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Dinosauria

Dinosaurs are large vertebrate creatures that first appeared on the planet about 230 million years ago. This large family of prehistoric creatures have been loved by generations of children and pursued by many enthusiasts. Most believing a massive natural catastrophe resulted in their extinction 65 million years ago. It's believed their bones have been discovered throughout history, resulting in many legends of giants, dragons and other large and monstrous creatures. It's also believed the first dinosaurs were small, bipedal predators, these primitive skeletons were found in Argentina, dated to be the earliest ancestors, the eoraptor. Other early ancestors of the largest dinosaurs were the archosaur and the lagosuchus. Many other prehistoric creatures are incorrectly referred to as dinosaurs, for example; pelycosaurs, winged reptiles like the pterosaur and aquatic creatures like the ichthyosaur, plesiosaur and mosasaurs.

Beginnings

Even though dinosaur fossils are believed to have been known for centuries, their true nature was not acknowledged until 1677 when William Buckland discovered the first dinosaur bone in a limestone quarry near Oxford, England. He correctly identified it as a femur and named it meglosaurus. It's discovery was followed in 1822 by Gideon Mantell who uncovered and named the iguanodon, followed a few year laters again by William Buckland who completed uncovering more meglosaur bones and became the first person to write about it in a scientific journal.

These discoveries began the first dinosaur mania in England, when paleontologist Richard Owen coined the term dinosaur, recognizing the discoveries of the; meglasaurus, iguanadon and a hylaeosaurus contained a number of like and distinct featurers, and chose to seperate them into a seperate group of creatures. With financial support from Prince Albert, the first natural history museum was established in South Kensington, London to display these amazing discoveries.

The discovery of a hadrosaur in Haddonfield, New Jersey by William Parker Foulke in 1858, was the first american dinosaur, and realizing it was a bipedal creature revolutuionized the hunt for dinosaurs. Discovering they were not just four legged lizards, many were bitten by the bug of discovery. This passion for unearthing these forgotten giants and mythical dragons reached new heights when two paleontologists, Edward Drinker Cope and Othniel Charles Marsh started what has become known as Bone Wars. The beginnings of this rivalry is believed to have started when Marsh publically pointed out that the reconstruction of an Elasmosaurus was flawed with the head of the plesiosaur placed on it's tail. This feud resulted in a thirty year battle that ended when Cope died in 1897, having spent his fortune finding dinosaurs, leaving Marsh as the victor, being better funded. An unfortunate side affect was the loss of many valuable dinosaur discoveries because of rough methods like dynamite and unknowing diggers. However they made many contributions to the world of paleontology, having discovered a total of 142 new species. Cope's collection can be found in the American Museum of Natural History in New York, and Marsh's collection is on location at the Peabody Museum of Natural History at Yale University.

Since then the fossilized bones of dinosaurs have been major attractions at a variety of theme parks and many museums. They dominate the imagination of all ages with stories, movies, and constant archealogical discoveries of what the dinosaurs truly were since 1897. The search for dinosaur fossils has extended to every continent, including Antarctica, the first dinosaur discovered on this icy land amss was an Ankylosaurus found on Ross Island in 1986, however it was not until 1994 that antartic species like the cryolophosaurus ellioti were formally discussed in a scientific journal.

Current dinosaur "hot spots" include southern South America and China, which has yielded many newly discovered feathered dinosaurs.

What are dinosaurs?

Their generalized scientific classification comes from the greek words deinos that can translate to terrible and saura that means lizard. There are a plethora of varieties for every taste; herbivores, carnivores, some were bipedal, others could walk as easily on four legs or two, most official dinosaurs were terrestrial based creatures.

The earliest dinosaurs that have been discovered to date contain certain modified traits of an archosaurian skeleton. All dinosaurs so far discovered share these certain alterations leaving many to believe the archosaur may be one of the first ancestors of all dinosaurs. Some later groups of dinosaur features are more distinct and altered forms, but most are typical among all dinosauria. These familial traits are known as synapomorphies, the most common features are; small fourth and fifth digits on the hands, reduced digits on the feet, three main toes, a sacrum made by three or more connected vertebrae near the region where the pelvis attaches to the vertebral column, they also include open hip sockets with holes in the center, seperating them from other tetrapods.

Other features that are generally agreed to have been common in all dinosaurs are; short forelimbs, secondary palates that allowed dinosaurs to eat and breath at the same time, a rather straight femur and a femoral head. They had two pairs of holes in the temporal area of hte skull and their elbows pointed to the rear and knees pointed forward on the hind limbs. These specialized hip joints allowed an erect stance with the hind limbs placed beneath the body, most like mammals of today, rather than any current reptile. It allowed these large animals to move at a faster rate of speed with more accuracy and allowed many to become bipedal.

