process. Ornithischia includes a variety of species which were primarily herbivores. ('''NB:''' the terms "lizard hip" and "bird hip" are misnomers – birds evolved from dinosaurs with "lizard hips".) | |||
| <center><gallery> | |||
| Image:Saurischia pelvis.png|]n pelvis structure (left side) | |||
| Image:Tyrannosaurus pelvis left.jpg|'']'' pelvis (showing saurischian structure – left side) | |||
| Image:Ornithischia pelvis.png|]n pelvis structure (left side) | |||
| Image:Edmontosaurus pelvis left.jpg|'']'' pelvis (showing ornithischian structure – left side) | |||
| </gallery></center> | |||
| ===Taxonomy=== | |||
| The following is a simplified classification of dinosaur groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz (2008).<ref name="Holtz2008">Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'' </ref> A more detailed version can be found at ]. | |||
| The cross (†) is used to signify groups with no living members. | |||
| *'''Dinosauria''' | |||
| :*''']''' ("lizard-hipped"; includes Theropoda and Sauropodomorpha) | |||
| ::*''']''' (all ]; most were carnivorous) | |||
| :::*†] (early bipedal carnivores) | |||
| :::*†] (small, early theropods; includes '']'' and close relatives) | |||
| :::*†] (early crested and carnivorous theropods) | |||
| :::*†] (generally elaborately horned, the dominant southern carnivores of the Cretaceous) | |||
| :::*] ("stiff tails"; includes most theropods) | |||
| ::::*†] (early group of large carnivores including the semi-aquatic spinosaurids) | |||
| ::::*†] ('']'' and close relatives, like '']'') | |||
| ::::*] (feathered theropods, with a range of body sizes and niches) | |||
| :::::*†] (common early coelurosaurs with reduced forelimbs) | |||
| :::::*†] ('']'' and close relatives; had reduced forelimbs) | |||
| :::::*†] ("]-mimics"; mostly toothless; carnivores to possible herbivores) | |||
| :::::*†] (small insectivores with reduced forelimbs each bearing one enlarged claw) | |||
| :::::*] ("hand snatchers"; had long, slender arms and fingers) | |||
| ::::::*†] (bipedal herbivores with large hand claws and small heads) | |||
| ::::::*†] (mostly toothless; their diet and lifestyle are uncertain) | |||
| ::::::*†] (small, winged theropods or primitive birds) | |||
| ::::::*†] (small- to medium-sized; bird-like, with a distinctive toe claw) | |||
| ::::::*] (modern birds and extinct relatives) | |||
| :::::::*†] (small primitive avialans with long third fingers) | |||
| :::::::*†] (large, early short-tailed avialans) | |||
| :::::::*†] (small toothless avialans) | |||
| :::::::*†] (primitive tree-dwelling, flying avialans) | |||
| :::::::*] (advanced flying birds) | |||
| ::::::::*†] (toothed Cretaceous Chinese birds) | |||
| ::::::::*†] (specialized aquatic diving birds) | |||
| ::::::::*''']''' (modern, beaked birds and their extinct relatives) | |||
| ] ]: from left to right '']'', '']'', '']'', and '']'']] | |||
| ::*†''']''' (herbivores with small heads, long necks, long tails) | |||
| :::*†] (small, primitive, omnivorous sauropodomorphs) | |||
| :::*†] (primitive, strictly bipedal "prosauropods") | |||
| :::*†] (small, primitive sauropodomorphs) | |||
| :::*†] (small, primitive sauropodomorphs) | |||
| :::*†] (very large and heavy, usually over 15 meters (49 feet) long; quadrupedal) | |||
| ::::*†] (primitive sauropods with pillar-like limbs) | |||
| ::::*†] ("true sauropods") | |||
| :::::*†] ("whale reptiles") | |||
| :::::*†] (European group of Jurassic and Cretaceous sauropods) | |||
| :::::*†] ("new sauropods") | |||
| ::::::*†] (skulls and tails elongated; teeth typically narrow and pencil-like) | |||
| ::::::*†] (boxy skulls; spoon- or pencil-shaped teeth) | |||
| :::::::*†] (long-necked, long-armed macronarians) | |||
| :::::::*†] (diverse; stocky, with wide hips; most common in the Late Cretaceous of southern continents) | |||
| ] dinosaurs and one ]. Far left: '']'', left: '']'', center background: '']'', center foreground: '']'', right: '']'', far right (small): '']'', far right (large) '']''.]] | |||
| :*†''']''' ("bird-hipped"; diverse bipedal and quadrupedal herbivores) | |||
| ::*†] (small basal ornithopod herbivores/omnivores with prominent ]) | |||
| ::*†] (armored dinosaurs; mostly quadrupeds) | |||
| :::*†''']''' (]s as primary armor; some had club-like tails) | |||
| :::*†''']''' (spikes and plates as primary armor) | |||
| ::*†] ("new ornithischians") | |||
| :::*†''']''' (various sizes; bipeds and quadrupeds; evolved a method of chewing using skull flexibility and numerous teeth) | |||
| :::*†] (characterized by a cranial growth) | |||
| ::::*†] (bipeds with domed or knobby growth on skulls) | |||
| ::::*†''']''' (quadrupeds with frills; many also had horns) | |||
| ==Biology== | |||
| Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including fossilized ]s, ], ]s, ]s, ]s, impressions of skin, ] and ]s.<ref name="softtissue">{{cite journal|author=Dal Sasso, C. and Signore, M. |year=1998|title=Exceptional soft-tissue preservation in a theropod dinosaur from Italy|journal=Nature|volume=392|issue=6674|pages=383–387|doi=10.1038/32884|bibcode=1998Natur.392..383D}}</ref><ref name="Schweitzer2005"/> Many fields of study contribute to our understanding of dinosaurs, including ] (especially ]), ], ], and the ] (of which ] is a sub-discipline). Two topics of particular interest and study have been dinosaur size and behavior. | |||
| ===Size=== | |||
| {{Main|Dinosaur size}} | |||
| ]s and a human]] | |||
| 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 ], most often fall into the 100 to 1000 kilogram (220 to 2200 lb) category, whereas ] predatory ]ns peak in the 10 to 100 kilogram (22 to 220 lb) category.<ref name=JF93/> The ] of dinosaur body masses is between one and ten metric tonnes.<ref name=Peczkis1994/> This contrasts sharply with the size of ] mammals, estimated by the ] as about 2 to 5 kilograms (5 to 10 lb).<ref name=NMNH/> | |||
| The ] were the largest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than anything else in their habitat, and the largest were an ] more massive than anything else that has since walked the Earth. Giant prehistoric ]s such as the '']'' (the largest land mammal ever) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in size.<ref>{{cite journal|author=Sander, P. Martin ''et al''.|year=2011|title=Biology of the sauropod dinosaurs: the evolution of gigantism|journal=Biological Reviews|volume=86|issue=1|pages=117–155|doi=10.1111/j.1469-185X.2010.00137.x|pmid=21251189|pmc=3045712}}</ref> There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in ]s interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.<ref name=KC06/> | |||
| ====Largest and smallest==== | |||
| Scientists will probably never be certain of the ]. This is because only a tiny percentage of animals ever fossilize,{{citation needed|date=October 2012}} 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. | |||
