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Understanding The Origin Of Feathers Essay

1152 words - 5 pages

 Feathers are complex, branched, keratinized epidermal features commonly associated with Class Aves, or birds (Bock, 2000). Cells in the epidermis called keratinocytes are the structural components of feathers; however, the protein keratin varies in its distribution and can be of different types (Prum, 2002). Many functions involved with feathers include thermal insulation, flight, cleaning of plumage, heat protection, sound production, chemical defenses, water repulsion of plumage, social communication, streamlining the body, and the sensation of touch (Bock, 2000; Prum, 2002). A wide variety of feathers have been characterized. Feathers covering the body are known as contour feathers ...view middle of the document...

Archaeopteryx fossils show detailed impressions of remiges and restrices in a closed pennaceous structure (Prum, 2002). Additionally, there was evidence of differentiated distal and proximal barbules, features that extant birds possess as well (Prum, 2002). Additionally, distal barbule structures seen in the upper primary covert feather of Archaeopteryx created distinct parallel impressions within a limestone matrix that showed the presence of melanosomes; the impressions were morphologically and angularly similar to those in distal barbules of extant pennaceous feathers (Carney et al., 2011). In addition to Archaeopteryx, novel finds of protofeathers on the non-avian dinosaurs from the Jehol Group (including Sinosauropteryx, Sinornithosaurus, Beipiaosaurus, and Microraptor) provide evidence that bridges the gap between the origin of feathers and extant feathers. With even more novel molecular evidence and fossils from the Early Cretaceous, the question persists about the origin of feathers.
In the past, there have been four hypothesized theories (now rejected) regarding the evolutionary origin of feathers. These approaches either analyze the 1) primitive feather characteristics in modern birds, 2) feather functionality, 3) evolution of feathers from reptile scales, or 4) keratinization patterns between reptile scales and feathers (Prum, 2002). Studies analyzing the primitive feathers in extant birds were rejected because of lack of understanding of phylogeny; if the studies were successful, it would mean that the feathers of all extant birds represent the most primitive avian feather morphology (Prum, 2002). This theory was ultimately rejected, as Archaeopteryx fossils showed that modern feathers are not indicative of primitive feathers as they have diversified multiple times (Prum, 2002). The second theory based on feather functionality indicated the functions of feathers prior to hypothesizing the ancestral form suitable for that function. However, this second theory proved to be inconclusive, as the form of the primitive feather is needed to understand their true function (Prum, 2002). The third theory that proposed the evolution of feathers from reptile scales has limitations in that it cannot explain the evolution of a variety of modern feather structures (Prum, 1999). Lastly, the fourth theory describing similarities in α and β-keratinization patterns in reptiles and birds could not detail the origin of feather form and function any more than the third theory (Prum, 2002). As these four hypotheses were proven incorrect, the developmental theory of the origin of feathers used an alternative approach that can successfully explain how feathers developed (Prum, 1999).

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