Who is lucy 0

> WHO IS LUCY?
Lesson Overview
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Last revised 21 December 2011
Overview: In this lesson, you will be introduced to “Lucy”, one of the most famous fossils
ever found. You’ll learn details about Lucy including her relationship to humans, her diet,
her appearance, and her form of locomotion. Then, you will apply your knowledge in the
activities that follow.
Objectives:
 To understand the impact of Lucy’s discovery on the study of human evolution.
 To understand the significance of identifying bipedalism within the fossil record.
 To become familiar with aspects of the human fossil record.
Outline:
A. An Introduction to Lucy
B. Lucy in Context
C. Lucy and Bipedalism
D. Conclusions
E. Activity: The Science of Lucy
F. Review Questions
G. References
H. Answer Key
Strategy:
 You will use known elements of Lucy’s morphology to identify primitive and derived
characteristics, including bipedalism.
 You will hypothesize the evolutionary relationship between Lucy’s species and
modern humans.
 You will apply what you learn about Lucy to the activity below.
Required Materials: Pen or pencil, colored pencils or pens, a straight edge such as a
ruler, and copies of sections A-G of this lesson.
Expected Classroom Hours: 1 hr (Assigning the reading outside of class may reduce total
classroom hours).
Suggested Supplemental Lessons or Resources:
 eLucy Comparative Anatomy
 On the Track of Prehistoric Humans
 Hominin Evolution: Genera Australopithecus and Parathropus
 eSkeletons
 eFossils or eLucy Glossary

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The discovery of Lucy
On November 24, 1974, Donald Johanson and his
student Tom Gray were surveying a site named Hadar
in the Afar region of Ethiopia, East Africa (shown
right) when they noticed a bone jutting out of the
ground. They began work to uncover the bone and
found many more bone fragments, which turned out
to be a remarkably complete early hominin skeleton
(illustrated below). Officially, the skeleton is
designated AL 288-1, denoting that it was discovered
at (A)far (L)ocality 288. The skeleton was nicknamed
“Lucy” after the Beatles’ song, “Lucy in the Sky with
Diamonds” that was playing while the research crew
celebrated the Lucy’s discovery. In Amharic, an
Ethiopian language, she is affectionately referred to
as “Dinquinesh,” meaning “wonderful thing.1
”
Lucy was allocated to the species, Australopithecus
afarensis, meaning “African southern ape from the Afar
region.” However, Lucy was not the first A. afarensis
discovery. An articulated knee joint dating to 3.4 million
years ago (Ma) was discovered a year earlier in 1973,
but it was not properly identified as A. afarensis until
1979. Still, Lucy’s discovery eclipsed nearly all earlier
findings because of the extraordinary completeness of
Lucy’s skeleton, making her one of the most important
paleoanthropological findings of our time. Roughly 40%
of Lucy’s skeleton is accounted for (hands and feet
excluded), including cranial material such as fragments
of the cranial vault, face, and jaw. Postcranial material
includes parts of the shoulder, spine, and pelvis. Much
of the limbs bones are also represented (upper arm and
forearm fragments, a carpal and finger bone, a partial
tibia and nearly complete femur)1
.
The preservation of so much of Lucy’s skeleton has
allowed researchers to study a number of aspects of her
anatomy, about how she moved in her environment
(locomotion), what she ate (diet), and even to
hypothesize about how she is related to modern
humans.
Hadar is located in Southern Ethiopia,
in the Afar Triangle.
An Illustration of Lucy’s
(AL 288-1) remains, found in 1974.
Drawn after Johanson
and Edgar 2006.