| ]'']] | |||
| The tallest and heaviest dinosaur known from good skeletons is '']'' (previously classified as a species of '']''). Its remains were discovered in ] between 1907–12. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the ];<ref name=EC68/> this mount is {{convert|12|m|ft|sp=us}} tall and {{convert|22.5|m|ft|sp=us}} long, and would have belonged to an animal that weighed between {{gaps|30|000}} and {{gaps|60|000}} kilograms ({{gaps|70|000}} and {{gaps|130|000}} lb). The longest complete dinosaur is the 27-meter (89 ft) long '']'', which was discovered in ] in the ] and displayed in ] ] in 1907. | |||
| ]'']] | |||
| There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest ] specimens on record were all discovered in the 1970s or later, and include the massive '']'', which may have weighed {{gaps|80|000}} to {{gaps|100|000}} kilograms (90 to 110 short tons); some of the longest were the {{convert|33.5|m|ft|sp=us}} long '']''<ref name=KC06/> (formerly ''Seismosaurus'') and the {{convert|33|m|ft|sp=us}} long '']'';<ref name=LHW07/> and the tallest, the {{convert|18|m|ft|sp=us}} tall '']'', which could have reached a sixth-floor window. The heaviest and longest of them all may have been '']'', known only from a now lost partial vertebral ] described in 1878. Extrapolating from the illustration of this bone, the animal may have been {{convert|58|m|ft|sp=us}} long and weighed over {{gaps|120|000}} kg ({{gaps|260|000}} lb).<ref name=KC06/> The largest known ] dinosaur was '']'', reaching a length of 16 to 18 meters (52 to 60 ft), and weighing in at 8150 kg ({{gaps|18|000}} lb).<ref name=SMBM06/> Other large meat-eaters included '']'', '']'' and '']''.<ref name=TH07/> | |||
| Not including birds (]), the smallest known dinosaurs were about the size of a ].<ref name=zhang2008/> Not surprisingly, the smallest dinosaurs were theropods closely related to birds. '']'', for example, had a total skeletal length of under 35 centimeters (1.1 ft).<ref name=zhang2008/><ref name=anchiadvance/> ''Anchiornis'' is currently the smallest dinosaur described from an adult specimen, with an estimated weight of 110 grams.<ref name=anchiadvance/> The smallest herbivorous non-avialan dinosaurs included '']'' and '']'', at about 60 cm (2 ft) long each.<ref name=Holtz2008/><ref name=butler&zhao2009/> | |||
| ===Behavior=== | |||
| ]'' was discovered in 1978.]] | |||
| Many modern birds are highly social, often found living in flocks. There is general agreement that some behaviors which are common in birds, as well as in crocodiles (birds' closest living relatives), were also common among extinct dinosaur groups. Interpretations of behavior in fossil species are generally based on the pose of skeletons and their ], ]s of their ], and comparisons with modern animals in similar ]s. | |||
| The first potential evidence for ]ing or ] as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31 '']'', ornithischians which were then thought to have perished together in ], ], after they fell into a deep, flooded ] and drowned.<ref name=Yans/> Other mass-death sites have been subsequently discovered. Those, along with multiple trackways, suggest that gregarious behavior was common in many early dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that ] (hadrosaurids) may have moved in great herds, like the ] or the African ]. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in ], England,<ref name=Day2002/> although there is not evidence for specific herd structures.<ref name=JLW05/> Congregated into herds may have evolved for defense, for ] purposes, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in ] that has yielded the remains of over 20 '']'', from one to seven years old. This assemblage is interpreted as a social group that was trapped in mud.<ref name=DVetal08sino/> The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as ]s working together to bring down large prey.<ref name=LG93/><ref name=maxwell&ostrom1995/> However, this lifestyle is uncommon among modern birds, ]s, and other reptiles, and the ] evidence suggesting mammal-like pack hunting in such theropods as '']'' and '']'' can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern ] predators.<ref name=RB07/> | |||
| ]'' engaged in intra-specific combat.]] | |||
| The crests and ] of some dinosaurs, like the ]ns, ]s and ]s, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and ]. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.<ref name=PC98/> | |||
| From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the ] in 1971. It included a '']'' attacking a '']'',<ref name=AMNH/> providing evidence that dinosaurs did indeed attack each other.<ref name=carpenter1998/> Additional evidence for attacking live prey is the partially healed tail of an '']'', 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/> ] amongst some species of dinosaurs was confirmed by tooth marks found in Madagascar in 2003, involving the theropod '']''.<ref name=rogersetal2003/> | |||
| Comparisons between the ]s of dinosaurs and modern birds and reptiles have been used to infer daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown that small predatory dinosaurs such as ], '']'', and '']'' were likely ]. Large and medium-sized ] and ] dinosaurs such as ]ns, ], ], ] may have been ], active during short intervals throughout the day, although the small ]n '']'' was inferred to be ].<ref name=SchmitzMotani2011/> | |||
| Based on current fossil evidence from dinosaurs such as '']'', some ornithischian species seem to have led a partially ] (burrowing) lifestyle.<ref name=VMK07/> Many modern birds are ] (tree climbing), and this was also true of many Mesozoic birds, especially the ]s.<ref>Chiappe, L.M. and Witmer, L.M. (2002). ''Mesozoic Birds: Above the Heads of Dinosaurs''. Berkeley: University of California Press. ISBN 0-520-20094-2</ref> While some early bird-like species may have already been arboreal as well (including ] such as '']''<ref name=chatterjee2007/>) most non-avialan 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 ], 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 name=alexander2006/> whether ]s could create ]s via ]-like tail snapping,<ref name=goriely/> and whether sauropods could float.<ref name=Henderson2006/> | |||
| ===Communication=== | |||
| ]'']] | |||
