Discussion of everything related to the Theory of Evolution.
The evolution of feathers is a good subject to discuss.We know that reptiles are cold blooded but the evolution of primitive feathers in dinosaurs might tell us that the dinosaurs were evolving into warm blooded species.Let us arrange the order of feather formation as follows:
1 The evolution of hair like structures in dinosaurs ex:Sinosauropteryx
2 These hairs might have evolved to bristles or even a down feather.
3 These down feathers might have evolved to primitive feathers leading to the mordern one.
The hair like forms might be used as insulators,the down feathers might show us the evolution of warm blooded species,the primitve feathers might have been used for providing lift or just staying in air for few seconds,the mordern feathers might have been aerodynamically designed,for camouflage,etc.
At some point the shafts of these structures needed to become hollow as well, adding a little more structural complexity.
When looking at archeopteryx and other fossils, don't just look at the feather imprints, look at the structure of the skeleton. In archeopteryx the collar bone and shoulder girdle are shaped to accomodate a wider range of motion than you would see in other clear-cut dinosaurs.
What did the parasitic Candiru fish say when it finally found a host? - - "Urethra!!"
Really? I wasn't aware of that! So archaeopteryx may not have been a true bird after all? Interesting.
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Absolutely. While it had some ancestral bird characteristics, it is far from a true bird. Some people think it had a limited capacity for flight. I'm of the opinion that it used its "wings" for buoyancy while running and for capturing prey (also insulation, protection of young, intimidation displays, etc). I don't think it flew. Perhaps it glided. A key characteristic of birds is the keeled breast-bone. Interestingly enough, pterodactyls independently evolved keeled breast-bones before they went extinct.
The keeled breast bone is necessary to attach the large amount of muscle required for powered flight. Archeopteryx lacks a keel, and many other avian features.
This doesn't mean that it isn't a proto-bird though. My professor refers to it as a dino-bird, somewhere in between the two classifications.
You're right. If it didn't have a keeled breastbone, it couldn't have large enough breast muscles to fly, although I think it could've glided. Don't forget that it also had teeth, a feature lacking in every modern bird. All of this makes it a very hard animal to classify, but perhaps dino-bird is as accurate as we can get.
What do you think about dinosaur metabolism? Do you think they were ectothermic (cold-blooded) or endothermic (warm-blooded)? Given their active lifestyles, I think most of them had to be at least partially endothermic. Most scientists used to think dinosaurs were as cold-blooded as the reptiles they came from, but I think many researchers are starting to drift the other way and saying that at last some, if not all, were probably warm-blooded. What do you think?
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Alex the dinosaurs first evolved would have been cold-blooded as during the triassic period the climate was dry but during the jurassic and cretaceous period the climate was quite cool this might mean the dinosaurs in the above periods might have been worm blooded.But still sails were present in ourangosaurs,spinosaurs,etc.This means they were cold blooded.Leaellynasaurus was probably warm blooded as it lived in antartica and deinonychus were fast moving dinosaurs and hence they might have been warm blooded.
Alex you said that dinosaurs donot fit in to reptiles or birds so they must be put into a seperate class I think this is true let me but some points to support Alex
1The skin of dinosaurs had bony lumps not epidermal scales but later dinosaurs had small hairs,feathers.
2 Some dinosaurs were cold blooded Ex:Ourangosaurs,Spinosaurs,etc.Some dinosaurs were warm blooded Ex:deinonychus,leallysaura,etc.
3 Some dinosaurs had three or four toes pointing foward and one backwards like birds Ex:Allosaurs,T-rex,etc.We must note that the theropods are suspected to be birds ancestors.
4 We must notice that dinosars walked in upright position not like the lizard do today.
5 Dinosaurs had two different hips one was lizard hipped the other bird hipped.The lizard hipped dinosaurs were the ones that evolved to birds.So the bird hippied dinosaurs did not have much relation with birds.
6 The presence of beak in the case of Iguanodon and ceratopsians donot have any relation with the beaks of birds as they were all bird hipped dinosaurs.
Many such points can be listed to support what Alex said.
