The scientific question of within which larger group of animals birds evolved has traditionally been called the ' origin of birds '. The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated during the Mesozoic Era. A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany.
Birds and extinct non-avian dinosaurs share many unique skeletal traits. There are even very small dinosaurs, such as Microraptor and Anchiorniswhich have long, vaned arm and leg feathers forming wings.
The Jurassic basal avialan Pedopenna also shows these long foot feathers. Paleontologist Lawrence Witmer concluded in that this evidence is sufficient to demonstrate that avian evolution went through a four-winged stage. Although the origin of birds has historically been a contentious topic within evolutionary biologyonly a few scientists still dispute the dinosaurian origin of birds, suggesting descent from other types of archosaurian reptiles.
Within the consensus that supports dinosaurian ancestry, the exact sequence of evolutionary events that gave rise to the early birds within maniraptoran theropods is disputed. The origin of bird flight is a separate but related question for which there are also several proposed answers. Scientific investigation into the origin of birds began shortly after the publication of Charles Darwin 's On the Origin of Species.
Christian Erich Hermann von Meyer described this feather as Archaeopteryx lithographica the next year.Graco modes jogger 2.0 travel system haven
Biologist Thomas Henry Huxleyknown as "Darwin's Bulldog" for his tenacious support of the new theory of evolution by means of natural selection, almost immediately seized upon Archaeopteryx as a transitional fossil between birds and reptiles.
Starting inand following earlier suggestions by Karl Gegenbaur and Edward Drinker Cope Huxley made detailed comparisons of Archaeopteryx with various prehistoric reptiles and found that it was most similar to dinosaurs like Hypsilophodon and Compsognathus. Like Cope, Huxley proposed an evolutionary relationship between birds and dinosaurs. Although Huxley was opposed by the very influential Owen, his conclusions were accepted by many biologists, including Baron Franz Nopcsa while others, notably Harry Seeley argued that the similarities were due to convergent evolution.
A turning point came in the early twentieth century with the writings of Gerhard Heilmann of Denmark. An artist by trade, Heilmann had a scholarly interest in birds and from toexpanding on earlier work by Othenio Abel published the results of his research in several parts, dealing with the anatomy, embryologybehavior, paleontology, and evolution of birds. Like Huxley, Heilmann compared Archaeopteryx and other birds to an exhaustive list of prehistoric reptiles, and also came to the conclusion that theropod dinosaurs like Compsognathus were the most similar.
However, Heilmann noted that birds had clavicles collar bones fused to form a bone called the furcula "wishbone"and while clavicles were known in more primitive reptiles, they had not yet been recognized in dinosaurs. Since he was a firm believer in Dollo's lawwhich states that evolution is not reversible, Heilmann could not accept that clavicles were lost in dinosaurs and re-evolved in birds.
He was therefore forced to rule out dinosaurs as bird ancestors and ascribe all of their similarities to convergent evolution. Heilmann stated that bird ancestors would instead be found among the more primitive " thecodont " grade of reptiles.Section 4; 22 p.
Chris Lele, Magoosh Tutor. Nova's GRE Prep. Toggle navigation Magoosh. The passage suggests that which of the following Biologists generally agree that birds and dinosaurs are somehow related to one another. The agreement ends there. Hypotheses regarding dinosaurian and avian evolution are unusually diverse—and often at odds with one another. Confusion consequently reigns over a broad spectrum of unanswered questions dealing with avian origins and the biology of dinosaurs and early birds.
This confusion has been exacerbated by a paucity of serious attempts to synthesize and evaluate available data on the details of avian and dinosaurian evolution. Consequently, both the public and the scientific community have often been misled by widespread dissemination of sensational but weakly founded hypotheses.
The passage suggests that which of the following could help remedy the problem described in the final sentence lines ?
An article written by a biologist for the general public summarizing current theories about avian and dinosaurian evolution, A close examination of available data on avian and dinosaurian evolution, A new hypothesis regarding the connection between avian and dinosaurian evolution.