| Modern birds are well known for ] using primarily visual and auditory signals, and the wide diversity of visual display structures among fossil dinosaur groups suggests that visual communication has always been important to dinosaur biology. However, the evolution of dinosaur vocalization is less certain. In 2008, paleontologist Phil Senter examined the evidence for vocalization in Mesozoic animal life, including dinosaurs.<ref name=senter2008/> Senter found that, contrary to popular depictions of roaring dinosaurs in motion pictures, it is likely that most Mesozoic dinosaurs were not capable of creating any ] (though the hollow crests of the lambeosaurines could have functioned as ]s used for a wide range of vocalizations).<ref name=JAH75/><ref name=DW98/> To draw this conclusion, Senter studied the distribution of vocal organs in modern reptiles and birds. He found that vocal cords in the ] probably evolved multiple times among reptiles, including ]ns, which are able to produce guttural roars. Birds, on the other hand, lack a larynx. Instead, bird calls are produced by the ], a vocal organ found only in birds, and which is not related to the larynx, meaning it evolved independently from the vocal organs in reptiles. The syrinx depends on the air sac system in birds to function; specifically, it requires the presence of a ''clavicular air sac'' near the wishbone or collar bone. This air sac leaves distinctive marks or opening on the bones, including a distinct opening in the upper arm bone (''humerus''). While extensive air sac systems are a unique characteristic of saurischian dinosaurs, the clavicular air sac necessary to vocalize does not appear in the fossil record until the ]s (one exception, '']'', probably evolved its clavicular air sac independently of birds for reasons other than vocalization).<ref name=senter2008/> | |||
| The most primitive dinosaurs with evidence of a vocalizing syrinx are the enantironithine birds. Any bird-line archosaurs more primitive than this probably did not make vocal calls. Rather, several lines of evidence suggest that early dinosaurs used primarily visual communication, in the form of distinctive-looking (and possibly brightly colored) horns, frills, crests, sails and feathers. This is similar to some modern reptile groups such as lizards, in which many forms are largely silent (though like dinosaurs they possess well-developed senses of hearing) but use complex coloration and display behaviors to communicate.<ref name=senter2008/> | |||
| In addition, dinosaurs use other methods of producing sound for communication. Other animals, including other reptiles, use a wide variety of non-vocal sound communication, including hissing, jaw grinding or clapping, use of environment (such as splashing), and wing beating (possible in winged ]n dinosaurs).<ref name=senter2008/> | |||
| ===Reproductive biology=== | |||
| ] ('']'').]] | |||
| All dinosaurs lay ]s with hard shells made mostly of ].{{citation needed|date=May 2012}} Eggs are usually laid in a ]. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.<ref name = "Hansell">Hansell M (2000). ''Bird Nests and Construction Behaviour''. University of Cambridge Press ISBN 0-521-46038-7</ref> Some species of modern bird have no nests; the cliff-nesting ] lays its eggs on bare rock, and male ]s keep eggs between their body and feet. Primitive birds and many non-avialan dinosaurs often lay eggs in communal nests, with males primarily incubating the eggs. While modern birds have only one functional oviduct and lay one egg at a time, more primitive birds and dinosaurs had two oviducts, like crocodiles. Some non-avialan dinosaurs, such as '']'', exhibited iterative laying, where the adult might lay a pair of eggs every one or two days, and then ensured simultaneous hatching by delaying brooding until all eggs were laid.<ref name="Varrichioetal.02">{{Cite journal | doi = 10.1671/0272-4634(2002)0222.0.CO;2 | last1 = Varricchio | first1 = David J. | last2 = Horner | first2 = John J. | last3 = Jackson | first3 = Frankie D. | year = 2002 | title = Embryos and eggs for the Cretaceous theropod dinosaur ''Troodon formosus'' | url = | journal = Journal of Vertebrate Paleontology | volume = 22 | issue = 3| pages = 564–576 }}</ref> | |||
| When laying eggs, females grow a special type of bone between the hard outer bone and the ] of their limbs. This medullary bone, which is rich in ], is used to make eggshells. A discovery of features in a '']'' ] provided evidence of medullary bone in extinct dinosaurs and, for the first time, allowed paleontologists to establish the sex of a fossil dinosaur specimen. Further research has found medullary bone in the theropod '']'' and the ornithopod '']''. Because the line of dinosaurs that includes ''Allosaurus'' and ''Tyrannosaurus'' diverged from the line that led to ''Tenontosaurus'' very early in the evolution of dinosaurs, this suggests that dinosaurs in general produced medullary tissue.<ref name=LW08/> | |||
| ] '']'', ]]] | |||
| Another widespread trait among modern birds is parental care for young after hatching. ] 1978 discovery of a '']'' ("good mother lizard") ]ing ground in ] demonstrated that parental care continued long after birth among ]s, suggesting this behavior might have been common to all dinosaurs.<ref name=HM79/> There is also evidence that other non-theropod dinosaurs, like ]n ]ian sauropods (1997 discovery), also nested in large groups.<ref name=LMCetal05/> A specimen of the ]n ] '']'' was discovered in a ]-like ] position in 1993, which indicates that they had begun using an insulating layer of feathers to keep the eggs warm.<ref name=search.eb/> Parental care being a trait common to all dinosaurs is supported by other finds. For example, the fossilized remains of a grouping of '']'' has been found, consisting of one adult and 34 juveniles; in this case, the large number of juveniles may be due to communal nesting.<ref name=mengetal2004/> Additionally, a dinosaur embryo (pertaining to the ] '']'') was found without teeth, indicating that some parental care was required to feed the young dinosaurs.<ref name=Reiszetal05/> Trackways have also confirmed parental behavior among ornithopods from the ] in northwestern ].<ref name=BBCtracks/> Nests and eggs have been found for most major groups of dinosaurs, and it appears likely that all dinosaurs cared for their young to some extent either before or shortly after hatching. | |||
| ===Waste=== | |||