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Who is Lucy related to?
Lucy’s evolutionary relationship to modern humans was one of the first questions asked by
scientists after the “Lucy” discovery. The process of determining relatedness among
organisms is called systematics. Unfortunately, we can’t travel back in time to answer this
question. However, in one type of systematics called cladistics, we can understand the
evolutionary relationships among organisms by grouping them together based on shared
characters (traits) (See the eFossils lesson “Evolution: From the Beginning” for more
information). Specifically, cladistics is concerned with features that are novel and unique,
termed derived features, to a particular subset of animals within a larger group. For
example, among mammals, primates have nails. Since, most other mammals have claws,
nails are a derived primate feature. In contrast, characters that everyone in the larger
group has are termed primitive characters. For example, primates have hair, but so do all
mammals. In this case, hair is a primitive feature that primates share with all mammals.
All organisms that share a derived character belong to a clade.
Humans and their fossil relatives all belong to a clade we refer to as hominins. This clade is
defined, in part, by the shared ability to walk bipedally. Bipedalism refers to locomotion
(how an animal moves or travels) on two legs. You move bipedally whenever you walk, jog,
run, or skip. However, most other animals, including chimpanzees, use quadrupedalism,
meaning to walk on four legs. Thus, although chimpanzees are our closest living relatives,
they are not part of the hominin clade. Bipedal walking is unique to hominins, and is
considered a novel acquisition since their divergence from the common ancestor that
hominins share with the African great apes.
The diagram shown left is called a
cladogram (think: diagram of
clades). A cladogram can contain
living and/or extinct species, and
tells about the relative timing of
speciation events, or when species
diverged from a common ancestor.
By extension, cladograms also tell
us about the relative antiquity
(i.e., old age) of these ancestors.
In the cladogram, each vertical line
represents a general group of
primates based on their taxonomic
classifications (i.e., family, genus, species). The diagonal line (or line running horizontally)
represents the ancestral species. The point where the vertical and horizontal lines meet is
called a node, and represents a speciation event. Let’s walk through an example together.
As mentioned, the “hominin” clade is defined by the ability to walk bipedally. Therefore,
bipedal locomotion must have evolved after the divergence of hominins from living apes.
That point is illustrated by placing “bipedal locomotion” after the node (large dot) where
hominins and apes diverge.
A cladogram depicting relationships between major primate groups

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Through analyses of Lucy’s skeletal morphology (see below), we are able to conclude that
she walked bipedally. Therefore, we can conclude that Lucy is a hominin. Lucy belongs to
the species A. afarensis that existed from 3.7 and 2.8 Ma2
. There are many other extinct
hominin species, but only one living hominin species: us, or Homo sapiens.

> WHO IS LUCY?
B. Lucy in Context
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How old is Lucy?
Lucy has two ages: one that refers to how old she was
when she died, her biological age, and the other that
refers to how long ago she lived, her geological age.
Lucy was an adult when she died. Scientists are able to
determine this age because Lucy had fully erupted
wisdom teeth (or third molars) and her bones appear
fully fused. Bones form in separate pieces and fuse
(connect) together at different times in life, just as
teeth erupt at different ages as an animal grows. By
the age of 35, most humans have fully erupted third
molars and completely fused bones.
Lucy’s geologic age dates to 3.2 Ma3
. After Lucy died,
her bones settled into dirt and rocks, called sediments.
She then was buried by many more layers of
sediments. The weight of all these sediments crushed
some of her bones. After a long time, the calcium in her bone was replaced with minerals
from the surrounding soils. This process is called mineralization. It turns the bone into rock
which help preserve it for a long time. Scientists can determine when Lucy lived by testing
chemicals, called Potassium-Argon and Argon-Argon, in layers of volcanic ash above and
below the rock layer where Lucy was found. Lucy was found in sandstone sediments
associated with a paleo-stream. In this context, it is possible that a stream carried Lucy’s
body some distance away from where she died4
.
Where did Lucy live?
Lucy probably lived in a mixed environment
from dense wooded areas to open grassland
areas, characterized by both wet and dry
conditions. Thus, Lucy was probably able to
tolerate the living conditions of a broad range of habitats. There is no evidence that Lucy or
other members of her species preferred one habitat over another 5
.
What did Lucy eat?
Lucy probably ate a mix of foods, including ripe fruits, nuts, and tubers from
both the forest and savanna. Incisor teeth are typically used to prepare the
food for mastication (think about biting off a piece of an apple), and molar
teeth are used to masticate, or chew, the food into a small pulp that can be
swallowed. Compared to chimpanzees, Lucy had relatively smaller incisor
teeth, but larger molar teeth, suggesting that she did little to dentally prepare
her food, and spent more time intensively chewing or breaking down the
food6
.
Superior view of Lucy’s mandible.
Fully erupted 3rd
molars are circled in
red. The state of wisdom tooth eruption
can help establish age.

