:: wikimiki.org ::
| Dinosaur |
Dinosaur
Dinosaurs are vertebrates that dominated the terrestrial ecosystem for over 160 million years. Non-avian dinosaurs became extinct at the end of the Cretaceous period, 65 million years ago. Knowledge about dinosaurs comes from both fossil and non-fossil records, including fossilized bones, feces, trackways, gastroliths, feathers, impressions of skin, internal organs and soft tissues.
Since the first dinosaur was recognized in the 19th century, their mounted, fossilized skeletons have become major attractions at museums 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 blockbuster films such as Jurassic Park, and new discoveries are regularly covered by the media. The term is also used informally to describe any prehistoric reptile, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs, and mosasaurs, though none of these are dinosaurs.
The on-going dinosaur renaissance began in the 1970s and was triggered, in part, by John Ostrom's discovery of Deinonychus, an active, vicious predator that may have been warm-blooded (homoeothermic), in marked contrast to the prevailing image of dinosaurs as sluggish and cold-blooded. Vertebrate paleontology has also become a global science, with major new discoveries in previously unexploited regions, including South America, Madagascar, Antarctica, and most significantly the amazingly well-preserved feathered dinosaurs in China, which have further solidified 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, which are still known from an incomplete fossil record.
What is a dinosaur?
Definition
fossil record at the Smithsonian National Museum of Natural History.]]
The superorder or clade "Dinosauria" was formally named by the English scientist Richard Owen in 1842. The term is a combination of the Greek words deinos ("terrible" or "fearfully great" or "formidable") and sauros ("lizard" or "reptile"). Contrary to popular perception, the name was chosen to express Owen's awe at the size and majesty of the extinct animals, not out of fear or trepidation at their size and formidable arsenal. Dinosaurs are extremely varied. Some were herbivorous, others carnivorous. Some dinosaurs were bipedal, others quadrupedal, while others could walk easily on both two and four legs, such as the dinosaur Ammosaurus.
Under phylogenetic taxonomy, Dinosaurs are defined as all descendants of the most recent common ancestor of Triceratops and modern birds. Ornithischia is defined as all taxa sharing a more recent common ancestor with Triceratops than with Saurischia. Saurischia is defined as all taxa sharing a more recent common ancestor with birds than with Ornithischia. It has also been suggested that Dinosauria be defined as as all the descendants of the most recent common ancestor of Megalosaurus and Iguanodon
There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct. Modern birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.
However, birds are morphologically distinct from their reptilian ancestors, and referring to birds as "avian dinosaurs" and to all other dinosaurs as "non-avian dinosaurs" is clumsy. Birds are still birds, at least in popular usage and among ornithologists. It is also technically correct under the older Linnaean classification system, which accepts taxa that exclude some descendants of a single common ancestor (paraphyletic taxa). Paleontologists mostly use cladistics in their classifications, which classifies birds as dinosaurs, but many other scientists do not. As a result, this article will use "dinosaur" as a synonym for "non-avian dinosaur", and "bird" as a synonym for "avian dinosaur".
Size
Only a tiny percentage of animals ever fossilize, and most of these remain buried in the earth. As a result, the smallest and largest dinosaurs will probably never be discovered. Even among those specimens that are recovered, few are known from complete skeletons, and impressions of skin and soft tissue are rare. Reconstructing a skeleton by comparing the size and morphology of bones to those of similar, better-known species is inexact, and restoring the muscles and other organs is, at best, educated guesswork.
smallest and largest dinosaurs.]]
smallest and largest dinosaurs
While the largest and smallest dinosaurs will probably remain unknown, and a comparison between existing specimens is imprecise, it is clear that, as a group, dinosaurs were large. By dinosaur standards the sauropods were gigantic. The smallest sauropods were larger than anything else in their habitat, and the largest were an order of magnitude more massive than anything else that has ever walked the Earth.
The tallest and heaviest dinosaur known from a complete skeleton is the Brachiosaurus, which was discovered in Tanzania between 1907–12. It is now mounted in the Humboldt Museum of Berlin and is 12 m (38 ft) tall and probably weighed between 30,000–60,000 kg (30–70 short tons). The longest dinosaur is the 27 m (89 ft) long Diplodocus, which was discovered in Wyoming and mounted in Pittsburgh's Carnegie Natural History Museum in 1907.
There were larger dinosaurs, but they are only known from a scant number of fossil samples. The largest specimens on record all date from the 1970s or later, and include the massive Argentinosaurus, which may have weighed 80,000–100,000 kg (90–110 tons); the longest, the 40 m (130 ft) long Supersaurus; and the tallest, the 18 m (60 ft) Sauroposeidon, which could have reached a sixth-floor window.
Dinosaurs were the largest of all terrestrial animals. The largest elephant on record weighed 12,000 kg (13.5 tons), and the tallest giraffe was 6 m (20 ft) tall. Even the giant prehistoric mammals such as the Indricotherium and the Columbian mammoth were dwarfed by the giant sauropods. Only a small handful of aquatic animals approach it in size, of which the blue whale is largest, reaching up to 190,000 kg (210 tons) and 33.5 m (110 ft) in length.
Not including modern birds like the bee hummingbird, the smallest dinosaurs known were about the size of a crow or a chicken. The Microraptor, Parvicursor, and Saltopus were all under 60 cm (2 ft) in length. In fact, most dinosaurs were much smaller than we would expect, with the average size of a dinosaur being around the size of a large sheep.
Behavior
Interpretations of behavior based on the pose of a body fossil and its habitat, computer simulations of their biomechanics, and comparison with modern animals in similar ecological niches rely on speculation and promise to generate controversy for the foreseeable future. However, it is likely that at least the behaviors common in both of their closest living relatives, crocodiles and birds, are also common among dinosaurs. It should be of note that nearly all interpretations of evidence are subject to change, as theories surrounding dinosaurs evolve continuously.
The first evidence of herding behavior was the 1878 discovery of 31 Iguanodon that perished together in Bernissart, Belgium, after they fell down a deep ravine, drowning as the latter was filled with rainwater. Similar mass deaths and trackways suggest that herd or pack behavior was common among many dinosaur groups. Trackways of hundreds or even thousands of herbivores indicate that duck-bills (hadrosaurids) may have moved in great herds, like the American Bison or the African Springbok. Sauropod tracks document that they traveled in groups composed of several different species, at least in Oxford, England, and others kept their young in the middle of the herd for defense according to trackways at Davenport Ranch, Texas. Dinosaurs may have congregated in herds for defense, migration, or to care for their young.
migration
Jack Horner's 1978 discovery of a Maiasaura ("good mother dinosaur") nesting ground in Montana demonstrated parental care long after birth among the ornithopods, and similar nesting behavior and even huge nesting colonies like those of penguins have been discovered of other Cretaceous dinosaurs like the Patagonian sauropod Saltasaurus (in 1997). The Mongolian maniraptoran Oviraptor was even discovered in a chicken-like brooding position in 1993, which may mean it was covered with an insulating layer of feathers that kept the eggs warm. Trackways have also confirmed parental behavior among sauropods and ornithopods from the Isle of Skye in the United Kingdom. Nests and eggs are known from most major groups of dinosaurs, and it appears likely that dinosaurs communicated with their young, like modern birds and crocodiles.
The crests and frills of some dinosaurs, like the marginocephalians, theropods and lambeosaurines, may have been too fragile for active defense, so they were probably used for sexual or aggressive displays, though little is known about dinosaur mating and territorialism. Communication is also an enigma, but the hollow crests of the lambeosaurines may have been resonance chambers used for a wide range of vocalizations.
One of the most valuable fossils, a Velociraptor attacking a Protoceratops, was discovered in the Gobi Desert in 1971, proving that dinosaurs did indeed attack and eat each other. While cannibalistic behavior among theropods is no surprise, it was confirmed by tooth marks from Madagascar in 2003.