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Origin of birds
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Your score will improve and your results will be more realistic. Is there something wrong with our timer? Let us know! I'll try it now.My maths book suicided because it had lots of problems in it Thanks m4 maths for helping to get placed in several companies. I must recommend this website for placement preparations. Previous Question: Questions 1 and 2 are based on this passage A portrait type that appeared with relentless frequency in eighteenth-century England is the familiar image of a gentleman poised with one hand inside his partially unbuttoned waistcoat.
Standard interpretations of this portrait posture offer observations of correspondence—demonstrating either that it mirrors actual social behavior or that it borrows from classical statuary. Such explanations, however, illuminate neither the source of this curious convention nor the reason for its popularity. Still, there were other ways of comporting the body that did not become winning portrait formulas.
Question 1 In the context of the passage as a whole, the primary function of the sentence in lines is to A emphasize the influence of a particular social class on the conventions of eighteenth-century English portraiture B account for the origin of a particular type of behavior frequently represented in eighteenth-century English portraiture C acknowledge a historical basis for two competing hypotheses about a particular portrait type D question the relevance of certain evidence frequently cited in support of an explanation for a particular portrait type E concede that one explanation for the prevalence of a particular portrait type has a basis in fact For the following question, consider each of the choices separately and select all that apply.
Question 2 Which of the following might provide an explanation for the popularity of hand-in portraits that would satisfy the author of the passage? While chocolate was highly esteemed in Mesoamerica, where it originated, its adoption in Europe was initially slow.
However, while Spaniards did put sugar, which was unknown to indigenous Americans, into chocolate beverages, this additive was not completely innovative. Mesoamericans were already sweetening chocolate with honey, and the step from honey to sugar—increasingly more available than honey because of expanding sugar plantations in the Americas—is a small one.
Likewise, although Spaniards adjusted Mesoamerican recipes by using European spices, the spices chosen suggest an attempt to replicate harder-to-find native flowers. There is no indication the Spaniards deliberately tried to change the original flavor of chocolate. Question 1 The author of the passage refers to the use of honey primarily to A identify the origins of an additive previously untried by Europeans B present an example of a product that was unknown to Europeans C correct the misapprehension that Mesoamericans used a sweetener that was not available in Europe D provide an example of an ingredient that was in the process of being displaced by a substitute E explain why the Spanish use of sugar in chocolate was not a sign of a need to transform chocolate Question 2 Which sentence presents a misconception that the passage challenges?
Read Solution 0 :. Login Register Resend. Congo, Rep. Barts St. M4Math helped me a lot. Vipul Chavan 5 Months ago. All rights are reserved to m4maths.You've probably been told dragons are mythical beasts. After all, a flying, fire-breathing reptile could never exist in real life, right?
It's true no fire-breathing dragons have ever been discovered, yet flying lizard-like creatures exist in the fossil record. Some may be found in the wild today. Take a look at the science of winged flight and possible mechanisms by which a dragon might even breathe fire. The question is whether they could be large enough to prey on people and livestock.
The answer is yes, at one time they were! The Late Cretaceous pterosaur Quetzlcoatlus northropi was one of the largest known flying animals. Estimates of its size vary, but even the most conservative estimates place its wingspan at 11 meters 36 feetwith a weight of around to kilograms to pounds. In other words, it weighed about as much as a modern tiger, which can certainly take down a man or goat.
There are several theories about why modern birds aren't as large as prehistoric dinosaurs. Some scientists believe the energy expenditure to maintain feathers determines size.
Others point to changes in the Earth's climate and atmospheric composition. While dragons of the past may have been large enough to carry off a sheep or human, modern dragons eat insects and sometimes birds and small mammals. These are the iguanian lizards, which belong to the family Agamidae.
