Sorting through how these changes affected life on Earth is no simple task, particularly after the cataclysmic meteorite mixed things up in the rock record, but paleontologists are sifting through the wreckage to better understand what happened. A moment of catastrophe can only make sense within the broader context of life before and after. The amount of information at any given location depends on how well the relevant rock layers are preserved and how accessible they are to scientists. Looking at the geologic record of southwest Saskatchewan, Bamforth says, local conditions such as the frequency of forest fires and the characteristics of a particular habitat were as important as what was happening on a global scale when determining patterns of ancient biodiversity.
As far as Saskatchewan goes, the ecological community at the time leading up to the extinction was like a big game of Jenga. The constantly shifting ecological stability made major upsets—like an asteroid striking at the wrong place, at the wrong time—especially disastrous. Species that survived the impact were typically small, semi-aquatic or made burrows, and able to subsist on a variety of foods, but there are some key contradictions.
There were some small non-avian dinosaurs that had these advantages and still went extinct, and many reptiles, birds and mammals died out despite belonging to broader groups that persisted. Generally speaking, smaller dinosaurs and other animals should have had better chances at survival than their larger relatives, but this was not always the case.
Pat Holroyd of the University of California Museum of Paleontology likens these investigations to what happens in the wake of airline accidents.
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Holroyd estimates that much of the relevant research about which species survived the impact has only been published or uploaded to the Paleobiology Database in the last decade. This new information allowed Holroyd and colleagues to study patterns of turnover—how long species persisted on land and in associated freshwater habitats—long before and after the asteroid impact. Some of the patterns were familiar. Fish, turtles, amphibians and crocodylians all generally fared better than strictly terrestrial organisms.
But the resilience of waterbound species had never been quantified in detail before, and the new analysis is revealing that the solution to the extinction pattern puzzle may have been right in front of us all along. Species living on land, particularly large species, tend not to persist as long as those living in freshwater environments. Terrestrial species often go extinct at a greater rate than those in aquatic environments even without a massive catastrophe to take them out of the picture. Holroyd notes that Cretaceous turtles, for example, lost fifty percent of their diversity globally, although only about twenty percent in the more localized area of western North America, further underscoring the importance of understanding local versus global patterns.
Marsupial mammals, for example, survived the mass extinction as a group but had their diversity and abundance drastically cut back. How local ecosystems were affected by these changes is the next step toward understanding how the extinction event affected the world. This dinosaur was ubiquitous across much of western North America at the end of the Cretaceous and was clearly a major component of its ecosystem.
These animals were the bison of their time, and, given how large herbivores alter their habitats through grazing and migration, the extinction of Triceratops undoubtedly had major implications for ecosystems recovering in the wake of the Cretaceous catastrophe. Plants that may have relied on Triceratops to disperse seeds would have suffered, for example, whereas other plants that were trampled down by the dinosaurs might have grown more freely. Based on the current distribution of fossil evidence, it appears that feathers were an ancestral dinosaurian trait, though one that may have been selectively lost in some species.
Simple, branched, feather-like structures are known from heterodontosaurids , primitive neornithischians  and theropods ,  and primitive ceratopsians. Evidence for true, vaned feathers similar to the flight feathers of modern birds has been found only in the theropod subgroup Maniraptora , which includes oviraptorosaurs, troodontids, dromaeosaurids, and birds. Archaeopteryx was the first fossil found that revealed a potential connection between dinosaurs and birds. It is considered a transitional fossil , in that it displays features of both groups.
Brought to light just two years after Darwin's seminal The Origin of Species , its discovery spurred the nascent debate between proponents of evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, at least one specimen was mistaken for Compsognathus. 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.
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 some purported feather-like fossils are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' skin,    and that maniraptoran dinosaurs with vaned feathers were not actually dinosaurs, but convergent with dinosaurs.
In , it was reported that a dinosaur tail with feathers had been found enclosed in amber. The fossil is about 99 million years old. Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the multiple skeletal features also shared by the two groups represent another important line of evidence for paleontologists. Areas of the skeleton with important similarities include the neck, pubis , wrist semi-lunate carpal , arm and pectoral girdle , furcula wishbone , and breast bone.
Comparison of bird and dinosaur skeletons through cladistic analysis strengthens the case for the link. Large meat-eating dinosaurs had a complex system of air sacs similar to those found in modern birds, according to a investigation led by Patrick M. The lungs of theropod dinosaurs carnivores that walked on two legs and had bird-like feet likely pumped air into hollow sacs in their skeletons , as is the case in birds.
