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Add to FavoritesThere is enough similarity between the fossils of dinosaurs and modern birds to conclude that birds did indeed evolve from dinosaurs.
The Wishbone
The furcula, or wish bone, has been found in many theropod dinosaurs. The furcula in birds is used to strengthen the skeleton for flight. In theropod dinosaurs the wishbone did not serve the same function and was less flexible than the corresponding bone in birds. The evolutionary connection is intriguing.
So Few Juvenile Fossils
There are very few juvenile dinosaurs found in the fossil record. This may be due to a correlation between the way birds and dinosaurs grew, very fast. If dinosaurs were more closely related to reptiles they would have a slower rate of growth, many growing after sexual maturity. The lack of juvenile fossils could be due to the fact that the rate of growth was more similar to birds. If dinosaurs grew at the rate of birds they were not juveniles very long, and that may be why we find so few fossilized in comparison to the amount of adults that have been discovered.
Eyes
Most predatory dinosaurs had forward facing eyes with evidence of well developed visual acuity. Birds have the most sophisticated vision of all species. Both predatory dinosaurs and modern birds used this well developed sense of sight for hunting their prey. It would be sensible to think that modern birds have evolved from the species that had the most developed sight in prehistoric times.
Bones
Many dinosaurs had honeycomb structures thorough their skeletal system. This honey comb structure would have given them a lighter skeleton, enabling them to be more active. Similarly, the skeletal system of birds is hollow to allow them to take flight. These hollow bones could easily have been an evolutionary step from the honeycombed ancestors of prehistory.
Avian Respiratory System
Modern birds have a very efficient respiratory system that is far superior to the respiratory system in mammals. Birds have a continues supply of new oxygen because their hollow bones actually become part of their respiratory systems. The system allows birds a higher degree of activity than their mammalian and reptilian counterparts who have inferior respiration abilities. There is evidence that dinosaurs shared this superior respiratory system. It is likely that if dinosaurs began this respiratory system birds perfected it as they evolved from dinosaurs.
In classification of animals characteristics of those animals are used to determine how alike or different those animals are. Using the classification systems that have been used for hundreds of years dinosaurs are more like birds than they are like anything else that has survived their extinction. Or, are they really extinct at all?
Source:
Larson, Peter, and Kristin Donnan. Rex Appeal. Montpelier, Vermont: Invisible Cities P, 2004.
Learn more about this author, Robin Hussey.
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No
The question before us here is whether birds evolved from dinosaurs, or whether birds evolved from something else. The question is not did birds poof into existence by magic. Although there is, as I shall argue, another option.
So, look out of your window - do you see any dinosaurs?
Are you sure? Look again. See that sparrow? It's a dinosaur. That thrush? A dinosaur also.
Dinosaurs did not evolve into birds. Birds ARE dinosaurs.
The discovery of Archaeopteryx, a 150-million year old fossil, at the end of the 19th century convinced many scientists that it was a bird to dinosaur transition. It had three clawed toes and presumably perched like a bird. It had feathers, like a bird. But it also had a dinosaur like jaw, complete with teeth and a spiny, dinosaur like tail. Joel Ostrom of Yale University, with his analysis of Deinonychus fossils published in the 1960s, laid out a convincing argument for a link between meat eating dinosaurs and birds, with 22 features of similarity. Such an argument forms the basis of the dinosaurs-to-birds theory that forms mainstream thought scientific today.
Doubters to this theory, such as Alan Fedducia, at the University of North Carolina and Larry Martin, from the University of Kansas, claim that Archaeopteryx is just an outlier - an experiment by Nature - that just co-incidentally looks like a transition between dinosaurs and birds. These scientists point to differences in the rib cage and digits of birds and dinosaurs to suggest they arose separately. They point out that it appears more likely that the birds gained flight by gliding down from trees, rather than flapping from the ground up to trees. Think flying squirrel here: membranes of skin between its limbs help it glide from branch to branch or ground, but do not allow powered flight. Supposed theropod ancestors of the Archaeopteryx were all ground dwelling dinosaurs. Real birds, these doubters argue, arose from a line of reptiles similar to but distinct from the dinosaurs. And they arose sooner than 150 million years ago. A bird fossil dated at 135 years old, Liaoningornis, had highly developed features similar to modern birds. Birds, Fedducia has argued, were a well established line at this point, and so must have begun their evolution earlier than Archaeopteryx.
A tantalizing possibility supporting Fedducia and Martin is a 210 million year old fossil, Protoavis, found recently in Texas by Sankar Chatterjee, that appears somewhat birdlike, but unlike any dinosaur fossil. If this find is verified, it will push back the origins of birds to a time when dinosaurs themselves were just getting started. However, much controversy exists as to whether these fossil fragments have been identified and constructed properly, and so Protoavis cannot be used at this time to support any origin-of-birds theory.
Feathered dinosaurs found recently in Liaoning Province in China switch the evidence back in favor of a dinosaur to bird transition. Today, at least 17 genera of feathered, flightless, theropod dinosaurs have been discovered. Indeed, even the mighty Tyrannosaurus rex might have had a soft downy coat, at least as a youngster. Microraptor had wing-like feathers not just on its arms, but on its legs too, and it has been called the "four winged dinosaur". These small dinosaurs could well have been arboreal (meaning they might have lived in trees) and so the tree down vs. ground up objection raised by Feduccia and Martin is negated.
Somewhat paradoxically, these Chinese fossils existed after Archaeopteryx, and true birds were alive at the same time. Thus, Microraptor and the other feathered dinosaurs of this period were not themselves the ancestors of modern birds. But they do provide startling evidence of how flight could have evolved from small, tree living, feathered dinosaurs. Today Ostrom's observations have been expanded, and almost 90 points of similarity are recognized, making birds essentially indistinguishable from dinosaurs.
So, look out you window again. Phylogeneticaly, birds really are dinosaurs.
Learn more about this author, Richard Heath.
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