Dinosaurs are divided into several groups depending on the pelvic structure; The bird hipped dinosaurs known as ornithischia and lizard hipped dinosaurs scientifically referred to as saurischias. Ornithischias had a four pronged pelvic design, that consisted of a rear pointing pubis bone. The saurischias differences were three pronged pelvic bones and a pubis bone that was pointed forward, a design commonly found in birds.

Size and Shape

The only thing that is clear about dinosarus that as a group of like creatures they were large. The sauropods were by far the largest of the creatures in any time on the earth, but many other dinosaur classifications were much smaller than even the tiniest sauropod. However with the variance of evidience from the triassic period, the jurrasic periods and cretaceous periods suggest that generally dinosaurs averaged between the weight of a large bear through the size of an elephant; comparing the size difference against modern creatures, most existing today would be comparable to a large rodent. Even the smallest dinosaur was biggger than two thirds of all mammals currently known.


The largest and heaviest complete dinosaur discovered to date is a brachiosaurus. The specimen was uncovered in Tanzania around 1907, and is currently mounted for display at the Humboldt Museum in Berlin. It measures 38 feet tall and estimated to have weighed between 30,000 and 60,000 kg. The longest complete dinosaur to be discovered is a 89 foot long diplodicus discovered in Wyoming and displayed in Pittsburgh's Carnegie Natural History Museum. There are believed to have been larger dinosaurs, but this information is based on a small number of incomplete fossil samples; these include an Argentinosaurus guessed to be about six stories high, an appropriatly named supersaurus measured to be 130 feet long and the tallest is believed to be a carnivore known as a spinosaurus measuring in at a mere 60 feet and possibly weighing in at 9 tons. More well known giants of the dinosaur world are meat eaters such as the gigantosaurus, the mapusaurus and the childhood favorite, the ferocious tyrranasaurus rex. The smallest known dinosaurs to date are the microraptor, parvicurusorand the adorable saltopus, most averaging no more than two feet in length.

Behavior

Most of what is assumed about how these gigantic creatures behaved are based on the design of the creatures fossilized body, their habitat, the surrounding environment, and comparing how modern animals of similiar design behave, mostly associated with birds and crocodiles, which are believed to be the closest living relatives of dinosaurs some crocodiles existing at the same time.

The first evidence accepted as herding behavior was due to a group of 31 iguanadons that perished together in Bernissart, Belgium, believed to have fallen into a deep, flooded crevice, quickly drowing. A group of maisauras found in a nesting ground. It's believed that hadrosaurids and other like sauropods moved in huge herds similiar to modern herd animals, using the massive group to protect the young, safely migrate and defense from predators. This assumption is based on trackways found in places like Oxford, England, Isle of Skye in Northwest Scottland and across the atlantic ocean in places like Davenport Ranch, Texas and Browning, Montana.

Well known paleontologist Jack Horner discovered a Maiasaura nesting ground in Montana that demonstrated some dinosaurs would care for their offspring long after birth, believed to be a common association among ornithopods. Even the ferocious tyrannosaurus rex is now believed to have been a parental dinosaur, along with cretaceous period sauropods like the; patagonia, a 1997 discovery of a saltasaurus and even an oviraptor was discovered in a brooding position, comparable to a chicken like nesting technique, found in 1993, suggested it was keeping eggs warm. Due to these discoveries and comparisons to their possible relatives; birds and crocodiles, it's also believed they could communicate with their young.

Some dinosarus had crests and frills that would have been to, thin to be used for any sort of defense. So it's guessed these dinosaurs like the marginocephalians, some theropods and [[lambeosaruin]es would have used these decorative additions for attracting mates and aggressive displays basing these observations on the behaviors of modern reptiles and some birds. It's even been suggested they may have been used for vocalization, resonating sounds through hollow crests.

The most fantastic behaviorial discovery to date was in 1971. A velociraptor was uncovered fossilised in a battle with a protoceratops. The discovery proving many ideals that dinosaurs did often attack and eat each other. This belief in cannibalism was further demonstrated in 2003 with the discovery of toothmarks found on a majungatholus atopus uncovered in Madagascar.


Scientific Studies

Most all knowledge concerning dinosaurs comes from a variety of fossilized sources; bones, feces, trackways, gastroliths, feathers, skin impressions, some internal organs and the scant discovery of soft tissue, the most exceptional found from a theropod in Italy. We can also attribute current knowledges about these creatures from studies in physics, chemistry, biology and paleontology being a sub group of earth science. Evidence and new discoveries concerning dinosaurs are found on every continent of the earth, including antartica, suggesting that there was at one time a large continent called Pangaea, which is believed to have seperated during the triassic period.