| Like other ]s, dinosaurs are primarily ], that is, their ]s extract nitrogenous wastes from their bloodstream and excrete it as ] instead of ] or ] via the ureters into the intestine. In most living species, uric acid is excreted along with feces as a semisolid waste.<ref>{{Cite web|last=Ehrlich |first=Paul R. |coauthors=David S. Dobkin, and Darryl Wheye |title=Drinking |url=http://www.stanford.edu/group/stanfordbirds/text/essays/Drinking.html |year=1988 |work=Birds of Stanford |publisher=Standford University |accessdate=2007-12-13}}</ref><ref>{{Cite journal|last=Tsahar |first=Ella |title=Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores |journal=Journal of Experimental Biology |volume=208 |issue=6 |pages=1025–34 |year=2005 |pmid=15767304 |doi=10.1242/jeb.01495 |month= March|issn=0022-0949 |url=http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=15767304 |format=Free full text |last2=Martínez Del Rio |first2=C |last3=Izhaki |first3=I |last4=Arad |first4=Z }}</ref><ref name=coprodeum>{{cite journal | doi= 10.1016/S1095-6433(03)00006-0 | last1= Skadhauge | first1= E | last2= Erlwanger | first2= KH | last3= Ruziwa | first3= SD | last4= Dantzer | first4= V | last5= Elbrønd | first5= VS | last6= Chamunorwa | first6= JP | title= Does the ostrich (''Struthio camelus'') coprodeum have the electrophysiological properties and microstructure of other birds? | journal= Comparative biochemistry and physiology. Part A, Molecular & integrative physiology | volume= 134 | issue= 4 | pages= 749–755 | year= 2003 | pmid = 12814783 }}</ref> However, at least some modern birds (such as ]s) can be facultatively ]<!-- Trying to clarify spelling at -->, excreting most of the nitrogenous wastes as ammonia.<ref>{{Cite journal|last=Preest |first=Marion R. |month=April |year=1997 |title=Ammonia excretion by hummingbirds |journal=Nature |volume=386 |issue= 6625|pages=561–62 |doi=10.1038/386561a0 |last2=Beuchat |first2=Carol A.|bibcode = 1997Natur.386..561P }}</ref> They also excrete ], rather than ] like mammals.<!--ORPHANED REF <ref name = "Gill"/>--> This material, as well as the output of the intestines, emerges from the ].<ref>{{Cite journal|last=Mora |first=J. |year=1965 |title=The Regulation of Urea-Biosynthesis Enzymes in Vertebrates |journal=] |volume=96 |pages=28–35 |pmid=14343146 |url=http://www.biochemj.org/bj/096/0028/0960028.pdf|format=PDF |month= July|issn=0264-6021 |last2=Martuscelli |first2=J |last3=Ortiz Pineda |first3=J |last4=Soberon |first4=G |pmc=1206904|issue=1}}</ref><ref>{{Cite journal|last=Packard |first=Gary C.|year=1966 |title=The Influence of Ambient Temperature and Aridity on Modes of Reproduction and Excretion of Amniote Vertebrates |journal=] |volume=100 |issue=916 |pages=667–82 |doi=10.1086/282459 |jstor=2459303}}</ref> In addition, many species regurgitate ], and fossil pellets that may have come from dinosaurs are known from as long ago as the Cretaceous period.<ref>{{Cite journal|last=Balgooyen |first=Thomas G. |date=1 October 1971|title=Pellet Regurgitation by Captive Sparrow Hawks (''Falco sparverius'') |journal=] |volume=73 |issue=3 |pages=382–85 |doi=10.2307/1365774 |url=http://elibrary.unm.edu/sora/Condor/files/issues/v073n03/p0382-p0385.pdf|format=PDF |issn=0010-5422 |jstor=1365774 }}</ref> | |||
| ===Physiology=== | |||
| {{Main|Physiology of dinosaurs}} | |||
| ] of an ] and a bird]] | |||
| Because both modern ]ns and ]s have four-chambered hearts (albeit modified in crocodilians), it is likely that this is a trait shared by all archosaurs, including all dinosaurs.<ref name=CH04/> While all modern birds have high metabolisms and are "warm blooded" (endothermic), a vigorous debate has been ongoing since the 1960s regarding how far back in the dinosaur lineage this trait extends. Originally, scientists broadly disagreed as to whether non-avian dinosaurs or even early birds were capable of regulating their body temperatures at all. More recently, ] for all dinosaurs has become the consensus view, and debate has focused on the mechanisms of temperature regulation {{Citation needed|date=November 2012}}. | |||
| After non-avian dinosaurs were discovered, paleontologists first posited that they were ]ic. This supposed "cold-bloodedness" was used to imply that the ancient dinosaurs were relatively slow, sluggish organisms, even though many modern reptiles are fast and light-footed despite relying on external sources of heat to regulate their body temperature. The idea of dinosaurs as ectothermic and sluggish remained a prevalent view until ], an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968.<ref>{{cite web|url=http://www.ucmp.berkeley.edu/diapsids/metabolism.html|title=Hot-Blooded or Cold-Blooded??|publisher=University of California Museum of Paleontology|accessdate=February 12, 2012}}</ref> | |||
| Modern evidence indicates that even non-avian dinosaurs and birds thrived in cooler temperate climates, and that at least some early species must have regulated their body temperature by internal biological means (aided by the animals' bulk in large species and feathers or other body coverings in smaller species). Evidence of ] in Mesozoic dinosaurs includes the discovery of ] and ] (where they would have experienced a cold, dark six-month winter), and analysis of blood-vessel structures within fossil bones that are typical of endotherms. Scientific debate continues regarding the specific ways in which dinosaur temperature regulation evolved.<ref name=parsons2001/> | |||
| In the ]n dinosaurs, higher metabolisms may have been supported by the evolution of a bird-like respiratory system characterized by an extensive system of air sacs that extended the lungs and invaded many of the bones in the skeleton, making them hollow.<ref name="SerenoMartinezEtAl2008AvianIntrathoracicAirSacsInNewPredatoryDinosaur">{{cite journal|year=2008|month=September|title=Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina|journal=PLoS ONE|editor1-first=Tom|volume=3|issue=9|editor1-last=Kemp|pages= e3303doi=10.1371/journal.pone.0003303|url=http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003303|doi=10.1371/journal.pone.0003303|accessdate=2008-09-29|author=Sereno PC, Martinez RN, Wilson JA, Varricchio DJ, Alcober OA, et al.|pmid=18825273|pmc=2553519|bibcode = 2008PLoSO...3.3303S }}</ref> | |||
| Early dinosaurian respiratory systems with air sacs may have been capable of sustaining higher activity levels than mammals of similar size and build can sustain. In addition to providing a very efficient supply of oxygen, the rapid airflow would have been an effective cooling mechanism, which is essential for animals that are active but too large to get rid of all the excess heat through their skin.<ref name="ReidInFarlowBrettSurman1997">{{Cite book |author=Reid, R.E.H. | contribution=Dinosaurian Physiology: the Case for "Intermediate" Dinosaurs |editor=Farlow, J.O., and Brett-Surman, M.K. |title=The Complete Dinosaur |year=1997 |publisher=Indiana University Press |location=Bloomington|isbn=0-253-33349-0 |pages=449–473 |url=http://books.google.com/?id=FOViD-lDPy0C&pg=PA449&lpg=PA449&dq=%22The+Complete+Dinosaur%22+%22intermediate+dinosaurs%22 | |||
| | accessdate=2008-09-12 | |||
| }}</ref> | |||
| ==Origin of birds== | |||
| {{Main|Origin of birds}} | |||