> WHO IS LUCY?
B. Lucy in Context
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Additionally, the enamel or hard outer shell of the tooth, and the body of the mandible
itself, were relatively thicker in Lucy than chimpanzees, affording greater strength for the
mastication of tough or hard-object foods. Foods that require a lot of chewing include nuts,
seeds, and underground storage organs (root vegetables). However, A. afarensis incisors
also show patterns of wear consistent with stripping leaves, and the canines show patterns
of wear consistent with puncturing or crushing foods7
. Thus, Lucy probably also ate ripe
fruits when they were seasonally available.
What did Lucy look like?
Lucy was a small-bodied female that probably stood about 3”6”
(107cm)8
tall and weighed roughly 60 pounds (27.3 kg)9
.
Scientists can tell that Lucy is female because the anatomy of
her pelvis generally resembles that of female modern humans.
In addition, Lucy’s body size overall, as well as those of other
female A. afarensis, is smaller than the body sizes of male A.
afarensis specimens. A difference in body size between males
and females of the same species is called sexual dimorphism,
meaning two (“di”) forms (“morph”) between sexes.
Lucy’s face was chimpanzee-like. Below her eyes, her face
projected forward beyond the plane of the eyes, a character
trait known as prognathism. Features that Lucy shares with
chimpanzees are called retained primitive features, meaning
that these features were present in the ape-like species from which Lucy’s species evolved,
and that Lucy’s species, A. afarensis, kept these features even after the species diverged
from that last common ancestor.
How big was Lucy’s brain?
Fossil remains of Lucy’s
braincase are fragmentary,
limiting the reconstruction of
her brain size. However, brain
size estimates from other
members of her species
suggest that Lucy’s brain was
probably about the size of a
modern chimpanzee’s (range
between 387 – 550 cc; average
446 cc)10
. Although it might appear as though these australopiths had small brains, it must
also be remembered that they were smaller-bodied than living humans. In fact, when her
brain size compared relative to her body size, her brain would actually be considered larger
than expected for a living ape of that body size11
. Importantly, Lucy’s relatively small brain
size (compared to humans) in combination with her bipedal adaptations of the lower limb,
reveal that bipedalism evolved before large brains.
Recreation of a male, female,
and infant A. afarensis.
Lateral views of 3 crania, from left to right: extant chimpanzee, A.
afarensis (not lucy), and modern human. All to scale.

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How did Lucy move?
Lucy was clearly bipedal, although she may have continued to locomote through trees (i.e.,
arboreal locomotion) with some ease. Scientists can deduce this information from her
skeleton, which is a combination of derived human-like features and retained primitive
chimpanzee-like features. Each section below discusses aspects of Lucy’s anatomy that
help us determine her mode of locomotion.
Limb proportions: An animal’s limb proportions can provide clues as to what mode of
locomotion an animal utilizes on a regular basis. A ratio of limb proportions is calculated by
dividing the forelimb length (humerus length + radius length) by the length of the hindlimb
(femur length + tibia length). This ratio is called an intermembral index (“inter” means
“between”, “membral” means “limb”).
Look at the picture (left) and examine
the length of the red lines that highlight
the forelimbs relative to the hindlimbs.
Humans have an intermembral index
between 68-7011
, meaning that their
hindlimbs are longer than their
forelimbs. A low intermembral index in
humans reflects the fact that they rely
exclusively on their hindlimbs for
propulsion during bipedal walking.
Chimpanzees have an intermembral
index of 10612
, meaning that their
forelimbs are longer than their
hindlimbs. A high intermembral index in
chimpanzees reflects the fact that they
rely heavily on their forelimbs for climbing and arm-hanging/swinging activities. Lucy's
intermembral index is 8811
. Thus, Lucy appears to have an intermediate measurement
between modern humans and chimpanzees. Measurements of the individual bones in the
index show that Lucy’s intermediate body proportions are a result of a shortened humerus.
Since the evolutionary trend in hominins is toward relatively longer hindlimbs than
forelimbs, as in modern humans, Lucy’s skeleton shows that arm length reduced before
thigh elongation2
. Functionally, Lucy probably relied on her hindlimbs for moving bipedally
and on her forelimbs for climbing.
Scapula: Some of Lucy’s primitive features, such as the orientation of her shoulder, suggest
that she might have spent some time in the trees (arboreal). The scapula (shoulder blade)
articulates with the humerus (upper arm bone) at the scapula’s glenoid fossa, a small
circular or oval depression located on the scapular head. A cranially (up, toward the head)
oriented glenoid fossa enhances an animal’s ability to climb or use forelimb-dominated
activities where the arms are held above the head. Like chimpanzees, and unlike humans,
the A. afarensis glenoid fossa faced cranially, suggesting Lucy probably used above-head
arm postures, consistent with the idea that she may have climbed trees11,13
.

