ACTIVITY 10 FOSSILIZED FOOTPRINTS
Teacher Resources III, “Assessment.” Explain to students that this is their
first opportunity to construct an argument in this unit, so they are not
expected to master this practice during this activity.
(literacy) Consider having students use Literacy Student Sheet 4b,
“Writing Frame—Engaging in Argument.” For more information on
using Writing Frames, see the Literacy section of Teacher Resources II,
“Diverse Learners.”222
b. Direct students to Procedure Steps 10 and 11, and instruct them to revise
or refine their arguments to explain the pattern of the footprints in light of
this new evidence.
PROCEDURE STEPS 10 AND 11 SAMPLE LEVEL-4 RESPONSE
The data in the first table show that the depth of the larger footprints on Card
3 increased.This increased depth provides evidence that the weight of the larger
animal may have increased.This supports the hypotheses that the larger animal
picked up a baby, carried off the smaller animal, or ate a carcass. It remains
unclear whether it was carrying an infant or a dead prey animal, either in its
mouth or in its stomach.
The data in the second table suggest that the larger animal did not become
substantially heavier, although the slight increase in depth of the footprints
(Card 3 compared with Card 1) may indicate the residue of a meal.This would
support the argument that the larger animal ate part of the smaller animal. It
cannot be inferred whether the larger animal attacked and killed the smaller
animal, or came upon the smaller animal after it had died. In addition, it is
possible that the larger animal carried off the smaller one or ate all of it; the
weight of the smaller animal might have been so much less than that of the
larger one that the added weight made little difference in track depth.The
increases in average footprint depth between Cards 1 and 2 might indicate that
the animals were striking the ground more powerfully as they struggled. (This
is consistent with two of the three major hypotheses.) However, even the drastic
increase in depth of the larger footprints on Card 3 of Scenario 1 may have
occurred simply because the soil was softer in that area.
BUILD UNDERSTANDING
4. Students discuss how studying fossils helps scientists understand evolution. 223224
a. Direct students to Analysis items 1–3.
These items help students understand the importance of fossils in
understanding evolutionary history and processes. Because scientists
222 SELTWF2
223 NGLS4A1
224 NGLS4A2
144 EVOLUTION
FOSSILIZED FOOTPRINTS ACTIVITY 10
cannot directly observe events that happened in the past, they make
inferences based on evidence to develop explanations. When new evidence
is discovered, this may cause scientists to infer something different
and change their explanations. This does not mean that the previous
explanation was “bad”; it was the best explanation at the time.
Decide which Analysis items you will have students respond to in their
science notebooks and which ones you will have students discuss in their
groups and/or as a class.
b. Discuss Analysis item 4 as a class.
Consider using Teacher Discussion Starters if your students need support
in generating and/or sustaining a class discussion.225
Let students know that in the next two activities, they will continue to use
data on fossils to explore evolutionary relationships.
SAMPLE RESPONSES TO ANALYSIS
1. What kind of information might be obtained from trace fossils that cannot be
obtained from the fossilized remains of the organism itself? 226
Trace fossils can help us make inferences about the behavior and habits of an extinct
organism. For example, the footprints allowed us to make inferences about what the
animal may have eaten or how it interacted with other species or its young.
2. Why is it important for scientists—and people in general—to distinguish
between observations and inferences when they develop hypotheses? 227228
As new evidence is gathered, scientists frequently have to modify or even abandon
their hypothesis, or preliminary explanation. It is important to keep observations and
inferences as separate as possible because earlier inferences can restrict how open one’s
mind is to both the possible implications of new evidence and the need to reinterpret
old evidence.
3. (quick check) Imagine that the team uncovered a fourth section of footprints.
Draw what you predict this fourth section might look like. Explain how it
would provide more support for the argument you favor. 229
Student responses may vary. One sample response is shown here:
If a fourth section of footprints showed a reappearance of the smaller set of footprints,
this would lend strong support for the picked-up-baby argument and refute the other
arguments.
225 SELTDS1
226 NGCCPA2
227 NGSPEA2
228 NGCCCE2
229 NGSPAD1
EVOLUTION 145
ACTIVITY 10 FOSSILIZED FOOTPRINTS
4. How does studying all kinds of fossils help us understand evolution? 230231
Fossils can help scientists learn about plants and animals that became extinct a long
time ago. Fossils can help scientists explain how a plant or animal looked based on
its structure. For animals, the fossils may help scientists understand what the animals
ate, where they lived, and how they died. Fossils are an important record of species
that otherwise may not have been known because they died long before people began
keeping records. Fossils from different time periods help us understand how species
have changed over time, and they might help us predict what will happen to living
species in the future.
REVISIT THE GUIDING QUESTION
What other kinds of information can we get from fossils?
Trace fossils can provide information about the behavior or habits of an organism,
and we can get additional information about the kind of environment the organism
lived in.
ACTIVITY RESOURCES
KEY VOCABULARY
hypothesis
inference
observation
trace fossils
BACKGROUND INFORMATION
TRACE FOSSILS
Broadly defined, fossils include the preserved impressions not only of organism
body parts but also of any interpretable mark left by a once-living organism. In
fact, for some soft-bodied organisms, such as some worms, the only kind of fossil
evidence obtained is from tracks, trails, and burrows. These are called trace fossils.
The footprints in this activity are based upon real preserved tracks unearthed at
Dinosaur Ridge (near Morrison, Colorado), an excavation site that has yielded
numerous bone fossils as well as footprint fossils. Little doubt remains that the
footprints found at this site were left by dinosaurs.
230 NGLS4A1
231 NGLS4A2
146 EVOLUTION
FOSSILIZED FOOTPRINTS ACTIVITY 10
The preservation of footprints does require fortuitous circumstances: The ground
must be soft enough to leave deep impressions, yet firm enough not to lose them
before they are preserved by rapid but gentle sedimentation. However, footprints
are much less rare than this might suggest, since every dinosaur produced many
footprints that could potentially become fossils. Evidence from footprints adds to
the picture of an organism that has been gleaned from fossil evidence. Fossilized
footprints are more dynamic than conventional fossils, providing evidence for
hypotheses about individual and social behavior. For example, if adult footprints
are found clustered around fossils of several young, parenting behavior can be
inferred. As with fossils of body impressions, specific characteristics of the rock
in which the footprints are found can allow inferences about habitat (different
environments produce different rock types). From habitat, scientists can infer
additional behavioral characteristics and speculate regarding the functions of
anatomical features.
OBSERVATION AND INFERENCE
This activity asks students to distinguish between observation and inference as
a way of organizing their thoughts during the analysis of evidence. Ideally, an
observation is a direct description of the evidence, whereas an inference is an
interpretation based on that evidence. However, in practice it can be difficult even
for professional scientists to pinpoint this distinction; what for one researcher
may be an objective observation may to another appear to be an unsubstantiated
conclusion that has been drawn using unarticulated or illogical reasoning.
REFERENCES
National Academy of Sciences. (1998). Teaching about evolution and the nature of
science. Washington, DC: National Academy Press.
EVOLUTION 147
11 Family Histories
i n v e s t i g at i o n
2 class sessions
ACTIVITY OVERVIEW
NGSS CONNECTIONS
Students analyze and interpret data to look for patterns in the evolution and
extinction of families from three classes of vertebrates. They summarize how life
forms have evolved over time, assuming that the same natural laws have always
operated and will continue to operate in the future. This activity provides an
opportunity to assess student work related to Performance Expectation MS-LS4-1.
NGSS CORRELATIONS
Performance Expectations
MS-LS4-1: Analyze and interpret data for patterns in the fossil record that
document the existence, diversity, extinction, and change of life forms throughout
the history of life on Earth under the assumption that natural laws operate today
as in the past.
Working towards MS-LS4-2: Apply scientific ideas to construct an explanation for
the anatomical similarities and differences among modern organisms and between
modern and fossil organisms to infer evolutionary relationships.
Disciplinary Core Ideas
MS-LS4.A Evidence of Common Ancestry and Diversity:
The collection of fossils and their placement in chronological order (e.g., through
the location of the sedimentary layers in which they are found or through radio-
active dating) is known as the fossil record. It documents the existence, diversity,
extinction, and change of many life forms throughout the history of life on Earth.
Anatomical similarities and differences between various organisms living today
and between them and organisms in the fossil record, enable the reconstruction of
evolutionary history and the inference of lines of evolutionary descent.
Comparison of the embryological development of different species also reveals
similarities that show relationships not evident in the fully-formed anatomy.
EVOLUTION 149
ACTIVITY 11 FAMILY HISTORIES
Science and Engineering Practices
Analyzing and Interpreting Data: Analyze and interpret data to determine
similarities and differences in findings.
Constructing Explanations and Designing Solutions: Apply scientific ideas to construct
an explanation for real world phenomena, examples, or events.
Connections to Nature of Science: Scientific Knowledge Is Based on Empirical Evidence:
Science knowledge is based upon logical and conceptual connections between
evidence and explanations
Crosscutting Concepts
Patterns: Graphs, charts, and images can be used to identify patterns in data.
Connections to Nature of Science: Scientific Knowledge Assumes an Order and
Consistency in Natural Systems: Science assumes that objects and events in
natural systems occur in consistent patterns that are understandable through
measurement and observation.