| The possibility that dinosaurs were the ancestors of birds was first suggested in 1868 by ].<ref name=huxley1868/> After the work of ] in the early 20th century, the theory of birds as dinosaur descendants was abandoned in favor of the idea of their being descendants of generalized ]s, with the key piece of evidence being the supposed lack of ]s in dinosaurs.<ref name=heilmann/> However, as later discoveries showed, clavicles (or a single fused ], which derived from separate clavicles) were not actually absent;<ref name=KP04/> they had been found as early as 1924 in ''Oviraptor'', but misidentified as an ].<ref name=HO24/> In the 1970s, ] revived the dinosaur–bird theory,<ref name=ostrom1973/> which gained momentum in the coming decades with the advent of cladistic analysis,<ref name=gauthier1986/> and a great increase in the discovery of small theropods and early birds.<ref name=TRHJ00/> Of particular note have been the fossils of the ], where a variety of theropods and early birds have been found, often with feathers of some type.<ref name=KP04/> Birds share over a hundred distinct anatomical features with theropod dinosaurs, which are now generally accepted to have been their closest ancient relatives.<ref name=Mayretal2005/> | |||
| They are most closely allied with ]n coelurosaurs.<ref name=KP04/> A minority of scientists, most notably ] and ], have proposed other evolutionary paths, including revised versions of Heilmann's basal archosaur proposal,<ref name=martin2004/> or that maniraptoran theropods are the ancestors of birds but themselves are not dinosaurs, only ] with dinosaurs.<ref name=AF02/> | |||
| ===Feathers=== | |||
| {{Main|Feathered dinosaurs}} | |||
| ] lithographica'']] | |||
| '']'' was the first fossil found which revealed a potential connection between dinosaurs and birds. It is considered a ], in that it displays features of both groups. Brought to light just two years after Darwin's seminal '']'', its discovery spurred the nascent debate between proponents of ] and ]. 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 '']''.<ref name=PW88/> | |||
| Since the 1990s, a number of additional ] have been found, providing even stronger evidence of the close relationship between dinosaurs and modern birds. Most of these specimens were unearthed in the ] of the Yixian Formation, ], northeastern ], which was part of an island continent during the Cretaceous. Though feathers have been found in only a few locations, 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 because delicate features like skin and feathers are not often preserved by fossilization and thus are absent from the fossil record. To this point, protofeathers (thin, filament-like structures) are known from dinosaurs at the base of Coelurosauria, such as ] like '']'' and ] ('']''),<ref name=Xuetal2004/> but barbed feathers are known only among the coelurosaur subgroup Maniraptora, which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds.<ref name=KP04/><ref name=GC06/> The description of feathered dinosaurs has not been without controversy; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that protofeathers are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' integument,<ref name=TLS03/><ref name=FLH05/><ref name=LSFX07/> and that maniraptoran dinosaurs with barbed feathers were not actually dinosaurs, but ] with dinosaurs.<ref name=AF02/><ref name=FLH05/> However, their views have for the most part not been accepted by other researchers, to the point that the question of the scientific nature of Feduccia's proposals has been raised.<ref name=Prum2003/> | |||
| ===Skeleton=== | |||
| Because feathers are often associated with birds, feathered dinosaurs are often touted as the ] between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for ]. Areas of the skeleton with important similarities include the neck, ], ] (semi-lunate ]), arm and ], furcula (wishbone), and ]. Comparison of bird and dinosaur skeletons through ] strengthens the case for the link. | |||
| ===Soft anatomy=== | |||
| ] of '']'']] | |||
| 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 ]. The lungs of theropod dinosaurs (carnivores that walked on two legs and had bird-like feet) likely pumped air into hollow sacs in their ]s, 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.<ref name=OConnorClaessens2005/> In a 2008 paper published in the online journal '']'', scientists described '']'', the skeleton of which supplies the strongest evidence to date of a dinosaur with a bird-like breathing system. ] of ''Aerosteon'''s fossil bones revealed evidence for the existence of air sacs within the animal's body cavity.<ref name=Sereno2008/><ref name=newswise2/> | |||
| ===Behavioral evidence=== | |||
| Fossils of the ]s '']'' and '']'' demonstrate that some dinosaurs slept with their heads tucked under their arms.<ref name=XUNorell2004/> This behavior, which may have helped to keep the head warm, is also characteristic of modern birds. Several ] and ] specimens have also been found preserved on top of their nests, likely brooding in a bird-like manner.<ref name="norell1995">{{cite journal | author = Norell M.A., Clark J.M., Chiappe L.M., Dashzeveg D. | year = 1995 | title = A nesting dinosaur | url = | journal = Nature | volume = 378 | issue =6559 | pages = 774–776 |doi=10.1038/378774a0|bibcode = 1995Natur.378..774N }}</ref> The ratio between egg volume and body mass of adults among these dinosaurs suggest that the eggs were primarily brooded by the male, and that the young were highly precocial, similar to many modern ground-dwelling birds.<ref name=Varricchioetal2008>{{cite journal | last1= Varricchio | first1= D. J. | last2= Moore | first2= J. R. | last3= Erickson | first3= G. M. | last4= Norell | first4= M. A. | last5= Jackson | first5= F. D. | last6= Borkowski | first6= J. J. | title= Avian Paternal Care Had Dinosaur Origin | journal= Science | volume= 322 | page= 1826 | year= 2008 | doi= 10.1126/science.1163245 |bibcode = 2008Sci...322.1826V | pmid=19095938 | issue= 5909 | pages= 1826–8}}</ref> | |||
| Some dinosaurs are known to have used ] stones like modern birds. These stones are swallowed by animals to aid digestion and break down food and hard fibers once they enter the stomach. When found in association with fossils, gizzard stones are called ]s.<ref name=wings2007/> | |||
| ==Extinction of major groups== | |||
| {{Main|Cretaceous–Paleogene extinction event}} | |||
| The discovery that birds are a type of dinosaur showed that dinosaurs in general are not, in fact, ] as is commonly stated.<ref name=mistaken>Dingus, L. and Rowe, T. (1998). ''The Mistaken Extinction – Dinosaur Evolution and the Origin of Birds''. New York: W. H. Freeman.</ref> However, all non-avian dinosaurs as well as many groups of birds did suddenly become ] approximately 65 million years ago. Many other groups of animals also became extinct at this time, including ]s (]-like ]s), ]s, ]s, ]s, and many groups of ]s.<ref name=MacLeod/> This ] is known as the ]. 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 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 Mesozoic, there were no ]s, and sea levels are estimated to have been from 100 to 250 meters (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 higher; the poles, for example, were 50 °C (90 °F) warmer than today.<ref name=pmid16311326/><ref name=McAetal2007/> | |||