Compared to the later mammalian radiation in the Cenozoic, there seem to be no burrowing and few climbing dinosaurs. Biomechanics has given insight into how fast dinosaurs could run, whether diplodocids could create sonic booms by snapping their tails like a whip, whether giant theropods had to slow down when rushing for food to avoid fatal injuries, and if sauropods could float.
Study of dinosaurs
Fields of study
Information on dinosaurs is obtained from a variety of fields of study including Physics, Chemistry, Biology, and the Earth Sciences (which includes Paleontology).
Activities include the discovery, reconstruction and conservation of dinosaur fossils and the interpretation of those fossils to better understand the evolution, classification and behavior of dinosaurs.
Classification
Main article: Dinosaur classification
Dinosaurs (including birds) are archosaurs, like modern crocodilians. These are set apart by having diapsid skulls, having two holes where jaw muscles attach, called temporal fenestrae. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Dinosaurs also have teeth that grow from sockets (an archosaur characteristic) rather than as direct extensions of the jaw bones, as well as various other characteristics. Within this group, the dinosaurs are set apart most noticeably by their gait. Instead of legs that sprawl out to the side, as found in lizards and crocodylians, they have legs held directly under their body. 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: these include plesiosaurs (which are not closely related to the dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic.
Dinosaurs are divided into two major orders, the Saurischia and the Ornithischia, on the basis of hip structure. Saurischians (from the Greek meaning "lizard hip") are dinosaurs that retained the hip structure of their ancestors. They include all the theropods (bipedal carnivores) and sauropods (long-necked herbivores). Ornithischians (from the Greek meaning "bird-hip") is the other dinosaurian order, most of which were quadrupedal herbivores.
Evolution
Dinosaurs split off from their archosaur ancestors during the Triassic period.
The first known dinosaurs appeared approximately 230 Mya, about 20 million years after the Permian-Triassic extinction event wiped out about 70 percent of all biological diversity on the planet. A few lines of primitive dinosaurs diversified rapidly after the Triassic, and quickly expanded until they filled most of the vacant ecological niches. During the reign of the dinosaurs, which encompassed the ensuing Jurassic and Cretaceous periods, nearly every terrestrial animal larger than 1 m in length (that we know of) was a dinosaur.
The Cretaceous-Tertiary extinction event, 65 Mya at the end of the Cretaceous, caused the extinction of all dinosaurs except for the line that had already led to the first birds.
Areas of debate
Warm-blooded?
Cretaceous-Tertiary extinction event
Scientists have waged a constant and vigorous debate over the temperature regulation of dinosaur blood; at first over its possibility, then over its method, a debate first popularized by Robert T. Bakker, also known as Bob Bakker. From the first discovery of dinosaurs, paleontologists posited that they were ectothermic creatures: "terrible lizards" as their name suggested. This axiomatic expectation implied that dinosaurs were mostly slow, sluggish organisms, comparable to modern reptiles, which need the sun to heat their bodies. However, new evidence of dinosaurs in chilly temperate climates, of polar dinosaurs in Australia and Antarctica where they experienced a six-month chilly and dark winter, of feathered dinosaurs whose feathers provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone, confirmed the possibility that some dinosaurs regulated their body temperature by internal biological methods, some aided partly by their very bulk. Skeletal structures suggest active lifestyles for theropods and other creatures, behavior more suitable for an endothermic cardiovascular system. Sauropods exhibit fewer endothermic characters. Perhaps some dinosaurs were endothermic and others not. Scientific debate over the details continues, although many paleontologists would now agree that endothermic systems are more likely (Parsons et al., 2001).
Complicating this debate, warm-bloodedness can emerge from more than one mechanism. Most discussions of dinosaur endothermia compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess insulation of some sort, such as fat, fur, or feathers, to slow down heat loss. However, large mammals, such as elephants, face a different problem due to their relatively small surface area to volume ratio (Haldane's principle). This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they lack fur, 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 faced the same situation: their size would dictate that they lost heat relatively slowly to the surrounding air, and so could have been what are called bulk endotherms, animals that are warmer than their environments through sheer size rather than any special adaptations like those of birds and mammals. However, so far this theory fails to explain the vast multitudes of dog- and goat-sized dinosaurs, which made up the bulk of the ecosystem in the mesozoic.
Feathered dinosaurs and the bird connection
A number of similiarities occur between birds and non-avian dinosaurs, in fact over a hundred distinct anatomical features are shared by avian dinosaurs and theropod dinosaurs.
Feathers
bulk endotherms.]]
The first good specimen of a "feathered dinosaur" was the 1861 discovery of the Archaeopteryx in Germany, in the Solnhofen limestone, which is a lagerstätte; one of the rare and remarkable geological formations known for their superbly detailed fossils. Coming just two years after Darwin's seminal The Origin of Species, the evidence of a transitional fossil between reptiles and birds spurred the debates between evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, the specimens are commonly mistaken for Compsognathus.
Since the 1990s, a number of feathered dinosaurs have been found, providing clear evidence of the close relationship between dinosaurs and birds. Most of these specimens were local to Liaoning province in northeastern China, which was part of an island continent in the Cretaceous. However, the feathers were only preserved by the lagerstätte of the Yixian Formation; it is therefore possible that dinosaurs elsewhere in the world may have been feathered too, even though the feathers have not been preserved.
The feathered dinosaurs discovered so far include Beipiaosaurus, Caudipteryx, Dilong, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, and Sinosauropteryx, and potentially Adasaurus; and dinosaur-like birds like Confuciusornis; all of which come from the same area and formation in northern China. The dromaeosauridae family in particular seems to have been heavily feathered, and at least one dromaeosaurid, Cryptovolans, may have been capable of flight.
Skeleton
Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the association of multiple skeletal features also shared by the two groups is the more important link for paleontologists. Furthermore, it is increasingly clear that the relationship between birds, dinosaurs and the evolution of flight is more complex than has been previously realized. For example, while it was once believed that birds evolved from dinosaurs in one linear progression, some scientists, most notably Gregory S. Paul, conclude that some dinosaurs, such as the dromaeosaurs, may have evolved from birds, losing the power of flight while keeping their feathers in a manner similar to the ostrich and other ratites.
Comparisons of bird and dinosaur skeletons, as well as cladistic analysis, strengthens the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include: the neck, pubis, wrists (semi-lunate carpal), arm and pectoral girdle, shoulder blade, clavicle and breast bone.
Reproduction biology
breast bone.]]
A discovery in a Tyrannosaurus rex skeleton provided more evidence that dinosaurs and birds evolved from a common ancestor and for the first time allowed paleontologists to sex a dinosaur. When laying eggs, female birds have a special type of bone, called a medullary bone, that grows in their limbs, forming a layer inside the hard outer bone. It is rich in calcium and used for making eggshells. The presence of endosteally derived bone tissues lining the interior marrow cavities of portions of the Tyrannosaurus rex specimen's hind limb elements suggested similar reproductive strategies, and revealed the specimen to be female (Schweitzer et al., 2005).
A dinosaur embryo was found without teeth, which suggests some parental care was required to feed the young dinosaur, possibly the adult dinosaur regurgitated nutrition into the young dinosaur's mouth. This behavior is seen in numerous modern-day bird species; the parent birds regurgitated food into the hatchling's mouth.
Lungs
Big meat-eating dinosaurs had a complex system of air sacs similar to the setup in today's birds, according to an investigation led by Patrick O'Connor of Ohio University. The lungs of theropod dinosaurs, carnivores that walked on two legs and had birdlike feet, likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds", O'Connor said. The study was funded in part by the National Science Foundation.
