Download Fossil Evidence for Evolution, Part 2

6‐7‐8 FOSSIL EVIDENCE FOR EVOLUTION-Part 2
LEARNING EXPERIENCE: We continue to explore the evidence for evolutionary change found in the fossil record. This is important to understanding biological evolution because fossils were among the earliest clues to change over time that people discovered, and continue to this day to provide valuable pieces to the puzzle of evolution. We will use discussion and observation to retrace one example of evolutionary lineage based on evidence found in its fossil record. OBJECTIVE: We will be able to explain the connection between what is seen in fossils and what can be learned about evolution. We will show that fossils provide evidence about evolutionary change. MATERIALS AND PREPARATION: LESSON: Set of pictures of fossils Focusing questions: What did fossils show early scientists about differences between living organisms of the past and those of the present? How were the similarities and differences between past and present organisms interpreted? Focus: Fossils were fascinating to early naturalists. In some ways, some fossils looked like stone copies of familiar creatures, like clams or scallops, crabs, or fish or leaves. But in other cases, fossils looked like stone copies of no kind of animal ever seen—giant sea monsters, perhaps, or dragons! It took some time before people studying these fossils began to think that perhaps the fossils were stone copies of animals that no longer could be seen on earth, because they no longer lived on earth: they were extinct. But in some cases, these extinct organisms had similarities to existing organisms. Could it be that such similarities pointed to connections between the organisms, past and present? Today we have many examples from the fossil record of successive changes that lead from fossil types of life to modern, living organisms. Fossils provide the evidentiary links in a chain of change that ties together life on earth, and that chain of change is evolution. Now, not every line of organismal change is complete; that is, we certainly do not have fossils that show every step along every path of evolution, but we can make predictions based on the evidence we have. We do have enough to show the pattern, and the general pattern (of change through time) is clearly established by the record of fossils. Explore: We have here a set of pictures of fossils from a lineage of organisms. Try to arrange them in what might be the order in which they evolved. What types of changes can be observed along this lineage? What did you observe that led you to put the pictures in this order? Do you have enough evidence here to make some claims about the evolution of this animal? Why or why not? Reflect: Scientists hypothesize that if evolution is true, we should be able to find fossil evidence of intermediate forms of organisms (if there are indeed intermediates). That is, if all life is descended, ultimately, from a common ancestor, there should be fossil evidence of organisms that are intermediate between major groups of modern organisms—like fishes and mammals, for example, or between reptiles and birds. In some cases we do not have fossil evidence of such intermediate organisms (although more fossils are always being discovered and more clues are always being added to the puzzle). But there are good examples of fossils of intermediate forms, two of which include Tiktaalik and Archaeopteryx. Tiktaalik is an example of an ancient type of "fish" that developed adaptations to the oxygen‐poor shallow‐water habitats of its time. One of these adaptaions was an ability to “walk” on its fins on land, where there was more oxygen. This adaptation led to the evolution of tetrapods. Archaeopteryx had many features of small dinosaurs, but it also had feathers and represents a link between dinosaurs and modern birds. ASSESSMENT: Ask your student to explain how fossils can help scientists reconstruct pathways of evolution. Ask him to explain what claims scientists can make based on their observations of the similarities and differences among fossil and existing organisms. EXTENSIONS: Explore the internet for more information about Tiktaalik, Archaeopteryx, and other “missing links” in the fossil record. SCIENCE GRADE LEVEL EXPECTATIONS ADDRESSED (WA State EALRs): Students know that: Students are expected to: 6‐8 ES3B Thousands of layers of sedimentary rock provide evidence that allows us to determine the age of Earth’s changing surface and to estimate the age of fossils found in the rocks. •
Explain how the age of landforms can be estimated by studying the number and thickness of rock layers, as well as fossils found within rock layers. 6‐8 LS3G Evidence for evolution includes similarities among anatomical and cell structures, and patterns of development make it possible to infer degree of relatedness among organisms. •
Infer the degree of relatedness of two species, given diagrams of anatomical features of the two species (e.g., chicken wing, whale flipper, human hand, bee leg). 4‐5 LS3D Fossils provide evidence that many plant and animal species are extinct and that species have changed over time. •
Compare and contrast fossils with one another and with living plants and animals to illustrate that fossils provide evidence that plant and animal species have changed over time.