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Classroom Cladogram

of
Vertebrate/Human Evolution

 

 

by Larry Flammer

 

EVOLUTION

Geological/Paleontological
Patterns

Time

 SYNOPSIS

Students prepare the components for building a Colossal Classroom Cladogram of vertebrate evolution, then put it together, showing the gradual, mosaic accumulation of the traits which we, as humans, possess. A major purpose of this is to dramatize the evidence that we (and in fact all living things) didn't suddenly pop into existence, but clearly evolved as an accumulation of traits over vast periods of time. A follow-up discussion helps focus on these concepts.

 PRINCIPAL CONCEPT

The fossil record shows a pattern of increasing diversity and large-scale change through time.

 

ASSOCIATED CONCEPTS

1. Transitional forms are generally a mosaic mix of "ancestral" and "derived" features; that is, some traits evolve faster than others, so each transitional is typically a mix of older and newer traits.

2. The groups-within-groups hierarchical pattern of Linnaean classification is a result of both extinction and branching from common ancestors.

3. The fossil record, as expected, has many gaps, for several good reasons.

4. There are many excellent sequences of fossils clearly showing transitions from one form to another.

5. Any given group of organisms possesses a collection of traits which individually accumulated over time.

6. In one sense, "Macroevolution" is simply an accumulation of microevolutionary changes over long periods of geological time.

 

ASSESSABLE OBJECTIVES

   Students will....

1. recognize that all of the physical characteristics which make us human beings can be traced in the fossil record of their gradual accumulation over the past 500 million years.

2. recognize that the many vertebrate groups which exist today (and some which no longer exist) clearly had their beginnings from earlier pre-human ancestors.

3. recognize that the many gaps in the fossil record are fully expected and consistent with the process of evolution, and can be logically explained.

4. recognize that there are numerous tight sequences of fossils showing gradual change, with all important transitional forms known.

5. recognize that the hierarchical pattern of Linnaean classification can be explained as the direct result of branching evolution and extinctions.

 

MATERIALS

To see the following boldface items, click on each one in turn. This will take you to a page suitable for copying that item. To return to this lesson page, just click the "Back" button on your browser. These pages are also available in PDF format at the end of this lesson.

1. Time-strip mounted diagonally on wall, with 10 vertical strips and labels handy as students build cladogram. See Diagram of this layout (before printing the Diagram page, reset your Page Setup to 90%).

2. Team Assignment Strips (two pages), each with an animal Group Name and the time that group First Appeared (one per team of 2-3).

3. Groups of Traits (one page), each cluster associated with the first appearance of a new group (clade). The clusters are arranged randomly and identified with the names of colors (to avoid any clues of sequence).

4. Procedures for students (print 1 sheet, BTB with "Groups of Traits").

5. Background Information packet for students.

6. Illustration Resources list (2 pages, print 1 sheet BTB [back to back])

7. Books, internet access, for students to research the animal groups (see a few online resources on the Resources list).

8. Key: Team Assignment Strips, with Associated Traits (for teacher only).

9. Set of 13 8-1/2 X 11 sheets displaying in large print (for each group) the 1) name of group, 2) time it first appeared, and 3) the list of new traits first shown by that group. This is available only in PDF format (end of lesson). Students should actually do these, but you could show them one as an example.

 TIME

Final Classroom Cladogram Assembly: minimum of one 40-60 minute period (plus brief part of an earlier period to assign groups and about 10-30 minutes the next day to check proper assignment of traits to each group, and to distribute materials).
STUDENT HANDOUTS

   (see end of lesson for the formatted handouts).

1. Team Assignment Strips (enough for one strip per student)

2. Groups of Traits - 1 page (one per student)

3. Procedures - 1 page (one per student; could be printed BTB with item #2)

4. Background Information packet - 6-7 pages (one packet per student)

5. Illustration Resources sheet - 2 pages BTB (one per student)

 

 TEACHING STRATEGY &
PREPARATION

A somewhat simpler approach might be preferred (especially in middle school life science or earth science). Try our Patterns in Time lesson, where students develop a more realistic understanding of deep time, along with the realization that the different vertabrate classes emerged separately over several 100s of millions of years, and did not exist prior to their emergence (as revealed in the fossil record). That lesson also demonstrates the accumulation of modified traits on top of the accumulated traits found in the previously emerged group, showing gradual, additive and mosaic changes over time. All of this provides a strong implication that each group descended from the earlier antecedents through gradual change over time.

