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9.3: Fossil Hominins

  • Page ID
    138542
    • Kristen A. Broehl
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    Fossil Hominins

    Format: In-person or online

    https://lh5.googleusercontent.com/D8-c_Efr6_jD6LTKtNIhJZFE2fYJ4EInmu7EM7Dh5eHEfJ6Ro1Wt3ECmFQavdQFTgPlPYyOgIh2dNrn2zyycgMKHb6wI4hrCTxGi-XXCNqJ7wYkUE09LLbpyYDC-PV5vuMXiTQw-
    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.

    Time needed: 60-90 minutes

    Learning Objectives

    • Identify hominin fossil features
    • Compare ape, Ardipithecus, Australopithecines, and modern human anatomy
    • Use fossil features to understand the emergence of bipedalism

    Supplies Needed

    • Skull casts of ape, Ardipithecus, gracile and robust Australopithecines, and modern Homo sapiens
    • Pelvis and foot casts of ape, gracile Australopithecine, and modern Homo sapiens
    • Student worksheet (below)

    Readings

    • Warren, Kerryn, et al. 2019. “Chapter 9: Early Hominins.” Explorations.

    Introduction

    This lab examines hominin fossils using a series of casts, reproductions, and photographs. This is an application of what students have already learned about human and primate anatomy in prior weeks of a typical Biological Anthropology lab course. This lab includes three exercises in which students examine and measure fossil casts. It is assumed that students have a good working knowledge of anatomy from the textbook, lectures, and/or previous exercises.

    Steps

    • Before class, the instructor should organize the fossil casts for students to analyze individually or in groups.
    • For Exercise 1, students will need access to skull casts of an ape, Ardipithecus, a gracile Australopithecus (such as Au. africanus or Au. afarensis), and a robust Australopithecine (Paranthropus).
    • For Exercise 2, students will need access to pelvis casts of an ape, Au. afarensis (or another gracile Australopithecine), and a modern human, as well as foot casts of an ape, Ardipithecus, and a modern human.
    • For Exercise 3, students will need access to a Paranthropus fossil skull cast.
    • Students will analyze fossils, complete charts, and answer questions on the worksheet.

    Review Questions

    • Compare Au. africanus and Au. afarensis to an ape and modern human. Why are these species considered to be hominins rather than apes?
    • Name three species of robust Australopithecines. Identify their most significant shared features.
    • Does the Australopithecine pelvis resemble most closely a hominin or an ape?

    Adapting for Online Learning

    If this is an in-person lab, rank how adaptable to online learning it would be (mark in bold):

    1 Not adaptable 2 Possible to adapt 3 Easy to adapt

    Much of the data students will collect for the worksheets is descriptive. For online courses, using photographs and online 3D rotation images, students can compare the skulls and pelvic girdles of the species. Many resources are free to post in online course management systems. Additional options could be available with subscriptions or other licensing agreements. See for example: https://africanfossils.org/, http://efossils.org/, https://sketchfab.com/, https://3d.si.edu/collections/hominin-fossils

    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. http://explorations.americananthro.org/

    Image Attributions

    Skeleton of human (1) and gorilla (2), unnaturally sketched by unknown from Brehms Tierleben, Small Edition 1927 is in the public domain.

    Sobotta 1909 fig.41 - The skull, inferior view - No labels by Johannes Sobotta is in the public domain. This item has been modified (arrows added).

    Sobotta 1909 fig.40 - The skull, lateral view - No labels by Johannes Sobotta is in the public domain. This item has been modified (arrows added).

    Australopithecine Worksheet

    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. Individual fossil specimens are usually identified by an abbreviation indicating the name of the site from which the fossil comes and a number given to each fossil from the site. For example, OH 5 stands for the fifth hominin fossil from Olduvai Gorge: Olduvai Hominin 5. The fossil casts for your class may or may not be labeled this way.

    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 four ways to fill in a cell, depending on how the statement of feature is phrased.

    1. 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 –.
    2. 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.”
    3. 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.
    4. Measure: In several tables you are asked to calculate an index. Measure for these boxes only. Write down both your measurements and the index. Diagrams showing how to take the measurements and calculate the indexes are shown below.

    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.

    Condylar Index = (basion to opisthocranion) / (basion to prosthion) x 100 Facial Index: [Upper Facial Height] Nasion (n) to prosthion (pr) / [Cranial height] basion (ba) to bregma (b) x 100
    Type Ape Ardipithecus Gracile Australopithecine “Robust” Australopithecine Paranthropus
    Species name & Specimen ID        
    Location of occipital condyles on base of skull        
    Condylar Index = (Ba to Op / Ba to Pr) x 100        
    Position of maximum skull breadth when viewed from back        
    Presence and degree of postorbital constriction in superior view        
    Size of neurocranium relative to size of facial skeleton as seen in the lateral view        
    Facial Index = (Upper Facial Height / Cranial Height) x 100        
    Degree of prognathism as seen in the lateral view        
    Presence and degree of development of supraorbital torus        
    Robustness of zygomatic arch        
    Presence of a sagittal crest        
    Presence of a mental eminence        

    Relative size of incisors vs. molars

    (M > or < or = I)

           

    Size of canines to other teeth

    (C > or = )

           

    In mandible: presence of

    diastema and sectorial premolar

           

    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.

    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.















    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?










    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.













      Ape Au. afarensis Modern human
    Specimen label      
    General shape of pelvis      
    Relative position of sacroiliac and acetabular joints      
    Position of iliac blade relative to spine      
    Shape of pelvic inlet      
    Breadth / Height of pelvic inlet x 100 = Pelvic Inlet Index      
    (Ilium Breadth / Ilium Height) x 100 = Ilium Index      
    Relative size of anterior inferior iliac spine      
    Relative length of ischium bone      

    How are modern humans and Au. afarensis similar? How are they different? What inferences can you make about bipedality in Au. afarensis?

    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.








    In contrast, what might have been the diet of gracile Australopithecine species? How do you know?












    This page titled 9.3: Fossil Hominins is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Kristen A. Broehl via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.