Common Core State Standards—Mathematics
6.SP.B.5: Summarize numerical data sets in relation to their context.
Common Core State Standards—ELA/Literacy
RST.6-8.7: Integrate quantitative or technical information expressed in words in
a text with a version of that information expressed visually (e.g., in a flowchart,
diagram, model, graph, or table).
WHAT STUDENTS DO
Students draw and compare double bar graphs showing changes in the numbers
of fossil families in the fish, reptile, and mammal classes over geologic time. From
this evidence, they can conclude that both speciation and extinction have occurred
in all classes of vertebrates for as long as each class has existed. Students discuss
how this evidence provides further support for a branching model for evolution.
MATERIALS AND ADVANCE PREPARATION
■■ For the teacher
1 Scoring Guide: analyzing and interpreting data (aid)
1 Visual Aid 11.1, “Comparing Fossil Families”
1 Visual Aid 11.2, “History of Fossil Amphibian Families”
150 EVOLUTION
FAMILY HISTORIES ACTIVITY 11
■■ For each student
2 colored pencils
1 Student Sheet 11.1, “Graphs of Fossil Families”
1 Scoring Guide: analyzing and interpreting data (aid) (optional)
1 Science Skills Student Sheets 4a and 4b, “Scatterplot and Line Graphing
Checklist” (optional)
*not included in kit
TEACHING SUMMARY
GET STARTED
1. Students consider what other kinds of patterns might exist in the fossil record.
a. Briefly review the kinds of information students have obtained from fossils
so far in the unit.
b. Have students read the scenario and introduction.
DO THE ACTIVITY
2. Students graph and interpret data on fossil families over geologic time.
a. Direct students to carry out Procedure Steps 1 and 2 with their partners.
b. Have a brief discussion about the possible causes for the appearance and
disappearance of a fossil family.
c. Direct students to Procedure Steps 3 and 4, and instruct them to create
double bar graphs from the information in the data provided for reptiles
and mammals.
d. Project Visual Aid 11.1, “Comparing Fossil Families,” which shows
completed graphs of the data for fish, reptiles, and mammals. (These are
the Sample Students Responses for Student Sheet 11.1)
BUILD UNDERSTANDING
3. Students analyze the evolutionary history of three classes of vertebrates.
a. (aid assessment) Direct students to Analysis item 1, and explain that they
will be assessed on their responses using the analyzing and interpreting
data (aid) Scoring Guide.
Analysis item 1 assesses Performance Expectation MS-LS4-1.
b. As a class, discuss Analysis items 2–4.
Use Visual Aid 11.2, “History of Fossil Amphibian Families,” for Analysis
item 3, if you wish.
EVOLUTION 151
ACTIVITY 11 FAMILY HISTORIES
TEACHING STEPS
GET STARTED
1. Students consider what other kinds of patterns might exist in the fossil record.232233234
a. Briefly review the kinds of information students have obtained from fossils
so far in the unit.
Ask students to brainstorm while you or another student record the ideas
on the board or chart paper.
b. Have students read the scenario and introduction.
Clarify that a family in science refers to a specific level of classification.
The introduction uses Felidae (cats) and Canidae (dogs) as relatively
familiar examples for students. Explain that there are many families of
mammals and many families of other types of organisms. Explain that this
activity focuses on families of fish, reptiles, and mammals.
Observant students may note that the oldest fossil dates back to 3.77 billion
years ago, but life existed 4.28 billion years ago. Explain that the evidence
of this early life is still being confirmed as scientists continue to verify that
the microscopic metallic detritus found in northern Quebec are indeed
microfossils from bacteria that lived around hydrothermal vents.235236
DO THE ACTIVITY
2. Students graph and interpret data on fossil families over geologic time.237
a. Direct students to carry out Procedure Steps 1 and 2 with their partners.
Remind students of “Interpreting Graphs” in Appendix C in their Student
Books. This resource offers suggestions to students about how to read and
interpret graphs. “Science Communication Skills” in Appendix D (bottom
row in table) offers additional support for students about interacting with
their peers while looking at graphs and text. Circulate throughout the
room and, if necessary, model how to use these two resources.238239
b. Have a brief discussion about the possible causes for the appearance and
disappearance of a fossil family.
The first appearance of a fossil family may mean that the family first
evolved from its ancestors at that time. It is also possible that it evolved
in a prior period but has not been discovered in the fossil record. A fossil
family may disappear in the fossil record because it has become extinct.
And because of the nature of the fossil record, it is possible for a family,
especially one with a small or geographically restricted set of populations,
232 NGCCPA2
233 NGLS4A1
234 NGLS4A2
235 NGSPNS1
236 NGCCNS3
237 NGSPAD1
238 SESSGI2
239 SESSRG1
152 EVOLUTION
FAMILY HISTORIES ACTIVITY 11
to have left very few fossils. Or perhaps those fossils were left only in a
region that has not yet been explored.
c. Direct students to Procedure Steps 3 and 4, and instruct them to create
double bar graphs from the information in the data provided for reptiles
and mammals. 240
Hand out Student Sheet 11.1, “Graphs of Fossil Families.” These graphs
have the axes already labeled to allow for direct comparison of the
Reptile and Mammal Graphs with the Fish Graph. Remind students of
Science Skills Student Sheets 4a and 4b, “Scatterplot and Line Graphing
Checklist” if they need continued support.241
One way to make sure that students understand the data presented in
the table is to discuss responses to the discussion questions in Procedure
Step 1. The fish family data presented in the Student Book represent all
four classes of fish combined (bony fish, cartilaginous fish, hagfishes, and
lampreys). The greatest numbers of fish families first appear in the fossil
record 0–65 mya. The greatest number of fish families disappear from the
fossil record 365–425 mya.
d. Project Visual Aid 11.1, “Comparing Fossil Families,” which shows
completed graphs of the data for fish, reptiles, and mammals. (These are
the Sample Students Responses for Student Sheet 11.1)
Note that data in this activity refer only indirectly to the total number
of families alive during each period of time. “First appearances” refer
to families new to the fossil record, whereas “last appearances” refer
to families that do not appear any later in the fossil record. To find the
change in the total number of families in existence that occurs during a
time period, subtract the number of last appearances from the number of
first appearances.
BUILD UNDERSTANDING
3. Students analyze the evolutionary history of three classes of vertebrates.
a. (aid assessment) Direct students to Analysis item 1, and explain that they
will be assessed on their responses using the analyzing and interpreting
data (aid) Scoring Guide. 242243244
Analysis item 1 assesses Performance Expectation MS-LS4-1.
240 MASP6B5 Review the levels and criteria in the Scoring Guide for integrating
241 SESSLG1 the Disciplinary Core Idea of Evidence of Common Ancestry and
242 SEASAD1 Diversity and the Crosscutting Concept of Patterns with the Science and
243 NGPEL41 Engineering Practice of Analyzing and Interpreting Data.
244 NGCCPA2
EVOLUTION 153
ACTIVITY 11 FAMILY HISTORIES
b. As a class, discuss Analysis items 2–4.
Use Visual Aid 11.2, “History of Fossil Amphibian Families,” for Analysis
item 3, if you wish.
The terms given to periods of time are based on the observation that once
a given group of vertebrates appears in the fossil record, it tends to go
through a period of great speciation. However, although new groups may
appear later in time, previously existing groups continue to evolve too,
as students can observe on their graphs. For example, the appearance of
reptiles in the fossil record indicates that they share a common ancestor
with later families of fish; this is typically, though misleadingly, described
as “reptiles evolving from fish.”
The figure showing a vertebrate evolutionary tree in the “History and
Diversity of Life” activity presents a simple evolutionary tree for fish,
reptiles, and mammals, indicating that the reptile lineage arose from the
fish lineage, and the mammalian lineage arose from the reptiles. Point out
to students the difference between this tree and a linear chain or ladder.
Emphasize that when reptiles evolved from fish, many branches of the
fish tree continued to evolve into new fish families and species, while one
branch of the tree evolved into reptiles.
SAMPLE RESPONSES TO ANALYSIS
1. (aid assessment, MS-LS4-1) Describe the patterns in the three graphs and what
these patterns tell you about the evolution of the three groups of organisms. Be
sure to include how they are similar and how they are different. 245246247248249250251
245 NGSPAD1 SAMPLE LEVEL-4 RESPONSE
246 SEASAD1
247 NGCCPA2 Fish appeared first, then reptiles, and then mammals.The number of new fish families
248 NGLS4A1 increased around 400 mya to about 155, but then many families went extinct shortly
249 NGLS4A2 after this time.The number remained low until 60 mya, when the number of new
250 NGPEL41 families appearing increased to 299, which is almost double the previous peak. Most
251 ELRS687 of the families remained, with only a small number going extinct. Reptile families
didn’t really appear in large number until around 300 mya.The number of families
154 EVOLUTION appearing and going extinct stayed relatively constant until around 65 mya, when
this number dropped to low levels for both first and last appearances. Mammal
families were at low levels until around 65 mya, when the number of new families
appearing increased by a very large amount. But the number of mammal families
going extinct was also high.This order suggests that fish evolved first, then reptiles,
and finally mammals. Perhaps the later-appearing animals evolved from the earli-
er-appearing ones through speciation events that eventually led to the appearance of
new groups of vertebrates.