The family includes domesticated bearded dragons and Chinese water dragons and also the wild genus Draco. Draco spp. Really, Draco is a master of gliding. The lizards glide distances as long as 60 meters feet by flattening their limbs and extending wing-like flaps. The lizards use their tail and neck flap gular flag to stabilize and control their descent. You can find these living flying dragons in South Asia, where they are relatively common.
The largest only grows to a length of 20 centimeters 7. While European dragons are massive winged beasts, Asian dragons are more akin to snakes with legs. Most of us think of snakes as ground-dwelling creatures, but there are snakes that "fly" in the sense they can glide through the air for long distances. How long a distance? Basically, these snakes can remain airborne the length of a soccer field or twice the length of an Olympic swimming pool!
Asian Chrysopelea spp. Scientists have found the optimal angle for a serpentine glide is 25 degrees, with the snake's head angled upward and tail downward. While wingless dragons couldn't technically fly, they could glide a very long distance.
If the animal somehow stored lighter-than-air gases, it might master flight.
To date, no fire-breathing animals have been found. However, it wouldn't be impossible for an animal to expel flames. The chemicals mix in the air and undergo an exothermic heat-releasing chemical reactionessentially spraying the offender with irritating, boiling hot fluid.
When you stop to think about it, living organisms produce flammable, reactive compounds and catalysts all the time. Even humans inhale more oxygen than they use. Hydrogen peroxide is a common metabolic by-product. Acids are used for digestion. Methane is a flammable by-product of digestion. Catalases improve the efficiency of chemical reactions. A dragon could store the necessary chemicals until it's time to use them, forcefully expel them, and ignite them either chemically or mechanically.Ask your average paleontologist who is familiar with the phylogeny of vertebrates and they will probably tell you that yes, birds avians are dinosaurs.
Using proper terminology, birds are avian dinosaurs; other dinosaurs are non-avian dinosaurs, and strange as it may sound birds are technically considered reptiles.
Overly technical? Just semantics? Perhaps, but still good science. In fact, the evidence is overwhelmingly in favor of birds being the descendants of a maniraptoran dinosaurprobably something similar but not identical to a small dromaeosaur. What is this evidence? We'll spare you the exhaustive amount of available cladistic studies; those alone would make a large book if compiled. Jacques Gauthier, during his time as a graduate student of Professor Kevin Padian here at Berkeley, did his dissertation research on this subject, creating the first well accepted, detailed phylogeny of the diapsids.
His work provided strong, compelling support for the theory that birds are theropod dinosaurs. If we look back into the history of the issue, it is apparent that many comparative anatomists during the 16th through 19th centuries noticed that birds were very similar to traditional reptiles.
Inshortly after the publication of Charles Darwin's influential work On the Origin of Species By Means of Natural Selectiona quarry worker in Germany spotted an unusual fossil in the limestone of the Solnhofen Formation late Jurassic period. This fossil turned out to be the famous 'London specimen' of Archaeopteryx lithographica.Provost's Lecture: Douglas J. Futuyma on Evolutionary Biology
It was a beautiful example of a "transitional form" between two vertebrate groups traditional reptiles and birds ; just what Darwin expected would eventually be found. Archaeopteryxgenerally accepted as being the oldest known bird, is an important link between birds and other coelurosaurs that has helped to illuminate the evolutionary history phylogeny of the group.
It is now widely held to be the ancestor of all living birds; this is a common misconception. In fact, recent expeditions in China, Mongolia, Madagascar, Argentina, and elsewhere may uncover dinosaurs that usurp the "urvogel" status of Archaeopteryx. Many scientists, including Thomas Henry Huxley a staunch supporter of Darwinsaw incredible similarities between birds and the theropod dinosaurs especially the coelurosaurs.
Others since Huxley also hinted at the striking resemblances.Licitatii terenuri moldova
Walker's "crocodylomorph" ancestor and G. Heilman's "thecodont" ancestor held sway for most of the 19th and 20th century, or else birds were simply dismissed as originating from some unknown reptile that didn't matter anyway.