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Innominates: Lucy’s lower body (pelvis and hindlimbs)
indicates that when Lucy was on the ground (terrestrial),
she walked bipedally. For example, Lucy’s innominate
blades (pelvic blades), and those of modern humans, are
short, broad, and curved forward, so that the iliac crest
courses toward the front of the body. In contrast, the
chimpanzee innominate blade is tall, narrow, and flat, so
that the iliac crest lies flat across the back. This difference
in the orientation of the pelvic blade affects the way some
of the gluteal muscles attached to the iliac crest (and the
femur’s greater trochanter) and action at the hip joint. In
chimpanzees, a flat iliac blade causes these muscles to
extend the leg backward at the hip. This action helps move
the limbs front-to-back during quadrupedal locomotion. In
humans, and in Lucy, the curved iliac blade moves these
muscles to the side of the body, causing these muscles to
pull the leg to the side at the hip. This action helps to
maintain the body’s support and prevent collapsing toward
the side that is unsupported by a leg during bipedal walking. That Lucy’s pelvic blades
appear closer to the human condition indicates she walked bipedally.
Sacrum: Additionally, Lucy’s sacrum is wide at the top (proximally) and short in length,
although not to the extent observed in humans13
. In contrast, the chimpanzee sacrum is
long and narrow. You can see these differences in the picture to the right. A proximally wide
sacrum positions the sacroiliac joint (where the sacrum articulates with the innominate)
over the hip joints (where the femoral head articulates with the innominate). By aligning
these joints, stress on the pelvis during bipedal walking is alleviated.
The size of the joint surfaces is related to the
amount of weight transmitted through the pelvis
during locomotion. A larger joint surface is better
able to dissipate weight than a smaller joint
surface. Lucy’s sacrum also has somewhat
expanded joint surfaces compared to chimpanzee.
However, again, they do not approximate the
human condition completely. Humans have large
sacral joint surfaces, even compared to gorillas!
Human sacral joint surfaces are so large because
their sacrum must withstand the entire weight of
the upper body during bipedal posture and
locomotion. In contrast, chimpanzees and gorillas
have smaller joint surfaces because some of their
body weight is transferred to the forelimbs during quadrupedal posture and locomotion.
Overall, Lucy’s sacrum trends toward the human condition, indicating that she employed
bipedal posture and locomotion.
Illustration of modern human
articulation of the gluteal muscles in
modern humans. Note that the
gluteal muscle originates dorsally
from the pelvis and inserts on the
femur’s greater trochanter.
Comparisons of three sacra.

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Femur: Lucy’s femur, or thigh bone, provides some
of the best evidence for bipedal locomotion. In
humans (shown on the left) the shaft of the femur
slants downward and medially toward the body’s
midline so that the knees are held close together,
forming an angle from the knee to the hip joint. This
angle is called the bicondylar angle. In this way,
the foot is closer to the body’s center of gravity
during single-foot support, relieving stress on the
knee joints and ensuring balance during bipedal
locomotion. Quadrupedal locomotion lacks a single
support phase. Thus, in quadrupedal animals, the
shaft of the femur is straight so that the knees are
separated and the legs are positioned directly
underneath the hip joints. By contrast, the
morphology of the human knee is called a valgus
knee, meaning “knock-kneed”. Lucy’s femur also
exhibited a bicondylar angle similar to that seen in
modern humans, and thus Lucy also had a valgus
knee.
Foot: Certain bones in the A. afarensis foot are long
and curved like those of chimpanzees11
. Curved toes
(phalanges) enhance a chimpanzee’s ability to grasp
a tree trunk or branch while climbing. Since humans
don’t regularly climb trees, humans have short,
straight toes instead, to help propel themselves
while walking. Although the transformation to
bipedalism was underway, Lucy probably continued
to climb trees to escape predators, reach for fruit, a
use the tree tops as a safe place for sleeping.
Human pelvis and femur articulation
showing the femur’s bicondylar angle
between the pelvis and the tibia.
Comparisons of a phalanx curvature from
Lucy, a modern human, and a modern
chimpanzee.