1. The Big Cladogram lesson probably works best near the end of your unit on classification. You could also use it following (or before) the lesson on Hominoid Cranial Comparison (the "skulls" lab), or as part of your introduction to evolution (as a dynamic example of a "picture" of evolution, using vertebrate/human evolution as the focus).

2. Lay out a narrow strip of paper (e.g. cash register paper), or heavy plastic ribbon (more durable for re-use), about 6 meters (20 feet) long. About 1 cm in from the right end, place a small mark (="NOW"). With a meter stick, mark the following distances from that first mark (each cm representing 1 million years ago): 4 cm, 30 cm, 65 cm, 2 meters, 2.5 m, 3 m, 3.6 m, 4 m, 4.3 m, 5 m, 5.3 m, and 5.4 m (=540 mya, the beginning of the Cambrian). You can use a shorter strip if space is a problem, but you will need to re-scale, and the spaces at the "NOW" end will be very crowded! (See different scales at the end of the Time Machine lesson on this site).

3. Mount this strip diagonally across the wall on the long side, front, or back of your classroom so that the right end ("NOW") is about 2 meters above the floor, and the left end is somewhat lower (about 30-60 cm above the floor).

4. If you don't already have a horizontal line (e.g. a chalkboard or window trim) level with the upper end, run a string from that end horizontally, so its left end is directly above the left (lower) end of the diagonal strip. This will be the "NOW" line in time.

5. Run 10 vertical strips up from the diagonal strip to the horizontal "NOW" line. See diagram. On that diagram, note the rectangular "pages" below each vertical line, numbered 1 - 10. They represent the location where students will place their enlarged list of traits when they "build" the cladogram. The pictures of early representatives (extinct) should be placed at the ends of short side-branches near the bottom of each vertical line (see diagram, where those boxes contain the names of possible examples).

6. Make Label Signs to be placed above the vertical strips on the wall, as the students build the cladogram. (These may not be necessary if students put these names on their pictures of the "modern" members of their groups). Use these words (change "HOMINIDS" sign to HOMININS):
AMPHIOXUS LAMPREYS MODERN FISH COELACANTH MODERN AMPHIBIANS MODERN REPTILES BIRDS MODERN MAMMALS MODERN PROSIMIANS MODERN APES HOMININS NOW

7. Run off 2-4 copies of the Team Assignment Strips for each class. Cut apart the 11 Assignment Strips in each set so there will be one set of identical strips for each team (one strip for each member of the team).

8. Make enough copies of the Groups of Traits, Background Information, Procedures, and Illustration Resources so there is one of each for every student.

9. Have books available which have information and pictures of the animal groups named on the assignment sheets (e.g. college texts on evolution), and as many computer terminals available to the internet as you can (arrange for added access in your library and/or computer lab, if possible). A copy of Stephen Jay Gould's book Wonderful Life would also be helpful, since it has a picture and some commentary about Pikaia (a probable Cephalochordate in the Cambrian Burgess shale) which is not easily found elsewhere.

 

 

PROCEDURES

NOTE: Student Procedures are on a separate sheet as a handout (see link above in "Materials", or PDF version at end of lesson).

1. On assignment day, divide your class into 11 groups of 2-3, then hand out the Assignment Strip sets randomly, one set per team (one strip per student). Now distribute the Groups of Traits list to everyone. Give them one day to figure out which cluster of traits first appeared in their assigned animal group.

2. Next day, have teams meet to reach consensus as to which cluster of traits best fits their assigned group; allow about 5 minutes. (Teacher: refer privately to the Key: Assignment Strips, with Associated Traits). Then team leaders are asked in turn to announce their consensus selections (list these on overhead or board, using team number and the "color" for each team's cluster selection). If there are any duplications, get the teams involved to openly discuss the conflict, citing their resources for authority. If necessary, input from other classmates can be used. Hopefully, all such conflicts can be resolved to everyone's satisfaction. Where this does not happen, the teacher can step in, pointing out the text or other source, and make the proper match. Sometimes this only requires the clarification of certain traits. This phase should only take about 15-20 minutes.