A part of a fossil dating back some 130 million years was foun in China. It's name is Confuciusornis dui . [Archaeopteryx which dates to 150 million years ago, had no beak but rather a very reptilian jaw with teeth.]This bird was more advanced than Archaeopteryx in that it had a beak but was less advanced in that it had two small openings in the rear of its skull very similar to the reptile progenitors of birds.C. sanctus is the cousin of this reptile.both species bore two long tail plumes indicating the sexes differed significantly from each other. Like its cousin, the new bird C. dui also grew asymmetric wing feathers characteristic of all modern flying birds. Ostriches and other birds that can't fly well sprout nearly symmetric feathers incapable of creating an airfoil and hence lift.Some other scientists had speculated that Confusciusornis was a ground-living predator whose beak may have been hooked like a hawk .What do you say guys?
Last edited by David George on Fri Mar 10, 2006 7:50 am, edited 2 times in total.
Sounds interesting, and certainly a more likely candidate for the ancestor of birds than Archaeopteryx. Of course it still might not be. Did it have a keeled breatbone? Can you provide a website?
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The types of non-avian theropods with confirmed furculae are dromaeosaurids, oviraptorids, tyrannosaurids, troodontids coelophysids and allosauroids.Yes C. dui did have a fused v shaped furcula.I did not find any web site for C. dui.only this gave little information http://www.bowdoin.edu/~dbensen/Dinosau ... isdui.html you can search about C. sanctus in the same web site especially the links.The picture is really good wht do you say.Now let us not forget about the beak.The keratin found in the modren birds beak and the modern birds leg are different.
just posting an image to show the evolution of birds.
The fossilized remains of a tiny bird has provided evidence that birds flew as nimbly 115 million years ago as their descendants do today, solving a major puzzle in the evolution of flight in birds. The fossilized bird, named Eoalulavis hoyasi, was found entombed between two slabs of rock in a limestone quarry in central Spain. The fossil was so perfectly preserved that the bird's feathers and its last meal of tiny shrimp can be seen, the science journal Nature reported August 1, 1996.
About the size of a goldfinch, the bird sports a tuft of feathers technically known as an alula, or bastard wing, that would have helped it stay aloft at slow speeds. Airplanes use a similar device, called leading-edge flaps, to keep from crashing when they land. Eoalulavis is the most primitive bird found with an alula, which would have allowed it to fly between tree branches as effortlessly as a sparrow, according to Luis Chiappe, one of seven paleontologists who described the fossil in the Nature article.
The bird, which lived during the Cretaceous Period (about 138 million to 65 million years ago), provides the first evolutionary explanation for the aerodynamic wing structure of modern birds. Most paleontologists agree that birds evolved from small, meat-eating dinosaurs like the Velociraptor, which ran along the ground, snatching up their prey in their outstretched claws. From there, many paleontologists believe, it was a short jump in evolution to the Archaeopteryx, the oldest known bird, which lived about 150 million years ago. Many scientists believe Archaeopteryx probably flapped and glided, but the ancient bird is not believed to have had an alula.
The fossil of the Eoalulavis provides scientists with the next piece of the evolutionary puzzle. Researchers concluded that some 30 million years after the Archaeopteryx, at least one group of early birds had developed the feathery alula and were able to fly easily. That same feature is now shared by all flying birds today.
The alula, a tuft of feathers attached to each side of the outer wing bones, enabled the Eoalulavis to brake its flight without creating a burst of turbulence in the air above its wings, which would cause it to crash to the ground. This would allow it to fly and maneuver at low speeds. The bird also had claws suited for perching in trees.
Eoalulavis hoyasi, which means "dawn bird with a bastard wing from Las Hoyas," was discovered at a fossil site in Cuenca province, where a freshwater lake existed millions of years ago. The bird may have hunted by wading in shallow water the way plovers and other shorebirds do today. The fossil, found by José Sanz, a paleontologist at the Universidad Autonoma de Madrid, provides the first direct evidence of this kind of aquatic bird life.
Eoalulavis belonged to the group Enantiornithes, which died out at about the same time the dinosaurs went extinct-65 million years ago. Modern birds are descended from another group, the Neornithes, which first appeared about 65 million years ago.
http://people.eku.edu/ritchisong/554notes2.html you can know about the evolution and the aerodynamics in this web site
http://www.dinosauria.com/jdp/jdp.htm you might be interested in this web page Alex.
"Nothing in biology makes sense except in the light of evolution"
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