> WHO IS LUCY?
D. Conclusions
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In 2007, Lucy kicked off her world tour at the Houston Museum of
Natural Science, where she went on public display outside Ethiopia
for the first time since her discovery. An estimated 210,000 people
viewed the exhibit before she moved on to museums in Seattle and
New York. Discussions continue on future exhibit opportunities.
2014 marks the 40th
anniversary of Lucy’s discovery, and she
continues to excite and stimulate new thinking about human
origins. To date, she remains of one of the oldest, most complete
A. afarensis specimens ever found. Lucy opened doors into our
understanding of early bipedal morphology that subsequent fossils
have built upon. The mosaic state of her anatomy suggested, for
the first time, that early hominins engaged in both bipedalism and
some arboreal locomotion, while still retaining a relatively small
brain size. Even now, Lucy is often referred to during bipedalism
debates, including the type of bipedalism A. afarensis and other
early hominins might have utilized. The growth of high resolution
X-ray scanning techniques may make it possible to look inside
Lucy’s fossilized skeleton, and analyze the structure of her bones
(i.e. trabecular bone). Once again, Lucy may be key to answering
these, and other long held questions.

> WHO IS LUCY?
E. Activities: The Science of Lucy
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Activity 1: Characters Chart
Complete the following based on your reading:
1. Fill out the chart (a) and answer the question (b).
a. Identify the following features of Lucy’s skeleton as either primitive (chimpanzee-like)
or derived (human-like).
Prognathic face
Brain size
Valgus knee
Wide, short pelvis
and sacrum
b. Using your answers from the chart above, how would
you describe the overall anatomy of Lucy? On what
do you base your conclusions?

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Activity 2: Primate Relationships
1. Using the cladogram below, place the following labels on the blue lines to correctly
depict the evolutionary relationships among these primates:
Humans Monkeys Australopithecus Apes
Now read the following clues. Identify when each of the derived traits listed in the box
below evolved by writing it next to its corresponding arrow. When you are finished,
answer the following questions.
Clue 1: All living apes lack tails.
Clue 2: The large human brain size is unique
a. What primates are characterized by bipedalism?
b. Did bipedal locomotion or bigger brain size evolve first?
Derived Traits: Bipedalism Bigger Brains Tail Loss

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Activity 3: Relative Brain Size
1. Plot the relative brain sizes in order to observe any trends in brain size as they relate to
a body mass scale (from small-bodied to large-bodied). You will plot the logarithm of
body mass (a proxy for body size) and cranial capacity (a proxy for brain size) on the
chart found on the following page. Take a look at the numbers in the parentheses in the
table below. Notice how wide-ranging the numbers are. The raw body mass (measured
in kilograms) of chimpanzees is 35 kg, while the body mass of gorillas is 105 kg. That
means a gorilla is 3 times the weight of a chimpanzee. We would need a really big chart
to fit all of those raw numbers on one graph! By logging these numbers, we reduce
these values to a smaller scope. Basically, we make it easier to plot these values on the
chart.
Taxon
X
Logged Body Mass
(raw value in
kilograms)
Y
Logged Cranial capacity
(raw value in cubic
centimeters)
Chimpanzee 3.56 (35 kg) 5.86 (350 cm3
)
Gorilla 4.65 (105 kg) 6.27 (530 cm3
)
Humans 4.0 (57 kg) 7.28 (1450 cm3
)
Australopithecus
afarensis
3.61 (37 kg) 6.06 (430 cm3
)
Chimpanzee Gorilla Australopithecus Human
Have you ever plotted numbers on a graph before? It’s easy! The table above tells us
that the X value is going to be “body mass”, and the Y value is going to be “cranial
capacity.” The X value is always plotted on the horizontal axis and the Y value is always
plotted on the vertical axis.
Let’s go over how we plotted our chimpanzee data point. First, find the X value for the
chimpanzee body mass. It’s 3.56. Find 3.56 along the X axis with your finger. Second,
find the Y values for chimpanzee cranial capacity. It’s 5.86. With your finger still on the
3.56 point along the horizontal axis, move your finger up the vertical axis until you
reach 5.86. Plot your data point at the intersection of these two numbers.

