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| {{Taxobox | color = pink | |||
| | name = Dinosaurs | |||
| | fossil_range = ] – ] (except avian) | |||
| | image = Saurier2.jpg | |||
| | image_width = 260px | |||
| | image_caption = Replica of '']'' at the ]. | |||
| | regnum = ]ia | |||
| | phylum = ] | |||
| | classis = ] | |||
| | subclassis = ]a | |||
| | infraclassis = ] | |||
| {{Taxobox_norank_entry | taxon = ]}} | |||
| {{Taxobox_norank_entry | taxon = ]}} | |||
| | superordo = '''Dinosauria''' ] | |||
| | superordo_authority = ], 1842 | |||
| | subdivision_ranks = Orders & Suborders | |||
| | subdivision = <div> | |||
| * ''']''' | |||
| ** ] | |||
| ** ] | |||
| * ''']''' | |||
| ** ] | |||
| ** ] | |||
| ** ] | |||
| </div> | |||
| }} | |||
| '''Dinosaurs''' were ] ]s that dominated ] ]s for over 160 million years, first appearing approximately 230 ]. At the end of the ] ], 65 million years ago, dinosaurs suffered a catastrophic ], which ended their dominance on land. ] consider modern birds to be the direct descendants of theropod dinosaurs. | |||
| Since the first dinosaur was recognized in the 19th century, mounted, fossilized dinosaur skeletons have become major attractions at ]s around the world. Dinosaurs have become a part of world culture and remain consistently popular, especially among children. They have been featured in best-selling books and films such as '']'', and new discoveries are regularly covered by the ]. | |||
| The term ''dinosaur'' is sometimes used informally to describe other prehistoric reptiles, such as the ] '']'', the winged ]s and the aquatic ]s, ]s and ]s, although technically none of these were dinosaurs. | |||
| ==What is a dinosaur?== | |||
| ===Definition=== | |||
| ] ] at the ] ].]] | |||
| The ] '''Dinosauria''' was formally named by the ] ] ] in 1842 as "a distinct tribe or suborder of Saurian reptiles".<ref>* Owen, Richard. 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 ] words δεινός (''deinos'' meaning "terrible", "fearsome" or "formidable") and σαύρα (''saura'' meaning "lizard" or "reptile"). Owen chose it to express his awe at the size and majesty of the extinct animals, not out of fear or trepidation at their size and often-formidable arsenal of teeth and claws. | |||
| Dinosaurs were an extremely varied group of animals; according to a 2006 study, 527 dinosaur genera have been identified with certainty so far, and 1,844 genera are believed to have existed.<ref>Fountain, Henry. "Many more dinosaurs still to be found." ''New York Times'': 12 Sept. 2006. </ref><ref>Wang, S.C., and Dobson, P. (2006). Estimating the Diversity of Dinosaurs. Proceedings of the National Academy of Sciences USA 103:37, pp. 13601-13605. </ref> Some were ], others ]. Some dinosaurs were ]s, some were ]s and others, such as '']'' and '']'', could walk just as easily on two or four legs. Regardless of body type, nearly all known dinosaurs were well-adapted for a predominantly terrestrial, rather than aquatic or aerial, habitat. | |||
| '''Dinosaur ]''' | |||
| All dinosaurs so far discovered 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 structures across a taxonomic group are called synapomorphies. | |||
| Dinosaur synapomorphies include: reduced fourth and fifth digits on the manus (hand), reduced number of digits on the pes (foot) to three main toes, a sacrum (the region of the vertebral column to which the pelvis attaches, composed of three or more fused vertebrae) and an open or perforate ] (hip socket with a hole its centre). Dinosaurs are unique among all ]s in having this perforate acetabulum. | |||
| '''Other shared anatomical features''' | |||
| Scientists generally agree that a variety of other anatomical features were shared by most dinosaurs. These include forelimbs shorter and lighter than hind limbs, an unusual secondary palate that permitted dinosaurs to eat and breathe simultaneously, a relatively straight femur with medially-directed femoral head, two pairs of holes in the temporal region of the skull (i.e. a ] skull), rearward-pointing elbows in the front limbs and forward-pointing knees in the hind limbs. | |||
| The hip joint arrangement described above allowed an erect stance, in which hind limbs were situated directly beneath the body or 'underslung'. This stance is like that of most mammals today but unlike that of other reptiles, which have a less erect posture and limbs splayed out to either side. The vertical action of the limbs in dinosaurs allowed for more efficient and faster locomotion, compared to the clumsier and slower movement of other 'sprawled' reptiles. It also allowed many types of dinosaurs to become bipedal. | |||