Heart and sleeping posture
Modern computerized tomography (CT) scans of dinosaur chest cavities, conducted in 2000, found the apparent remnants of complex four-chambered hearts, much like those of today's mammals and birds. A recently discovered troodont fossil demonstrates that the dinosaurs slept like certain birds today, with their heads tucked under their arms. This would allow the head to be kept warm as is shown by modern birds.
Gizzard
Another piece of evidence that birds and dinosaurs are closely connected is that both birds and dinosaurs have used gizzard stones. The stones are swallowed by the animal to aid digestion and break down hard fibres and food once it enters the stomach. When found in association with fossils, they are called gastroliths. Paleontologists use the stones found in the dinosaur's stomach to determine migration routes, for example, the stone could have been swallowed at a certain point before being carried to another point during migration.
Evidence for Cenozoic dinosaurs
It has been claimed that fossils from El Ojo, South America, represent remains of dinosaurs surviving the extinction and still thriving in the Paleocene epoch. There are also other sporadic claims of post-Cretaceous dinosaur fossils (even a very doubtful finding of dinosaur eggs as late as Eocene). While it is certainly not improbable that some scattered population of some (presumably small) dinosaur species could have survived at least some hundreds of years after the mass extinction, evidence now points to El Ojo (and most other) findings as Cretaceous fossils contaminating Paleocene strata. Nevertheless, it is still theorized that some dinosaur population could have survived the main extinction event isolated in Antarctica, and then being killed by the climatic change.
Bringing dinosaurs back to life
Antarctica.]]
There has been much speculation about the availability of technology to bring dinosaurs back to life. The idea proposed in Michael Crichton's book Jurassic Park, using blood from fossilized mosquitos that have been suspended in tree sap since the Mesozoic and then filling in the gaps with frog genes to create the DNA of a dinosaur, is probably impossible. A problem with this theory is that DNA decays over time by exposure to air, water and radiation, thus depleting the chances of salvaging any useful DNA. Decay can be measured by a racemization test.
There have been two claims about the successful extraction of ancient DNA from dinosaur fossils, but upon further inspection, neither of these reports could be confirmed (Wang et al., 1997). However, a working visual peptide of a (theoretical) dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of still-living related species (reptiles and birds) (Chang et al., 2002).
Discovery of probable soft tissue from dinosaur fossils
In the March 2005 issue of Science, (Schweitzer et al.) announced material, after rehydrating, that resembled soft tissue was discovered inside a Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana, from about 68 million years ago.
When the fossilized bone was treated over several weeks to remove mineral content (demineralize) from the fossilized bone marrow cavity, Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). Scrutiny under microscope further revealed the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. It has not been made clear of what this flexible material is actually composed, although many news reports immediately linked it with the movie "Jurassic Park", and the interpretation of the artifact as well as the relative importance of Dr. Schweitzer's discovery is still undecided.
Extinction theories
The extinction of the non-avian dinosaurs is one of the most intriguing problems in paleontology. Only since the 1970s has the nature of this extinction become researched in detail, showing some possible causes of the dinosaur extinction.
Asteroid collision
paleontology, the impact of which may have caused the Dinosaur extinction.]]
The theory first proposed by Walter Alvarez in the late 1970s, linked the extinction event at the end of the Cretaceous period to a bolide impact about 65.5 million years ago, based on a sudden change in Iridium levels in fossilized layers. The bulk of the evidence now indicates that a 10 km wide bolide hit the Yucatán Peninsula 65 million years ago, creating the 170 km wide Chicxulub Crater and causing the extinction. Scientists are still disputing whether dinosaurs were in steady decline or still thriving before the meteor struck. Some scientists state that the meteor would have caused an unnatural winter, while others claim that it would have created an unusual heat wave.
Although the speed of extinction cannot be deduced from the fossil record alone, the latest models suggest the extinction was extremely rapid. It appears to have been caused by heat from the meteorite impact and the matter ejected from the crater reentering the Earth's atmosphere around the world.
The Oort cloud
Similar to Alvarez's theory, which involved a single comet, the Oort cloud suggests that a vast shower of comets that were dislodged in an astral phenomenon hit the Earth at the same time, causing world wide extinction. The end result would again be an unnatural winter, ultimately freezing the dinosaurs.
Environment changes
The environment during the late Cretaceous was changing dramatically. Volcanic activity was decreasing. This led to a cooling trend as the levels of carbon dioxide diminished. At the eras peak, sea levels are estimated to have been between 100 metres (330 feet) to 250 metres (820 feet) higher than now with no polar ice caps. The planet's temperature was much more uniform, with only a 25 degrees C difference from the polar regions to the equator and much warmer with the poles 50 degrees C warmer than today.
The atmosphere's composition had carbon dioxide levels 12 times higher than today's levels, and oxygen formed 32 to 35 percent of the atmosphere, as compared with 21 percent today. But toward the end of the Cretaceous, these levels started to fluctuate wildly. Some hypothesize that climate change combined with the fall of oxygen levels might have led to many species demise, especially if the dinosaurs had a respiratory system commonly found in today's birds - something that would be difficult for an animal as large as a dinosaur with lower oxygen levels to breathe in.
Other groups besides dinosaurs became extinct at the same time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most kinds of birds, and many groups of mammals.
History of discovery
Dinosaur fossils have been known about for millennia, though their true nature was not recognized; the Chinese considered them to be dragon bones, while Europeans believed them to be the remains of giants and other creatures killed by the Great Flood. The first dinosaur species to be identified and named was Iguanodon, discovered in 1822 by the English geologist Gideon Mantell, who recognized similarities between his fossils and the bones of modern iguanas. Two years later, the Rev William Buckland, professor of geology at Oxford University, became the first person to describe a dinosaur in a scientific journal, in this case Megalosaurus bucklandii, found near Oxford. The study of these "great fossil lizards" became of great interest to European and American scientists, and in 1842 the English paleontologist Richard Owen coined the term "dinosaur". He recognized that the remains that had been found so far, Iguanodon, Megalosaurus and Hylaeosaurus, had a number of features in common, so decided to present them as a distinct taxonomic group. With the backing of Prince Albert of Saxe-Coburg-Gotha, husband of Queen Victoria, Owen established the Natural History Museum in South Kensington, London, to display the national collection of dinosaur fossils and other biological and geological exhibits.
London
London
In 1858, the first known American dinosaur was discovered in marl pits of the small town of Haddonfield, New Jersey (although fossils had been found before, their nature had not been identified). The creature was named Hadrosaurus foulkii, after the town and the discoverer, William Parker Foulke. It was an extremely important find: Hadrosaurus was the first nearly complete dinosaur skeleton ever found and it was clearly a bipedal creature. This was a revolutionary discovery, as most scientists had thought that dinosaurs walked on four feet like lizards. Foulke's discoveries sparked a dinosaur mania in the United States, which was exemplified by the fierce rivalry of Edward Drinker Cope and Othniel Charles Marsh, who each competed to outdo the other in finding new dinosaurs in what came to be known as the Bone Wars. The feud was probably started when Marsh criticized Cope for putting the bones of a Elastomosaurus on back to front. This started the jealousy and madness of a fight which ensued for the next 30 years, only ending in 1897 when Cope died after spending his entire fortune in the dinosaur hunt. Marsh won the contest by virtue of being better funded through the US Geological Survey. Unfortunately, many of the valuable dinosaur specimens were destroyed or damaged due to the pair's rough approach; often the diggers used dynamite to unearth bones. All together, they discovered 142 new species of dinosaur, with Marsh unearthing 86 new species, while Cope only discovered 56 species. Cope's collection is now at the American Museum of Natural History in New York, while Marsh's is displayed at the Peabody Museum of Natural History at Yale University.
Since then, the search for dinosaurs has been carried to every continent on Earth. This includes Antarctica, where the first dinosaur, a nodosaurid Ankylosaurus, was discovered on Ross Island in 1986, though it was 1994 before an Antarctic dinosaur, the Cryolophosaurus ellioti, was formally named and described in a scientific journal.
