Comparative Vertebrate Anatomy, Integrated Science 4, 1/10 Name ______________________________ Per. _______ Introduction

Scientists gather evidence of organisms’ structure and function through dissection and observation. Once this is done, information is used to categorize organisms based on similarities and differences. This allows scientists to develop a hypothesis about organisms’ evolutionary relationships. Currently, the most reliable method for completing this process is known as cladistics.

To understand evolutionary relationships scientists analyze both primitive and derived traits. Primitive traits are those traits that all members of the group possess (evolved early). Whereas, derived traits are advanced traits that only some members of the group possess (evolved later). By analyzing primitive and derived traits, family trees can be drawn which hypothesize the evolutionary relationships among groups. Branching points (nodes) on the tree are created every time a derived trait (or group of them) is identified which one group possesses and another does not. These family trees are called cladograms.

In this activity you will be using cladistics to predict the evolutionary relationships among the existing vertebrates based on dissected specimens and prior research. You will construct a cladogram to hypothesize the relationships among them. Finally, you will consider the appropriate classification of the extinct dinosaurs on your cladogram.

Procedures 1. Observe the dissected specimens in the classroom: fish (perch and shark), amphibian (frog), reptile (turtle), and bird (pigeon). On the

attached Specimen Drawings template, color and label structures from each of the major organ systems as indicated. Dissection manuals will be available to help you.

2. On the table below, complete the row for the mammal (pig) based on your observations from the mammalian dissection and prior research. 3. For each of the remaining vertebrates, place a zero (0) in the column if the vertebrate does NOT possess the trait possessed by the mammal

(represented by the fetal pig) and a one (1) if the vertebrate does possess the trait. 4. Add the numbers in each row and record the totals. The higher the number, a) the more derived traits the organism possesses, b) the more

closely related to the mammal (the pig in this case), and c) the further to the right on the cladogram it belongs.

External Nervous/Skeletal Circulatory Respiratory Digestive Reproductive Behavioral

Vertebrates

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pr

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TOTAL in

common with

mammal

Mammal (pig)

Fish (perch)

Fish (shark)

Amphibian (frog)

Reptile (turtle)

Bird (pigeon)

5. Construct a vertebrate cladogram (use the diagram to the right) following these rules: a. The primitive traits, those traits shared by all vertebrate classes,

should be labeled at the base of the cladogram. b. Label the first branch ( ) of the cladogram with the vertebrate

class that shares the fewest traits with the mammal. c. Label the first node/dot (•) with the most common derived

trait(s) among the remaining vertebrate classes. Remember, the traits to the right of the node are not present in any of the organisms to the left, but are shared by all of the organisms to the right.

d. Identify the next most common derived trait(s), find the vertebrate that lacks this trait/these traits and label it/them on the second branch. Continue with the same procedures until all the vertebrates and traits have been labeled.

Discussion 1. Explain how evolutionary relationships are determined using cladistics. In your explanation, define primitive and derived traits. 2. What does the cladogram show about the vertebrates? 3. Analyze the data for the circulatory system, respiratory system and temperature control in the data table on the reverse. Identify the specific

anatomical features of both the circulatory system and respiratory systems that influence its temperature control from each of the dissected specimens that you observed.

Comparative Vertebrate Anatomy - Specimen Drawings

Organ System Color Structures to Label

Circulatory. Heart Respiratory Trachea,

Lungs, Gills (fish only)

Digestive Stomach, Liver, Intestines, Crop and Gizzard (bird only)

Urinary/ Excretory

Kidney, Bladder

Reproductive *Parts vary