| ] skeleton at the ] in ].]] | |||
| '''Taxonomic definition''' | |||
| Under ], dinosaurs are defined as all descendants of the most recent common ancestor of '']'' and modern ]. They are divided into ] (''bird-hipped'') and ] (''lizard-hipped''), depending upon ] structure. Ornithischian dinosaurs had a four-pronged pelvic configuration, incorporating a caudally-directed (rear-pointing) ] bone with (most commonly) a forward-pointing process. By contrast, the pelvic structure of saurischian dinosaurs was three-pronged, and featured a pubis bone directed cranially, or forwards, only. Ornithischia includes all ] sharing a more recent common ancestor with ''Triceratops'' than with Saurischia, while Saurischia includes those taxa sharing a more recent common ancestor with ''birds'' than with Ornithischia. It has also been suggested that Dinosauria be defined as all the descendants of the most recent common ancestor of '']'' and '']''. | |||
| There is an almost universal consensus among paleontologists that ]s are the descendants of ] dinosaurs. Using the strict ] definition that all descendants of a single common ancestor are related, modern birds ''are'' dinosaurs and dinosaurs are, therefore, not extinct. Modern ]s are classified by most paleontologists as belonging to the subgroup ], which are ]s, which are ], which are ], which are dinosaurs. | |||
| 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 ]s. It is also technically correct to refer to birds as a distinct group under the older ] system, which accepts ] taxa that exclude some descendants of a single common ancestor. Paleontologists mostly use ], which classifies birds as dinosaurs, but some biologists of the older generation do not. | |||
| For clarity, this article will use 'dinosaur' as a synonym for 'non-avian dinosaur', and 'bird' as a synonym for 'avian dinosaur' (meaning any animal that evolved from the common ancestor of '']'' and modern birds). The term 'non-avian dinosaur' will be used for emphasis as needed. It should be noted that this article's definition of 'bird' differs from the definition common in everyday language; to most non-scientists, a 'bird' is simply a two-legged animal with wings and feathers. | |||
| ===Size=== | |||
| While the evidence is incomplete, it is clear that, as a group, dinosaurs were large. Even by dinosaur standards, the ]s were gigantic. 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 '']'' and the Columbian ] were dwarfed by the giant sauropods, and only a handful of modern aquatic animals approach them in size — most notably the ], which reaches up to 190,000 kg (209 tons) and 33.5 m (110 ft) in length. | |||
| 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> Working hypothesis for body size.</ref> According to paleontologist Bill Erickson, estimates of median dinosaur weight range from 500 kg to 5 ]s; a recent study of 63 dinosaur genera yielded an average weight in excess of 850 kg — comparable to the weight of a grizzly bear — and a median weight of nearly 2 tons, or about as much as a giraffe. This contrasts sharply with the size of modern mammals; on average, mammals weigh only 863 grams, or about as much as a large rodent. The smallest dinosaur was bigger than two-thirds of all current mammals; the majority of dinosaurs were bigger than all but 2% of living mammals. <ref> Soruce of Erickson quote.</ref> | |||
| ]'', outside the ].]] | |||
| '''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 ]. | |||
| ]''.]] | |||
| The tallest and heaviest dinosaur known from a complete skeleton is the '']'' specimen that was discovered in ] between 1907–12. It is now mounted and on display at the ] of ] and is 12 m (38 ft) tall and probably weighed between 30,000–60,000 kg (33–66 ]s). The longest complete dinosaur is the 27 m (89 ft) long '']'', which was discovered in ] in the ] and displayed in ]'s ] in 1907. | |||
| There were larger dinosaurs, but knowledge of them is based entirely on a small number of incomplete fossil samples. The largest ] specimens on record were all discovered in the 1970s or later, and include the massive '']'', which may have weighed 80,000–100,000 kg (88–121 tons); the longest, the 40 m (130 ft) long '']''; and the tallest, the 18 m (60 ft) '']'', which could have reached a sixth-floor window. The largest known ] dinosaur was '']'', reaching a length of 16-18 meters (53-60 ft), and weighing in at 9 tons. Other large meat-eaters included '']'', '']'', '']'' and '']''. | |||
| Not including modern birds like the ], the smallest dinosaurs known were about the size of a ] or a ]. The theropods '']'', '']'', and '']'' were all under 60 cm (2 ft) in length. | |||