FAMILY HISTORIES ACTIVITY 11
2. Scientists sometimes label periods of time by what organisms were common at
the time.
a. The period of time from 65 mya until today is often referred to as the age
of mammals. Using evidence from this activity, explain why.
Around 65 mya on the fossil record, there is a huge increase in the diversity
of mammals, as indicated by the fact that there are many more mammalian
families than there were before this time.
b. Based on evidence from this activity, what would you call the period of
time from 305 mya to 65 mya? Explain your reasoning.
The time period could be called the “age of reptiles.” Reptiles display the largest
increase in number of fossil families during that era, as evidenced by the greater
number of “first appearance” than “last appearance” families.
3. Look at your answer for Analysis item 1 and the following table and graph.
Where do you think scientists have placed the amphibian family? Explain your
answer.
History of Fossil Amphibian Families
TIME (MYA) >545 485 425 365 305 245 185 125 65 0
Number of first 0 00 3 35 33 19 11 5 15
appearances
0 00 3 16 53 18 51 5
Number of last
appearances
Graph of Fossil Amphibian Families Over Time
200 rst appearances
last appearances
Number of Families 150
185 125
100
50
0 >545 485 425 365 305 245 65 0
Millions of years ago
Scientists probably placed the amphibian family after the fish and before the
reptile families.TFLhiagbeuArfeidi:rsEsvStoEP3fiUesPThEIA1fP1aS_m2Eviolliuetsiona3pepeared around 500 mya, and the first
fossil reptile famiMliyersiaadPpropReeagr9e.d5/1a1round 300 mya.The first amphibian families
appeared in the last part of the early Paleozoic period.The first amphibians
appeared around 425 mya, so they seem to come between fish and reptiles.
EVOLUTION 155
ACTIVITY 11 FAMILY HISTORIES
4. Does the evidence in this activity support the figure of the vertebrate evolu-
tionary tree in the activity, “History and Diversity of Life”? 252
The figure shows that fish evolved first, then amphibians, then reptiles/bird,
and then mammals.The evidence from the fossils in this activity supports that
evolutionary tree. But the tree does not show all reptiles, only crocodiles, so I am not
sure how the evidence collected here about reptiles fits with that figure.
REVISIT THE GUIDING QUESTION
What can you learn about evolution by comparing the fossil records of fish,
mammals, and reptiles?
Fish evolved first and became very abundant for a period of time. Then
amphibians evolved, followed by reptiles/birds and mammals. Each group has had
a period of time when they seemed to be more successful than other groups.
ACTIVITY RESOURCES
KEY VOCABULARY
evolution
fossil
BACKGROUND INFORMATION
THE FOSSIL RECORD
It is estimated that 10 million different species are alive today and that 5–50 billion
species have existed at some time in Earth’s history! The number of species that have
existed can only be estimated because of the nature of the fossil record. The fossil
record is the name given to all the different fossils that have been found anywhere
on Earth. This record is by no means a complete record of every type of organism
that has ever lived. In fact, although scientists have a good understanding of a
large number of the different types of organisms that have lived in the past, a great
many more are poorly understood or have yet to be discovered. One of the inherent
biases of the fossil record is that vertebrates and other organisms with hard body
parts (e.g., shells, bones, or teeth) are much more likely to be preserved as fossils
than those organisms with only soft body parts. Another inherent bias is toward
organisms that live in the water because a watery environment provides geologic
conditions much more suitable for preserving organisms than the conditions found
on land.Yet another bias is toward organisms that have large populations.
252 NGSPCE6
156 EVOLUTION
FAMILY HISTORIES ACTIVITY 11
Although fossils have been found in Precambrian Era rocks as old as 3.5 billion
years, most fossils have been found in Paleozoic, Mesozoic, and Cenozoic rocks,
a period spanning only the past 550 million years. There are two main reasons for
the much greater abundance and diversity of fossils found in rocks younger than
Precambrian. The first reason is that for much of the Precambrian Era, there was
nothing alive that was easily fossilized. When geologists first began naming geologic
time periods, the boundary between Cambrian and Precambrian was defined as
that point before which no fossils have been found. Although many fossils have
now been found in Precambrian rocks, the Cambrian Era is still associated with
a huge jump in the diversity of fossilized organisms. The ecological conditions
that existed during the early Cambrian, coupled with the genetic diversity of the
already existing organisms, are thought to have favored this explosion of new life
forms with hard body parts, including the first vertebrates—jawless fish. These
hard body parts are better preserved than the bodies of earlier life forms, most of
which were soft-bodied organisms.
The second reason that there are more fossils from recent eras is that older rocks
have been subjected longer to the various forces of nature (e.g., erosion, the heat
and pressure of burial, and tectonic movements), which can completely remove
fossilized material or make it unrecognizable. Therefore, younger rocks, just by
virtue of being younger, have a better chance of containing a more complete set
of fossils than older rocks; the finer detail in younger rocks also allows for more
precise identification and classification.
The double bar graphs used in this activity simultaneously track inferred
extinctions and speciations (more precisely, loss and gain of diversity as measured
by the disappearance and diversification of fossil families). As more new fossil
families of a vertebrate group appear in the fossil record, a greater number of
families disappear (in general). Often, the extinction of a group is accompanied
by the evolution of a new group that occupies its vacant (but modified) niche.
More generally, more groups of species in existence means more species with the
potential to die out. For a given time period, the overall diversity of families that
exist within a group of vertebrates can be approximated by subtracting the number
of last appearances from the number of first appearances that have occurred to
that point. However, the intended focus of this activity is that extinction and
the appearance of new life forms by the branching of pre-existing forms are the
normal condition throughout the history of life.
REFERENCES
Benton, M. J. (Ed.) (1993). The fossil record 2. London, UK: Chapman & Hall.
EVOLUTION 157
Name______________________________________________________________ Date____________
STUDENT SHEET 11.1
GRAPHS OF FOSSIL FAMILIES
First appearances
200 Last appearances
Number of families 150
100
50
0 >545 485 425 365 305 245 185 125 65 0
0
Millions of years ago
LabAids SEPUP IAPS Evolution 3e First appearances
Figure: Evo3e TE 11_3a StudentSheet Last appearances
MyriadPro Reg 9.5/11
450 185 125
400
350
©2017 The Regents of the University of California 300
Number of families 250
200
150
100
50
0 >545 485 425 365 305 245 65
Millions of years ago
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 11_3b StudentSheet
MyriadPro Reg 9.5/11
VISUAL AID 11.1
COMPARING FOSSIL FAMILIES
Fossil Fish Families Over Time 299
65 0
200 First appearances 65 0
Last appearances
Number of families 150
365 305 245 185 125
100 Millions of years ago
First appearances
50 Last appearances
0 >545 485 425 365 305 245 185 125
Millions of years ago
Fossil ReLpatbilAeidFsaSmEiPliUePs OIAvPeSrETviomluetion 3e
Figure: Evo3e TE 11_4a Visual Aid
200 MyriadPro Reg 9.5/11
Number of families 150
100
50
0 >545 485 425
LabAids SEPUP IAPS Evolution 3e First appearances 404
Fossil MaFMimgyurmiraead:lPEFrvoaomR3eeilgTieE9s.15O1/1_v14ebr TViimsueal Aid Last appearances 262
200 365 305 245 185 125 65 0
Millions of years ago
©2017 The Regents of the University of California 150
Number of families 100
50
0 >545 485 425
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 11_4c Visual Aid
MyriadPro Reg 9.5/11
PRECAMBRIAN EARLY PALEOZOIC LATE PALEOZOIC MESOZOIC CENOZOIC
TIME (MYA) >545 485 425 365 305 245 185 125 65 0
Number of first 6 14 33 404
VIaSppUeaAranLceAs ID 110.2 00 0 0 0 2 8 33 262
0 0
Number of last
HISapTpOeaRraYncOesF FOSSI0L AMPHIB0IAN F0AMILIE0S
History of Fossil Amphibian Families
PRECAMBRIAN EARLY PALEOZOIC LATE PALEOZOIC MESOZOIC CENOZOIC
TIME (MYA) >545 485 425 365 305 245 185 125 65 0
Number of first 0 00 3 35 33 19 11 5 15
appearances
5
Number of last 0 0 0 3 16 53 18 5 1
appearances
Number of Families rst appearances
200 last appearances
150
100
50
0 >545 485 425 365 305 245 185 125 65 0
Millions of years ago
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e SB 11_8
MyriadPro Reg 9.5/11
©2017 The Regents of the University of California
12 A Whale of a Tale
i n v e s t i g at i o n
2 class sessions
ACTIVITY OVERVIEW
NGSS CONNECTIONS
Students compare anatomical structures in modern adult whales and embryos
with fossil whales to construct an explanation about the evolutionary history and
relationships of whales. The activity provides an opportunity to assess student work
related to Performance Expectation MS-LS4-2.
NGSS CORRELATIONS
Performance Expectations
MS-LS4-2: Apply scientific ideas to construct an explanation for the anatomical
similarities and differences among modern organisms and between modern and
fossil organisms to infer evolutionary relationships.
