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Enfin, et comme le précise la NASA, la fonte est d'autant plus rapide que la fragmentation est plus importante.La fonte s'effectue par la surface exposée et non pas par le coeur.Mantell acquired a more complete specimen in 1834 which was a partial individual on a bed of rock. Dubbed the Maidstone skeleton (after where it was recovered) this specimen also included Iguanodon's famous thumb spike, although Mantell's idea was very different. Mantell believed the spikes correct place was actually on top of the end of Iguanodon's snout. The overall body shape of early restorations was also very iguana-like with a low quadrupedal body, fore and hind limbs being the same size as one another and a long trailing tail. This depiction continued until Richard Owen began work upon reconstructing and classifying these animals. Owen was a staunch supporter of creationism and rejected the teachings of transmutation, the theory that was the precursor to Charles Darwin's theory of evolution. Owen created the dinosaur group from Megalosaurus, Iguanodon and Hylaeosaurus, but rather than depicting them as reptiles, Owen perceived them to be more mammal-like. Under Owen's thinking this was an argument against evolution as mammal-like creatures could not evolve from reptiles (something that today can actually be proven by the existence of synapsids and the later therapsids like Thrinaxodon as well as later forms like Megazostrodon). Rather than being seen as lizards, dinosaurs were now envisioned as being elephantine creatures with scaly skin and mouths full of sharp teeth. The culmination of this vision were the Crystal Palace dinosaur sculptures built from concrete sculpted around brick and steel frames by Benjamin Waterhouse Hawkins, who was guided by Owen in their construction. Another famous story associated with these sculptures is that Hawkins held a dinner party within the body of the standing Iguanodon sculpture before it was finished, however this party actually took place within the mould that was used to cast the sculpture. The exact discovery of Iguanodon has become something of a popular story, but with successive retelling some of the details have become a little blurred. The main area of this is just who discovered the first Iguanodon teeth, one Gideon Mantell, or his wife Mary Ann. Gideon Mantell was a practising obstetrician and the popular version of this story is that his wife Mary Ann discovered the first teeth in a quarry in Whiteman's Green, Sussex while he was visiting a patient in 1822. However a statement by Gideon Mantell himself in 1851 stated that it was he who had found the original teeth. Mantell's notes dating back to 1820 also show that he had discovered other material as well as different teeth from what we would call today a carnivorous theropod. There is also a mention of the discovery of teeth that seem to have belonged to a herbivore. This is why who discovered the Iguanodon teeth varies depending upon who is telling the story. - On the ornithoidichnites of the Wealden - Quarterly Journal of the Geological Society of London 10: 456–464. Fossil representation: Many specimens resulting in reconstruction of complete examples. Iguanodon has a firm place within dinosaur history books, not just because of the large expanse of fossil material attributed to it, but because it was the second dinosaur to ever be identified and named. The first dinosaur was actually Megalosaurus which was named a year earlier, and back then the term dinosaur didn't even exist. Iguanodon as a living animal Today Iguanodon is usually depicted as a primarily quadrupedal animal that could comfortably shift to a bipedal posture for high browsing or possibly other purposes. The main argument for this comes not from the overall body shape but the actual construction of the forelimbs. Firstly these limbs are about three quarters of the total length of the hindlimbs which would result in a fairly comfortable walking gait when fully extended, while the elbow could still be bent to bring the head closer to the ground for easier browsing on low vegetation. - Journal of Vertebrate Paleontology 23 (Supplement to Number 3): 45A. The next bit of Iguanodon's forelimb specialisation is the hand itself, specifically the five digits. Easiest thing to do here is if you look at the back of your hand and open your fingers up so that you can easily see all five of your digits (four fingers and a thumb). The centre three digits of Iguanodon's hand were robust and packed close together. This would be like you putting your three central digits (index, middle and ring fingers) close together so that they were one. As you may now appreciate this results in an inflexible portion of the hand, but in Iguanodon this was not a problem as it provided the main weight bearing area of the limb when Iguanodon was walking on all fours. This leaves the thumb which in Iguanodon was just a single large spike. The remaining fifth digit (your little finger, or 'pinkie') was actually very flexible to the point of being prehensile. Easiest way to describe what prehensile means is if you look a picture of a chameleon you may notice that its tail is curved around the branch it is holding on to, this is an extreme case of a prehensile tail. The little finger of Iguanodon however, probably could not flex to this extreme. The finger was however capable of wrapping itself around a high piece of vegetation so that Iguanodon could pull it down and feed upon parts of a plant that would otherwise have been out of reach.