3. Hand out the Background Information packet, Procedures for them to follow, and the Illustration Resources sheet. Then, give teams one or two days to prepare their sheets for building the cladogram. A set of 13 big sheets (with large print) can be found at end of this lesson in PDF format. You could show one of them, along with one of the pictures, as examples of what students are expected to do.

NOTE: If you like, prepare and assign a worksheet of reading questions for students to complete by reading the Background information.

4. Meanwhile, (optionally) do the lessons on Making Cladograms and related lessons on this site (if not already done), so students become familiar with cladograms. During this time, you could elicit student help to build the "skeleton" of their "Colossal Classroom Cladogram".

5. On "Cladogram Day", your class will finish your classroom cladogram. Before class, you have already mounted (with student help) the long "time-line" sloping upward, with 10 vertical strips extending from the time-line up to the horizontal "now" line. Now have each team add its (usually) three sheets to the cladogram, starting with the earliest group (Cephalochordates), working upwards through time and to the right. Allow about 2 minutes for each team to place its sheets on the cladogram and share a few items of information about its assigned group.

6. When the classroom cladogram is done, ask your students to volunteer what it seems to tell them. Encourage a variety of perspectives to be contributed without much comment. Then ask for some summaries, or generalized conclusions based on those individual perspectives. Enhance and clarify as needed (with the intended concepts in mind). Ask students to record in their notebooks what they did, and what main concepts they learned.

7. NOTE 1: It is very important to emphasize that this cladogram is only a simplified "pathway" tracing the main fossil vertebrate record toward humans, a diagram showing the sequence of accumulating traits in the intermediate forms leading to US, and indicating where other major animal groups (clades) have branched away from that pathway. It is not intended to represent the more realistic picture of the evolutionary "bush" of life. Nor does it imply that humans are "the most highly evolved species". A similar cladogram could just as easily be made for any other species, on which we would just be a "side group". A chimp, cat, dog or whale is just as "highly evolved" as we are, just in a slightly different direction. (See the UCMP discussion of cladograms for examples of this).

8. NOTE 2: It is also very important to point out that the "pathway" follows an exclusive sequence of the accumulation of the key traits. There are NO amphibian fossils found that pre-date the earliest fishes, NO reptile fossils which pre-date the earliest amphibians, and NO mammal fossils which pre-date the earliest reptile fossils. Likewise, amphibians have all the previously noted fish traits, PLUS a few new "amphibian" traits; reptiles have all those early "amphibian" traits, PLUS some new "reptile" traits, and the earliest mammals have all the early reptile traits PLUS the unique mammal traits. The sequence is very straightforward, and there are NO exceptions, NO indications at all that these animals somehow appeared all at one time. The fossils tell us so!

ASSESSMENT

1. Prepare a test in which students are asked to express one or more concepts the "Giant Cladogram" lesson was supposed to illustrate.

2. For a more "objective" type test (a matching test, easier to check), provide a list of concepts (including intended answers and a few logical detractors), then point out or list various elements of the Giant Cladogram and ask which concept each one best illustrates.

3. Refer to the Assessable Objectives for specific information for testing.

 

EXTENSIONS

& VARIATIONS   

1. A variation on the above approach is to just have students go through the procedures, then introduce the name "cladogram" when they are all done and have discussed it.

2. When the cladogram is done, ask your class to show where they think dinosaurs should go (see diagram). Have a large print "Dinosaur" sheet available for someone (or you) to place and move about on the cladogram as the class dictates. Your students might also find it interesting to see where the class "Aves" originated, actually from a group of dinosaurs (specifically the same group to which T. rex and velociraptors belong), a major branch of reptiles.

3. It is also interesting to note (and point out, if the responsible team does not), that the last of the mammal-like reptiles (synapsids) had become extinct by the end of the Triassic (having earlier produced the earliest mammals). No other vestige of that group survives today.