Working towards MS-LS4-3: Analyze displays of pictorial data to compare patterns
of similarities in the embryological development across multiple species to identify
relationships not evident in the fully formed anatomy.
Applying MS-LS4-1: Analyze and interpret data for patterns in the fossil record
that document the existence, diversity, extinction, and change of life forms
throughout the history of life on Earth under the assumption that natural laws
operate today as in the past.
Disciplinary Core Ideas
MS-LS4.A Evidence of Common Ancestry and Diversity:
The collection of fossils and their placement in chronological order (e.g., through
the location of the sedimentary layers in which they are found or through
radioactive dating) is known as the fossil record. It documents the existence,
diversity, extinction, and change of many life forms throughout the history of life
on Earth.
Anatomical similarities and differences between various organisms living today
and between them and organisms in the fossil record, enable the reconstruction of
evolutionary history and the inference of lines of evolutionary descent.
EVOLUTION 161
ACTIVITY 12 A WHALE OF A TALE
Comparison of the embryological development of different species also reveals
similarities that show relationships not evident in the fully-formed anatomy.
MS-ES1.C The History of Planet Earth: The geologic time scale interpreted from
rock strata provides a way to organize Earth’s history. Analyses of rock strata and
the fossil record provide only relative dates, not an absolute scale.
Science and Engineering Practices
Constructing Explanations and Designing Solutions: Apply scientific ideas to
construct an explanation for real-world phenomena, examples, or events.
Analyzing and Interpreting Data: Analyze displays of data to identify linear and
nonlinear relationships.
Engaging in Argument from Evidence: Use an oral and written argument supported
by evidence to support or refute an explanation or a model for a phenomenon.
Crosscutting Concepts
Patterns:
Patterns can be used to identify cause and effect relationships.
Graphs, charts, and images can be used to identify patterns in data.
Connections to Nature of Science: Science Knowledge Assumes an Order and Consistency
in Natural Systems: Science assumes that objects and events in natural systems
occur in consistent patterns that are understandable through measurement and
observation.
Common Core State Standards—Mathematics
6.SP.B.5: Summarize numerical data sets in relation to their context.
Common Core State Standards—ELA/Literacy
RST.6-8.7: Integrate quantitative or technical information expressed in words in
a text with a version of that information expressed visually (e.g., in a flowchart,
diagram, model, graph, or table).
WHAT STUDENTS DO
Students investigate how fossil history provides another line of evidence for
evolution. They compare the skeleton of a living whale to fossils of its extinct
ancestors and use anatomical differences to arrange the skeletons in order.
Students apply the theory of natural selection to whale evolution, using anatomical
adaptations to infer the habitats and lifestyles of extinct species.
162 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
MATERIALS AND ADVANCE PREPARATION
■■ For the teacher
1 Scoring Guide: constructing explanations (exp)
1 Visual Aid 12.1, “Whale Evolutionary Tree”
1 Visual Aid 12.2, “Scientific Illustration of Ambulocetid”
1 Visual Aid 12.3, “Whale Skeleton Cards”
■■ For each pair of students
1 set of 5 Whale Skeleton Cards
1 metric ruler (optional)
■■ For each student
1 Student Sheet 12.1, “Whale Fossil Chart”
1 Scoring Guide: constructing explanations (exp) (optional)
1 Literacy Student Sheet 4a, “Writing Frame—Constructing Explanations”
(optional)
*not included in kit
TEACHING SUMMARY
GET STARTED
1. Students are introduced to the problem of how modern whales evolved.
a. Ask students, “How do you think whales evolved? Do you think that some
mammals moved from land to sea or that a type of fish evolved to have
mammalian traits?”
b. Ask students, “What type of evidence could help answer this question?”
c. Have students read the introduction in the Student Book.
DO THE ACTIVITY
2. Students group five whale and whale-ancestor skeletons according to similari-
ties and differences.
a. Distribute a set of five Skeleton Cards to each pair of students while they
read the scenario “The Fossil Exhibit.”
b. Direct students to Procedure Step 1.
c. Support student sensemaking by monitoring students as they create their
Venn diagrams in Procedure Steps 2 and 3.
d. Instruct students to organize the skeletons into a sequence in Procedure
Step 4 depending on similarities and differences.
EVOLUTION 163
ACTIVITY 12 A WHALE OF A TALE
e. Direct students to Procedure Steps 5 and 6, in which they obtain
additional embryological evidence to inform their sequences.
f. Pass out Student Sheet 12.1, “Whale Fossil Chart,” which includes
additional evidence for Procedure Steps 7 and 8.
g. Once groups have finished revising their arrangements, have groups of two
pair up into groups of four and compare both their earlier arrangements
and their revised ones.
BUILD UNDERSTANDING
3. Students have a whole-class discussion around Analysis items 1 and 2.
a. Ask a few student pairs to share what they have observed about skeletal
changes that have occurred and what changes in the environment might
have been associated with them.
b. Facilitate a discussion around how natural selection led to these changes.
4. (exp assessment) Students answer Analysis item 4.
5. Have students answer Analysis items 5 and 6.
a. After students have had time to answer Analysis item 5, have a discussion
about it.
b. Show Visual Aid 12.2, “Scientific Illustration of Ambulocetid,” once
students have finished answering Analysis item 6.
TEACHING STEPS
GET STARTED
1. Students are introduced to the problem of how modern whales evolved.
a. Ask students, “How do you think whales evolved? Do you think that some
mammals moved from land to sea or that a type of fish evolved to have
mammalian traits?”
Allow students to share their ideas.
b. Ask students, “What type of evidence could help answer this question?”
Encourage students to think about as many lines of evidence as they can.
Students are likely to refer to fossils and/or DNA evidence. If they do,
encourage them to suggest ways in which this type of evidence could be
used to reconstruct whale evolution.
c. Have students read the introduction in the Student Book.
Inform students that they will be using the fossil record to investigate
part of the evolutionary history of whales. They will examine skeletons
164 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
of several different species of whales to reconstruct how whales
evolved.253254255
DO THE ACTIVITY
2. Students group five whale and whale-ancestor skeletons according to similari-
ties and differences.
a. Distribute a set of five Skeleton Cards to each pair of students while they
read the scenario “The Fossil Exhibit.”
You may wish to have a student read the scenario out loud for the whole
class or have students read the scenario in their groups or individually.
b. Direct students to Procedure Step 1.
Students are first asked to sort the skeletons into two group. The group
containing Skeleton A should be referred to as Group 1 to allow groups to
compare their sortings. Most students are likely to place Skeletons A and
M in Group 1 and Skeletons B, D, and O in Group 2. However, accept
any reasonable sorting at this point.256257
If students ask, confirm that all skeletons have limbs in pairs, just as
Skeleton M clearly does.
c. Support student sensemaking by monitoring students as they create their
Venn diagrams in Procedure Steps 2 and 3.
If students are struggling, help them get started by thinking of one
characteristic that all of the skeletons have in common; that characteristic
should be placed in the space where the circles intersect. Then help
students identify one characteristic that all skeletons in Group 1 share
with each other but not with Group 2.
A completed Venn diagram might look like this:
253 NGLS4A1
254 NGLS4A2
255 NGES1C1
256 NGCCNS3
257 NGSPAD4
Group 1 • four limbs that • heads with • only two limbs Group 2
Skeletons A and M seem like legs jaws that seem like Skeletons B, D, and O
(they point ns
down) • eye sockets
• tails • flat heads that
• rounded heads • ribs are relatively
that are small
relatively big
LabAids SEPUP IAPS Evolution 3e EVOLUTION 165
Figure: Evo3e TE 12_1
MyriadPro Reg 9.5/11
ACTIVITY 12 A WHALE OF A TALE
d. Instruct students to organize the skeletons into a sequence in Procedure
Step 4 depending on similarities and differences.258259260
Their sequence may not be completely linear, since this lineage of whales
includes one skeleton that should branch off the main line (see Visual
Aid 12.1, “Whale Evolutionary Tree”). However, do not inform students
about his branch. Instead, allow them to discover for themselves that
they are constructing a time-based sequence of the evolution of modern
whales.
The sequence in which students place the Skeleton Cards will vary.
Encourage them to identify the characteristics they are using to order the
skeletons and to describe how those characteristics might relate to the
evolution of whales. Accept all reasonable sequences at this point.
Some student pairs may order the skeletons as M, A, O, D, B and justify
this as a progression to smaller skull sizes and skinnier bodies.You may
wish to point out that skeleton O has no hind limb bones at all and,
therefore, this sequence would require hind limb bones to disappear and
then reappear later. In addition, D and B have forelimbs that look more
leg-like as compared to the flipper-like forelimbs of O.
Note that some pairs may arrange and describe their skeletons as
displaying evolution from sea to land—an expression of a widely held
misconception about one-way progressions in evolution.
e. Direct students to Procedure Steps 5 and 6, in which they obtain
additional embryological evidence to inform their sequences.261
The phenomenon that whale embryos have hair is intended to help
students realize that whales evolved from land mammals, where hair and
limbs are useful. If whales evolved first, from a fish-like ancestor, there
would have been no selection favoring the presence of hair or limbs.
f. Pass out Student Sheet 12.1, “Whale Fossil Chart,” which includes
additional evidence for Procedure Steps 7 and 8.