Current "hotspots" include southern South America (especially Argentina) and China, which has produced many exceptional feathered dinosaur specimens due to the arid climate having preserved the skeleton.
In popular culture
feathered dinosaur
Dinosaurs were highly successful life forms for some 150 million years; however, even more than their success, it is their extinction that has become part of human culture. Hence dinosaur is sometimes used as a metaphor for people and things that are perceived as being out of date or no longer in touch with the spirit of the times, and therefore ought to be extinct. An example was the manner in which the punk movement described the "progressive" bands that preceded them as "dinosaur groups".
One of the most ground breaking movies of its time, Jurassic Park, brought dinosaurs into the media spotlight, proving that dinosaurs were a good selling point for producers. Jurassic Park led to two sequels, The Lost World: Jurassic Park and Jurassic Park 3, both blockbusters in their own right. Due to the popularity of the movies, and their portrayal of T rex as king of the dinosaurs, dinosaurs have become a permanent fixture in today's world, with the Tyrannosaurus rex being the most popular due to the movies portraying him as king of the dinosaur. The Jurassic Park movies also inspired a couple of console games, such as Jurassic Park the video game.
Dinosaurs, because of their sizes and perceived aggressiveness, have both long fascinated and terrified the public mind in fictional as well as non-fictional works. This makes them a favorite of both young and old.
fictional.]]
Notable examples of fictional works include Arthur Conan Doyle's book The Lost World, the 1933 film King Kong and Godzilla. Thus, the possibility of humans and dinosaurs living together has been a recurring theme in fiction: The Valley of Gwangi (1969) and One Million Years BC (1966) (famously starring Raquel Welch in a fur bikini). Ray Harryhausen brought the dinosaurs to life in both films using model animation. Other classic films where dinosaurs have been in the spotlight are Pterodactyl and Spot from The Munsters.
The Munsters
The development of Computer-generated imagery further enhanced that fantasy and also allowed the production of documentaries; 1999 BBC series Walking with Dinosaurs is a notable example. Dinosaurs, however are not only depicted as cold-blooded reptiles but also as warm-loving and even with friendly personalities, either to appeal to young children such as the 1970s show Land of the Lost, the 1990s' Dinosaurs and the more recent Barney & Friends. For cartoons The Flintstones showcased a stone age family living with dinosaurs, while comic strips such as Calvin and Hobbes and The Far Side feature dinosaur orientated strips frequently.
Due to their consumer appeal, many computer and console games have featured dinosaurs as characters. Crash Bandicoot: Warped, Ape Escape, the Turok series, and even Zoo Tycoon have involved dinosaurs in their story lines.
Notes
#Dal Sasso, C. and Singnore, M. (1998). Exceptional soft-tissue preservation in a theropod dinosaur from Italy. Nature 292:383-387. [http://www.dinosauria.com/jdp/misc/scipionyx.html See commentary on the article]
# Schweitzer, M.H., Wittmeyer, J.L. and Horner, J.R. (2005). Soft-Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. Science 307:1952 - 1955. [http://news.bbc.co.uk/2/hi/science/nature/4379577.stm See commentary on the article]
#[http://news.nationalgeographic.com/news/2002/05/0529_020529_sauropods.html Sauropod tracks] Sauropod tracks are giving paleontologists new information.
# Lessem, D. and Glut, D.F. (1993). The Dinosaur Society's Dinosaur Encyclopedia. Random House Inc. ISBN 0679417702. [http://www.isgs.uiuc.edu/faq/dino-faqs/pdq76.html See commentary on the article]
# [http://www.browningmontana.com/dinosaurs.html Juvenile Tyrannosaur] A juvenile Tyrannosaur skeleton was found.
# [http://search.eb.com/dinosaurs/dinosaurs/BRa.html Oviraptor nesting] Oviraptor nests or Protoceratops?
# [http://news.bbc.co.uk/1/hi/scotland/3255494.stm Dinosaur family tracks] Footprints show maternal instinct after leaving the nest.
# [http://www.amnh.org/exhibitions/fightingdinos/ex-fd.html Joined forever in death] The discovery of two fossil dinosaurs entangled together proved many theories.
# [http://news.nationalgeographic.com/news/2002/12/1219_021219_dinocannibal.html Cannibalistic Dinosaur] The mystery of a dinosaur cannibal.
# [http://www.nsf.gov/od/lpa/news/03/pr0336.htm Madagascar cannibal] A cannibal dinosaur is uncovered in Madagascar.
# [http://palaeo.gly.bris.ac.uk/Palaeofiles/Tracks/Report7/Speed.html Gait and Dinosaur speed] Gait and his formula on estimating a dinosaur's speed.
# [http://www.shef.ac.uk/~es/DINOC01/dinocal1.html Calculate your own Dinosaur speed] More on Gait and his speed calculations.
# [http://news.bbc.co.uk/1/hi/sci/tech/78905.stm Injuries from rushing] Dinosaurs were so eager to eat food, they broke their ribs!
# [http://www.nserc.ca/news/features/dinosaurs_e.htm Sauropods that floated] Sauropods were the largest animals to float.
# [http://news.nationalgeographic.com/news/2005/12/1201_051201_archaeopteryx_2.html Archaeopteryx related to the Deinonychosaurs?] Archaeopteryx is proven to be closely related to Deinonychosaurs.
# 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.
# [http://www.guardian.co.uk/life/news/story/0,12976,1326559,00.html Bird-like sleeping position for Dinosaur] Even more evidence proving birds are dinosaurs.
# [http://www.sciencemag.org/cgi/content/full/sci;307/5717/1952 Cellular preservation inside T rex blood vessels] Can these cells be used to bring the Tyrannosaurus rex back to life?
# Koeberl, C. and MacLeod, K.G. (2002). Catastrophic Events and Mass Extinctions. Geological Society of America. ISBN 0813723566.
See also
- Fossils
- List of dinosaurs
- List of dinosaur classifications
- Prehistoric life
- Prehistoric reptiles
- Various forms of Creationism dispute the age and significance of dinosaur fossils
References
- Kevin Padian, and Philip J. Currie. (1997). Encyclopedia of Dinosaurs. Academic Press. ISBN 0122268105. (Articles are written by experts in the field).
- Paul, Gregory S. (2000). The Scientific American Book of Dinosaurs. St. Martin's Press. ISBN 0312262264.
- 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 0801867630.
- M Schweitzer, JL Wittmeyer and JR Horne (2005). Gender-Specific Reproductive Tissue in Ratites and Tyrannosaurus rex. Science 308; 5727:1456-60.
- Weishampel, David B. (2004). The Dinosauria. University of California Press; 2nd edition. ISBN 0520242092.
- Keith M Parsons. (2001). Drawing Out Leviathan. Indiana University Press. ISBN 0253339375.
;Technical papers
- Belinda S. W. Chang, Karolina Jönsson, Manija A. Kazmi, Michael J. Donoghue and Thomas P. Sakmar. (2002). [http://mbe.oupjournals.org/cgi/content/full/19/9/1483 Recreating a functional ancestral archosaur visual pigment]. Molecular Biology and Evolution 19 (9), 1483–1489.
- Hai-Lin Wang, Zi-Yang Yan and Dong-Yan Jin. (1997). [http://mbe.oupjournals.org/cgi/reprint/14/5/589 Reanalysis of published DNA sequence amplified from Cretaceous dinosaur egg fossil]. Molecular Biology and Evolution 14 (5), 589–591.
External links and sources
;For children
- [http://www.mantyweb.com/dinosaur/ Dinosaur Time Machine from MantyWeb Educational Software] From MantyWeb Educational Software. Kid's site, facts, games.
- [http://yahooligans.yahoo.com/content/science/dinosaurs Dinopedia] From Yahooligans! Science. Glossaries, dino cards and indexes.
