The primary purpose of this passage is most likely to

It's been called the world's most dangerous bird. The Cassowary—a large, emu-like, flightless bird—is in fact responsible for the recent death of at least one human. But what excites scientists about the is its distinctive look. With its black iridescent feathered body, its blue, turquoise and magenta neck and horned crest or casque, one might even describe cassowaries as looking like a "high-fashion dinosaur." The cassowary has a brilliant blue and turquoise face. These birds are rather large. A typical cassowary amazingly can measure a little over a meter tall. With very dense bones. The southern cassowary can inflict serious injury with its dagger-like claw. Each of its three-toed feet has a claw that can be up to 4 inches or 10 centimeters long, allowing it to slice open a predator with a single kick, according to the San Diego Zoo. These birds are also extremely fast. Cassowaries can run up to 31 miles per hour through dense forest and jump up to 7 feet (2 meters). The three species of cassowary are native to parts of northern Queensland, Australia and New Guinea. They live on fruit.

New research on the feathers taken from a dead cassowary has now revealed what gives cassowary feathers their glossy black shine. The southern cassowary has shiny feather structures. Unlike in other shiny birds, such as hummingbirds or crows, the cassowary's glossiness is produced by the rachis, or the spine of the feather, rather than the barbules, or minute filaments fringing a feather. Since the fluffy barbules on cassowary feathers are pretty sparse, the rachis gets more exposure to light than in "thick-feathered" birds, giving it a chance to literally shine.The glossiness of the cassowaries’ feathers comes from a totally different part of the feather than other glossy feathered birds. If one pictures a feather as if it were a tree, the gloss is in the trunk of the tree, not the branches. 

Some scientists who have conducted recent studies on the cassowaries suggest that the cassowary's unique gloss-producing mechanism would have evolved gradually over time, with an ancestral bird losing its barbules and the cassowary developing a thicker central feather shaft. These scientists contend that the flightlessness of cassowaries might have given the cassowaries more evolutionary room to develop their odd-shaped feathers. They posit that the need to be able to fly is a very strong stabilizing force on wing shape. So, by losing, the need to fly, cassowaries’ wings were able to evolve a feather morphology that produces gloss in a way that a flying bird might not.

discuss how cassowaries are killer birds with sharp claws.
discuss one theory that explains how cassowaries evolved a different type of feather than other birds with glossy wings.
explain how cassowaries evolved with a different feather type than some other birds with glossy feathers.
express an opinion about why cassowaries are a beautiful bird.
explain the difference between a bird’s rachis and barbules.