If necessary, explain that this chart shows the approximate rock layers in
which the various skeletons have been found. The letters represent the
scientific names of the various skeletons. A stands for ambulocetids, B
stands for balisosaurids, D for dorudontids, M for mesonychids, and O
for odontocetes, or modern toothed whales. Skeleton O is the skeleton of
a modern dolphin. Students should use this new evidence to evaluate and
possibly revise their arrangement of skeletons.
258 NGCCPA2
259 MASP6B5
260 NGCCPA1
261 NGLS4A3
166 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
g. Once groups have finished revising their arrangements, have groups of two
pair up into groups of four and compare both their earlier arrangements
and their revised ones. 262
As you circulate, confirm that finding Skeletons B and D in the same rock
layers means that they cannot be ordered relative to each other based
on the fossil evidence. Therefore, using reasoning based on the law of
superposition, the best inferred order at this point is the following:
Most Recent
(modern)
O
D, B
A
M
Earliest
(oldest)
BUILD UNDERSTANDING
3. Students have a whole-class discussion around Analysis items 1 and 2.
a. Ask a few student pairs to share what they have observed about skeletal
changes that have occurred and what changes in the environment might
have been associated with them.
These questions reinforce patterns and likely cause-and-effect
relationships.
b. Facilitate a discussion around how natural selection led to these changes.
This discussion reinforces these two concepts learned earlier in the unit:
(1) Changes in the environment result in changes in natural selection, and
(2) only certain traits are adaptive in that altered environment.
4. (exp assessment) Students answer Analysis item 4.263264265266267
Direct students to Analysis item 4, and explain that they will be assessed on
their responses using the exp Scoring Guide.
Analysis item 4 assesses Performance Expectation MS-LS4-2.
Review the levels and criteria in the Scoring Guide for integrating the
Disciplinary Core Idea of Evidence of Common Ancestry and Diversity
and the Crosscutting Concept of Patterns with the Science and Engineering
Practice of Constructing Explanations.
262 NGSPEA2
263 SEASEX1
264 NGSPAD4
265 NGPEL42
266 ELRS687
267 NGSPCE6
EVOLUTION 167
ACTIVITY 12 A WHALE OF A TALE
Consider providing students with Literacy Student Sheet 4a, “Writing
Frame—Constructing Explanations,” as a scaffolding tool to help them
combine the evidence from the fossil skeletons and the embryos.268
5. Have students answer Analysis items 5 and 6.
a. After students have had time to answer Analysis item 5, have a discussion
about it.
Explain that in the next activity, “Embryology,” students will further
explore how embryos provide evidence for evolutionary relationships.
b. Show Visual Aid 12.2, “Scientific Illustration of Ambulocetid,” once
students have finished answering Analysis item 6.
Have students share how close their predictions are compared with this
picture drawn by a scientist.
SAMPLE RESPONSES TO ANALYSIS
1. During the evolution of whales,
a. what kinds of skeletal changes have occurred?
External hind limbs were lost, and the bones were either greatly reduced or lost
entirely; the skull changed size and shape in various ways; forelimbs turned into
fins; the tail elongated due to the loss of the pelvis and external hind limbs; and
the tail vertebrae become thicker and larger. One much more subtle observation
is that the enlarged neck vertebrae shrank, an indication of decreased need for
powerful neck muscles to support the weight of the head under water.
b. what changes in habitat might have occurred at the same time? 269
These changes indicate a transition from predominantly land-dwelling animals
to ones that lived partly on land and partly in shallow water, and eventually to
animals with an exclusively aquatic habitat.
2. Use natural selection to explain how these changes (or one of these changes)
could have occurred. 270
Originally, there was some variation in the whale ancestor population.This variation
was a genetic mutation passed from parents to offspring. Although they all lived in the
water, some had larger back legs and some had smaller back legs.Those with smaller
back legs could survive better because it was easier for them to swim (they were more
streamlined), and they could catch more food.They could also escape from predators
more easily. (This was especially important when they were young.) These whales
lived to produce more young. Every generation, more whales with smaller back legs
survived. Over many, many generations, the average size of the back legs decreased.
268 SELTWF1
269 NGCCPA1
270 NGSPCE6
168 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
3. How does the observation that whale embryos have hair and hind limb buds
help you understand whale evolution? 271
The observation that whale embryos have hair supports the argument that whales
evolved from land mammals. If whales evolved from fish and then whales evolved
into land animals, you would only expect to see hair and limbs appear on the first
land animals.The presence of hair and limbs in whale embryos but not the mature
animals suggests that they evolved from ancestors that did have hair and limbs.These
ancestors are most likely land mammals. At some point, evolution of whales led to
the loss of hair and hind limbs in the mature animal, even though some hair and
evidence of hind limb structures are still present on the embryo.
4. (exp assessment, MS-LS4-2) Answer the question in the introduction: Did sea
mammals appear first and then evolve into land mammals, or did it happen the
other way around? Explain using evidence and scientific reasoning. 272273274275276
SAMPLE LEVEL-4 RESPONSE
Whales evolved from land mammals.The evidence for this answer is based on
both examination of the skeletons for these mammals and evidence about when the
mammals appear in the fossil record.The structures of the skeletons suggest a range
from those organisms that appear to have lived on land or in shallow water and those
that live in the ocean.These structures could be used to infer relationships between
the five species. If land mammals evolved from sea whales, you would expect the sea
whale fossil skeletons to be older than the land animal skeletons. But instead, the land
animal fossil skeletons are older than the more modern whale skeletons.
5. In this activity, you examined extinct and modern whale skeletons. How does
the study of these skeletons provide evidence about how species are related?
Comparing skeletons can show similarities and differences between species. By looking
at the number of differences and similarities, scientists can infer the relationships
between different groups of organisms. If enough fossils of a particular group of
organism are found, an evolutionary tree can be constructed. Scientists can, therefore,
use fossil skeletons to help figure out which living species a group is most closely
related to. For example, whales and dolphins are “cousins” of cows and sheep.
6. Look again at Skeleton A. This is known as an ambulocetid (am-byoo-low-
SEE-tid). The word ambulocetid means “walking whale.” Where do you think
the ambulocetids lived? Describe how you think they lived. 277
271 NGLS4A3 This whale probably lived in shallow water or near-water habitats.They had large
272 NGPEL42 limbs compared with the other skeletons.They must have used these hind limbs on
273 NGLS4A1 land because they would not be very useful in a completely aquatic environment.
274 NGLS4A2
275 NGLS4A3 EVOLUTION 169
276 SEASEX1
277 NGSPEA2
ACTIVITY 12 A WHALE OF A TALE
EXTENSION
For students who are interested in how DNA evidence is used to investigate the
evolutionary history of whales, encourage them to visit the SEPUP Third Edition
Evolution page of the SEPUP website at www.sepuplhs.org/middle/third-edition and
go the to the whale DNA link. Students can compare how the DNA and fossil
evidence compare.
An optional supplemental activity is found on the Teacher Portal for this activity.
This supplemental activity, "A Whale of a Tale: DNA Evidence" has students
examine simulated DNA to determine the evolutionary relationship of whales
to other vertebrates. Students can then compare the evidence from DNA to the
evidence from fossils.
REVISIT THE GUIDING QUESTION
How did whales evolve?
Whales evolved from land mammals. Natural selection favored land mammals with
traits that allowed them to survive in aquatic environments. Originally whales lived
near shore, but eventually they evolved to live entirely in the water, losing hair and
hind limbs entirely as adults.
ACTIVITY RESOURCES
KEY VOCABULARY
DNA
embryo
evolution
extinct
natural selection
BACKGROUND INFORMATION
CETACEAN EVOLUTION
Although most people tend to view evolution as a transition from sea creatures
to land creatures, there is evidence of quite a few instances where a lineage of
land creatures evolved into sea creatures. For instance, the aquatic mammals—
pinnipeds (seals, sea lions, and walruses), sirenians (manatees, dugongs, and
the recently extinct Stellar’s sea cow), and cetaceans (whales, dolphins, and
porpoises)—all have land-dwelling ancestors. In fact, the pinnipeds are not
170 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
completely aquatic, providing an example of an intermediate state during the
transition from land to water.
Whales, dolphins, and porpoises make up the order Cetacea, which includes 40
genera of living cetaceans and approximately 140 genera of known extinct cetacean
ancestors. The cetacean evolutionary tree, shown on Visual Aid 12.1, illustrates
the relationships between the various extinct whale ancestors, the whales that exist
today, and their living land-dwelling relatives. Many of the scientific names of
whale ancestors contain the root “cet-“ to indicate that these animals are related to
modern cetaceans.
Animals recognizable as modern whales have been swimming the seas and rivers
for at least a few million years. Their mammalian characteristics (produce milk,
have lungs, are “warm-blooded,” and have vestigial hair) and forelimb structure
have long suggested a terrestrial origin, well supported by DNA evidence.
However, it wasn’t until the 1990s that fossils were unearthed that allowed the
whale lineage to be traced to its 55-million-year-old ancestors: small land-dwelling
mammals. The skeleton reconstructions used in this activity are from ancestral
whales for which the fossil evidence allows a complete drawing to be made with
confidence. There are numerous other partial skeletons of other whale ancestors,
intermediate in age to the ones provided in this activity, but unfortunately, the
skeletons of these are too incomplete to provide obvious evidence of transitional
features to non-paleontologists.
