Then create the phylogenic tree for Caminalcules. Caminalcules as a Model of the Fossil RecordCaminalcules were imaginary animals invented by the late University of Kansas evolutionary biologist, Joseph Camin. They make ideal model organisms for introducing students to evolution. In this lab, you will construct an evolutionary history of the caminalcules using fossil species. In the process of doing this exercise, you are introduced to concepts, such as convergent evolution and vestigial structures. As a consequence of Darwin's work, taxonomic classifications must be actual reflections of the evolutionary history of the group being studied.
For example, Linnaeus put humans and wolves in the class Mammalia, within the phylum Chordata, because they share certain characteristics (e.g., backbone, hair, etc.). We now interpret this similarity as reflecting the shared evolutionary history of both species through their descent from a common ancestor. Generally speaking, the more resemblance between two species, the more recently they diverged from their common ancestor. Thus, when we say that the human and wolf are more closely related to each other than either is to the honeybee, we mean that they share a common ancestor that is not shared with the honeybee.Another way of showing the evolutionary relationship between organisms is in the form of a phylogenetic tree (Gk. phylon, stock, tribe + genus, birth, origin):The vertical axis in this figure is the timeline, typically shown over millions of years. The separation of two lines indicates when that lineage split from each other, despite their common ancestor. For example, the diagram shows us that mammals diverged from reptiles about 150
million years ago. The most recent common ancestor shared by mammals and reptiles is indicated by point A in the diagram. The horizontal axis represents, in a general way, the amount of divergence that has occurred between different groups; the greater the distance, the more divergence has happened and the further back in time is the common ancestor. Since they share a fairly recent ancestor, species within the same group (such as the class Mammalia) tend to be closer to each other at the top of the tree than they are to members of other groups. Several types of evidence can elucidate the evolutionary relationship between organisms. One approach is to compare living species. The greater the differences between them, the longer ago they presumably diverged. There are, however, pitfalls with this approach. Occasionally, species resemble each other because they independently evolved similar structures in response to similar environments or ways of life, not because of a recent common ancestor. This is called convergent evolution; distantly related species seem to have converged on a common set of adaptations. Examples of convergent evolution include the wings of bats, birds, and insects, or the streamlined shape of dolphins and fish. At first glance, it might appear that dolphins are fish. However, further examination shows this resemblance is superficial, resulting from the fact that dolphins and fish have adapted to the same environment. The presence of hair, the ability to lactate and homeothermy clearly demonstrate that dolphins are mammals. Fish lack these features. The fossil record can also be helpful for constructing phylogenetic trees. For example, bears were once thought to be within the order Carnivora. Recently discovered fossils, however, show that they actually diverged from the Canidae (wolves, etc.) fairly recently. The use of fossils is not without its problems, however. The most notable, and perhaps greatest problem, is the incomplete nature of the fossil record. This is more of a problem for some organisms than others. For example, organisms with shells or bony skeletons are more likely to be preserved than those without hard body parts.Construct a Phylogenetic Tree for the Caminalcules1. Obtain a large sheet of paper on which to construct a phylogenetic tree for the caminalcules. 2. Use a meter stick to draw 20 equally spaced horizontal lines on the paper. • Use each line to indicate an interval of one million years. • Label each line so that the one at the bottom of the paper represents an age of 19 million years and the top line represents the present (0 years). 3. Download the caminalcules Handout and cut out all the caminalcules (including the living species).4. Put them in piles according to their age (the number in parentheses indicates age in millions of years). 5. Beginning with the oldest fossils, arrange the caminalcules on the tree according to their evolutionary relationship. Remember, the oldest forms are at the bottom of the tree. Hints, Suggestions and Warningsa. Use a pencil to faintly draw lines indicating the path of evolution. Only after you are sure of the correctness of your tree should you glue the figures in place and darken the lines.b. Branching should involve only two lines at a time: Like this Not thisc. Some living forms are also found in the fossil record.d. There are gaps in the fossil record for some lineages. Also, some species went extinct without leaving any descendants.e. The caminalcules numbering is random; the numbers provide no clues to evolutionary relationships.f. There is only one correct phylogenetic tree in this exercise. This is because of the way that Joseph Camin derived his imaginary animals. He started with the most primitive form (#73) and gradually modified it using a process that mimics evolution in real organisms. After you complete your phylogeny, compare it with Camin's original found in the course content.
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