Fossil Hominins
Compared to gorillas (right) and other apes, humans (left) have highly specialized adaptations to facilitate bipedal locomotion.
Author: Rebecca Frank
Source: “Activity 14.” 2019. Frank, Rebecca, Brian Pierson, Philip Stein. LAVC Anthro 111 Lab Manual. 7th Edition.
Learning Objectives
- Identify hominin fossil features
- Compare ape, Ardipithecus, Australopithecines, and modern human anatomy
- Use fossil features to understand the emergence of bipedalism
Review Questions
- Compare Au. africanus and Au. afarensis to an ape and modern human. Why are these species considered to be hominins rather than non-hominin apes?
- Name three species of robust Australopithecines. Identify their most significant shared features.
- Does the Australopithecine pelvis resemble most closely a hominin or a non-hominin ape?
References
Frank, Rebecca. 2019. “Activity 14: The Hominin Fossils: Australopithecines.” In LAVC Anthro 111 Lab Manual, 7th Edition, edited by Frank, Rebecca, Brian Pierson, and Philip Stein.
Warren, Kerryn, Lindsay Hunter, Navashni Naidoo, Silindokuhle Mavuso, Kimberleigh Tommy, Rosa Moll, Nomawethu Hlazo. 2019. “Chapter 9: Early Hominins.” In Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association.
Instructions
In this lab, you will compare sets of fossil casts and record your comparisons on a chart. The term specimen in the chart refers to the specific fossil or primate species being studied. The name of the species is filled in at the head of the column.
The early hominins include a diverse group of African fossils that include the genera Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, and Paranthropus. The many species represented by these genera lived from about 7 million years ago (mya) to almost 1.0 mya. Early hominin fossils are found in South Africa, East Africa, and Chad (north central Africa). None are found outside of Africa.
- The early hominins are those that show many transitional features between the apes and later hominins. They include Sahelanthropus tchadensis, Orrorin tugenensis, Ardipithecus ramidus, and Ardipithecus kadabba. These species lived between 6.8 and 4.4 mya.
- Three of the well known gracile Australopithecines are Australopithecus anamensis and Australopithecus afarensis from East Africa, and Australopithecus africanus from South Africa. They lived between 4.2 and 2.1 mya.
- Many paleoanthropologists classify the robust Australopithecines in the genus Paranthropus. There are three known species: Paranthropus aethiopicus and Paranthropus boisei from East Africa and Paranthropus robustus from South Africa. They lived between 2.7 and 1.0 mya and were contemporary with the genus Homo.
Exercise 1. The Gracile Australopithecines
While Sahelanthropus, Orrorin, and Ardipithecus are considered transitional genera, the gracile Australopithecines (Australopithecus africanus and Australopithecus afarensis) are clearly hominins. In Exercise 1, you will look closely at some of these species.
Your instructor will tell you which four species’ skulls to compare in the table on the worksheet. There are three ways to fill in a cell, depending on how the statement of feature is phrased.
- Present or absent: When a feature is either there or not, you can use a + for present and – for absent. For example, “presence of sagittal crest” can be answered + or –.
- Describe: When you are asked to describe a feature, do so with a few words or short phrase. For example, “shape of dental arcade” can be answered “U-shaped.”
- Compare: When you are asked to compare, you need to ask “compare to what?” If there are three skulls being compared, you might say X and Y are smaller than Z. Or X is smaller than Y and Y is larger than Z.
We will measure and calculate the Condylar Index and the Facial Index. The Facial Index assesses the relative size of the face (and teeth and chewing features) vs. the size of the brain.
Record your measurements and comparisons to complete “Exercise 1” on the worksheet.