There are two suborders of modern whales: the Odontoceti (or toothed whales)
and the Mysticeti (or baleen whales). Toothed whales are predators and include
porpoises, dolphins, orcas (killer whales), narwhals, and sperm whales. Baleen
whales, such as humpback, gray, and blue whales, have huge mouths spanned by
large sieves made of keratin that strain plankton from the seawater. It is generally
accepted that both the toothed whales and the baleen whales are descended
from the same group of aquatic ancestors—the dorudontids—although a few
researchers propose independent origins of baleen and toothed whales from
different land mammal groups. Additional fossil findings may eventually help
resolve this debate by filling in more positions on the whale evolutionary tree.
The stepwise shift in habitat from land to shallow water to open ocean involved
many adaptations, which occurred in large part over the 20 million years between
about 55 and 35 mya. (Note that because of the incompleteness of the fossil
record, the exact time these adaptations evolved cannot be pinpointed. Similarly,
the branch points indicated on Visual Aid 12.1 are only approximate inferences.)
These adaptations include a shift of the nostrils backward and upward on the
skull, appearance of coverings for the nostrils, streamlining of the body shape,
reduction and elimination of the hind limbs, transformation of the forelimbs
EVOLUTION 171
ACTIVITY 12 A WHALE OF A TALE
into flippers, strengthening of the tail, addition of tail flukes, modification of ears
and eyes, loss of most hair, and acquisition of a layer of insulating blubber. In
general, the features of a fossil that most clearly show whether an ancestor of an
aquatic mammal lived on land or in the water are those skeletal features related to
breathing, hearing, and locomotion.
Modern whales have no external hind limbs; they have either no pelvic or hind limb
bones at all, or very small ones that are disconnected from the rest of the skeleton
and are vestigial (except as attachment points of genital muscles). On the other
hand, whale forelimbs contain large, flattened out, paddle-like bones, modified
for use as flippers. Whales also have adaptations to their ears and nostrils that are
advantageous for swimming and diving. For example, whales and dolphins have a
blowhole on the back of the head instead of a nose between their eyes and mouths.
ANCESTORS OF MODERN WHALES
The descent of modern whales can be traced to a now-extinct group of whales
called dorudontids; the diversification of forms seen among modern cetaceans
occurred during the last 35 million years. Dorudontids were about 6 m (20
feet) long and proportionally more like dolphins than whales. They had a long
snout with many sharp, triangular teeth, and their forelimbs were small, flattened
flippers. The rear limbs were only about 10 cm (4 inches) long. They may have
spent some of their time on land, perhaps for breeding. Dorudontids lived during
the same time period as basilosaurids (between about 41 and 35 mya); the two
groups share a common ancestor, one of the protocetids (see Visual Aid 12.1).
Basilosaurids are one of the most common whale ancestors in the fossil record and
probably inhabited all oceans of the world. These enormous animals—possibly
up to 25 m (80 feet) long—had snake-like bodies with very small hind legs and
pelvises, resembling mythical sea serpents more than modern whales. Their
1.5-meter-long jaws contained cone-shaped teeth in the front, which caught
and held its prey while triangular-shaped teeth in the rear of the mouth sliced
them up. Basilosaurids most likely ate fish, squid, and their smaller cousins,
the dorudontids; however, basilosaurids appear to have left no descendants.
Dorudontids and basilosaurids were descendants of the small, seal-like protocetids.
While no complete protocetid skeletons have yet been found, they appear to
have been a widespread group that evolved to a mostly aquatic existence. These
creatures had small yet well-developed forelimbs and hind limbs, which may have
allowed them to waddle on land. However, they also had a detached pelvis (poorly
suited to supporting the body’s weight on land), powerful tails, and a water-
adapted inner ear. Protocetids were probably quick, agile hunters who preyed on
smaller sea creatures. Some species had nostrils behind the eyes, but none had the
blowhole characteristic of modern whales.
172 EVOLUTION
A WHALE OF A TALE ACTIVITY 12
Ambulocetids, the ancestors of protocetids, had large hind limbs and probably
filled an ecological niche similar to that of modern crocodiles, which they may
have resembled in form. Their fossilized skeletons have been found only in
rocks of the Indian subcontinent that were formed in near-shore environments.
Ambulocetids could move both on land and in water; their pelvis, like that of
modern land-dwelling mammals, was fused to the backbone. They probably
ambushed their prey in shallow, near-shore waters using their strong jaws and large
teeth. The Ambulocetus natans (meaning “walking whale that swims”) was about
the size of a sea lion—3 m (10 feet) long and about 300 kg (650 pounds)—and
probably swam similarly to a modern otter, using large hind limbs as paddles. Its
fossils are about 49 million years old.
Remingtonocetids, an odd group of animals that lived at about the same time
as ambulocetids, appear to have left no descendants. Similar to ambulocetids in
their large hind limbs, they differ in having smaller eyes, long and slender snouts,
and widely separated ears. These may have been adaptations for enhanced use of
hearing to locate prey.
Ambulocetids and remingtonocetids appear to be descendants of the earliest
known whales, the pakicetids, fossils that first appear in rocks found in Pakistan
and were formed around 55 mya. Although thought to have spent considerable
time in the water, pakicetids had four fully developed legs to support their weight
on land, as well as nostrils and ears typical of land mammals. Their bones are very
similar to those of an extinct group of land mammals called mesonychids, of whom
pakicetids may be direct descendants. Though some paleontologists do not agree
that whales are descended specifically from mesonychids, almost all agree that
whale ancestors of that time were members of a larger, less-well-defined group of
hoofed land mammals called paraxonians.
REFERENCES
Culotta, E. (1996, Winter). It’s a long way from Ambulocetus: The whales’ journey
to the sea. Pacific Discovery, 14–18.
Gould, S. J. (1995). Hooking Leviathan by its past. Dinosaur in a haystack. New
York, NY: Crown Publisher’s, Inc.
Kellogg, R. (1936). A review of the Archaeoceti. Washington, DC: Carnegie
Institution.
Thewissen, J. G. M. (Ed.) (1998). The emergence of whales: Evolutionary patterns in
the origin Cetacea. New York, NY: Plenum Press.
Zimmer, C. (1998). At the water’s edge. New York, NY: Simon and Schuster.
EVOLUTION 173
©2017 The Regents of the University of California Name______________________________________________________________ Date____________
STUDENT SHEET 12.1
WHALE FOSSIL CHART
O
B and D
A
M
VISUAL AID 12.1
WHALE EVOLUTIONARY TREE
Modern cows sheep pigs hippopotami toothed and baleen
whales (including O)
25 mya
basilosaurs (B) dorudontids
(D)
protocetids
remingtonocetids
ambulocetids (A)
pakicetids
©2017 The Regents of the University of California 65 mya mesonychids (M)
paraxonians (hoofed land mammals)
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 12_3 VisualAid
MyriadPro Reg 9.5/11
VISUAL AID 12.2
SCIENTIFIC ILLUSTRATION OF AMBULOCETID
©2017 The Regents of the University of California
©2017 The Regents of the University of California VISUAL AID 12.3 M
WHALE SKELETON CARDS A
B
1 meter D
O
1 meter
1 meter
1 meter
1 meter
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 12_5 VisualAid
MyriadPro Reg 9.5/11
13 Embryology
i n v e s t i g at i o n
2 class sessions
ACTIVITY OVERVIEW
NGSS CONNECTIONS
Students analyze and interpret skeletal and embryological images to identify
patterns of similarities and differences across species that look very different
as mature animals. Students identify patterns of similarities throughout
developmental time to infer evolutionary relationships not obvious in the mature
animals. This activity provides an opportunity to assess student work related to
Performance Expectation MS-LS4-3.
NGSS CORRELATIONS
Performance Expectations
MS-LS4-3: Analyze displays of pictorial data to compare patterns of similarities in
the embryological development across multiple species to identify relationships not
evident in the fully formed anatomy.
Applying MS-LS4-2: Apply scientific ideas to construct an explanation for the
anatomical similarities and differences among modern organisms and between
modern and fossil organisms to infer evolutionary relationships.
Disciplinary Core Ideas
MS-LS4.A Evidence of Common Ancestry and Diversity:
Comparison of the embryological development of different species also reveals
similarities that show relationships not fully evident in the fully formed anatomy.
Anatomical similarities and differences between various organisms living today
and between them and organisms in the fossil record, enable the reconstruction of
evolutionary history and the inference of lines of evolutionary descent.
Science and Engineering Practices
Analyzing and Interpreting Data: Analyze linear displays of data to identify linear
and nonlinear relationships.
EVOLUTION 179
ACTIVITY 13 EMBRYOLOGY
Crosscutting Concepts
Patterns: Graphs, charts, and images can be used to identify patterns in data.
Structure and Function: Complex and microscopic structures and systems can
be visualized, modeled, and used to describe how their function depends on the
shapes, composition, and relationships among its parts, therefore complex natural
structures/systems can be analyzed to determine how they function.