- [http://www.enchantedlearning.com/subjects/dinosaurs/ Zoom Dinosaurs] From Enchanted Learning. Kid's site, info pages, theories, history.
;Popular
- [http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/index.html Dinosaurs & other extinct creatures] From the Natural History Museum. London popular site, well illustrated dino directory.
- [http://www.arches.uga.edu/~rfreeman/GEOL3350_'4HistoryDinoSt.htm History of Dinosaur discovery] Timeline of the discovery of Dinosaurs.
- [http://pubs.usgs.gov/gip/dinosaurs/ Dinosaurs: Facts and Fiction] From the United States Geological Survey. Popular overview.
- [http://www.bbc.co.uk/dinosaurs/ Dinosaurs] From the BBC. Popular site, very well illustrated.
- [http://www.dinodata.net/Discussions/dinosaurs.html Discussions] From DinoData. Summaries of modern debates about dinosaurs.
- [http://www.ucmp.berkeley.edu/diapsids/dinosaur.html Dinosauria] From UC Berkeley Museum of Paleontology Detailed information - scroll down for menu.
- [http://www.dinosaurnews.org/ The Dinosaur News] The Dino-headlines from around the world. Recent news on dinsaurs, including finds and discoveries, lots of links.
- [http://www.bowdoin.edu/~dbensen/ OPUS: Dinosaur by Daniel Bensen] A gallery of dino-paintings.
;Technical
- [http://www.prehistoricplanet.com/ Prehistoric Planet] From PaleoClones. Current dino news.
- [http://www.wired.com/news/technology/0,1282,63613,00.html A Fiery Death for Dinosaurs? by Amit Asaravala] From Wired. Article on the rapid extinction of dinosaurs.
- [http://www.newscientist.com/hottopics/dinosaurs/ The Rex Files] From the New Scientist. Articles, latest news but out of date.
- [http://palaeo-electronica.org/ Palaeontologia Electronica] From Coquina Press. Online technical journal.
- [http://www.thunderbolts.info/tpod/2005/arch05/050623impossible-dinosaur.htm Impossible Dinosaurs] Article on a gravity-based approach for the extinction by David Talbott and Wallace Thornhill.
- [http://uk.arxiv.org/abs/hep-ph/0002255 TeV scale gravity, mirror universe, and ... dinosaurs] Article from [http://th-www.if.uj.edu.pl/acta/ Acta Physica Polonica B] by Z.K. Silagadze.
;Very technical
- [http://www.dinodata.net DinoData] Technical site, essays, classification, anatomy.
- [http://www.dinosauria.com/dml/dml.htm Dinosauria On-Line] Technical site, essays, pronunciation, dictionary.
- [http://dino.lm.com/ The Dinosauricon] By T. Michael Keesey. Technical site, cladogram, illustrations and animations.
- [http://www.palaeos.com/Vertebrates/Units/Unit310/000.html Dinosauromorpha Cladogram] From [http://www.Palaeos.com Palaeos]. A detailed and wonderful amateur site about all things paleo.
- [http://palaeo.gly.bris.ac.uk/dinobase/dinopage.html Dinobase] AA dinosaur database with dinosaur lists, classification, pictures, and more.
;Bird-dinosaur discussion
- [http://www.ucmp.berkeley.edu/diapsids/avians.html DinoBuzz] Are birds Dinosaurs?
- [http://www.dinosauria.com/ Dinosauria] Site focussing on the Dino-Bird aspect.
-
Category:Paleontology
Category:Paleozoology
Category:Prehistoric reptiles
Vertebrate
Conodonta
Hyperoartia
:Petromyzontidae (lampreys)
Pteraspidomorphi (early jawless fish)
Thelodonti
Anaspida
Cephalaspidomorphi (early jawless fish)
:Galeaspida
:Pituriaspida
:Osteostraci
Gnathostomata (jawed vertebrates)
:Placodermi
:Chondrichthyes (cartilaginous fish)
:Acanthodii
:Osteichthyes (bony fish)
::Actinopterygii (ray-finned fish)
::Sarcopterygii (lobe-finned fish)
:::Actinistia (coelacanths)
:::Dipnoi (lungfish)
:::Tetrapoda
::::Amphibia
::::Amniota
:::::Sauropsida/(Reptiles)
::::::Aves (Birds)
:::::Synapsida
::::::Mammalia
Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. Vertebrates started to evolve about 530 million years ago during the Cambrian explosion, which is part of the Cambrian period (first known vertebrate is Myllokunmingia). The bones of the spinal column (or vertebral column) are called vertebrae. Vertebrata is the largest subphylum of chordates, and contains most animals with which people are generally familiar (except insects). Fish (including lampreys, but traditionally not hagfish, though this is now disputed), amphibians, reptiles, birds, and mammals (including humans) are vertebrates. Additional characteristics of the subphylum are a muscular system that mostly consists of paired masses, as well as a central nervous system which is partly located inside the backbone.
The internal skeleton which defines vertebrates consists of cartilage or bone, or in some cases both. The skeleton provides support to the organism during the period of growth. For this reason vertebrates can achieve larger sizes than invertebrates, and on average vertebrates are in fact larger. The skeleton of most vertebrates, that is excluding the most primitive ones, consists of a skull, the vertebral column and two pairs of limbs. In some forms of vertebrates, one or both of these pairs of limbs may be absent, such as in snakes or whales. These limbs have been lost in the course of evolution.
The skull is thought to have facilitated the development of intelligence as it protects vital organs such as the brain, the eyes and the ears. The protection of these organs is also thought to have positively influenced the development of high responsiveness to the environment often found in vertebrates.
Both the vertebral column and the limbs support the body of the vertebrate overall. This support facilitates movement. Movement is normally achieved with muscles that are attached directly to the bones or cartilages. The contour of the body of a vertebrate is formed by the muscles. A skin covers the inner parts of a vertebrate's body. The skin sometimes acts as a structure for protective features, such as horny scales or fur. Feathers are also attached to the skin.
The trunk of a vertebrate is hollow and houses the internal organs. The heart and the respiratory organs are protected in the trunk. The heart is located behind the gills, or where there are lungs, in between the lungs.
The central nervous system of a vertebrate consists of the brain and the spinal cord. Both of these are characterized by being hollow. In lower vertebrates the brain mostly controls the functioning of the sense organs. In higher vertebrates the size of the brain relative to the size of the body is larger. This larger brain enables more intensive exchange of information between the different parts of the brain. The nerves from the spinal cord, which lies behind the brain, extend to the skin, the inner organs and the muscles. Some nerves are directly connected to the brain, linking the brain with the ears and lungs.
Vertebrates have been traced back to the ostracoderms of the Silurian Period (444 million to 409 million years ago) and the conodonts, a group of eel-like vertebrates characterized by multiple pairs of bony toothplates.
All vertebrates have: the ability to form bones; paired, specialised sensory organs and a brain.
