GO IN DEPTH

Feathers Teacher Sheet

Feathers Teacher Sheet

Introduction

You can use this sheet to help guide discussion toward learning goals and reveal student misconceptions.


Key Concept

General Definitions—from all sources

1. Miracle of feathers

Author Hanson finds feathers particularly amazing in nature because of the multiple roles they play in a bird's survival—not just a single role.

 

 

2. Identify four feather functions.

Feathers insulate, cool, make aerodynamic flight possible, aid communication through color and courtship displays, provide protection from predators through camouflage, and protection from the elements through waterproofing.

 

 

3. Summarize the Ground-up Theory of Flight and relate it to the experiment a Montana University professor conducted to see how ground-nesting birds learn to fly. Hint: What do baby birds have in common with a Formula 1 Race Car?

In discussing the origin of flight and feathers' role in flight, scientists tend to fall into two theoretical camps: Ground-Up and Tree-Down. Ground-uppers believe flight developed in fleet-footed therapod dinosaurs—running and flapping and leaping like startled chickens, until one day, all that commotion produced lift and flight. The top down group believe flight evolved in tree-dwelling creatures as a means to extend the distance covered hopping branch to branch. (p.118). This University of Montana experiment helped settled it: Chukar Partridge baby birds were observed learning to fly in a ground enclosure with a bale of hay. They used the hay as a ramp to run to and up—using legs and wings cooperatively to develop lift and thrust. The investigator in charge of the experiment made this analogy to the ramp-running flight: "It's like a spoiler on the back of a race car." (p.127)—a big fin that pushes the car down as it speeds. The birds used the same physics to help them gain traction to scramble up the ramps in a method of flight dubbed WAIR: Wing-assisted incline running. Some species use it to run up ramps steeper than 90 degrees. In terms of evolution, WAIR provides an explanation for the transition from a body covering to modern flight feathers, since feathers are needed to develop the powerful, propelling air currents for flapping flight.

 

 

4. What was the traditional view of how feathers evolved?

Until recently, feathers were thought to have evolved to support flight. The explanation as functional, focused on the "why" aspect of the evolution of feathers.

 

 

5. What is the focus of the modern theory of the evolution of feathers?

It focuses on five developmental phases of feathers, not on the functional roles feathers play.

It's an approach focused on "how" feathers evolved—not why.

 

 

6. What do Las Vegas dancers have in common with birds? Hint: Think "swish"..

Both have to manage a feather coat—birds as part of their natural covering, and dancers as part of their costumes. One dancer said the "swish" factor is challenging—turning rapidly with feathers.

 

 

7. Feathers serve important roles in the lives and survival of birds. Name three roles feathers have played in human cultures of the world.

(1) Since antiquity feathers have served as writing instruments, 2) feathers and plumes were used for decorations on hats in Europe and America until the rise of conservation movements in the late 1800s, and 3) ceremonial decorations in many tribal cultures.

 

 

8. Define Archaeopteryx.

The fossil discovered in Germany in 1861 that was the first to suggest an evolutionary link between dinosaurs and birds.

 

 

9. Define Sinosauropteryx.

The fossil discovered in 1996 in China that provided physical evidence that some early dinosaurs had feathers.

 

 

10. Who are Richard Prum and Xu Xing and why are they important?

SHORT answer: Dr. Prum is scientist at Yale University who was the first to suggest a new theory of feather evolution—one that was based on the way feathers develop, starting with a follicle and tube formation. His model does not assume that flight feathers develop first so flight is supported. Xu Xing is the Chinese expert who discovered fossil evidence that supports this theory, Sinosauropteryx.

LONG answer that integrates Prum's and Xing's work:  Richard Prum's 1999 phased developmental model of feather evolution displaced the traditional hypotheses of the origin of feathers that focused on functional aspects of feathers, such as flight, insulation, and courtship display. In the traditional functional approach, the function of a structure explained its origin. For example, the aerodynamic requirements of flight were hypothesized to be the driving forces in remodeling a reptilian scale into a feather element. It was held that natural selection favored the function of flight because flighted animals had survival advantages. These advantages of flight could be the ability to escape predation, colonize new habitats, or capture more food with less competition. The function of flight therefore enabled them to live to reproduce more offspring.

Prum took a different approach. He said five phases of biological development drives the origin of feathers—not function. See p. 279 for illustrated explanation of the five phases. Once flight feathers develop—a Stage IV event—then natural selection does in fact act on it. Prum detailed the early developmental steps that occur before flight feathers appear, starting with Stage I with the development of the feather follicle in the skin.

One of the key aspects to appreciate about Prum's model is how it opened up new possibilities for understanding the relationship between birds and dinosaurs. Although naturalists had speculated a relationship between birds and dinosaurs for more than 100 years, the functional hypothesis—that feathers evolved for flight—always shut down that line of inquiry because dinosaurs as a group were land-bound, terrestrial beings, not flighted creatures. No flight, no relationship.

Prum's hypothesis helped changed that. By focusing on the phased development of feather stages and structure, his model was the only one that could fully make sense of the discovery of feather- like structures in 1996 of the theropod called Sinosauropteryx, by Xu XingIt was a historic discovery because its fossil remains provided the first physical evidence of a feathered dinosaur—a layer of filaments covering its back and tail that were thin and hollow, suggesting what many of us would recognize today as the base of a feather. Astonishingly, the fossil evidence contains pigment clues, so now scientists believe not only did Sinosauropteryx have feathers on its tail—but they were in a red and white striped pattern.

Sinosauropteryx was just one of many exciting new paleontology finds in China that occurred in the late 20th century as Communist rule relaxed, advanced education in the sciences was again offered in China, and international scientific exchanges were permitted.  Sinosauropteryx provided important evidence for the predictive power of Prum's feather hypothesis because the structures in the fossil—known as integumental structures—fit with his model's predictions of the form of early feathers, Stage I or II. Prum's further work with Alan Brush discovered a molecular switch that determines the fate of scales and feathers. In one position, the switch pushes early feathers vertically up, which is how down emerges on a baby bird. In another position, this switch causes horizontal growth in a structure: a scale.

Today, continuing discoveries of "China's feathered fossils" further strengthen the relationship between birds and dinosaurs. The birds we see today are considered to be direct descendants of a group of dinosaurs known as Maniraptoran dinosaurs, which went extinct millions of years ago. But their relatives, the birds, fly on.

To learn more about how birds are related to dinosaurs, you can go to Birds in the Family Tree, part of Dinosaurs’ Living Descendents.

 

This teacher sheet is a part of the Feathers: The Evolution of a Natural Miracle lesson.

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