Common Core State Standards—ELA/Literacy
RST.6-8.7: Integrate quantitative or technical information expressed in words in
a text with a version of that information expressed visually (e.g., in a flowchart,
diagram, model, graph, or table).
WHAT STUDENTS DO
Students first examine forelimb skeletons of six species to identify bones with
homologous structures and functions. Although the fully formed limbs appear
different on the outside, students are able to identify similarities at the skeletal
level. Students then examine embryological development of limbs and notice many
similarities between different species. Finally. students examine the development of
whole embryos of different species to infer evolutionary relationships.
MATERIALS AND ADVANCE PREPARATION
■■ For the teacher
1 Scoring Guide: analyzing and interpreting data (aid)
1 Visual Aid 13.1, “Comparison of Vertebrate Forelimbs”
1 Visual Aid 13.2, “Embryonic Limbs”
1 Visual Aid 13.3, “Whole Embryo Sorting”
* 64 envelopes (optional)
* 64 paper clips (optional)
■■ For each group of four students
colored pencils
■■ For each pair of students
1 set of 12 Embryonic Limb Cards
1 set of 20 Whole Embryo Cards
■■ For each student
1 Student Sheet 13.1, “Comparison of Vertebrate Forelimbs”
1 Scoring Guide: analyzing and interpreting data (aid) (optional)
* not included in kit
180 EVOLUTION
EMBRYOLOGY ACTIVITY 13
You will distribute an entire set of Embryonic Limb Cards to each pair of students. It
may be helpful to put these into envelopes or paper clip them together ahead of time.
You will distribute the Whole Embryo Cards to each pair of students based on the
developmental stage. First, they will receive the animal names and the early stage
embryos. Second, they will receive the middle stage embryos. And last, they will
receive the late stage embryos. To make it easier to hand out at the appropriate
time, you may want to sort these into envelopes or paper clip them together by
developmental stage.
TEACHING SUMMARY
GET STARTED
1. Introduce this activity by connecting it to content learned in the earlier activity
“A Whale of a Tale.”
a. Ask students to describe how they used skeletons to determine evolu-
tionary relationships.
b. Review embryos.
c. Direct students to read the introduction.
2. Let students know that they will investigate skeletons of adult animals and
then of developing embryos.
DO THE ACTIVITY
3. Students compare forelimb skeletons of three species in Part A.
a. Distribute Student Sheet 13.1, “Comparison of Vertebrate Forelimbs.”
b. Show Visual Aid 13.1, “Comparison of Vertebrate Forelimbs,” and allow
students to compare and discuss their identifications.
c. Have students discuss whether they think the animals are related based on
the structure and function of the forelimbs.
4. Students sort and try to identify embryonic limb images in Part B.
a. Distribute a set of Embryonic Limb Cards to each pair of students.
b. Explain why stages are given as early, middle, and late stage development
rather than specific times.
c. Have students compare and then sort the cards and record their reasoning
for sorting in their science notebooks.
d. Show students correct sorting using Visual Aid 13.2, “Embryonic Limbs.”
EVOLUTION 181
ACTIVITY 13 EMBRYOLOGY
5. Students sort and try to identify whole embryo images in Part C.
a. Distribute the first set of Whole Embryo Cards to each pair of students.
b. Distribute the middle stage set of Whole Embryo Cards to each pair of
students.
c. Distribute the late stage set of Whole Embryo Cards to each pair of
students.
BUILD UNDERSTANDING
6. Have pairs of students share their sorting and reasoning with each other.
a. Have students discuss how they sorted their embryo images and their
rationale.
b. Use Visual Aid 13.3, “Whole Embryo Sorting,” to show students the
correct sorting.
7. Relate the crosscutting concepts of patterns and structure and function to this
activity.
a. Relate patterns to this activity.278
b. Relate structure and function to this activity.
8. Discuss the use of embryological and skeletal data as evidence for evolutionary
relationships.
a. Review how scientists are able to make inferences about how species are
related even if their mature forms look very different.
b. (aid assessment) Assess student understanding of how patterns of
similarities in embryological development can provide evidence for
relationships between species.
TEACHING STEPS
GET STARTED
1. Introduce this activity by connecting it to content learned in the earlier activity
“A Whale of a Tale.”
a. Ask students to describe how they used skeletons to determine evolu-
tionary relationships.
Review how students made observations of different whale skeletons to
identify similarities and differences. The more similarities suggest that the
whales were more closely related.279280
278 NGCCPA2
279 NGLS4A2
280 NGCCPA2
182 EVOLUTION
EMBRYOLOGY ACTIVITY 13
b. Review embryos.
Students were introduced to the concept of embryos in the previous
activity, “A Whale of a Tale.” Remind them that an embryo is the devel-
oping animal from fertilization through birth or hatching.281
c. Direct students to read the introduction.
Students should recall from the previous activity that in whales, hair and
hind limbs were present on the embryos but absent in the adults.
2. Let students know that they will investigate skeletons of adult animals and
then of developing embryos.
Explain that they will analyze images in order to make observations and
develop explanations about evolutionary relationships.
DO THE ACTIVITY
3. Students compare forelimb skeletons of three species in Part A.
a. Distribute Student Sheet 13.1, “Comparison of Vertebrate
Forelimbs.”282283
Students should first make observations about the forelimbs and try to
identify specific structures, including the hand/foot, wrist, forearm, and
upper arm. If necessary, you can guide students through identifying
the structures in the human arm first; students are then likely to base
their identifications on the structural similarities of the bones. The
horse forelimb will likely cause some confusion. To help them figure out
comparable structures, have students consider which part of the leg moves
(or functions) similar to a human arm.
Emphasize that the color coding is to help students easily communicate
their thinking and visualize similar structures. They should not spend too
much time trying to make beautiful artwork.
b. Show Visual Aid 13.1, “Comparison of Vertebrate Forelimbs,” and allow
students to compare and discuss their identifications.
Facilitate a discussion about the similarities and differences between the
structure and function of the different forelimbs.
Although the external structure of the forelimbs is varied, the internal
skeletal structure is very similar. Students should notice that animals that
have a bigger “hand” tend to have more finger-like bones. This observation
reinforces the crosscutting concept of structure and function. A horse’s
forelimb varies the most, especially in terms of the number of bones.
281 NGLS4A3
282 NGSPAD4
283 NGCCSF1
EVOLUTION 183
ACTIVITY 13 EMBRYOLOGY
c. Have students discuss whether they think the animals are related based on
the structure and function of the forelimbs.
Ask students if skeletal images provide any evidence that these animals
might be related. Discuss (a) whether similar structures and functions
would develop in different animals independently or (b) whether those
animals might be related and possibly have evolved from a common
ancestor.
4. Students sort and try to identify embryonic limb images in Part B.284285286
a. Distribute a set of Embryonic Limb Cards to each pair of students.
There are 12 total cards in each set: three cards that indicate the type of
animal and limb, three early stage embryonic limbs, three middle stage
embryonic limbs, and three late stage embryonic limbs.
b. Explain why stages are given as early, middle, and late stage development
rather than specific times.
The stages are identified as early, middle, and late based on the total
length of embryonic development for the animal. Since animals develop
over various lengths of time, it is easier to compare stages as opposed to
specific days of development. For example, a human embryo develops
over 36 weeks, whereas a chicken develops over 3 weeks. This means an
early human embryo can be up to 12 weeks old, whereas an early chicken
embryo would be only a few days old.
c. Have students compare and then sort the cards and record their reasoning
for sorting in their science notebooks.
Students should find that the embryonic forelimbs of all three animals
look very similar at each developmental stage, so much so that it is hard
to know to which animal they belong. Emphasize the significant similarity
of structure among the limbs in the early and middle stages. In fact,
students might find it hard to distinguish between the limbs’ owners until
late in development. The bat wing is a good example of this. Although
the embryonic limbs look different in the mature animals, the similar
embryonic development suggests that these structures evolved from a
common ancestor.
d. Show students correct sorting using Visual Aid 13.2, “Embryonic Limbs.”
Discuss why students found it easy or difficult to sort the limbs. For
example, at the early and middle stages, all three limbs are almost
indistinguishable, making it hard to attribute them to different animals.
284 NGLS4A3
285 NGCCPA2
286 NGSPAD4
184 EVOLUTION
EMBRYOLOGY ACTIVITY 13
5. Students sort and try to identify whole embryo images in Part C.
a. Distribute the first set of Whole Embryo Cards to each pair of students.287
This first set includes five animal name cards and five early stage embryos.
Students will find it difficult to identify which animal is which. Allow
them to struggle with trying to identify which embryo matches which
animal card. Tell them they can change their sorting with the next set
of cards.
Make sure students record observations in their science notebooks.
Observations should include structures they can identify, similarities and
differences between the embryos, and the rationale for their sorting. At this
stage of development, they may notice that each embryo has an end that
resembles a head while the other end looks like a tail. They might also notice
where the eyes might form on the embryo later in development. Students
might also notice gill slits in some of the embryos, most notably in the bat
and human. Make a point to identify the gill slits if students do not see them.
287 NGSPAD4
gill slit
eye
forelimb
tail
EVOLUTION 185
LabAids SEPUP IAPS Evolution 3e
ACTIVITY 13 EMBRYOLOGY
b. Distribute the middle stage set of Whole Embryo Cards to each pair of
students.