A surge of activity began in the 1970's, triggered by the discovery of the vicious predator deinonychus possibly being a warmed blooded creature, contrasting the general image as cold blooded and sluggish creatures. The primary branch of dinosaur discovery is vertebrate paleontology with new discoveries in countries like; India, South America, Antartica and the stupendous discovery of well preserved feathered dinosaurs that further support the theory of birds being the most recent descendents of these mighty beasts. Many modern techniques such as cladistic analysis and dna sciences help to fill in the missing spaces of fractured or fragments of various fossilized discoveries.

Debates

The only thing most can agree on, is that they were large creatures, some of the more popular debates are.

Warm or cold blooded

One of the hottest debates going on since the 1960's is whether dinosaurs were cold blooded like most reptiles, or warm blooded mammals.

The earliest discoveries led paleontologists to originally believe they were ecothermic, cold blooded lizard types in their physiology. Cold blooded creatures that would have moved slowly and needed a large amount of time in the sun like many modern reptiles to keep their temperatures regulated. It was a dominat belief until 1968 when one of the first papers written suggesting they were endothermic was released by Robert T. "Bob" Bakker which influenced many paleontologists to reconsider their original theories.

The theory for their endothermic physiology is further supported by discoveries of dinosaurs existing in colder climates, including polar dinosaurs in Australia and Antartica, dinosaurs that had feathers that may have been used for insulation and modern science's ability to analyze blood vessel structures. These discovered within fossilized theropod bones further support the theory they were endothermic creatures. Their body structures suggest they were active and quick, and would have required an endothermic system. However the discovery of some sauropods suggest they were ecothermic, their structure and design suggesting slower creatures that would not require regulated warmth to survive, so this debate is still thriving among paleontologists of today.

An avian connection

There are many common features found between birds and many types of dinosaurs, mostly in theropods; the most famous of these is the archaeopteryx, but there have been many kinds of fossils recently discovered, further confirming this theory.

Feathers

This feathered dinosaur was first discovered in Solnhofen Limestone found in southern Germany in 1861. It's considered to be a transitional fossil that contains both the features of modern reptiles and birds. It's this discovery that started the debate if birds are direct descendents of dinosaurs or an entirely different species. It's so dinosaur like, that if there were no feathers it is could be mistaken for a compsognathus. Beginning in the 1990's even more varieties of feathered dinosaurs have been uncovered, offering stronger evidence of the close relations between dinosaurs and modern birds. Most are found in the Liaoning Province of Northeastern China. What makes these discoveries so spectacular is that feathers and other delicate skins are not often preserved, and may simply be unknown to many species of dinosaurs. However the feathered dinosaurs that have been preserved are; the Beipiaosaurus, Caudipteryx, Dilong paradoxus, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, Sinosauropteryx, and Jinfengopteryx. There are also a few dinosaur like birds that have been uncovered in Northern China, these are the [[dromaesauridea]s, which were heavily feathered and one of this family the cryptovolans are believed to have had the ability to fly.

Skeleton

The easiest association between the relation of the two creatures are feathers, however these missing links, also have similiar skeletal structures, which offer an important link for paleontologists that favor this theory.

Scientists like Gregory S. Paul believe that dromaesaurs may have actually evolved from birds, losing the ability to fly, but retaining feathers similiar to ostriches, emus and other ratites. Cladisitic analaysis helps lend confirmation to the theory of this relation, particularly with the discovery of maniraptors, who skeletal resemblances include the; neck, pubis, wrist, arm, pectoral girdles, shoulder blades, the clavical and the breast bones.

Reproduction

A suprising discovery from a tyrannasaurus rex provided more concrete evidence there's a relation between our birds and these extinct beasts. The fossil showed a special bone that female birds develop in their limbs in order to lay eggs. This medullary bone is rich in calcium and forms a layer inside the hard shells of their eggs; finding this same tissue lining the interior marrow of this dinosaur's hind limb suggests a similiar reproductive technique designated the tyrannasaur clearly a female.

Furthermore, a recently discovered dinosaur embryo was found without teeth. This suggested that some parental care was required to keep the young fed. The most practical assumption would be a form of reguriatation as demonstrated by modern birds feeding their own young.

Lungs

An investigation led by Patrick O'Connor from Ohio University found that large carnivorous dinosaurs had a complex system of air sacs, resembling those found in modern birds. The lungs of these theropods known to walk on two legs with bird like feet more than likely pumped air into the hollow sacs of their skeletons. The basic pulmonary design of flow through ventilations once thought exclusive to birds are now being found in non avian theropods, it' s an exciting discovery, further confirming that there may be a shared ancestor.


Sleeping and the heart

The current use of computerized tomography had been used to scan dinosaur chest cavities. In 2000 this technique was able to find remnants of four chambered hearts in dinosaurs, similiar to many modern mammals and birds. A recently discovered troodontidae in China, demonstrated that dinosaurs slept with their heads tucked under their arms, like many birds do today.

