Classroom Cladogram of Vertebrate/Human Evolution

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. Students will create a classroom cladogram to classify organisms.

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Standards & Objectives

Learning objectives:

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.
Recognize that the many vertebrate groups which exist today (and some which no longer exist) clearly had their beginnings from earlier pre-human ancestors.
Recognize that the many gaps in the fossil record are fully expected and consistent with the process of evolution, and can be logically explained.
Recognize that there are numerous tight sequences of fossils showing gradual change, with all important transitional forms known.
Recognize that the hierarchical pattern of Linnaean classification can be explained as the direct result of branching evolution and extinctions.

Lesson Variations

Blooms taxonomy level:

Understanding

Extension suggestions:

Extensions and Variations:

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

Helpful Hints

Materials:

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%).
Team Assignment Strips (two pages), each with an animal Group Name and the time that group First Appeared (one per team of 2-3).
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).
Procedures for students (print 1 sheet, BTB with "Groups of Traits").
Background Information packet for students.
Illustration Resources list (2 pages, print 1 sheet BTB [back to back])
Books, internet access, for students to research the animal groups (see a few online resources on the Resources list).
Key: Team Assignment Strips, with Associated Traits (for teacher only).
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.

References

Contributors:

Lisa Courson

Originator:

Ayers Institute for Learning & Innovation