| ===Behavior=== | |||
| ]'' was discovered in 1978.]] | |||
| Interpretations of dinosaur behavior are generally based on the pose of body fossils and their ], ]s of their ], and comparisons with modern animals in similar ]s. 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 perceived direct evidence of ]ing behavior was the 1878 discovery of 31 '']'' dinosaurs which were thought to have perished together in ], ], after they fell into a deep, flooded ] and drowned<ref>Johan Yans, Jean Dejax, Denise Pons, Christian Dupuis, Philippe Taquet.(2005) Palaeontological and geodynamical implications of the palynological dating of the wealden facies sediments of Bernissart (Mons Basin, Belgium). ''C. R. Palevol 4 (2005)'' 135–150.</ref>. Despite the deposition of those skeletons being now regarded as more gradual<ref>Deposition of ''Iguanodon'' skeletons ocurred in at least 3 different events.</ref>, other, well supported, mass death sites were subsequently discovered. Those, along with multiple trackways, suggest that ] or ] behavior was common in many dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that ]s (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>Day, J.J. and Upchurch, P. (2002). Sauropod Trackways, Evolution, and Behavior. ''Science'' 296:1659. </ref> and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, ]. Dinosaurs may have congregated in herds for defense, for ] purposes, or to provide protection for their young. | |||
| ]'s 1978 discovery of a '']'' ("good mother dinosaur") ]ing ground in ] demonstrated that parental care continued long after birth among the ]s.<ref>Lessem, D. and Glut, D.F. (1993). ''The Dinosaur Society's Dinosaur Encyclopedia''. Random House Inc. ISBN 0-679-41770-2. </ref><ref> A juvenile ] skeleton was found.</ref> There is also evidence that other Cretaceous-era dinosaurs, like the ]n sauropod '']'' (1997 discovery), had similar nesting behaviors, and that the animals congregated in huge nesting colonies like those of ]s. The ]n ]n '']'' was discovered in a ]-like ]ing position in 1993, which may mean it was covered with an insulating layer of feathers that kept the ] warm.<ref> ] nests or ]?</ref> Trackways have also confirmed parental behavior among sauropods and ornithopods from the ] in northwestern ].<ref> 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 ]s and frills of some dinosaurs, like the ]ns, ]s and ]es, 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 ]. The nature of dinosaur ] also remains enigmatic, and is an active area of research. For example, recent evidence suggests that the hollow crests of the lambeosaurines may have functioned as ]s used for a wide range of ]s. | |||
| From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the ] in 1971. It included a '']'' attacking a '']'',<ref> The discovery of two ] dinosaurs entangled together proved many theories.</ref> proving that dinosaurs did indeed attack and eat each other. While ]istic behavior among ]s is no surprise,<ref> The mystery of a dinosaur ].</ref> this too was confirmed by tooth marks from Madagascar in 2003.<ref>Rogers, R.R., Krause, D.W. and Rogers, K.C. (2003). Cannibalism in the Madagascan dinosaur Majungatholus atopus. ''Nature'' 422:515-518..</ref> | |||
| There seem to have been no burrowing species of dinosaur and few climbing species. This is somewhat surprising when compared to the later mammalian radiation in the ], which included many species of these types. As to how the animals moved, ] has provided significant insight. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have demonstrated how fast dinosaurs could run,<ref> Gait and his formula on estimating a dinosaur's speed.</ref><ref> More on Gait and his speed calculations.</ref> whether ]s could create ]s via ]-like tail snapping,<ref>Douglas, K. and Young, S. (1998). The dinosaur detectives. ''New Scientist'' 2130:24. .</ref> whether giant theropods had to slow down when rushing for food to avoid fatal injuries,<ref>Hecht, J. (1998). The deadly dinos that took a dive. ''New Scientist'' 2130. .</ref> and if sauropods could float.<ref>Henderson, D.M. (2003). Effects of stomach stones on the buoyancy and equilibrium of a floating crocodilian: A computational analysis. ''Canadian Journal of Zoology'' 81:1346-1357. .</ref> | |||
| ==Evolution of dinosaurs== | |||
| ]'', an early dinosaur.]] | |||
