Guided Inquiry Forensics Lab hapter 26 Lab Investigating Hominoid Fossils Problem What can a comparison of skulls and hands reveal about the evolution of humans? Introduction paleontologist takes photographs of a newly discovered fossil while it is in the ground and after it is removed. He or she also makes many measurements. These observations make it easier to compare the new fossil to fossils that have already been classified. How can a scientist know whether a skeleton is typical of its species? For example, a scientist may find that one skeleton is much taller than another. Does this variation in height indicate that the individuals were members of two different species? Does it reflect a range of heights within the same species? To deal with this problem, scientists use indexes. n index is a ratio that compares the value of one measurement in relation to another. Indexes are useful because they do not depend on overall size. Very tall and very short members of the same species should have similar indexes. With indexes, it is more likely that variations are related to differences in species, not just differences in size. In this lab, you will measure the skulls and hands of different hominoid species. You will use your measurements to calculate indexes that will help you compare these species. ig Idea The changes that occurred in certain bones as hominines evolved facilitated bipedal locomotion and tool use. Skills Objectives Students will be able to calculate indexes from pairs of related measurements. relate skeletal indexes to differences among species. lass Time 45 minutes Group Size Individuals Skills Focus Measure, nalyze Data, ompare and ontrast Materials metric ruler Term uild Vocabulary variation Definition The degree, or extent, to which a set of similar items differ, or vary uild Vocabulary Students will have a more successful lab experience if they understand these terms. proportion part considered in relation to the whole 161
Pre-Lab Questions 1. Use Models What will you use instead of actual skulls and hands to make your measurements? I will be using images of skulls and hands. 2. Interpret Visuals The bony cavities in a skull that protect the eyes are called orbits, or eye sockets. On the skulls, what does line measure? What does line measure? Line measures the distance from the bottom of the eye socket to the top of the skull. Line measures the distance from the top of the eye socket to the top of the skull. 3. Use nalogies Shoe sizes such as 9 and 11E (or 9 narrow and 11 extra-wide) are an example of an index. What two measurements are being compared in a shoe index? Sample answer: In a shoe size, the width of the shoe is being compared to the length of the shoe. Teaching Tip If possible, have at least one skull available for students to observe and discuss. Procedure Part : Supraorbital Height Index in Hominoids Figure 1 shows side views of skulls from four hominoid species. You will use these drawings to determine distances from the top of the skull to the upper and lower edges of the eye socket. Then you will calculate the supraorbital height index (SHI). This index indicates the proportion of the skull that is above the eyes. The prefix supra- means above. 1. Measure the distances and in centimeters for each skull. Record the measurements in Data Table 1. 2. For each species, divide the value of by the value of and multiply the result by 100. The result is the supraorbital height index (SHI). Round the answers to the nearest whole number, and record them in Data Table 1. Sample Data Data Table 1: Skull Measurements Species (cm) (cm) SHI Pan troglodytes 1.6 4.1 39 ustralopithecus afarensis 2.0 4.2 48 Homo erectus 2.9 4.7 62 Homo sapiens 3.4 4.7 72 162
Figure 1 Hominoid skulls Pan troglodytes ustralopithecus afarensis 163
Homo erectus Homo sapiens 164
Part : Thumb Index in Hominoids Figure 2 depicts the thumb and index finger of Pan troglodytes, ustralopithecus afarensis, and Homo sapiens. You will use these drawings to calculate a thumb index for each species. The thumb index compares the length of the thumb to the length of the hand. 3. For each species, measure the length of the thumb and the length of the index finger in centimeters. Make these measurements from the tip of the digit to the point where the finger and thumb meet at the wrist joint. Record your results in Data Table 2. 4. To calculate the thumb index, divide thumb length by index finger length and multiply the result by 100. Round the answer to the nearest whole number and record the result in the table. Sample Data Data Table 2: Hand Measurements Thumb Length (cm) Index Finger Length (cm) Thumb Index Pan troglodytes 1.8 4.7 38 Part Homo erectus is not included in Part because there are no known thumb bone fossils for this species. ustralopithecus afarensis 2.8 4.5 62 Homo sapiens 3.0 4.7 64 Figure 2 Hand bones of three hominoids Pan troglodytes ustralopithecus afarensis Homo sapiens 165
nalyze and onclude 1. nalyze Data Of the species you investigated, which had the smallest SHI and which had the largest? What is the relationship between the SHI value and the shape of the skull? Sample answer: Pan had the smallest SHI and Homo sapiens had the largest. In skulls with a higher SHI value, a larger proportion of the skull is above the eye. 2. Infer How might an increase in a hominoid s SHI value affect the size of its brain? Sample answer: When the proportion of the skull above the eyes increases, there is more room for the brain. Thus, the size of the brain could increase relative to the overall size of the skull. 3. nalyze Data Does the data support the hypothesis that the thumb index increased as the opposable thumb hand evolved? Explain. Sample answer: The data (although limited) seems to support this hypothesis because Pan, which does not have an opposable thumb, has a smaller thumb index than H. sapiens, which has an opposable thumb. 4. Relate ause and Effect How could an increase in the thumb index affect a hominoid s ability to use its hands? Sample answer: s the thumb index increases, the length of the thumb increases in relation to the rest of the hand. Longer thumbs can touch the fingertips, making it easier to grasp objects and use them as tools. 5. Design an Experiment Suppose you repeated this lab with drawings that were half the size of the drawings you used. Would your results be the same? Why or why not? Sample answer: The measurements would have been different, but the indexes would not have changed because the drawings would have the same proportions. uild Science Skills skeleton retains clues about the life of its owner. How can fossils be used to determine a hominid skeleton s age, sex, or diet? How can fossils be used to tell how heavy or muscular an individual was? Students may know about wisdom teeth and pelvic shape (from a previous lab). one fusing is another clue to age. Teeth wear provides clues to diet. one mass and surface texture are clues to musculature. 166