Students should try to identify which early stage embryos these
correspond to. In addition, they should also look for similarities and
difference between the middle stage embryos and then between the early
and middle stage embryos. Eyes are becoming more prominent as are
limb buds. Heads are also increasing in size.
Allow students to re-sort their cards if they think that they matched an
early embryo to an animal incorrectly. Make sure they record their new
sorting and rationale.
c. Distribute the late stage set of Whole Embryo Cards to each pair of
students.
Final forms of the mature animals are evident in this last set of cards.
Ears and limbs, including appendages, are fully developed. Tails have
disappeared on the human (and possibly the bat).
Allow students to re-sort their cards if they think that they matched an
early embryo to an animal incorrectly. Make sure they record their new
sorting and rationale.
BUILD UNDERSTANDING
6. Have pairs of students share their sorting and reasoning with each other.
a. Have students discuss how they sorted their embryo images and their
rationale.
Students’ sorting should reflect their comparison of the appearances
(and sometimes disappearances) of various structures from early to late
development. Based on discussion, let students re-sort their images.
b. Use Visual Aid 13.3, “Whole Embryo Sorting,” to show students the
correct sorting.
7. Relate the crosscutting concepts of patterns and structure and function to this
activity.
a. Relate patterns to this activity.288
Students should be able to identify patterns in the embryo images—
structures that are similar and different, structures that appear and/or
disappear at the same time. Students will use the patterns they identified
to answer Analysis items 1 and 2.
288 NGCCPA2
186 EVOLUTION
EMBRYOLOGY ACTIVITY 13
Discuss why students found it easy or difficult to identify patterns
and sort the embryo images. Students may find it difficult to identify
developing structures. Structures also vary between different species. The
presence or absence of a tail or head may be easier than other features for
students to identify.
b. Relate structure and function to this activity.
Students should be able to explain that related but different structures in
different organisms may have similar functions, and these structures likely
form at a similar stage during development.
8. Discuss the use of embryological and skeletal data as evidence for evolutionary
relationships.289290
a. Review how scientists are able to make inferences about how species are
related even if their mature forms look very different.
In the “A Whale of a Tale” activity, students used skeletal evidence to infer
relatedness. In this activity, students used embryological data. If embryos
have similarities (e.g., the presence or absence of structures), they are
likely to be more closely related and to have evolved from a more recent
common ancestor than less similar embryos. Embryos with fewer similar
structures during development are likely to be more distantly related.
To emphasize this point, have students discuss the similarities and
differences between the mature animals and their developing embryos.
Have students identify structures that may have been present that are no
longer present in the mature form, such as gill slits in humans.
b. (aid assessment) Assess student understanding of how patterns of
similarities in embryological development can provide evidence for
relationships between species.291292293
Analysis item 3 in this activity can be assessed using the aid Scoring
Guide. Optionally project or distribute the Scoring Guide, and point out
the different descriptions for each level. Review the levels as needed. For
more information, see Teacher Resources III, “Assessment.”
Analysis item 3 assesses Performance Expectation MS-LS4-3.
Review the levels and criteria in the Scoring Guide for integrating
the Disciplinary Core Idea of Evidence of Common Ancestry and
Diversity and the Crosscutting Concept of Patterns with the Science and
Engineering Practice of Analyzing and Interpreting Data.
289 NGLS4A2
290 NGLS4A3
291 NGPEL43
292 NGSPAD4
293 SEASAD1
EVOLUTION 187
ACTIVITY 13 EMBRYOLOGY
EXTENSION
Encourage students to watch the video of a developing chick embryo on the
SEPUP Third Edition Evolution website at www.sepuplhs.org/middle/third-edition.
Students can identify which points in the movie correspond to the images of the
early, middle, and late embryos in Part C.
SAMPLE RESPONSES TO ANALYSIS
1. Was it easy to identify the animal when looking at the embryological images?
Why or why not? 294
It was hard to identify the species for the early and middle stage embryos because
they looked very similar.When we got the late stage embryo cards, the pictures looked
closer to what the mature animals looked like, so it was easier to identify them.
2. Review the observations you recorded in your science notebook. 295
a. What patterns did you observe?
Hint: A pattern is something that happens in a repeated and predictable way.
There is a pattern in how they look more similar at the beginning and then over
time begin to look more like the mature animal.They all looked pretty similar at
the early stage with a rounder-looking head on one end and a tail on the other
end. Another pattern is that some of the structures appeared at the same stage in
the different animals. By the middle stage they all had what looked like eyes and
some sort of limbs.
b. What structures appeared and when?
They all had heads and tails in the early stage, and you could also see where the
eyes might form. By the middle stage, you could see eyes in all of the embryos,
and the limb buds were forming. By the late stage, you could see all of the formed
structures—the head, ears, eyes, limbs, mouths.
c. What structures disappeared and when?
Between the middle and late stages, the tail disappeared from the human. It was
hard to tell in the picture if the bat also lost its tail.The gill slits also disappeared
by the late stage in all the animals except the salmon.
294 NGCCPA2
295 NGCCPA2
188 EVOLUTION
EMBRYOLOGY ACTIVITY 13
3. (aid assessment, MS-LS4-3) What relationships across different animal species
can you see in embryological data that you cannot observe by comparing mature
animals? Use data from your investigation to support your answer. 296297298299300301
SAMPLE LEVEL-4 RESPONSE
I can see that early human embryos had gills and tails, just like fish.This means
we are related to fish! Other animals like the snake and bat also have gills as early
embryos, so they must be related to fish, too. I also saw that all five of the animals
started with a tail, but humans lost it somewhere after the middle stage.When looking
at the early stage embryos, it was really hard to tell them all apart because they
looked so similar, except the fish.
REVISIT THE GUIDING QUESTION
How can embryos provide evidence about evolutionary relationships?
Students should be able to identify patterns of similarities and differences between
embryological images from different species and explain that similarities often
provide evidence of relatively closer evolutionary relationships. For example, a
human hand, a mouse hind limb, and a bat wing are almost indistinguishable
early in development, suggesting a similar structure and function, and a common
ancestor. In another example, early human and snake embryos have gill slits
that disappear through development. The presence of these gill slits early in
development suggests that humans and snakes are evolutionarily related to fish
and other species with gills.
This is a good time to revisit the third driving question for this sequence of
learning. Revisit and add to or revise students' ideas as needed.
ACTIVITY RESOURCES
KEY VOCABULARY
embryo
pattern
BACKGROUND INFORMATION
EMBRYOS
Ever since Darwin, scientists have looked at embryos and wondered what they
might reveal about evolution. Some wondered whether the sequence of embryonic
development revealed the actual evolutionary history of the organism. That is,
they wondered whether “ontogeny recapitulates phylogeny.” This line of inquiry
296 NGPEL43
297 NGSPAD4
298 NGCCPA2
299 NGLS4A3
300 ELRS687
301 SEASAD1
EVOLUTION 189
ACTIVITY 13 EMBRYOLOGY
they wondered whether “ontogeny recapitulates phylogeny.” This line of inquiry
reached its peak in the late 1800s with the work of Ernst Haeckel. He championed
this idea, naming it the biogenetic law. Essentially, he maintained that evolution is
unidirectional, with organisms moving along a single trajectory towards “higher”
life forms. While numerous examples could be found that supported his idea, a
growing number of cases refuted it. With the discovery of genes and their mecha-
nism of action, scientists discovered that mutations can cause organisms to move
along many paths, not just one leading to an ever “higher” form. His “law” was
eventually dismissed. Nevertheless, as seen in this activity, embryos do indicate
evolutionary relationships and can reveal relationships that are not apparent in
adult forms. As scientists learn more about genetics, especially Hox genes, which
control the development of major body parts and segments, we gain greater insight
into evolutionary history and relationships.
REFERENCES
Richardson, M. K., Hanken, J., Selwood, L., Wright, G. M., Richards, R. J.,
& Raynaud, A. (1998) Haeckel, embryos, and evolution. Science, 280, 5366.
doi:10.1126/science.280.5366.983c
Wang, Z., Dai, M., Wang,Y., Cooper, K. L., Zhu, T., Dong, D., … Zhang, S.
(2014, April). Unique expression patterns of multiple key genes associated
with the evolution of mammalian flight. Proceedings of the Royal Society B, 281,
20133133. doi:10.1098/rspb.2013.3133
190 EVOLUTION
Name______________________________________________________________ Date____________
STUDENT SHEET 13.1
COMPARISON OF VERTEBRATE FORELIMBS
horse
whale
human
bat
©2017 The Regents of the University of California crocodile bird
©2017 The Regents of the University of California
upper VISUAL AID 13.1
arm
COMPARISON OF VERTEBRATE FORELIMBS
forearm
wrist
hand/foot
crocodile bird bat human whale horse
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 13_4 VisualAid
MyriadPro Reg 9.5/11
VISUAL AID 13.2
EMBRYONIC LIMBS
bat forelimb
bat hindlimb
mouse hindlimb
early middle late
stage stage stage
LabAids SEPUP IAPS Evolution 3e
Figure: Evo3e TE 13_6 VisualAid
MyriadPro Reg 9.5/11
©2017 The Regents of the University of California
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