Feathers on Dinosaurs before Feathers on Birds
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The feathers of a bird are an example of the many evolutionary novelties that came forth from the findings of fossils. These fossils provide evidence that primitive feathers originated from carnivorous, bipedal theropod dinosaurs even before the origins of modern-day birds and flight came about. The wings of modern-day birds are homologous in structure to the forelimbs of their earthbound theropod ancestors. This developmental theory, based upon the studies of Prum, Brush, and other participating individuals, explains exaptation, in which the origin of feathers could have been used for other functions, such as: insulation, water repellency, courtship, camouflage, and defense even before the function of flight. The different uses in these functions are evident from the various arrangements on the components that make up a feather: the barbs, barbules, and rachis that help structure the usage of feathers. For example, the plumulaceous (downy) type of feathers has no vane, but has soft and tangled plumes that provide lightweight insulation, whereas the pennaceous type of feathers provides the aerodynamic advantage for flight.
This developmental theory (exaptation) encompasses the idea that the structure and function of feathers evolved over time by the gradual modifications of earlier structures for new and different functions each time. Therefore, this would further support Darwin's theory of evolution, in which these significant changes are being made by natural selection and descent with modification through an accumulation of small changes.
Literature Cited
Prum, Richard O., Brush Alan H. 2003. Dinosaur Feathers: Which Came First, the Feather or the Bird? Scientific American. Mar 2003: 83-93.
--Reviews by Kathy Nguyen, 2004.
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