External links
- [http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_vertebrates Tree of Life]
- [http://reference.allrefer.com/encyclopedia/categories/vertz.html Vertebrate Zoology]
Category:Chordates
ko:척추동물
ms:Vertebrata
ja:脊椎動物
simple:Vertebrate
th:สัตว์มีกระดูกสันหลัง
LandLand may refer to:
- Land, the part of the Earth that is not covered by water
- Landform, a feature of the land
- Landscape, the layout, appearance and character of a land area
- Land bridge, a feature exposed during periods of low sea level
- A landing, the end point of a flight or ocean voyage
A synonym for a region belonging to a people:
- A country, a geographical area that connotes an independent political entity
- A nation, particularly in the absence of a state or government
- Motherland, fatherland, and homeland, a person's country of affiliation, birth or ancestral origin
- Specific regions:
- Länder, states of Germany
- Bundesländer, states of Austria (sometimes used for states of Germany as well)
- Lands of Sweden
- Lands of Denmark
- Land, Norway, a region in Norway
- Land borders, a list of the borders of various nations
In law:
- Real property, real estate and ownership interests
- Estate in land, law regarding land ownership and titles
- See Torrens title for modern land ownership and titles in Australia
- Landlord, the owner of real estate which is leased
- Land claims, disputed lands
- Land rights
In economics:
- Land (economics), a factor of production comprising all naturally occurring resources
- Land economy, the study of land usage and development
- Land grant, a gift of land made by the government for public projects
- Land reform, the redistribution of land
Other:
- Land Camera, the first "instant camera"
- Land Institute, a non-profit agricultural study center Kansas USA
See also
- Holy Land
- No Man's Land
- Promised land
ja:陸
Extinct
In biology and ecology, extinction is the ceasing of existence of a species or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species. Extinction is usually a natural phenomenon; it is estimated that more than 99.9% of all species that have ever lived are now extinct. Through evolution, new species are created by speciation — where new organisms arise and thrive when they are able to find and exploit an ecological niche — and species become extinct when are no longer able to survive in changing conditions or against superior competition. A typical species becomes extinct within 10 million years of its first appearance, although some species survive virtually unchanged for hundreds of millions of years.
Descendants may or may not exist for extinct species. Daughter species that evolve from a parent species carry on most of the parent species' genetic information, and even though the parent species may become extinct, the daughter species lives on. In other cases, species have produced no new variants, or none that are able to survive the parent species' extinction.
Extinction of a parent species where daughter species or subspecies are still alive is also called pseudoextinction. Many of prehistoric extinct species have evolved into new species; for example the extinct Hyracotherium (an ancient horse-like animal) was the ancestor of several extant species including the horse, the zebra and the donkey. The Hyracotherium itself is no more, but its descendants live on. It is therefore said to be pseudoextinct.
Currently, many environmental groups and governments are concerned with the extinction of species due to human intervention, and are attempting to combat further extinctions. Humans can cause extinction of a species through overharvesting, pollution, destruction of habitat, introduction of new predators and food competitors, and other influences. According to the World Conservation Union (WCU, formerly the IUCN), 784 extinctions have been recorded since the year 1500 (the arbitrary date selected to define "modern" extinctions), with many more likely to have gone unnoticed. Most of these modern extinctions can be attributed directly or indirectly to human effects. Endangered species are species that are in danger of becoming extinct; several organizations attempt to preserve recognized endangered species through a variety of conservation programs.
Species which are not extinct are termed extant.
Definition
A species becomes extinct when the last existing member of that species dies. Extinction therefore becomes a certainty when no surviving specimens are able to reproduce and create a new generation. A species may become functionally extinct when only a handful of individuals survive, which are unable to reproduce due to health, age, lack of both sexes (in species that reproduce sexually), or other reasons.
In addition to actual extinction, human attempts to preserve critically endangered species have caused the creation of the conservation status extinct in the wild. Species listed under this status by the WCU are not known to have any living specimens in the wild, and are maintained only in zoos or other artificial environments. Some of these species are functionally extinct. When possible, modern zoological institutions attempt to maintain a viable population for species preservation and possible future reintroduction to the wild through use of carefully planned breeding programs.
Pinpointing the extinction or pseudoextinction of a species requires a clear definition of that species. The species in question must be identified uniquely from any daughter species, as well as its ancestor species or other closely related populations, if it is to be declared extinct. For further discussion, see definition of species.
Extinction (or replacement) of species by a daughter species plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge.
Permanence
Until recently, it had been universally accepted that the extinction of a species meant the end of its time on Earth. However, recent technological advances have encouraged the hypothesis that through the process of cloning, extinct species may be "brought back to life." Proposed targets for cloning include the mammoth and thylacine. In order for such a program to succeed, a sufficient number of individuals would need to be cloned (in the case of sexually reproducing organisms) to create a viable population size. The cloning of an extinct species has not yet been attempted, due to technological limitations, as well as ethical and philosophical questions.
This concept was fictionalized in the popular novel and movie Jurassic Park.
Causes
There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. Most simply, any species that is unable to survive or reproduce in its environment, and unable to move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out competition for food to newer, better adapted competitors. Around three species of birds die out every year due to competition.
Genetic and demographic causes
Genetic and demographic phenomena affect the evolution, and therefore extinction, of species. Regarding the possibility of extinction, small populations which represent an entire species are much more vulnerable to these types of effects.
Natural selection acts to propagate beneficial genetic traits and eliminate weaknesses. However, it is sometimes possible for a deleterious mutation to be spread throughout a population through the effect of genetic drift.
A diverse or "deep" gene pool gives a population a higher chance of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity can increase the chances of extinction of a species. Population bottlenecks can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding more frequent. The founder effect can cause rapid, individual-based speciation and is the most dramatic example of a population bottleneck.
Habitat degradation
The degradation of a species' habitat may alter the fitness landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic, or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species.
Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness. DDT played such a role in killing off bald eagles and other birds by thinning the egg shell walls of affected birds, thus lowering the survivability of offspring. Since this effect was discovered, DDT has been banned in many parts of the world and affected bird populations are recovering.
Habitat degradation can also take the form of a physical destruction of niche habitats. The widespread destruction of tropical rainforests and replacement with open pastureland is widely sited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive with no forest to house it.
Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing unwelcome competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources.
Vital resources including water and food can also be limited during habitat degradation, causing some species to become extinct.
Predation, competition, and disease
Coextinction
Effects
Mass extinctions
:Main article: Mass extinction
There have been at least five mass extinctions in the history of life,and four in the last 3.5 billion years in which many species have disappeared in a relatively short period of geological time. These are covered in more detail in the article on extinction events. The most recent of these, the K-T extinction 65 million years ago at the end of the Cretaceous period, is best known for having wiped out the non-feathered dinosaurs, called the non-avian dinosaurs, among many other species.
According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70 percent of biologists believe that we are currently in the early stages of a human-caused mass extinction, known as the Holocene extinction event. In that survey, the same proportion of respondents agreed with the prediction that up to 20 percent of all living species could become extinct within 30 years (by 2028). Biologist E.O. Wilson estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all species of life on earth will be extinct in 100 years.
Human extinction
Human extinction refers to the possibility that the human species may become extinct. Although humans are relatively intelligent and adaptive, they could cause an extinction through their own actions, or allow a natural extinction event to occur through negligence. Humans can also possibly die out because of an event that they are incapable of preventing, such as another meteor strike.
Human attitudes on extinction
Extinction in species other than Homo sapiens
Because humans are a reasonably intelligent species capable of abstract thought, the views on the extinction of species other than Homo sapiens tend to be diverse, ranging from the preservative views of the most vehement eco-warrior to general apathy in the matter. However, it is seen that humans as a whole generally will act to protect against the extinction of species (primarily species that have a direct impact on human agriculture, such as cattle), if only to further preserve and perpetuate the human species. This is evidenced by organizations such as the United States Environmental Protection Agency (http://www.epa.gov).
Extinction in the species Homo sapiens
In a normal human being, a very strong instinctual urge to survive and, upon puberty and physical development, procreate (or at the very least have sexual contact, which normally leads to procreation) is prominent. Because of this, the general consensus of the human species can be presumed to be against the extinction of humankind. The natural urge to both survive as long as possible and mate can be and often is overcome by things such as personal, organizational, or religious beliefs, such as is the case with the Voluntary Human Extinction Movement (http://www.vhemt.org), by mental illness (possibly leading up to suicide and thus a zero percent chance of both living and continued mating), or sometimes by trained willpower strong enough to overcome the natural functions of the brain. Laws against genocide have been ratified to help prevent human extinction as a direct result of unnatural death caused by another human being or group of human beings.