La tempête a arraché un grand morceau de la mer de glace au Nord de la mer de Chukchi et l'a repoussé vers le Sud dans les eaux plus chaudes qui l'ont complètement fondu.In 1822 the herbivore teeth were submitted to the Geological Society of London, but the response was not positive as the members declared the teeth to belong to either a rhinoceros or possibly a fish. Interestingly one of these members was William Buckland, who under two years later would actually go on to name the first dinosaur, Megalosaurus. Just over a year after this in 1823, Charles Lyell showed some of the teeth to Georges Cuvier, A French naturalist who used techniques of comparative anatomy to identify fossil animals. One of Cuvier’s most famous successes was that he was the first person to correctly identify the pterosaur Pterodactylus as a flying reptile. Initially Cuvier had the same conclusion as the Geological society in that the teeth were of a rhinoceros, but the next day he actually doubted that interpretation. Unfortunately Lyell's communication to Mantell only contained Cuvier's initial opinion of the teeth, something that resulted in Mantell putting the teeth to one side. William Buckland's 1824 description of Megalosaurus sent shock waves throughout the scientific community and caused many to start thinking about the kinds of animals that once lived and how they could be different. Buckland himself visited Mantell soon after to look at his collection of bones and realised immediately that Mantell had a creature that appeared to be similar to Megalosaurus. The idea of giant 'lizards' like Megalosaurus being carnivores was still fresh in the head however, and Buckland still insisted that what Mantell had was a carnivore and not a herbivore. At least encouraged by Buckland's identification of the bones, Mantell sent the herbivore teeth to Cuvier so that he may have a second opportunity to examine them. Cuvier remembered his doubts after initially declaring the teeth to be those of a rhinoceros, and this time his interpretation was very different. Cuvier replied and confirmed to Mantell that the teeth were reptilian, and could be those of a herbivore. On top of this Cuvier printed a public retraction of his first interpretation and confirmed that he now believed the teeth to be reptilian, not mammalian. Georges Cuvier was a highly respected scientist in natural history circles and when he spoke, others stopped and listened. - Early and "Middle" Cretaceous Iguanodonts in Time and Space. The answer for this question actually goes back to when the Iguanodon was within its egg. Eggs have to form a protected space where an embryo can develop, while also at the same time be as small as practically possible so that the egg can pass out of the mothers body. If Iguanodon (and other dinosaurs with stiff tails) had bones to support the tail (caudal) vertebrae then the egg would have to be elongated to fit because bones can't bend. Tendons however can bend, which means the tail could curve around the developing embryo so that it could fit within the smallest space possible. Upon hatching Iguanodon's tail would probably have been quite limp and droopy but as the tendons stiffened with age, perhaps as soon as a few days or weeks after hatching, the tail would begin to resemble an adults. Now that the individual in question did not need a flexible tail the tendons would slowly turn to bone, making the supporting fixture of the vertebrae permanent. Probably the main advantage of having a stiffened tail like this is that it would form a counter balance that would have allowed Iguanodon to more easily switch between quadrupedal and bipedal postures. - On the ornithischian dinosaur Iguanodon bernissartensis of Bernissart (Belgium). The famous teeth of Iguanodon were only present towards the rear of the jaws with the teeth of the lower jaw arranged so that they would rub against the internal sides of the upper teeth. This rubbing motion would create a shearing action similar to how a pair of scissors work, something which enabled Iguanodon to bite through tougher vegetation. As with all dinosaurs these teeth were constantly replaced throughout the animals entire life, although Iguanodon seems to have had only one spare replacement for each tooth at a time. Later forms of large ornithopods like the hadrosaurs would develop several replacement teeth. Iguanodon most probably also had cheeks that prevented food from falling out of the sides of the mouth as it was bearing mashed between the teeth. - Mmoires de l'Institut Royal des Sciences Naturelles de Belgique 178: 1–105. - On the anatomy of Iguanodon atherfieldensis (Ornithischia: Ornithopoda).