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Because we’re interested in the
brain sizes of humans and
australopiths compared to
those of living apes, we’ve
gone ahead and plotted
chimpanzees and gorillas for
you. Then we drew a line
connecting the chimpanzee and
gorilla data points. This line is
called a regression line, and
illustrates any trends in the
data. In this case, the
regression line that we drew
help us determine us what
brain size we should expect in
A. afarensis for any given body
size, based on what we observe
in living apes.
Let’s plot human and
Australopithecus brain sizes.
Then, turn to the page to
continue.

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2. Take another look at the location of the human and A. afarensis data points. Are they
above or below the trend line? If the data point falls below the trend line, then the
observed brain size is relatively SMALL in comparison to living apes. If our data point
falls above the trend line, then the observed brain size is relatively LARGE in comparison
to living apes. Use this information, and the chart, to answer the following questions.
a. Is the relative cranial capacity of A. afarensis larger or smaller than that of the
living African apes? How did you come to this conclusion?
b. How do humans compare to both the living African apes and A. afarensis?

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Activity 4: Bipedal Adaptations
1. Recall that the human pelvis (shown below right) looks very different from a chimpanzee
pelvis (shown below left). Examine the pelves below. On the chimpanzee and
Australopithecus pelves, trace the orientation of the iliac blades, their width and height,
and the width of the sacrum. We have done this for you on the human pelvis, which you
can use as a guide. Then, fill in the chart below and answer the questions.
Species
Iliac blade
orientation
(Curved forward or Flat)
Iliac blade
width/height
(Broad/Short or Narrow/Tall)
Sacrum Width
(Broad or Narrow)
Humans Curved forward Broad/ Short Broad
Chimpanzees
Australopithecus
a. Does Australopithecus appear to have more chimpanzee-like or human-like pelvic
morphology?
b. Based on your answer, what would you say about the locomotion of Lucy?

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2. Recall that humans have a valgus knee as a result of a bicondylar angle that tilts the
shaft of the femur toward the body’s midline. We’ve drawn the human bicondylar angle
on the image below to illustrate this point.
a. Why is a bicondylar angle important for a biped?
b. Draw the bicondylar angles for A. afarensis and a chimpanzee. To draw the angle,
first draw a line perpendicular to the blue line, starting at the green dot. Then,
draw a line through the middle of the femur’s shaft.
Line perpendicular
to blue line
(infracondylar plane)
Line through
shaft of femur

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c. Based on your drawing, does the Australopithecus femur exhibit a more human-
like or more chimp-like bicondylar angle?
d. What can you conclude about the locomotion of Lucy based on your answer?

> WHO IS LUCY?
F. Review: Topic Review Questions
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Based on your reading and the above exercise, answer the following questions:
1. Why was the discovery of Lucy so important?
2. What is a good way to determine Lucy’s evolutionary relationship to humans and
other living primates? Why? Hint: Think of a type of systematics discussed above
using derived and primitive characters.
3. What happened to Lucy, after her death, that allows us to observer her as a fossil
today? Describe the process(es)?
4. What did Lucy look like?

> WHO IS LUCY?
F. Review: Topic Review Questions
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5. Lucy had a unique way of moving around in her environment. List and then describe
the features of her skeletal anatomy that were discussed in the reading, and
determine if this was a primitive or derived character for hominins. Remember
hominins include human and other primates that walked bipedally.