4. It might also be useful to show students where there are still a few major gaps in the fossil record. Ask students to suggest reasons for those gaps (which they should be able to do from their reading of the Background Information). Add any reasons not mentioned for those gaps, and how, every now and then, some new fossils are found which help fill some of the gaps, and how the fossils before and after the gap still present a logical series, regardless. There are three major gaps relevant to this cladogram. The earliest comes near the end of the Silurian (about 400 mya) and runs into the early Devonian (about 410 mya). The second gap runs for 30 my in the late Triassic (239-208 mya), and the most recent consists of a very spotty fossil record for about 12 my of the Oligocene period (35-23 mya). . See the Background Information (abstracted from the Talk.Origins Archive "Transitional Vertebrate Fossils", by Kathleen Hunt). Download and print out all 5 sections of that document (some 37 pages!) for student access, if you like. It is mildly anti-creationist in places, but is generally very tactful while making a very strong case for the abundant evidence of transitional vertebrates and rational explanations for the expected gaps in the fossil record. If every student would just read one or two of the series of transitional fossils (maybe one or two pages), even with all the technical jargon and scientific names, it's hard to imagine that they could ever accept the notion that there are "no transitional fossils". The flow and continuity of life through time becomes increasingly compelling the more pages you read.

5. Prepare a reading guide (questions) to help students pull out the main ideas and other important points from the Background reading.

6. If you have more than one class of Biology in the same room, you will need to figure out a way to retain each class' cladogram over the day or two you will need to complete the lesson. Possible strategies:
- a. Use a smaller scale, and have each class' cladogram posted on a different part of the wall (see other scales at the end of the Time Machine lesson on this site).
- b. Find some large panels, one for each class (get some refrigerator packing boxes, or equivalent, open them up), and place a reduced-scale cladogram on each carton. Just pull out and display the appropriate one for the current class.
- c. One member of each team could remove its 3 sheets from the cladogram at the end of the period, leave them with the teacher, and quickly re-mount them the next day. Use of paper clips or double-stick tape and cladogram lines made of heavy plastic or other durable material could facilitate this.

7. Have examples of pictures and big "traits" sheets available to fill in wherever they could not be found or were forgotten by any team. Such examples are available and can be downloaded at the end of this lesson. See the Illustration Resources page.

8. FEEDBACK: Since this lesson has not yet been thoroughly classroom tested, if you give it a good try, please give us any feedback you can:
- a. did it work?
- b. did your kids enjoy it? Did YOU enjoy it?
- c. did your kids learn the concepts?
- d. any problems? If so, how did you resolve them?
- e. any suggestions for improvement?

 OTHER RESOURCES

Here are some WWW sites which provide useful information:

Journey into Cladistics: http://www.ucmp.berkeley.edu/clad/clad4.html

Chordate Morphology: http://www.ucmp.berkeley.edu/chordata/chordatamm.html

Tetrapod Morphology: http://www.ucmp.berkeley.edu/vertebrates/tetrapods/tetramm.html

Vertebrate Flight: http://www.ucmp.berkeley.edu/vertebrates/flight/enter.html

Synapsids: http://www.ucmp.berkeley.edu/synapsids/synapsida.html

BioSci.Images: http://nitro.biosci.arizona.edu/courses/EEB182/Lecture11/lect11.html

Hip Bones (chimp, Australo., H. sapiens): http://ibis.nott.ac.uk/~plzkjc/bones.html

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: Larry Flammer (9/99), with special gratitude to:
- former colleague Ben Burma, PhD, for much of the information and resources
- Kathleen E. Hunt, Univ. of Washington, for her excellent review of transitional vertebrate fossils, published in The TalkOrigin Archive, from which the "Background Information" for this lesson was derived.
- Martin Nickels for encouragement and suggestions
- Jennifer Johnson (SENSI 96) for finding several illustration resources

2. Initial Classroom Testing by: Dorothy Reardon (ENSI '94): 10/99

3. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 10/99

4. Edited / Revised for website by L. Flammer 12/20/99


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