| The atmosphere's composition during the Mesozoic is a matter for debate. While some academics argue that oxygen levels were much higher than today, others argue that biological adaptations seen in birds and dinosaurs indicate that respiratory systems evolved beyond what would be necessary if oxygen levels were high.<ref>{{cite book|author=Paul, Gregory S.|year=2002|title=Dinosaurs of the air: the evolution and loss of flight in dinosaurs and birds|publisher=Johns Hopkins University Press|isbn=0-8018-6763-0|page=397}}</ref> 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=== | |||
| {{Main|Chicxulub crater}} | |||
| ] at the tip of the ]; the impactor that formed this crater may have caused the dinosaur extinction.]] | |||
| The asteroid collision theory, which was brought to wide attention in 1980 by ] and colleagues, links the ] at the end of the Cretaceous period to a ] impact approximately 65.5 million years ago. Alvarez ''et al.'' proposed that a sudden increase in ] levels, recorded around the world in the period's rock stratum, was direct evidence of the impact.<ref name=Alvarezetal80/> The bulk of the evidence now suggests that a ] 5 to 15 kilometers (3 to 9 mi) wide hit in the vicinity of the ] (in southeastern ]), creating the approximately {{convert|180|km|mi|abbr=on}} ] and triggering the ].<ref name=ARHetal91/><ref name=KPetal96/> Scientists are not certain whether dinosaurs were thriving or declining before the ]. 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. 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). Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid, being down to hours rather than years.<ref>{{cite journal|last=Robertson|first=D.S.|coauthors=et al.|title=Survival in the first hours of the Cenozoic|journal=Geological Society of America Bulletin|date=30 September 2003|volume=116|issue=5/6|pages=760–768|doi=10.1130/B25402.1|url=http://webh01.ua.ac.be/funmorph/raoul/macroevolutie/Robertson2004.pdf|accessdate=15 June 2011}}</ref> | |||
| In September 2007, U.S. researchers led by William Bottke of the ] in ], and ] scientists used ] simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that an asteroid named ], approximately {{convert|160|km|mi|abbr=on}} in diameter, orbiting in the asteroid belt which lies between ] and ], was struck by a smaller unnamed asteroid about 55 km (35 mi) in diameter about 160 million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the ]. Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the {{convert|10|km|mi|abbr=on}} wide ] which struck ]'s ] ] 65 million years ago, creating the Chicxulub crater.<ref name=Billiards/> In 2011, new data from the ] revised the date of the collision which created the ] to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub Crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.<ref name="Universe Today">{{cite news | first=Tammy | last=Plotner | title=Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... | url=http://www.universetoday.com/89050/did-asteroid-baptistina-kill-the-dinosaurs-think-other-wise/#more-89050 | work=Universe Today | year=2011| accessdate=2011-09-20}}</ref> | |||
| A similar but more controversial explanation proposes that "passages of the solar companion star ] through the ] would trigger comet showers."<ref name=Koeberl/> One or more of these comets 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===<!-- This section is linked from ] --> | |||
| {{Main|Deccan Traps}} | |||
| Before 2000, arguments that the ] ]s caused the ] were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 ] and lasted for over 2 million years. However, there is evidence that two thirds of the Deccan Traps were created in only 1 million years about 65.5 million years ago, and so these eruptions would have caused a fairly rapid extinction, possibly over a period of thousands of years, but still longer than would be expected from a single impact event.<ref name=wwnjsd/><ref name=Duncan/> | |||
| The Deccan Traps could have caused extinction through several mechanisms, including the release into the air of dust and sulphuric aerosols, which might have blocked sunlight and thereby reduced photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions, which would have increased the ] when the dust and aerosols cleared from the atmosphere.<ref name=Duncan/> Before the mass extinction of the dinosaurs, the release of ]es during the formation of the ] "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 ]]."<ref name=wwnjsd/><ref name=Duncan/> | |||
| In the years when the Deccan Traps theory was linked to a slower extinction, ] (who died in 1988) replied that ] were being misled by ]. 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 ] and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.<ref name=Alvarez1997/> | |||
| ===Failure to adapt to changing conditions=== | |||
| Lloyd ''et al.'' (2008) noted that, in the Mid Cretaceous, the flowering, ] plants became a major part of terrestrial ]s, which had previously been dominated by ]s such as conifers. Dinosaur ]–fossilized dung–indicate that, while some ate angiosperms, most herbivorous dinosaurs ate mainly gymnosperms. Statistical analysis by Lloyd ''et al.'' concluded that, contrary to earlier studies, dinosaurs did not diversify very much in the Late Cretaceous. Lloyd ''et al.'' suggested that dinosaurs' failure to diversify as ecosystems were changing doomed them to extinction.<ref name="LDPEtAl2008" /> | |||
| ===Possible Paleocene survivors=== | |||
| {{Main|Paleocene dinosaurs}} | |||
| Non-avian dinosaur remains are occasionally found above the ]. In 2001, paleontologists Zielinski and Budahn reported the discovery of a single ] leg-bone fossil in the San Juan Basin, New Mexico, and described it as evidence of ]. The formation in which the bone was discovered has been dated to the early ] epoch, approximately 64.5 million years ago. If the bone was not re-deposited into that ] 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/> Other evidence includes the finding of dinosaur remains in the ] up to 1.3 meters (51 in) above ({{gaps|40|000}} years later than) the Cretaceous–Paleogene boundary. Similar reports have come from other parts of the world, including China.<ref name=Sloan/> Many scientists, however, dismissed the supposed Paleocene dinosaurs as re-worked, that is, washed out of their original locations and then re-buried in much later sediments.<ref name=FS05/><ref name=Sullivan/> However, direct dating of the bones themselves has supported the later date, with U–Pb dating methods resulting in a precise age of 64.8 ± 0.9 million years ago.<ref name=fassettetall2011/> 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 study== | |||
| {{Further|History of paleontology}} | |||