Planned extinction
Olivia Judson is one of few modern scientists to have advocated the deliberate extinction of any species. Her controversial 2003 NY Times article advocates "specicide" of thirty mosquito species through the introduction of recessive "knockout genes". Her defense of such an extreme measure rests on:
- Anopheles mosquitoes and Aedes mosquito represent only 30 species; eradicating these would save at least one million human lives per annum at a cost of reducing the genetic diversity of the family Culicidae by only 1%.
- She writes that since species go extinct "all the time" the disappearance of a few more will not destroy the ecosystem: "We're not left with a wasteland every time a species vanishes. Removing one species sometimes causes shifts in the populations of other species -- but different need not mean worse."
- Anti-malarial & mosquito control programs offer little realistic hope to the 300 million people in developing nations who will be infected with acute illnesses this year; although trials are ongoing she writes that if they fail: "We should consider the ultimate swatting."
Scientists
Although scientists are generally opposed to future extinctions they have found historic extinctions very useful for research; in the early nineteenth century Georges Cuvier's observations of fossil bones convinced him that they did not originate in extant animals. This discovery was critical for the spread of uniformitarianism and lead to the first book publicizing the idea of evolution.
Environmental movement
The environmental movement is strongly opposed to further extinction, and generally sees habitat preservation as preferable to prevention of extinction through captive breeding programs.
Commercial and industrial interests
When commercial technologies are tested the testing tends to concentrate on human effects. However, some technologies with no proven harmful effects on Homo sapiens can be devastating to wildlife (most famously DDT). In extreme case these new processes can in themselves cause unintended extinctions as a side-effect of business operations. Although most companies were formerly more concerned with bottom-line profits than corporate image, a move began (under campaign pressure) to account for corporate reputational risk from such environmental catastrophes.
The most recent example of the potential clash between industrial technology and species survival is in the wireless communication revolution. Although extensive studies have rejected the hypothesis that low-level exposure to microwave-frequency communication is harmful to human health (or is not statistically significant) few studies have been carried out on the effects of microwaves in other life forms. For instance, the dielectric heating studies are limited to their effects on human beings. Currently 1mW/cm² is taken to be the acceptable power density of such radiation. The most glaring omission is the absence of any study on other living species, and hence on the existing fragile eco-system.
The rapidly dwindling species of dragon-flies, butterflies and fireflies from densely populated areas (where satellite foot-prints and mobile communication infrastructures are plentiful, India or China for instance) has been blamed by some on the rise of the mobile phone, although in the absence of studies, this is speculative.
Governments and international organizations
Governments sometimes see the loss of native species as a loss to ecotourism, and can enact laws with severe punishment against the trade in native species (in an effort to prevent extinction in the wild). Some endangered species are considered symbolically important.
Indigenous populations
People who live close to nature can be dependent on the survival of all the species in their environment and are some of the people most concerned about extinction risks.
Endangered species
:Main article: Endangered species
See also
- Coextinction
- List of extinct animals
- Biodiversity
- Lazarus taxon
- Unified neutral theory of biodiversity
- Population genetics
External links
- [http://www.lassp.cornell.edu/newmme/science/extinction.html A mathematical model for mass extinction]
- [http://www.msnbc.msn.com/id/6502368/ Species disappearing at an alarming rate (MSNBC)]
- [http://www.iucnredlist.org/ Red List of Threatened Species]
- [http://www.wild-earth.org/cms/page1090.cfm The Wildlands Project] takes action on wildlife conservation to address the extinction crisis in the Americas.
- [http://extinct.petermaas.nl/ The Extinction Website]
- [http://extinctanimals.proboards22.com/ Extinction forum]
- [http://creo.amnh.org/ Committee on recently extinct organisms]
References
- [http://www.well.com/user/davidu/extinction.html Mass Extinction Underway | Biodiversity Crisis | Global Species Loss]
- [http://nitro.biosci.arizona.edu/courses/EEB105/lectures/extinction/extinction.html Univ. of Arizona lecture on extinction]
Notes
[http://www.unc.edu/courses/2000fall/geol018-001/Lecture34.html A mass extinction summary lecture] from the University of North Carolina estimates that living creations are drawn from only fifty million species, but that fifty billion species may have lived on the planet. It estimates a background extinction rate (aside from the mass extinctions) at 2-4 families per million years. The [http://www.amnh.org/exhibitions/dinosaurs/extinction/mass.php American Museum of Natural History] says that scientists estimate that "at least" 99.9% of all species of plants and animals that have ever lived are now extinct. The Permian-Triassic extinction alone killed off about 90 percent of marine species and 70 percent of the terrestrial vertebrate species then alive.
Biologist E.O. Wilson, Professor Emeritus and honorary curator of entomology at Harvard University, in his 2002 book The Future of Life (ISBN 0679768114). See also: The Sixth Extinction : Patterns of Life and the Future of Humankind by Richard Leakey ( ISBN 0385468091 ).
See: Niles Eldredge, Time Frames: Rethinking of Darwinian Evolution and the Theory of Punctuated Equilibria, 1986, Heinemann ISBN 0434226106
The pro-specicide article's full fair use text is available on [http://www.animana.org/tab2/22abugsdeath.shtml the animana pages (a socioecology blog)].
The prologue of Ideas: A History from Fire to Freud (Peter Watson Weidenfeld & Nicolson ISBN 029760726X) makes this connection (on page 16), and says that there had been the hope that some of these extinct species would be found in undiscovered parts of the earth before the huge variety of prehistoric life was uncovered.
Robert Chambers, 1844, Vestiges of the Natural History of Creation, 1994 reprint: University of Chicago Press ISBN 0226100731
Category:Ecology
Category:Evolutionary biology
Category:Extinction
ja:絶滅
CretaceousThe Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period, about 146 million years ago (Ma), to the beginning of the Paleocene epoch of the Tertiary period (65.5 Ma). The end of the Cretaceous also defines the boundary between the Mesozoic and Cenozoic eras.
Name and dating
As with other older geologic periods, the rock beds that define the Cretaceous are well identified, but the exact dates of the period's start and end are uncertain by a few million years. No great extinction or burst of diversity separated the Cretaceous from the Jurassic. However, the end of the period is most sharply defined, being placed at an iridium-rich layer found worldwide that is believed to be associated with the Chicxulub impact crater in Yucatan and the Gulf of Mexico. This layer has been tightly dated at 65.5 Ma. This bolide collision is probably responsible for the major, extensively-studied Cretaceous-Tertiary extinction event. The Cretaceous (from Latin creta, for chalk) was named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates) found in the upper Cretaceous of Britain and adjacent continental Europe.
Divisions
The Cretaceous is usually separated into Lower and Upper Cretaceous Epochs. The faunal stages from youngest to oldest are:
Paleogeography
During the Cretaceous, the late Paleozoic - early Mesozoic supercontinent of Pangea completed its breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened and South America drifted westwards, Gondwana itself broke up as Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached). Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Within the continents, a broad shallow sea advanced across central North America (the Western Interior Seaway) and then started to recede, leaving thick marine deposits sandwiched between coal beds.
Other important Cretaceous exposures occur in Europe and China. In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene. Climates were warm, and even polar regions had no permanent ice.
Flora
Flowering plants first appeared, although they did not become predominant until near the end of the period (Campanian age). Their evolution aided by the appearance of bees, in fact angiosperms and insects are a good example of mutual evolution. The first representatives of many modern trees, including figs, planes and magnolias for example, appear in the Cretaceous. At the same time, some earlier Mesozoic gymnosperms, like Conifers continued to thrive, although other taxa like Bennettitales died out before the end of the period.
Fauna
Land animals
On land, mammals were a small and still relatively minor component of the fauna. The fauna was dominated by archosaurian reptiles, especially dinosaurs, which were at their most diverse. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialised families remained.