| 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 life on Earth.<ref>Citation for Permian/Triassic extinction event, percentage of animal species that went extinct. </ref> <ref>Another citation for P/T event data. </ref> ] of fossils from the early dinosaur ] '']'' establishes its presence in the fossil record at this time. Paleontologists believe ''Eoraptor'' resembles the ] of all dinosaurs; <ref>Hayward, T. (1997). The First Dinosaurs. ''Dinosaur Cards''. Orbis Publishing Ltd. D36040612.</ref> if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.<ref>Sereno, P.C., C.A. Forster, R.R. Rogers, and A.M. Monetta. 1993. Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria. Nature 361:64-66.</ref> Such a notion is corroborated by the more primitive dinosaur-like ornithodirans hailing from ] strata of Argentina such as '']'' and '']'', which were also small bipedal, perhaps leaping, predators. | |||
| The first few lines of primitive dinosaurs ] through the rest of the Triassic period; dinosaur species quickly evolved the specialized features and range of sizes needed to exploit nearly every terrestrial ]. During the period of dinosaur predominance, which encompassed the ensuing ] and ] periods, nearly every known land animal larger than 1 meter in length was a dinosaur. | |||
| The ], 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. Other ] species related to the dinosaurs also survived the event. | |||
| ==Study of dinosaurs== | |||
| Knowledge about dinosaurs is derived from a variety of fossil and non-fossil records, including ]ized ]s, ], ]s, ]s, ]s, impressions of ], ] and ]s.<ref name="softtissue">Dal Sasso, C. and Signore, M. (1998). Exceptional soft-tissue preservation in a theropod dinosaur from Italy. ''Nature'' 292:383-387. </ref><ref>Schweitzer, M.H., Wittmeyer, J.L. and Horner, J.R. (2005). Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. ''Science'' 307:1952 - 1955. </ref> Many fields of study contribute to our understanding of dinosaurs, including ], ], ], and the ] (of which ] is a sub-discipline). | |||
| Dinosaur remains have been found on every continent on Earth, including ]. Numerous fossils of the same dinosaur species have been found on completely different continents, corroborating the generally-accepted theory that all land masses were at one time connected in a super-continent called ]. Pangaea began to break apart during the ] period roughly 230 million years ago.<ref>Evans, J. (1998). ''Ultimate Visual Dictionary - 1998 Edition''. Dorling Kindersley Books. 66-69. ISBN 1-871854-00-8.</ref> | |||
| ===The current "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 ]'s discovery of '']'', an active, vicious ] that may have been ], in marked contrast to the prevailing image of dinosaurs as sluggish and ]. ], arguably the primary scientific discipline involved in dinosaur research, has become a global ]. Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including ], ], ], ], and most significantly in ] (the amazingly well-preserved ] in ] have further solidified the link between dinosaurs and their conjectured living descendants, modern ]s). 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 ]. | |||
| ===Classification=== | |||
| ''Main article'': ] | |||
| Dinosaurs (including birds) are ]s, like modern ]s. Archosaurs' ] skulls have two holes located where the jaw muscles attach, called ]. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called ]s; and ]s, with no temporal fenestra, are ]s. 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. All dinosaurs were land animals. | |||
| Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs, including ]s (which are not closely related to the dinosaurs) and ], which developed separately from reptilian ancestors in the late Triassic period. | |||
| Collectively, dinosaurs are usually regarded as a ] or an unranked ]. They are divided into two ], the '']'' and the '']'', on the basis of their hip structure. Saurischians ('lizard-hipped', from the ] ''sauros'' (''σαυρος'') meaning 'lizard' and ''ischion'' (''ισχιον'') meaning 'hip joint') are dinosaurs that originally retained the hip structure of their ancestors. They include all the ] (bipedal ]s) and ]s (long-necked ]s). Ornithischians ('bird-hipped', from the ] ''ornitheos'' (''ορνιθειος'') meaning 'of a bird' and ''ischion'' (''ισχιον'') meaning 'hip joint') is the other dinosaurian order, most of which were ]al herbivores. ('''NB:''' the terms "lizard hip" and "bird-hip" are misnomers -- birds evolved from dinosaurs with "lizard hips".) | |||
| <center><gallery> | |||
| Image:Saurischia.png|]n pelvis structure (left side) | |||
| Image:Tyrannosaurus pelvis left.JPG|'']'' pelvis (showing saurischian structure - left side) | |||
| Image:Ornithischia.png|]n pelvis structure (left side). | |||
| Image:Edmontosaurus pelvis left.JPG|'']'' pelvis (showing ornithischian structure - left side) | |||