Gracile australopithecine comparison
| Ape |
Ardipithecus |
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Ardipithecus ramidus mandible
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Gracile and robust australipithecine comparison
| Gracile australopithecine |
Robust australopithecine |
Australopithecus afarensis
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Australopithecus afarensis mandible
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Paranthropus boisei mandible
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Gracile and robust australopithecine notes
| Type |
Ape
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Ardipithecus
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Gracile Australopithecine
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“Robust” Australopithecine Paranthropus
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| Species name |
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| Location of occipital condyles on base of skull (oval shaped structure that connects skull to the vertebral column) |
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| Position of maximum skull breadth when viewed from back |
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| Presence and degree of postorbital constriction in superior view (pinch behind eyes) |
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| Size of neurocranium relative to size of facial skeleton as seen in the lateral view |
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| Degree of prognathism as seen in the lateral view (protrusion of jaw) |
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| Presence and degree of development of supraorbital torus (brow ridge) |
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| Robustness of zygomatic arch (cheek bone) |
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| Presence of a sagittal crest (ridge of bone along the top midline of the skull) |
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| Presence of a mental eminence (projecting chin) |
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Relative size of incisors vs. molars
(M > or < or = I)
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Size of canines to other teeth
(C > or = )
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In mandible (lower jaw): presence of
diastema (gap to make room for a canine tooth)
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Exercise 2. Bipedal Adaptations: Pelvis and Foot
Our earliest hominin ancestors were essentially bipedal apes. The first hominins walked on two legs but had small brains and retained adaptations for climbing trees. When a new fossil is discovered, paleoanthropologists spend a great deal of time and care studying the remains to determine the locomotor pattern for that species. It is not a straightforward process and claims that recent discoveries such as Sahelanthropus, Orrorin, and Ardipithecus species are bipedal have generated a lot of discussion.
In this exercise we will examine the pelves of an ape, Au. afarensis, and a modern human, and consider changes that occurred as our ancestors evolved from quadrupeds to bipeds. We will also look at, and compare, the feet of an ape, Ardipithecus, and modern human.
The pelvis underwent significant changes as part of this process, but other parts of the postcranial skeleton were also affected by selection for bipedality. It is also important to remember that bipedal locomotion in the earlier hominins was not identical to the way we now move. This will be apparent as we compare pelves today. You may want to review the textbook descriptions of the modern human pelvis and ape pelvis, as well as descriptions of Australopithecine pelvis and feet.
Answer the questions and record your answers in the chart.
Pelvis adaptations
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Australopithecus afarensis
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Compare the shape of the pelvis between humans, ape, and Au. afarensis. How are they different? Discuss how features in the two hominins enabled bipedal walking.
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Compare the shape of the humans, ape, and Ardipithecus foot. How are they different? How do the features in the two hominins enable bipedal walking?
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Other adaptations
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Australopithecus afarensis
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What other parts of the skeleton (besides the pelvis) have been reshaped for bipedal locomotion and might be useful in identifying a fossil as being hominin? Describe changes that have occurred.
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bipedal adaptations notes
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Ape |
Au. afarensis |
Modern human |
| Specimen label |
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| General shape of pelvis |
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| Relative position of sacroiliac (connection between pelvis and sacrum) and acetabular joints (connection between pelvis and femur) |
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| Position of iliac blade (the fan-like portion of the hip bone) relative to spine |
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| Shape of pelvic inlet |
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| Relative size of anterior inferior iliac spine (bony ridge along the outer edge of the pelvis above the leg joint) |
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| Relative length of ischium bone (irregularly shaped bone that forms the lower and back of the hip bone) |
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question
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How are modern humans and Au. afarensis similar? How are they different? What inferences can you make about bipedality in Au. afarensis?
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Exercise 3. Paranthropus “Robust” Australopithecines
Between three and one million years ago, some hominins begin to exhibit larger posterior dentition, changes in dental enamel, and cranial evidence that suggest variation in dietary strategies among hominins. The large-molared hominins can be referred to as “robust” Australopithecines (in contrast to “gracile” Australopithecines like Au. africanus), though many researchers have placed them into a separate genus: Paranthropus. Some have speculated that they developed specializations in the jaws and teeth that allowed for processing tough, fibrous material such as grasses and hard seeds. The relationship between the two groups is unknown, but both have been found in the same sites, although at different time periods.
Paleoanthropologists recognize three species of robust Australopithecines or Paranthropus:
- Paranthropus aethiopicus is known from East Africa. It is the oldest of the group, dated at 2.7 - 2.3 mya, and is somewhat more primitive than later forms. It was discovered in 1984.
- Paranthropus robustus is a species that existed in South Africa between 2.3 and 1 mya. It was first discovered between 1936 and 1939 by Robert Broom.
- Paranthropus boisei is a species that existed in East Africa between 2.4 and 1.4 mya. It has larger posterior teeth and more developed jaw musculature than those living in the south. It was first discovered by Mary Leakey at Olduvai Gorge in 1959.
Examine the Paranthropus fossil casts and then answer these questions.
List three anatomical features suggest that Paranthropus ate a diet of tough, fibrous plant material.
adaptations for heavy chewing
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In contrast, what might have been the diet of gracile Australopithecine species? How do you know?