> WHO IS LUCY?
G. References
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1. Johanson DC, Lovejoy CO, Kimbel WH, White TD, Ward SC, Bush ME, Latimer BM and Coppens Y.
1982. Morphology of the Pliocene partial hominid skeleton (A.L. 288-1) from the Hadar formation,
Ethiopia. American Journal of Physical Anthropology 57(4):403-451.
2. Kimbel, W H and Delezene LK. 2009. “Lucy” redux: A review of research on Australopithecus
afarensis. Yearbook of Physical Anthropology 52:2–48.
3. Walter RC. 1994. Age of Lucy and the first family: single-crystal 40Ar/39Ar dating of the Denen
Dora and lower Kada Hadar members of the Hadar Formation, Ethiopia. Geology 22:6–10.
4. Aronson JL and Taieb M. 1981. Geology and paleogeography of the Hadar hominid site, Ethiopia.
In G Rapp and CF Vondra (eds.): Hominid Sites: Their Geologic Setting; A.A.A.S. Selected
Symposium No. 63. Boulder: Westview, pp. 165-195.
5. Reed KE. 2008. Paleoecological patterns at the Hadar hominin site, Afar Regional State, Ethiopia.
Journal of Human Evolution 54:743–768.
6. Teaford, MF and Ungar PS. 2000. Diet and the evolution of the earliest human ancestors.
Proceedings of the National Academy of Sciences 97:13506–13511.
7. Ryan AS, Johanson DC. 1989. Anterior dental microwear in Australopithecus afarensis:
comparisons with human and nonhuman primates. Journal of Human Evolution 18:235–268.
8. Jungers WL. 1988. Lucy’s length: stature reconstruction in Australopithecus afarensis (A.L. 288-1)
with implications for other small bodied hominids. American Journal of Physical Anthropology
76:227-232.
9. McHenry HM. 1992. Body size and proportions in early hominids. American Journal of Physical
Anthropology 87:407–431.
10. Klein RG. 2009. The Human Career: Human Biological and Cultural Origins, 3rd ed. Chicago:
University of Chicago Press.
11. Cartmill M and Smith FH. 2009. The Human Lineage. New York: John Wiley Sons.
12. Morbeck ME and Zihlman AL. 1989. Body size and proportions in chimpanzees, with special
reference to Pan troglodytes schweinfurthii from Gombe National Park, Tanzania. Primates 30,
369–382.
13. Stern JT and Susman RL. 1983. The locomotor anatomy of Australopithecus afarensis. American
Journal of Physical Anthropology 60:279–317.

> WHO IS LUCY?
H. Answer Key
Page 22 of 26
©eFOSSILS.org
Activity 1: Character States
1. Identify the following features of Lucy’s skeleton as either primitive (chimpanzee-like) or derived
(human-like).
Prognathic face Primitive
Brain size Primitive
Valgus knee Derived
Wide, short pelvis and sacrum Derived
a. Using your answers, how would you describe the overall anatomy of Lucy? On what do you
base your conclusions?
Lucy exhibits a mosaic of primitive and derived traits. Her brain size and face shape are more
similar to chimpanzees, indicating that she shared these traits with her ancestors. Her knee
and pelvis shape are derived (more human) traits that she shares with later hominins.
Activity 2: Primate Relationships
1. Using the cladogram below, place the following labels on the blue lines to correctly depict the
evolutionary relationships among these primates:
Humans Monkeys Australopithecus Apes
Now read the following clues. Identify where each derived trait in the box below evolved by
placing it next to its corresponding red line.
Clue 1: All living apes lack tails.
Clue 2: Bigger brains evolved after bipedalism.
a. What primates are characterized by bipedalism? Hominins (A. afarensis and humans)
b. Did bipedal locomotion or bigger brains size evolve first? Bipedal locomotion

> WHO IS LUCY?
H. Answer Key
Page 23 of 26
©eFOSSILS.org
2. Take another look at the location of
the human and A. afarensis data
points. Are they above or below the
trend line? If the data point falls
below the trend line, then the
observed brain size is relatively
SMALL in comparison to living apes. If
our data point falls above the trend
line, then the observed brain size is
relatively LARGE in comparison to
living apes. Use this information, and
the chart, to answer the following
questions.
a. Is the relative cranial capacity of
A. afarensis larger or smaller
than that of the living African
apes? How did you come to this
conclusion?
Larger. The plotted brain size
lies above the regression line.
b. How do humans compare to both
the living African apes and A.
afarensis?
Humans have a much large
relative brain size.