| </gallery></center> | |||
| The following is a simplified classification of dinosaur families. A more detailed version can be found at ]. | |||
| The dagger (†) is used to indicate taxa that are ]. | |||
| ===Order ]=== | |||
| * †Infraorder ] | |||
| * Suborder ] | |||
| ** †Superfamily ] | |||
| ** †Infraorder ] | |||
| *** †Family ] | |||
| ** (unranked) ] | |||
| *** †Superfamily ] | |||
| *** †Infraorder ] | |||
| *** Infraorder ] | |||
| **** †Family ] | |||
| **** †Superfamily ] | |||
| **** †(unranked) ] | |||
| **** (unranked) ] | |||
| ***** †(unranked) Oviraptoriformes | |||
| ****** †(unranked) ] | |||
| ****** †(unranked) ] | |||
| ***** †(unranked) ] | |||
| ****** †Family ] | |||
| ****** †Family ] | |||
| ***** Class ] (birds) | |||
| * †Suborder ] | |||
| ** †'']'' | |||
| ** †Infraorder ] | |||
| ** †Infraorder ] | |||
| *** †Superfamily ] | |||
| *** †Superfamily ] | |||
| **** †Family ] | |||
| **** †(unranked) ] | |||
| === Order ] === | |||
| * †Suborder ] | |||
| ** †Infraorder ] | |||
| ** †Infraorder ] | |||
| * †(unranked) ] | |||
| ** †Family ] | |||
| ** †Suborder ] | |||
| *** †Infraorder ] | |||
| *** †Infraorder ] | |||
| **** †Family ] | |||
| **** †Family ] | |||
| **** †Family ] | |||
| ** †Suborder ] | |||
| *** †Family ] | |||
| *** †Infraorder ] | |||
| **** †Family ] | |||
| **** †Family ] | |||
| ==Areas of debate== | |||
| ===Warm-bloodedness=== | |||
| ].]] | |||
| {{main|Warm-bloodedness 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 ]y 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 ]ic creatures: "terrible ]s" 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 ], 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 ]ism in dinosaurs includes the discovery of ] and ] (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 ], such as ], ], or ]s, which slows down heat loss. However, large mammals, such as elephants, face a different problem due to their relatively small ratio of surface area to volume (]'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 would dictate that they lost heat relatively slowly to the surrounding air, and so could have been what are called ], 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 period. | |||
| ===Feathered dinosaurs and the bird connection=== | |||
| {{main|Feathered dinosaurs}} | |||
| {{main|Dinosaur-bird connection}} | |||
| Birds and non-avian dinosaurs share many features. Birds share over a hundred distinct anatomical features with ] dinosaurs, which are generally accepted to have been their closest ancient relatives.<ref>Mayr, G., Pohl, B. and Peters, D.S. (2005). A Well-Preserved Archaeopteryx Specimen with Theropod Features. ''Science'' 310:1483-1486..</ref> | |||
| '''Feathers''' | |||
| ]'' on display at the ].]] | |||
| '']'', the first good example of a "feathered dinosaur", was discovered in 1861. The initial specimen was found in the ] in southern Germany, which is a '']'', a rare and remarkable geological formation known for its superbly detailed fossils. Archaeopteryx is a ], with features clearly intermediate between those of modern reptiles and birds. 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, specimens are commonly mistaken for '']''.{{citation needed}} | |||
| 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 ] province in northeastern ], which was part of an island continent during the Cretaceous period. Though feathers have been found only in the ] of the ] 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 ]ization and thus are absent from the fossil record. | |||
| The feathered dinosaurs discovered so far include '']'', '']'', '']'', '']'', '']'', '']'', '']'', '']'', and '']''. Dinosaur-like birds like '']'', which are anatomically closer to modern avians, have also been discovered. All of these specimens come from the same formation in northern China. The ] family in particular seems to have been heavily feathered, and at least one dromaeosaurid, '']'', may have been capable of flight. | |||
| '''Skeleton''' | |||
| ]'' skeleton at the ].]] | |||
| 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 the more important link for ]s. 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 ], conclude that dinosaurs such as the ]s may have evolved from birds, losing the power of flight while keeping their feathers in a manner similar to the modern ostrich and other ]s. | |||
| Comparison of bird and dinosaur skeletons, as well as ], strengthens the case for the link, particularly for a branch of theropods called ]s. Skeletal similarities include the ], ], ] (semi-lunate ]), ] and ], ], ] and ]. | |||
| '''Reproductive biology''' | |||