CT-scanning of Aerosteon' s fossil bones revealed evidence for the existence of air sacs within the animal's body cavity. Fossils of the troodonts Mei and Sinornithoides demonstrate that some dinosaurs slept with their heads tucked under their arms. Several deinonychosaur and oviraptorosaur specimens have also been found preserved on top of their nests, likely brooding in a bird-like manner. Some dinosaurs are known to have used gizzard 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 gastroliths. The discovery that birds are a type of dinosaur showed that dinosaurs in general are not, in fact, extinct as is commonly stated. It has been suggested that because small mammals, squamata and birds occupied the ecological niches suited for small body size, non-avian dinosaurs never evolved a diverse fauna of small-bodied species, which led to their downfall when large-bodied terrestrial tetrapods were hit by the mass extinction event.
This mass extinction is known as the Cretaceous—Paleogene extinction event. The nature of the event that caused this mass extinction has been extensively studied since the s; 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. Some scientists propose that the meteorite impact 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. The Deccan Traps in India could have caused extinction through several mechanisms, including the release into the air of dust and sulfuric 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 greenhouse effect when the dust and aerosols cleared from the atmosphere. In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez who died in replied that paleontologists were being misled by sparse data. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact.
However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps , and these may have contributed to the extinctions. Non-avian dinosaur remains are occasionally found above the Cretaceous—Paleogene boundary.
In , paleontologists Zielinski and Budahn reported the discovery of a single hadrosaur leg-bone fossil in the San Juan Basin, New Mexico, and described it as evidence of Paleocene dinosaurs. The formation in which the bone was discovered has been dated to the early Paleocene epoch, approximately If the bone was not re-deposited into that stratum by weathering action, it would provide evidence that some dinosaur populations may have survived at least a half million years into the Cenozoic Era.
Similar reports have come from other parts of the world, including China. Dinosaur fossils have been known for millennia, although their true nature was not recognized. The Chinese considered them to be dragon bones and documented them as such. Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in England. Part of a bone, now known to have been the femur of a Megalosaurus ,  was recovered from a limestone quarry at Cornwell near Chipping Norton , Oxfordshire , in The fragment was sent to Robert Plot , Professor of Chemistry at the University of Oxford and first curator of the Ashmolean Museum , who published a description in his Natural History of Oxfordshire in He correctly identified the bone as the lower extremity of the femur 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 giant human similar to those mentioned in the Bible. In , Edward Lhuyd , a friend of Sir Isaac Newton , was responsible for the first published scientific treatment of what would now be recognized as a dinosaur when he described and named a sauropod tooth , " Rutellum implicatum ",   that had been found in Caswell, near Witney, Oxfordshire. Between and , the Rev William Buckland , a professor of geology at Oxford, collected more fossilized bones of Megalosaurus and became the first person to describe a dinosaur in a scientific journal.
Gideon Mantell recognized similarities between his fossils and the bones of modern iguanas. He published his findings in The study of these "great fossil lizards" soon became of great interest to European and American scientists, and in the English paleontologist Richard Owen coined the term "dinosaur". He recognized that the remains that had been found so far, Iguanodon , Megalosaurus and Hylaeosaurus , shared a number of distinctive features, and so decided to present them as a distinct taxonomic group.
With the backing of Prince Albert , the husband of Queen Victoria , Owen established the Natural History Museum, London , to display the national collection of dinosaur fossils and other biological and geological exhibits. In , William Parker Foulke discovered the first known American dinosaur, in marl pits in the small town of Haddonfield, New Jersey.
Although fossils had been found before, their nature had not been correctly discerned. The creature was named Hadrosaurus foulkii. It was an extremely important find: Hadrosaurus was one of the first nearly complete dinosaur skeletons found the first was in , in Maidstone, England , and it was clearly a bipedal creature. This was a revolutionary discovery as, until that point, most scientists had believed dinosaurs walked on four feet, like other lizards.
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Foulke's discoveries sparked a wave of dinosaur mania in the United States. Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Othniel Charles Marsh , both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars. The feud probably originated when Marsh publicly pointed out that Cope's reconstruction of an Elasmosaurus skeleton was flawed: Cope had inadvertently placed the plesiosaur 's head at what should have been the animal's tail end.
The fight between the two scientists lasted for over 30 years, ending in when Cope died after spending his entire fortune on the dinosaur hunt. Marsh 'won' the contest primarily because he was better funded through a relationship with the US Geological Survey. Unfortunately, many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods: 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 new species. After , the search for dinosaur fossils extended to every continent, including Antarctica.
