Name
Class
Date
Guided Inquiry • Forensics Lab
Chapter 26 Lab
Investigating Hominoid Fossils
Big Idea
Problem
What can a comparison of skulls and hands reveal about the
evolution of humans?
The changes that occurred in
certain bones as hominines
evolved facilitated bipedal
locomotion and tool use.
Skills Objectives
Introduction
A 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. An 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.
Students will be able to
• calculate indexes from pairs
of related measurements.
• relate skeletal indexes to
differences among species.
Class Time
45 minutes
Group Size
Individuals
Skills Focus
Measure, Analyze Data, Compare and Contrast
Materials
• metric ruler
Build Vocabulary
Term
Build Vocabulary
Students will have a more
successful lab experience if
they understand these terms.
Definition
variation
The degree, or extent, to which a set of similar items
differ, or vary
proportion
A part considered in relation to the whole
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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 AC measure? What does line BC measure?
Line AC measures the distance from the bottom of the eye socket to the
top of the skull. Line BC measures the distance from the top of the eye
socket to the top of the skull.
3. Use Analogies Shoe sizes such as 9A 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.
Procedure
Teaching Tip
If possible, have at least one
skull available for students to
observe and discuss.
Part A: 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 AC and BC in centimeters for each skull.
Record the measurements in Data Table 1.
2. For each species, divide the value of BC by the value of AC 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
BC (cm)
AC (cm)
SHI
Pan troglodytes
1.6
4.1
39
Australopithecus afarensis
2.0
4.2
48
Homo erectus
2.9
4.7
62
Homo sapiens
3.4
4.7
72
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Name
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Figure 1 Hominoid skulls
C
B
A
Pan troglodytes
C
B
A
Australopithecus afarensis
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C
B
A
Homo erectus
C
B
A
Homo sapiens
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Part B: Thumb Index in Hominoids
Figure 2 depicts the thumb and index finger of Pan troglodytes,
Australopithecus 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
Date
Part B
Homo erectus is not included
in Part B because there are no
known thumb bone fossils for
this species.
Data Table 2: Hand Measurements
Thumb
Length (cm)
Index Finger
Length (cm)
Thumb Index
Pan troglodytes
1.8
4.7
38
Australopithecus afarensis
2.8
4.5
62
Homo sapiens
3.0
4.7
64
Figure 2 Hand bones of three hominoids
Pan troglodytes
Australopithecus afarensis
Homo sapiens
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Analyze and Conclude
1. Analyze 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. Analyze 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 Cause and Effect How could an increase in the thumb index affect a
hominoid’s ability to use its hands?
Sample answer: As 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.
Build Science Skills
A 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). Bone
fusing is another clue to age. Teeth wear provides clues to diet. Bone mass and surface
texture are clues to musculature.
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