Gizzards

More evidence that birds and dinosaurs are closely related is the discovery they used gizzard stones. Birds swallow stones to aid in digesting and breaking down food and hard substances once they enter their stomach. When related to dinosaur finds they are called gastroliths. Paleontologists have used these stones to efficiently trace possible migration routes. Finding many stones were picked up and swallowed at one location and then carried to another.


Cloning dinosaurs

Many discuss the theory that some scientists could use current technology to recreate dinosaurs. Michael Chrichton stirred this ideal in his book Jurrassic Park, suggesting blood used from mosquitos locked in amber could be used to recreate an actual dinosaur. However dna decays over time when exposed to air, water, or radiation, rendering it impossible to recover any useful samples. Compounded by the fact that there are no closely enough related species or known environment for incubation, the idea of recreating dinosaurs is still in a science fictional stage.

There have been a few rare cases where it was claimed viable dinosaur dna was extracted on two seperate occassions, but closer inspection by peers could not confirm either report, however with the reanalyzing of published dna sequences from a cretaceous period fossilized ege, had not completely elimnated the possibility.

Soft tissue

Currently the best examples of soft tissue impression left by a fossilized dinosaur was discovered in Petraroia, Italy, in 1998. It was described as a small, very young Coelurosaur. The tiny fossil includes portions of intestines, the colon, the liver, some muscles, and the windpipe of this tiny dinosaur.

An article printed in the March 2005 Science Journal by Dr. Mary Higby Schweitser announced the discovery of flexible material, possibly soft tissue inside the leg bone of a 68 million year old tyrannosaurs rex, that was discovered in the Hell Creek Formation in Montana. The tissue was successfully rehydrated by her team. Allowing the discovery of intact structures including blood vessels, bone matrixes and bone fibers. Further analysis showed the tissue had maintained it's microstructures at a cellular level. The nature and composition of the material is not yet understood, so the possibility is ongoing.

Extinction theories

A sudden and mass extinction of non-avian dinosaurs, that occurred about 65 million years ago, still stands as one of the most enigmatic mysteries for fans and paleontologist alike. While there were a great many other prehistoric dinosaur like animals that became extinct at this time, such as; mosasaurs, plesiosaurs, pterosaurs, a variety of turtles, some crocodiles, and most birds, along with and many groups of mammals, dinosaurs are by far the most fascinating of these losses. What caused this large scale extinction has been studied since the 1970's, only a few several related theories have stood the test of science, supported by many of the most respected paleontologists.

A massive asteroid

This collision theory was first proposed by Walter Alvarez in the late 1970s. It suggests that at the end of the cretaceous period a giant asteroid impacted with the Yucatan Peninsula about 65.5 million years ago. Alvarez suggested that the resulting increase of iridium levels verified around the world in rock stratum from that time was evidence of the impact. The supporting evidence for this theory suggests a 10 km wide asteroid hit in the area, resulting in the creation of the Chicxulub Crater, causing global conditions that led to a mass extinction. Scientists are unable to decide whether dinosaurs were thriving or on a decline before the impact. One subtle deviation from this theory suggests that the meteorite resulted in a long and unnatural drop of Earth's atmospheric temperature, another theory is that it resulted in an unnaturally hot heat wave.

However an inability to decide the length of this extinction from the fossil record alone, several models have been designed that suggest the extinction was quick and painless. Many scientists who support this theory suggest that the massive impact caused direct extinction because of directe impact and indirectly by cooling the world when the debris generated blocked the warmth of the sun.

Multiple collisions or the Oort cloud

Similar to Alvarez's impact theory (which involved a single asteroid or comet), this theory proposes that a stream of comets was dislodged from the Oort cloud due to the gravitational disruption caused by a passing star. One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.

Environment changes

At the peak of the dinosaur era, there was no polar ice, sea levels are estimated to have been anywhere from 330 to 820 feet higher than they are today. The planet's temperature is believed to have been much more uniform, with only 25 degrees Celsius separating average polar temperatures from those at the equator. The atmosphere occuring during age of dinosaurs was as vastly different. Carbon dioxide levels were 12 times higher, oxygen formed 32 to 35% of the atmosphere, but by the late Cretaceous period, the environment began to change dramatically. Volcanic activity was decreasing, leading to a cooling down of temperatures whie the high levels of carbon dioxide lowered. Oxygen levels in the atmosphere started to fluctuate, eventually falling. These changes resulted in some scientists to began hypothesizing it led to their extinction. If the dinosaurs did have bird like repiratory systems, it would have been difficult for them to breath in these changes, given the demand for high oxygen levels their enormous size would have required, exlplaining why it was the smaller mammals that survived.

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