The first Antarctic dinosaur to be discovered, the ankylosaurid Antarctopelta oliveroi , was found on James Ross Island in ,  although it was before an Antarctic species, the theropod Cryolophosaurus ellioti , was formally named and described in a scientific journal. Current dinosaur "hot spots" include southern South America especially Argentina and China. China in particular has produced many exceptional feathered dinosaur specimens due to the unique geology of its dinosaur beds, as well as an ancient arid climate particularly conducive to fossilization.
The field of dinosaur research has enjoyed a surge in activity that began in the s and is ongoing. This was triggered, in part, by John Ostrom 's discovery of Deinonychus , an active predator that may have been warm-blooded , in marked contrast to the then-prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology has become a global science.
Major new dinosaur discoveries have been made by paleontologists working in previously unexploited regions, including India , South America, Madagascar , Antarctica , and most significantly China the amazingly well-preserved feathered dinosaurs  in China have further consolidated the link between dinosaurs and their living descendants, modern birds.
The widespread application of cladistics , which rigorously analyzes the relationships between biological organisms, has also proved tremendously useful in classifying dinosaurs.
Cladistic analysis, among other modern techniques, helps to compensate for an often incomplete and fragmentary fossil record. One of the best examples of soft-tissue impressions in a fossil dinosaur was discovered in Pietraroia, Italy. The discovery was reported in , and described the specimen of a small, very young coelurosaur , Scipionyx samniticus. The fossil includes portions of the intestines, colon, liver, muscles, and windpipe of this immature dinosaur.
In the March issue of Science , the paleontologist Mary Higby Schweitzer and her team announced the discovery of flexible material resembling actual soft tissue inside a million-year-old Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana. After recovery, the tissue was rehydrated by the science team. 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.
In , a team including Schweitzer announced that, using even more careful methodology, they had duplicated their results by finding similar soft tissue in a duck-billed dinosaur , Brachylophosaurus canadensis , found in the Judith River Formation of Montana. This included even more detailed tissue, down to preserved bone cells that seem even to have visible remnants of nuclei and what seem to be red blood cells. Among other materials found in the bone was collagen , as in the Tyrannosaurus bone. The type of collagen an animal has in its bones varies according to its DNA and, in both cases, this collagen was of the same type found in modern chickens and ostriches.
The extraction of ancient DNA from dinosaur fossils has been reported on two separate occasions;  upon further inspection and peer review , however, neither of these reports could be confirmed. In , researchers reported finding structures similar to blood cells and collagen fibers, preserved in the bone fossils of six Cretaceous dinosaur specimens, which are approximately 75 million years old.
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 vernacular reflects the animals' cultural importance: Public enthusiasm for dinosaurs first developed in Victorian England, where in , three decades after the first scientific descriptions of dinosaur remains, a menagerie of lifelike dinosaur sculptures were unveiled in London 's Crystal Palace Park.
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 museums around the world, ensuring that successive generations would be introduced to the animals in an immersive and exciting way. In the United States, for example, the competition between museums for public attention led directly to the Bone Wars of the s and s, during which a pair of feuding paleontologists made enormous scientific contributions.
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The popular preoccupation with dinosaurs has ensured their appearance in literature , film , and other media. Beginning in with a passing mention in Charles Dickens ' Bleak House ,  dinosaurs have been featured in large numbers of fictional works. Jules Verne 's novel Journey to the Center of the Earth , Sir Arthur Conan Doyle 's book The Lost World , the iconic film King Kong , the Godzilla and its many sequels, the best-selling novel Jurassic Park by Michael Crichton and its film adaptation are just a few notable examples of dinosaur appearances in fiction.
Authors of general-interest non-fiction 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 advertising ; numerous companies 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. From Wikipedia, the free encyclopedia.
For other uses, see Dinosaur disambiguation. Late Triassic — Present , Saurischian pelvis structure left side. Ornithischian pelvis structure left side. Cultural depictions of dinosaurs. Animal track Dinosaur diet and feeding Evolutionary history of life Lists of dinosaur-bearing stratigraphic units List of dinosaur genera List of unavailable dinosaur genera. A Middle Triassic dinosauriform from Tanzania". Fleur, Nicholas 8 December It Was a Dinosaur Tail". The New York Times. Retrieved 8 December Retrieved August 2, Archived from the original PDF on February 4, Retrieved June 22, Journal of the Geological Society.
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List of U.S. state dinosaurs
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