Now, there are some, known as BANDits, who contest this fact yet (as we shall see) have little to no evidence to support an alternative hypothesis on the evolution of birds.
Let us start with what defines a Bird.
According to Wikipedia (a trustworthy source when it comes to basic science) Birds are characterized as having:
*feathers
*high metabolisms
*toothless beaks
*hollow bones
and lay hard-shelled eggs.
Now, what defines a Dinosaur? This took a little more digging, I'll tell you!
According to Bakker, Wikipedia, and a few other sources from whom I've drawn in the past, a Dinosaur's a Dinosaur when:
*It has hollow bones
*Has a high metabolic rate (as supported by analysis of bone growth and oxygen isotopes in the teeth)
*a gracile, S-shaped neck
*Hinged ankles
*It lays hard-shelled eggs
Now, if you've been paying attention, every feature that defines a Dinosaur is applicable to birds!
Birds' ankles are hinges which only rotate on one axis and their necks are delicate and S-shaped.
In fact, upon inspection, there are no features which distinguish birds /from/ dinosaurs!
The mere fact that they have neither teeth nor tails is insufficient to exclude them from the group; if it were, then Humans and Anteaters shouldn't be considered mammals.
Now, what do the BANDits bring to the table?
As Cal supplies above, there is one animal of interest, a certain Longisquama. In short, there is absolutely nothing (David Peters' photomanipulation aside) suggesting that Longisquama has feathers, or any other feature linking it with birds. The alleged "feathers" more readily resemble plant fronds than they do plumage.
Now, as for Dinosaurs, there have been many fossil specimens that are both younger and /older/ than the famous Archaeopteryx lithographica, or "first bird." Take, for example, Anchiornis: a small theropod dinosaur with long, plumaceous feathers that not only covered its arms, but its feet and lover legs as well! This configuration made it resemble a sort of "Dinosaurian biplane."
Furthermore, simply googling "Feathered dinosaur fossil" will bring up hundreds of images of dinosaurs, trapped forever in sedimentary rock, proudly displaying their feathers and featherlike integument.
In short, not only are birds descended from dinosaurs, they /are/ dinosaurs, and not even strange dinosaurs at that!
There is no consensus. Most paleontologists are cladists, and practically all cladists believe that birds evolved from a dinosaur. There are also many biologists who have not kept up with the latest research on bird origins, and they were taught as undergraduates that birds evolved from a dinosaur similar to Deinonychus if they received their university education since the late 1960s. These 2 groups add up to over 50% of scientists. Starting in the mid-1990s, however, more and more scientists now doubt that birds evolved from a dinosaur. It started with developmental evidence by scientists such as Richard Hinchliffe, who found that birds most likely had fingers 2-3-4 but fossil evidence strongly suggests that theropod dinosaurs have fingers 1-2-3. Then scientists like John Ruben, Alan Feduccia, and Larry Martin did research that show that the taxonomic characters uniting theropod dinosaurs and birds are extremely unlikely to be homologous, suggesting instead that they are only superficially similar. Then, in 2000, a paper based on the re-examination of the fossil Longisquama, which was part of the group of fossils being brought to the USA from Russia, shows that it has feathers that were likely homologous with those of birds. Since Longisquama is not a dinosaur by any stretch of the definition or the imagination, it dealt a severe blow to the view that birds evolved from a dinosaur.
Knowing that Longisquama feathers would deal their cladistic religion and their careers a severe blow, because they would have to admit that cladistic analysis failed time after time to come up with the correct answer about the real ancestor of birds, some paleontologists tried to bury the facts. They claim that Longisquama does not have feathers. Some even claim that it is not even an archosaur. Meanwhile they try to conflate the fuzzy body coverings found on the outline of some dinosaurs, such as Sinosauropteryx, with bird feathers, even though those filaments have been shown by scientists to be probably little more than collagen fibers, and even though the cladists provide no evidence to show homology, just an inane cladogram. Simultaneously, they began classifying feathered fossils such as Anchiornis and Microraptor as "dinosaurs" despite the fact that these small fossils had no dinosaurian characters but lots of birdy characters. They suggest that these feathers did not evolve for flight but for "display". Display does not bring an animal food or water, so one wonders why these dinosaurs are so fond of displaying that they evolved features that would tie up their hands and legs so badly that they cannot grasp prey or run swiftly. IOW, the claim that these "dinosaurs" evolved feathers for "display" is patently non-Darwinian and downright nonsensical. That is not all, the cladists are spending time courting the popular press and ignorant journalists to continue propping up the theory that birds evolved from a dinosaur.
The facts simply do not support the dinosaurian origin of birds, because there is no known fossil that has the features of Deinonychus and that lived in a period of time before the oldest known birds. As we go further back in time, theropods were less and less birdlike. Herrerasaurus and Coelophysis, for example, are not at all bird-like. Besides, the fossil theropod Scipionyx has a diaphragm, according to John Ruben of Oregon State University. Therefore theropods could not have evolved the air sac breathing system that birds use, since the transitional animal would have a hernia in the diaphragm. In humans, a hernia in the diaphragm requires emergency surgery because it is a life-threatening illness. Of course, cladists once again deny this piece of evidence, as they had done to all other pieces of evidence that contradict the dinosaurian origin of birds.
So, in short, if a paleontologist's career or career opportunity is dependent on adhering to the largely refuted dinosaurian origin of birds, then he/she probably has little choice but to keep on pretending that birds evolved from a dinosaur and bury both the facts and his/her own integrity. OTOH, scientists who are interested solely in a better understanding of nature are joining the small but growing number of real scientists who have abandoned the dinosaurian origin of birds.
You have received a semi-religious, anti-dinosaur screed from one Y/A member who uses some of the same smear tactics as creationists. The fact is that a large majority of paleontologists see clear evidence that birds evolved from a clade of theropod dinosaurs called maniraptorans.
Some people think so. I don't and have little use for cladists.
Same as above, please check out my question, it's URGENT.