> WHO IS LUCY?
H. Answer Key
Page 24 of 26
©eFOSSILS.org
Activity 3: Relative Brain Size
1. Recall that the human pelvis (shown bottom right) looks very different from a chimpanzee
pelvis (shown left). Examine the pelves below. On the chimpanzee and Australopithecus
pelves, trace the orientation of the iliac blades, their width and height, and the width of the
sacrum. We have done this for you on the human pelvis, which you can use as a guide. Then,
fill in the chart below and answer the questions.
Species
Iliac blade
orientation
(curved forward or
flat)
Iliac blade width/
height
(Broad/Short or
Narrow/Tall)
Sacrum Width
(Broad/Narrow)
Humans Curved forward Broad/ Short Broad
Chimpanzees Flat Narrow/Tall Narrow
Australopithecus Curved forward Broad/Short Broad
c. Does Australopithecus appear to have more chimpanzee-like or human-like pelvic
morphology? Human-like
d. Based on your answer, what would you say about the locomotion of Lucy?
She walked bipedally
2. Recall that humans have a valgus knee as a result of a bicondylar angle that tilts the shaft of the
femur toward the body’s midline. We’ve drawn the human bicondylar angle on the image below to
illustrate this point.
a. Why is a bicondylar angle important for a biped?
It places the knees closer to the center of gravity in the body, relieving stress on the joints,
and ensuring balance during single-support phase bipedalism.

> WHO IS LUCY?
H. Answer Key
Page 25 of 26
©eFOSSILS.org
b. Draw the bicondylar angles for A. afaresnsis and a chimpanzee. To draw the angle, first draw
a line perpendicular to the blue line, starting at the green dot. Then draw a line through the
middle of the femur’s shaft.
c. Based on your drawing, does the Australopithecus femur exhibit a more human-like or
more chimp-like bicondylar angle? Human-like
d. What can you conclude about the locomotion of Lucy based on your answer?
She was most likely bipedal when on the ground.
Topic Review Questions
Based on your reading and the above exercise, answer the following questions:
1. Why was the discovery of Lucy so important?
Lucy’s completeness (40%) as a fossil skeleton is a rarity. Through analyzing the different
bones from one skeleton we are able to better understand her locomotion, diet, and
relatedness to humans. (Pg. 2 and Pg. 4)
2. What is a good way to determine Lucy’s evolutionary relationship to humans and other living
primates? Why? Think of a type of systematics discussed above using derived and primitive
characters.
Cladistics helps us understand the evolutionary relationships among organisms by using
Line perpendicular
to blue line
(infracondylar
plane)
Line through shaft
of femur

> WHO IS LUCY?
H. Answer Key
Page 26 of 26
©eFOSSILS.org
primitive and derived characters to determine the most likely shared ancestry between
groups. (Pg. 3)
3. What happened to Lucy, after her death, that allows us to observer her as a fossil today?
Describe the process(es)?
After Lucy died, her bones settled in sediments. As the sediments built up over time, part of
her skeleton was crushed. The calcium in her bones was replaced by the minerals of the
surrounding soils (mineralization) and eventually the bones became hard like rocks. Time and
erosion eventually brought Lucy, now a fossil, to the surface. (Pg. 5)
4. What did Lucy look like?
Lucy was small in height (3”6’ or 107 cm) and weighed about 60 pounds (27.3 kg). She was
also a female, and probably had a chimpanzee-like face (facial prognathism). (Pg. 6)
5. Lucy had a unique way of moving around in her environment. List and then describe the
features of her skeletal anatomy that were discussed in the reading, and determine if this was
a primitive or derived character for hominins. Remember hominins include human and other
primates that walked bipedally.
Limb proportions – Lucy has an intermediate intermembral index between chimpanzees and
humans. This is a derived character, since this is evidence that the skeletal morphology of
hominins was evolving towards longer legs. (Pg. 7)
Scapula – The orientation of the glenoid fossa (which faced cranially) indicates she was able to
climb trees with ease. This is a primitive character since arboreal locomotion is present in
many primates. (Pg. 7)
Innominate – Lucy’s innominate blades are short, broad and curved forward – traits that
affects muscle attachment in the hips, aiding in bipedal locomotion. This is a derived
character since Lucy’s innominate was very similar to humans and different than the tall,
narrow and flat innominate of chimpanzees. (Pg. 8)
Sacrum – Lucy’s sacrum is wide at the top and short in length, similar to humans. Chimpanzee
sacra are tall and narrow, so therefore Lucy’s sacrum is a derived character. (Pg. 8)
Femur – Lucy’s femur exhibits a bicondylar angle, which also results in a valgus knee. These
traits are hallmarks of bipedal locomotion. This is not present in quadrupedal apes, and
therefore is a derived character. (Pg. 9)
Foot – Lucy has long and curved toes which were advantageous for tree climbing. This is a
primitive character. (Pg. 9)

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