| ]'' skull and upper vertebral column, Palais de la Découverte, Paris.]] | |||
| ]'' was a typical "armored dinosaur" of the ] superfamily.]] | |||
| A discovery of features in a '']'' ] 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 ], 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 '']'' specimen's hind limb suggested that ''T. rex'' used similar reproductive strategies, and revealed the specimen to be female. | |||
| A dinosaur embryo was found without teeth, suggesting that some parental care was required to feed the young dinosaur. 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 ] of ]. The lungs of theropod dinosaurs (carnivores that walked on two legs and had birdlike 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. The study was funded in part by the ].<ref>O'Connor, P.M. and Claessens, L.P.A.M. (2005). Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs. ''Nature'' 436:253.</ref> | |||
| '''Heart and sleeping posture''' | |||
| Modern ] (CT) scans of dinosaur chest cavities (conducted in 2000) found the apparent remnants of complex four-chambered hearts, much like those found in today's mammals and birds. A recently discovered ] fossil demonstrates that the dinosaurs slept like certain modern birds, with their heads tucked under their arms.<ref>Xu, X. and Norell, M.A. (2004). A new troodontid dinosaur from China with avian-like sleeping posture. ''Nature'' 431:838-841..</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 ] 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 ]s, gizzard stones are called ]s. Because a particular stone could have been swallowed at one location before being carried to another during migration, paleontologists sometimes use the stones found in dinosaur stomachs to establish possible ] routes. | |||
| ===Evidence for Cenozoic dinosaurs=== | |||
| In 2002, paleontologists Zielinski and Budahn reported the discovery of a single ] leg bone fossil in the San Juan Basin, New Mexico. 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>Fassett, J, R.A. Zielinski, & J.R. Budahn. (2002). Dinosaurs that did not die; evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone, San Juan Basin, New Mexico. In: Catastrophic events and mass extinctions; impacts and beyond. (Eds. Koeberl, C. & K. MacLeod): ''Special Paper - Geological Society of America'' 356: 307-336.</ref> | |||
| ===Bringing dinosaurs back to life=== | |||
| ] model of '']''.]] | |||
| There has been much speculation about the use of technology to bring dinosaurs back to life. In ]'s book '']'' (later adapted into ]), which popularized the idea, scientists use blood from fossilized ]s that have been suspended in ] since the Mesozoic to reconstruct the ] of dinosaurs, filling chromosomal gaps with modern ] genes. It is probably impossible to resurrect dinosaurs in this manner. One problem with the amber extraction method is that DNA decays over time by exposure to air, water and radiation, making it unlikely that such an approach would recover any useful DNA (DNA decay can be measured by a ] test). | |||
| 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>Wang, H., Yan, Z. and Jin, D. (1997). Reanalysis of published DNA sequence amplified from Cretaceous dinosaur egg fossil. ''Molecular Biology and Evolution''. 14:589-591. .</ref> However, a functional visual ] of a (theoretical) dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of still-living related species (reptiles and birds).<ref>Chang, B.S.W., Jönsson, K., Kazmi, M.A., Donoghue, M.J. and Sakmar, T.P. (2002). Recreating a Functional Ancestral Archosaur Visual Pigment. ''Molecular Biology and Evolution'' 19:1483-1489. .</ref> | |||
| Even if dinosaur DNA could be reconstructed, it would be exceedingly difficult to "grow" dinosaurs using current technology since no closely related species exist to provide ]s or a suitable environment for ]. | |||
| ===Soft tissue in dinosaur fossils=== | |||
| One of the best examples of soft tissue impressions in a fossil dinosaur was discovered in ], ]. 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 '']'', Dr. Mary Higby Schweitzer 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. | |||
| 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 are not yet clear, although many news reports immediately linked it with the movie '']''. Interpretation of the artifact is ongoing, and the relative importance of Dr. Schweitzer's discovery is not yet clear.<ref>Schweitzer, M.H., Wittmeyer, J.L. and Horner, J.R. (2005). Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. ''Science'' 307:1952-1955. Also covers the ]. </ref> | |||
| ==Extinction theories== | |||