| 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 ] ]s and documented them as such. For example, ''Hua Yang Guo Zhi'', a book written by Zhang Qu during the ], reported the discovery of dragon bones at Wucheng in ] Province.<ref name=dong1992/> Villagers in central China have long unearthed fossilized "dragon bones" for use in traditional medicines, a practice that continues today.<ref name=BBCdinobonemed/> In Europe, dinosaur fossils were generally believed to be the remains of ] and other creatures killed by the ]. | |||
| ]'', a dinosaur he described and named in 1877.]] | |||
| Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in ]. Part of a bone, now known to have been the ] of a '']'',<ref name=WAS97/> was recovered from a limestone quarry at Cornwell near ], ], England, in 1676. The fragment was sent to ], Professor of Chemistry at the ] and first curator of the ], who published a description in his ''Natural History of Oxfordshire'' in 1677. He correctly identified the bone as the lower extremity of the ] of a large animal, and recognized that it was too large to belong to any known species. He therefore concluded it to be the thigh bone of a ] similar to those mentioned in the ]. In 1699, ], a friend of ], was responsible for the first published scientific treatment of what would now be recognized as a dinosaur when he described and named a ] ], "]",<ref name=L99/><ref name=DS02/> that had been found in Caswell, near Witney, Oxfordshire.<ref name=G45/> | |||
| ]]] | |||
| Between 1815 and 1824, the Rev ], a professor of ] at ], collected more fossilized bones of ''Megalosaurus'' and became the first person to describe a dinosaur in a ].<ref name=WAS97/><ref name=buckland1824/> The second dinosaur genus to be identified, '']'', was discovered in 1822 by Mary Ann Mantell – the wife of English geologist ]. Gideon Mantell recognized similarities between and the bones of modern ]s. He published his findings in 1825.<ref name=GM25/><ref name=HDS97/> | |||
| The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in 1842 the English paleontologist ] coined the term "dinosaur". He recognized that the remains that had been found so far, ''Iguanodon'', ''Megalosaurus'' and '']'', shared a number of distinctive features, and so decided to present them as a distinct taxonomic group. With the backing of ], the husband of ], Owen established the ] in ], ], to display the national collection of dinosaur fossils and other biological and geological exhibits. | |||
| In 1858, the first known American dinosaur was discovered, in ] pits in the small town of ] (although fossils had been found before, their nature had not been correctly discerned). The creature was named ''] foulkii''. It was an extremely important find: ''Hadrosaurus'' was one of the first nearly complete dinosaur skeletons found (] was in 1834, in Maidstone, Kent, England), and it was clearly a ] 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 ]. | |||
| ], 19th century photograph]] | |||
| ], 19th century photograph]] | |||
| Dinosaur mania was exemplified by the fierce rivalry between ] and ], both of whom raced to be the first to find new dinosaurs in what came to be known as the ]. The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an '']'' skeleton was flawed: Cope had inadvertently placed the ]'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 ]. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods: for example, their diggers often used ] 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, a total of 142 new species. Cope's collection is now at the ] in ], while Marsh's is on display at the ] at ].<ref name=Holmes/> | |||
| After 1897, the search for dinosaur fossils extended to every continent, including ]. The first ] to be discovered, the ]id '']'', was found on ] in 1986, although it was 1994 before an Antarctic species, the theropod '']'', was formally named and described in a scientific journal. | |||
| Current dinosaur "hot spots" include southern South America (especially ]) and ]. China in particular has produced many exceptional ] 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|Dinosaur renaissance}} | |||
| ] with mounted skeleton of a tyrannosaurid ('']'')]] | |||
| 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 ]'s discovery of '']'', an active predator that may have been ], in marked contrast to the then-prevailing image of dinosaurs as sluggish and ]. ] has become a global ]. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including ], South America, ], ], and most significantly ] (the amazingly well-preserved ] in ] have further consolidated the link between dinosaurs and their conjectured living descendants, modern birds). The widespread application of ], which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in ] dinosaurs. Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record. | |||
| ===Soft tissue and DNA=== | |||
| One of the best examples of soft-tissue impressions in a fossil dinosaur was discovered in Petraroia, ]. The discovery was reported in 1998, and described the specimen of a small, very young ], ''] 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 '']'', the paleontologist ] and her team announced the discovery of flexible material resembling actual soft tissue inside a 68-million-year-old '']'' leg ] from the ] in ]. 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 ]s, 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 Schweitzer's discovery, are not yet clear; study and interpretation of the material is ongoing.<ref name=Schweitzer2005/> | |||
| The successful extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions, but, upon further inspection and ], neither of these reports could be confirmed.<ref name=Wangetal1997/> However, a functional visual ] 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 name=changetal2002/> In addition, several ]s, including hemoglobin,<ref name=Schweitzeretal1997/> have putatively been detected in dinosaur fossils.<ref name=Emberyatal2003/><ref> | |||
| {{Cite journal | |||
| | last1 = Peterson | first1 = JE | last2 = Lenczewski | first2 = ME | last3 = Reed | first3 = PS | |||
| | title = Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs | |||
| | journal = PLoS ONE | volume = 5 | |||
| | issue = 10 | |||
| | pages = 13A | |||
| | date = October 2010 | |||
| | doi = 10.1371/journal.pone.0013334 | |||
| | editor1-last = Stepanova | |||
| | editor1-first = Anna}} | |||
| </ref> | |||
| ==Cultural depictions== | |||
| {{Main|Cultural depictions of dinosaurs}} | |||
| ]'' statues created by ] for the Crystal Palace Park in 1853.]] | |||
| ]''' skeleton in ] ].]] | |||
| By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the popular imagination and become an enduring part of human culture. Entry of the word "dinosaur" into the common ] reflects the animals' cultural importance: in English, "dinosaur" is commonly used to describe anything that is impractically large, obsolete, or bound for extinction.<ref name=m-w/> | |||