That would change. Ostrom 's description of Deinonychus antirrhopus and its similarities to Archaeopteryx was the major step: his work since the 's has provided the impetus for a paradigm shift in paleontologists' visions of the origin of birds and the evolution of flight.
Gauthier's cladistic work in the mid's provided the best analytical systematic support for the theory that birds are the descendants of dinosaurs. Several independent analyses by other scientists have repeatedly upheld Gauthier's results. Today the important issue seems to be specifically which dinosaurs are the closest relatives of birds.
The controversy over the dinosaurian status of birds had its heyday in the 's, but the coverage of the issue today by the press might make you think it was still a problematic matter. For those that have actually seen the relevant specimens and considered all of the relevant data which is a basic procedure for any scientistit is becoming increasingly difficult to draw the line between "bird" and "non-avian dinosaur".
Some researchers today do not agree that dinosaurs gave rise to birds, and are working to falsify this theory, but so far the evidence for the theory has swamped their efforts. If they were to conclusively establish that birds are more likely descended from another group Crocodylomorpha, the group containing crocodiles, has been suggestedthat would be a major upheaval in our knowledge of phylogeny. One single well-preserved fossil bird unequivocably of Triassic age might shed some doubt on the theory of the maniraptoran affinities of birds.
That would be a major find.Nazi x planes
Some bird-like fossils have been presented as Triassic birds, but so far have not held up under peer review. Such is the dynamic nature of science. So you may be thinking now, what are these striking resemblances between birds and other dinosaurs? The ratite birds, three of which are pictured in this article, are quite similar to theropod dinosaurs.
Some of the similarities may be superficial, but others may be too obvious to dismiss, and in any case all available data must be considered. We'll start with the "reptilian" similarities of birds. Like all other reptiles, birds have scales feathers are produced by tissues similar to those that produce scales, and birds have scales on their feet.Sylvia needs to be a social butterfly and make some friends in order to have any type of political power in the house.
Good competitors have crumbled in the elimination arena. Sylvia has thrived in those situations. A good performance for Sylvia would be making it to the halfway point having seen no eliminations and not losing to anyone perceived as weaker than her. If Sylvia lost to Jemmye or Natalie, it would be a bad season for her. In terms of her chances of winning.
They are almost non-existent. She struggled mightily in the mini final on Invasion. There is a path for Sylvia to make the final and make money. She needs to do average in the challenges, wait for the fat to be trimmed, and then hope for Kailah and Cara Maria to go to war against each other. Let the powerhouses fight each other, sneak under the radar and take their spot in the final.
SportsThe ChallengeMTVTelevisionReality TVBlockedUnblockFollowFollowingAllan Aguirre21 years old. See the latest listings of ballet and dance performances in New York City, including schedules and venues. The filmmaker Charles Atlas, who returns to filming dance after a ten-year hiatus, was a frequent and innovative Cunningham collaborator.
Are Birds Really Dinosaurs?
And Silas Riener and Rashaun Mitchell were two of the most striking performers in the final iteration of the company. In 1932, for example, he created sets and costumes for the American avant-garde dancer and choreographer Ruth Page. Afterward, Dakin Hart, a Noguchi scholar, and Meglin will hold a discussion. Harkness became home to the first faculty of modern dance in the United States, and its ranks over the years have attracted many pioneers in the field.
Every year, the Harkness Dance Festival and various performance series bring choreographers and performers at various stages of their careers to Buttenwieser Hall to celebrate the history and future of modern dance. The production, a miniature version of the story, is only an hour long, performed in front of an ingenious set piece that transforms itself over the course of the evening.
The British naval administrator and parliamentarian Samuel Pepys, for example, went on at great length in his journals about everything, from his bladder stones and his sexual escapades to what he had for lunch.Acche acche cartoon gudiya wale
When Merce Cunningham died, in 2009, his collaborators spun off in all directions, like planets in a solar system that has lost its sun.
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