| {{main|Cretaceous-Tertiary extinction event}} | |||
| The sudden ] of the non-avian dinosaurs, which occurred around 65 million years ago, is one of the most intriguing mysteries in ]. Many other groups of animals also became extinct at this time, including ]s (]-like ]s), ]s, plesiosaurs, pterosaurs, herbivorous ]s and ]s, most birds, and many groups of mammals.<ref name="changes">(Nov 2000). ''Earthwatch'' :6-13.</ref> The nature of the event that caused this mass extinction has been extensively studied since the 1970s. At present, several related theories are broadly supported by paleontologists. | |||
| ===Asteroid collision=== | |||
| ] at the tip of the ], the impact of which may have caused the dinosaur extinction.]] | |||
| The asteroid collision theory, which was first proposed by ] in the late 1970s, links the ] at the end of the Cretaceous period to a ] impact approximately 65.5 million years ago. Alvarez proposed that a sudden increase in ] 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 5-15 km wide ] hit in the vicinity of the ], creating the 170 km-wide ] and triggering the ]. 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 ] 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). | |||
| ===Multiple collisions—the Oort cloud=== | |||
| While similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that a stream of comets was dislodged from the ] due to the gravitational disruption caused by a passing star. 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>Koeberl, C. and MacLeod, K.G. (2002). ''Catastrophic Events and Mass Extinctions''. Geological Society of America. ISBN 0-8137-2356-6.</ref> | |||
| ===Environment changes=== | |||
| 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 metres (330 to 820 feet) higher than they are today. The planet's temperature was also much more uniform, with only 25 degrees Celsius separating average polar temperatures from those at the equator. On average, atmospheric temperatures were also much warmer; the poles, for example, were 50 °C warmer than today. <ref> The effect climate change may have had on the extinction of the Dinosaurs</ref><ref> Sea levels during the dinosaur era; ]; November 29, 2005</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 with 21% today. However, by the late ], 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="changes" /> | |||
| ==History of discovery== | |||
| Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese, whose own 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>{{cite book|author=]|year=1992|title=Dinosaurian Faunas of China|publisher=China Ocean Press, Beijing|id=ISBN 3-540-52084-8}}</ref>. In Europe, dinosaur fossils were generally believed to be the remains of ]s and other creatures killed by the ]. | |||
| ]]] | |||
| '']'' was the first dinosaur to be formally described, in 1677, when part of a bone was recovered from a ] ] at ] near ], ]. This bone fragment was identified correctly as the lower extremity of the ] of an animal larger than anything living in modern times. The second dinosaur species to be identified, '']'', was discovered in 1822 by the English geologist ], who recognized similarities between his fossils and the bones of modern ]s. Two years later, the Rev ], a professor of ] at ], unearthed more fossilized bones of ''Megalosaurus'' and became the first person to describe dinosaurs in a ]. | |||
| 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'', after the town and the discoverer, ]. It was an extremely important find; ''Hadrosaurus'' was the first nearly complete dinosaur skeleton found 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 the pair's unrefined methods, their contributions 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 ] in ], while Marsh's is on display at the ] at ].<ref>Williams, P. (1997). The Battle of the Bones. ''Dinosaur Cards''. Orbis Publishing Ltd. D36040607.</ref> | |||
| Since 1897, the search for dinosaur fossils has extended to every continent, including ]. The first Antarctic dinosaur 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 ]ization. | |||
| ==In popular culture== | |||
| ].]] | |||
| {{main|Dinosaurs in popular culture}} | |||
| By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured people's imagination and become an enduring part of human popular culture. Dinosaur exhibitions, parks and museum exhibits around the world both cater to and reinforce the public's interest. The popular preoccupation with dinosaurs is also reflected in a broad array of ] and ] works. | |||
| Notable examples of older fictional works featuring dinosaurs include ]'s book '']''; the 1933 film '']''; and '']''. | |||