| Public enthusiasm for dinosaurs first developed in ] England, where in 1854, three decades after the first scientific descriptions of dinosaur remains, the famous ] were unveiled in ]'s ]. The Crystal Palace dinosaurs proved so popular that a strong market in smaller replicas soon developed. In subsequent decades, dinosaur exhibits opened at parks and ] around the world, ensuring that successive generations would be introduced to the animals in an immersive and exciting way.<ref name=torrens1993/> Dinosaurs' enduring popularity, in its turn, has resulted in significant public funding for dinosaur science, and has frequently spurred new discoveries. In the United States, for example, the competition between museums for public attention led directly to the ] of the 1880s and 1890s, during which a pair of feuding paleontologists made enormous scientific contributions.<ref name=breithaupt1997/> | |||
| The popular preoccupation with dinosaurs has ensured their appearance in ], ], and other ]. Beginning in 1852 with a passing mention in ] '']'',<ref name=bleakhouse/> dinosaurs have been featured in large numbers of ]al works. ]'s 1864 novel '']'', ]'s 1912 book '']'', the iconic 1933 ] '']'', the 1954 '']'' and its many sequels, the best-selling 1990 novel '']'' by ] and its 1993 ] are just a few notable examples of dinosaur appearances in fiction. Authors of general-interest ] works about dinosaurs, including some prominent paleontologists, have often sought to use the animals as a way to educate readers about science in general. Dinosaurs are ubiquitous in ]; numerous ] have referenced dinosaurs in printed or televised advertisements, either in order to sell their own products or in order to characterize their rivals as slow-moving, dim-witted, or obsolete.<ref name=DFGlut1997/> Even ] have featured dinosaurs in their works. | |||
| ==See also== | |||
| {{Commons category|Dinosauria}} | |||
| {{seealsosection| portal=Dinosaurs| Evolutionary history of life|List of dinosaurs| List of dinosaur-bearing rock formations|Physiology of dinosaurs| Prehistoric reptile}} | |||
| ==Notes and references== | |||
| {{Reflist|colwidth=30em|refs= | |||
| <ref name=AF02>{{cite journal |last=Feduccia |first=A. |year=2002 |title=Birds are dinosaurs: simple answer to a complex problem |journal=The Auk |volume=119 |pages=1187–1201 |doi=10.1642/0004-8038(2002)1192.0.CO;2 |issn=0004-8038 |issue=4}}</ref> | |||
| <ref name=AF04>{{cite book |last=Archibald |first=J. David |coauthors=and Fastovsky, David E. |editor=]; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year=2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=672–684 |chapter=Dinosaur Extinction}}</ref> | |||
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| <ref name=Alfaroetal2009>{{cite journal|author=Alfaro, M.E., F. Santini, C. Brock, H. Alamillo, A. Dornburg. D.L. Rabosky, G. Carnevale, and L.J. Harmon |year=2009|title=Nine exceptional radiations plus high turnover explain species diversity in jawed vertebrates|journal=Proceedings of the National Academy of Sciences USA|volume=106|issue=32|pages=13410–13414|pmid=19633192|doi=10.1073/pnas.0811087106|pmc=2715324|bibcode = 2009PNAS..10613410A }}</ref> | |||
| <ref name=Alvarez1997>{{cite book|author=Alvarez, W|title=T. rex and the Crater of Doom|year=1997|publisher=Princeton University Press|isbn=978-0-691-01630-6|pages=130–146}}</ref> | |||
| <ref name=Alvarezetal80>{{cite journal|title=Extraterrestrial cause for the Cretaceous–Tertiary extinction|author=Alvarez, LW, Alvarez, W, Asaro, F, and Michel, HV|year=1980|journal=Science|volume=208|issue=4448|pages=1095–1108|doi=10.1126/science.208.4448.1095|pmid=17783054|bibcode=1980Sci...208.1095A}}</ref> | |||
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| <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.''" {{cite book|author=Dickens CJH|year=1852|title=Bleak House|location=London|publisher=Bradbury & Evans|page=1}}</ref> | |||
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| }} | |||
| ==Further reading== | |||
| *Bakker, Robert T. (1986). '']''. New York: Morrow. ISBN 0-688-04287-2. | |||
| *] (2007). '']''. New York: Random House. ISBN 978-0-375-82419-7. | |||
| *] (2000). ''The Scientific American Book of Dinosaurs''. New York: St. Martin's Press. ISBN 0-312-26226-4. | |||
| *Paul, Gregory S. (2002). ''Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds''. Baltimore: The Johns Hopkins University Press. ISBN 0-8018-6763-0. | |||
| * {{cite web | url=http://www.worldcat.org/title/humongous-book-of-dinosaurs/oclc/36301321&referer=brief_results | title=''The Humongous Book of Dinosaurs'' | publisher=New York: Stewart, Tabori & Chang | year=1997 | accessdate=May 17, 2012 | author=Stewart, Tabori & Chang}} ISBN 1556705964 (Article: ]) | |||
| ==External links== | |||
| {{wiktionary|dinosaur}} | |||
| <!--Sorted (roughly) from least to most technical--> | |||
| {{Spoken Misplaced Pages|Dinosaur.ogg|2005-12-30}} | |||
| <!-- link to the recorded version: http://en.wikipedia.org/search/?title=Dinosaur&oldid=33253062– It should be inserted into the template, as an actual link, because it's rather laborious to roll back among thousands of changes and find a specific revision in the history.--> | |||
| ;General | |||
| * | |||
| ;Images | |||
| <!--*, featuring skeletal restorations of a variety of prehistoric animals.--> | |||
| * Influential paleontologist's anatomy art and paintings | |||
| * Professional restorations of numerous dinosaurs, and discussions of dinosaur anatomy. | |||
| ;Video | |||
| *BBC Nature: | |||
| ;Popular | |||
| *: From the ], a well illustrated dinosaur directory. | |||
| <!--* (''www.dinosaur.org'') The first online dinosaur magazine.(cited in ''The Dinosauria'')--> | |||
| * (''www.dinosaurnews.org'') The dinosaur-related headlines from around the world. Recent news on dinosaurs, including finds and discoveries, and many links. | |||
| * From UC Berkeley Museum of Paleontology Detailed information – scroll down for menu. | |||
| * All about dinosaurs, with current featured articles. | |||
| * (''www.enchantedlearning.com'') From Enchanted Learning. Kids' site, info pages and stats, theories, history. | |||
| * contains data tables on nearly every published Mesozoic dinosaur genus as of January 2011. | |||
| * Giant Dinosaurs Get Downsized by ''LiveScience'', June 21, 2009 | |||
| ;Technical | |||
| * From Coquina Press. Online technical journal. | |||
| * A searchable dinosaur database, from the University of Bristol, with dinosaur lists, classification, pictures, and more. | |||
| * (''www.dinodata.org'') Technical site, essays, classification, anatomy. | |||
| * By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species. | |||
| {{Featured article}} | |||
| {{Archosauromorpha}} | |||
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Revision as of 16:20, 12 December 2012
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