A fascinating glimpse of life in the Early Cretaceous is provided by the Liaoning lagerstätte (Chaomidianzi formation) in China, where the beautifully preserved remains of a number of types of small dinosaurs, birds, and mammals have been found. The coelurosaur dinosaurs found there represent a number of types of the group maniraptora, which is transitional between dinosaurs and birds, and are remarkable for the presence of hair-like feathers.
During the Cretaceous the insects began to diversify, and the oldest known ants, termites and butterflies appeared. Aphids, grasshoppers, and gall wasps appeared. Another important insect to evolve was the eusocial bee, which was integral to the ecology and evolution of flowering plants.
Marine animals
In the seas, rays, modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous, plesiosaurs throughout the entire period, and mosasaurs in the late Cretaceous.
Baculites, a straight-shelled form of ammonite, flourished in the seas. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera thrived. The Cretaceous also saw the first radiation of the diatoms in the oceans (freshwater diatoms did not appear until the Miocene).
Extinction
Main article: Cretaceous-Tertiary extinction event
In the extinction event that defines the end of the Cretaceous, a significant number of species (~50%) and known families (~25%) disappeared. Plants were nearly unscathed, while marine organisms were hit the hardest. These include a large number (~95%) of types of planktic foraminifers (excepting the Globigerinida), an even larger number of Coccolithophores, all the ammonite and belemnite cephalopods, and all reef-forming rudist molluscs), as well as all marine reptiles except turtles and crocodiles. Dinosaurs are the most famous victims of the Cretaceous extinction. Dinosaurs that were unique to the very end of the period (such as Tyrannosaurus rex, Triceratops, and Ankylosaurus) were wiped out. The last of the pterosaurs went extinct and the vast majority of birds did as well, including the Enantiornithes and Hesperornithiformes.
See also
- Chalk Formation
- Gault Clay
- Western Interior Seaway
References and further reading
Neal L Larson, Steven D Jorgensen, Robert A Farrar and Peter L Larson. Ammonites and the other Cephalopods of the Pierre Seaway. Geoscience Press, 1997.
ja:白亜紀
Million years ago
:For other uses of mya, see mya (disambiguation).
In astronomy, geology, and paleontology, mya is an acronym for million years ago and is used as a unit of time to denote length of time before the present. Specifically, one mya is equal to 106 years ago. The term 'mya' is now replaced in scientific literature with Ma (mega annum).
It should be noted that like the related unit bya ("billion years ago"), mya is traditionally written in lowercase. This is different from the related unit Gya, which capitalizes the first letter. The term bya is now replaced in scientific literature with Ga (giga annum).
See also
- annum
- Before Present
- bya
- tya
Category:Units of time
Bone
, a typically recognized bone.]]
Bone, also called osseous tissue, (Latin: "os") is a type of hard endoskeletal connective tissue found in many vertebrate animals. Bones support body structures, protect internal organs, and (in conjunction with muscles) facilitate movement; are also involved with cell formation, calcium metabolism, and mineral storage. The bones of an animal are, collectively, known as the skeleton. Bone has a different composition than cartilage, and both are derived from mesoderm. In common parlance, cartilage can also be called "bone", certainly when referring to animals that only have cartilage as hard connective tissue, such as cartilaginous fish (Chondrichthyes) like sharks. True bone is present in bony fish (Osteichthyes) and all tetrapods.
There are several evolutionary alternatives to bone. These evolutionary solutions are not completely functionally analogous to bone.
- Exoskeletal protection is offered by shells, carapaces (consisting of calcium compounds or silica) and chitinous exoskelotons.
- A true endoskeleton (that is, protective tissue derived from mesoderm) is also present in Echinoderms. Porifera (sponges) possess simple endoskeletons that consist of calcareous or siliceous spicules and a spongin fiber network.
Bones and skeletons are studied in osteology. Bones can be prepared for study by several methods, such as maceration. Maceration is done by boiling fleshed bone with dish detergent and a little bleach until all large particles are off. The bones are then cleaned by hand, usually with a toothbrush and a degreaser.
Functions
Long bones can be connected to muscles via tendons. Bones connect at joints by ligaments. The interaction between bone and muscle is studied in biomechanics.
Post-mortem functions
Cut and polished bone from a variety of animals is sometimes used as material for jewelry and other crafts. Ground cattle bone is sometimes used as fertilizer. In the Stone Age bone was used to manufacture art, weapons, needles, etc.
Structure
art
art
Bone is a relatively hard and lightweight composite material, formed mostly of calcium phosphate in the chemical arrangement termed calcium hydroxyapatite. It has relatively high compressive strength but poor tensile strength. While bone is essentially brittle, it does have a degree of significant elasticity contributed by its organic components (chiefly collagen). Bone has an internal mesh-like structure, the density of which may vary at different points.
Bone can be either compact or cancellous (spongy). Cortical (outer layer) bone is compact; the two terms are often used interchangeably. Cortical bone makes up a large portion of skeletal mass; but, because of its density, it has a low surface area. Cancellous bone is trabecular (honeycomb structure), it has a relatively high surface area, but forms a smaller portion of the skeleton.
Bone can also be either woven or lamellar. Woven bone is put down rapidly during growth or repair. It is so called because its fibres are aligned at random, and as a result has low strength. In contrast lamellar bone has parallel fibres and is much stronger. Woven bone is often replaced by lamellar bone as growth continues.
Long bones are tubular in structure (e.g. the tibia). The central shaft of a long bone is called the diaphysis, and has a hollow middle—the medullar cavity filled with bone marrow. Surrounding the medullar cavity is a thin layer of cancellous bone that also contains marrow. The extremities of the bone are called the epiphyses and are mostly cancellous bone covered by a relatively thin cortical of compact bone. In children, the bones are filled with red marrow, which is gradually replaced with yellow marrow as the child ages.
Short bones (e.g. finger bones) have a similar structure to long bones, except that they have no medullar cavity.
Flat bones (e.g. the skull and ribs) consist of two layers of compact bone with a zone of cancellous bone sandwiched between them.
Irregular bones are bones which do not conform to any of the previous forms (e.g. vertebrae).
All bones consist of living cells embedded in a mineralised organic matrix that makes up the main bone material.
Cells
Bone Heads include osteoblasts, so called Bone Lining Cells, osteocytes and osteoclasts. Osteoblasts are typically viewed as bone forming cells. They are located near to the surface of bone and their functions are to make osteoid and manufacture hormones such as prostaglandin which act on bone itself. Osteoblasts are mononucleate. Active osteoblasts are situated on the surface of osteoid seams and communicate with each other via gap-junctions. They contain alkaline phosphatase—a chemical which has a role in the mineralisation of bone.
Bone Lining Cells (BLCs) share a common lineage with osteogenesis (bone forming) cells. They function as a barrier for certain ions, induced osteogenetic cells. They are flattened, mononucleate cells which line bone.
However, osteocytes do originate from osteoblasts which have migrated into and become trapped and surrounded by bone matrix which they themselves produce. The space which they occupy is known as a lacuna. Osteocytes have many processes which reach out to meet osteoblasts probably for the purposes of communication. Their functions include to varying degrees: formation of bone, matrix maintenance and calcium homeostasis. They possibly act as mechano-sensory receptors—regulating the bones' response to stress.
If osteoblasts can be described as bone forming cells, the osteoclasts can be described as bone destroying cells. Osteoclasts are large, multinucleated cells located on bone surfaces in what are called Howship's lacunae. These lacunae, or resorption pits, are left behind after the breakdown of bone and often present as scalloped surfaces. Because the osteoclasts are derived from a monocyte stem-cell lineage, they are equipped with engulfment strategies similar to circulating macrophages. Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival active enzymes, such as acid phosphatase, are secreted against the mineral substrate. This process, called bone resorption, allows stored calcium to be released into systemic circulation and is an important process in regulating calcium balance. As bone formation actively | | |