| ==Religious views== | |||
| {{main|Religious perspectives on dinosaurs}} | |||
| Various religious groups have views about dinosaurs that differ from those held by scientists. While many mainstream scientists respect these views as ] positions, they argue that religiously-inspired interpretations of dinosaurs do not withstand serious ]. See the referenced article for specific examples and further context. | |||
| ==See also== | |||
| *] | |||
| *]s | |||
| *] | |||
| *] | |||
| *]s | |||
| * ] - The Senckenberg Museum in ], ] boasts the largest exhibition of large dinosaurs in ]. | |||
| ==Notes and references== | |||
| <div class="references-small"> | |||
| <!-- Dead note "reptilia": From the classical standpoint, reptiles included all the amniotes except birds and mammals. Thus reptiles were defined as the set of animals that includes crocodiles, alligators, tuatara, lizards, snakes, amphisbaenians and turtles, grouped together as the class Reptilia. However, many taxonomists have begun to insist that taxa should be monophyletic, that is, groups should include all descendants of a particular form. The reptiles as defined here would be paraphyletic, since they exclude both birds and mammals, although these also developed from the original reptile. Thus, some cladists redefine Reptilia as a monophyletic group, including both the classic reptiles as well as the birds and perhaps the mammals (depending on ideas about their relationships). Others abandon it as a formal taxon altogether, dividing it into several different classes. --> | |||
| <references /> | |||
| <!-- Dead note "jpii": Catholic Opinions on Evolutionary Origins. --> | |||
| </div> | |||
| ==General references== | |||
| <div class="references-small"> | |||
| * Kevin Padian, and Philip J. Currie. (1997). ''Encyclopedia of Dinosaurs''. Academic Press. ISBN 0-12-226810-5. (Articles are written by experts in the field). | |||
| * ] (2000). ''The Scientific American Book of Dinosaurs''. 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. | |||
| *] (2004). ''The Dinosauria''. University of California Press; 2nd edition. ISBN 0-520-24209-2. | |||
| </div> | |||
| ==External links== | |||
| <!--Sorted (roughly) from least to most technical--> | |||
| {{commons|Dinosauria}} | |||
| {{Spoken Misplaced Pages|Dinosaur.ogg|2005-12-30}} | |||
| ;For children | |||
| * From MantyWeb Educational Software. Kid's site, facts, games. | |||
| * From Yahooligans! Science. Glossaries, dino cards and indexes. | |||
| * From Enchanted Learning. Kid's site, info pages, theories, history. | |||
| * so the dinos get into your fingers, also for adults. | |||
| * Award-winning online children's science magazine. | |||
| ;Popular | |||
| * From the ]. London popular site, well illustrated dino directory. | |||
| * Humorous educational video about the dinosaur basics. | |||
| * The Dino-headlines from around the world. Recent news on dinosaurs, including finds and discoveries, lots of links. | |||
| * The Discoveries of Dr. Joan Wiffen, New Zealand's Dinosaur Lady | |||
| * Timeline of the discovery of Dinosaurs. | |||
| * From the ]. Popular overview. | |||
| * From the ]. Popular site, very well illustrated. | |||
| * From DinoData. Summaries of modern debates about dinosaurs. | |||
| * From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu. | |||
| * A gallery of dino-paintings. | |||
| * | |||
| * All about Dinosaurs with current featured articles. | |||
| ;Technical | |||
| * | |||
| * From PaleoClones. Current dino news. | |||
| * From '']''. Article on the rapid extinction of dinosaurs. | |||
| * From the '']''. Articles, latest news but out of date. | |||
| * From Coquina Press. Online technical journal. | |||
| * Article from by Z.K. Silagadze. | |||
| ;Very technical | |||
| * Technical site, essays, classification, anatomy. | |||
| * Technical site, essays, pronunciation, dictionary. | |||
| * By T. Michael Keesey. Technical site, cladogram, illustrations and animations. | |||
| * By Justin Tweet. Includes a cladogram and small essays on each relevant genera and species. | |||
| * From . A detailed and wonderful amateur site about all things paleo. | |||
| * A dinosaur database with dinosaur lists, classification, pictures, and more. | |||
| * A very extensive site regarding dinosaur information. | |||
| ;Bird-dinosaur and dinosaur warm-bloodedness discussion | |||
| * Are birds Dinosaurs? | |||
| * Site focusing on the dinosaur-bird relationship. | |||
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Revision as of 12:03, 28 September 2006
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