Bipedalism Lab STUDENT 10.31.23 TU(1)

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3873

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Anthropology

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Dec 6, 2023

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YOUR NAME:_______________________ LAB SECTION:__________________ THE BIPEDAL ADAPTATION This lab is designed to introduce you to the human body as it compares to our closest living relative, the chimpanzee, and our fossil relatives. The lab mainly focuses on aspects of the skeleton that relate to bipedal locomotion, and how to apply what we learn from extant species to those in the fossil record. Lab Objectives • Describe the shape and orientation differences between certain aspects of ape and human anatomy • Identify similarities of fossil casts to modern humans • Document characteristics that show differences in the early hominins Station 1 – Knee Joints The shaft of the femur in humans and apes is either in line with the tibia (non-valgus knee/ straight femur), or at an angle to the tibia at the knee joint (valgus knee/bicondylar angle present). You can see whether or not the femur is angled when you stand the femur on its distal end on the table. View it from the front – does the femur stand straight up from the table, or is it at an angle? Alternatively, you can look at the condyles of the femur at the knee. A condyle is either of the two large articular surfaces on the distal femur. If the medial condyle is larger, the shaft of the femur will sit at an angle on the tibia such that the knee angles inward. Describe the angle of the knee and femur in the non-human primate and hominin (humans and their fossil relatives) taxa below: Non-human primates 1. What patterns do you observe in the angulation (or lack of angulation) of the knee in non- human primates vs. hominins? They have a straight and valgus pattern Feature Baboon ( Papio hamadryas ) Chimp ( Pan troglodytes ) A. afarensis H. erectus Human ( H. sapiens ) Knee angle Non-valgus/ Straight Straight Valgus Valgus Valgus 1

2. What is the effect of having a valgus angle on the position of the knees under the body? How would having a valgus knee benefit a biped? It allows the development of bipedalism because the skull is held upright on the spine. 3. How does the knee joint of Homo erectus compare to the non-human primates and other hominins? Homo erectus had a larger, rounder cranium and smaller teeth. It was the first to have human-like proportions 4. What can you infer about the locomotion of Homo erectus ? It has large bodies, longer limbs, and increases the locomotor efficiency 5. How does the knee joint of Australopithecus afarensis compare to the non-human primates and other hominins? The knee joint is more smaller and thinner and is broken into two joints 6. What can you infer about the locomotion of Australopithecus afarensis ? The locomotion of Australopithecus afarenis shows that they were traveling bipedally 2

Station 2 – Skull characteristics Now, compare the lemur, macaque, chimp, gorilla, human, Sahelanthropus , Ardipithecus and Paranthropus skulls . For each specimen, describe the position of the foramen magnum as anterior, posterior, or intermediate. 1. What anatomical structure passes through the foramen magnum? The foramen magnum passes through the medulla, meninges, the vertebral, the anterior and posterior spinal arteries. 2. What is the relationship between foramen magnum position and locomotion? The relationship is the anterior position of the foramen magnum that is related to bipedal locomotor behavior. 3. In the features discussed above, do you think Sahelanthropus is more like a chimpanzee, like a human, or is it unique? What about Ardipithecus and Paranthropus ? Compare the foramen magnum position in all three of these fossil species. What does this position tell us about locomotion in these species? Support your opinion with specific examples! I think the Sahelanthropus is similar to a lemur and is very unique because of its skull size. The Ardipithecus and Paranthropus is very similar to the Sahelanthropus in skull size These primates suggest that they walked upright on two legs. Feature Ring-tail lemur ( Lemur catta ) Rhesus macaque ( Macaca mulatta ) Chimpanzee ( Pan troglodytes ) Gorilla ( Gorilla gorilla ) Foramen magnum position Posterior Intermediate Posterior Anterior Feature Sahelanthropus Ardipithecus Paranthropus Human ( Homo sapiens ) Foramen magnum position Anterior Intermediate Posterior Anterior 3

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Station 3 – Pelvis Shape Pelvis shape is strongly related to locomotion. The shape and orientation of the iliac blades (the superior portions of the pelvis that are broad and flat) is particularly important for the orientation of the gluteal muscles. In humans, these muscles help stabilize the torso during bipedal walking. Compare the orientation of the iliac blade in the following species, making sure to describe the iliac blades as more coronally oriented (i.e., facing posteriorly) or more sagittally oriented (i.e., facing more laterally). Shape of the iliac blades also varies; in each of these species, describe the relative height and width of the iliac blade. Is it short, tall, narrow, and/or wide? 1. Compare the shape of the iliac blade in Homo sapiens and Pan troglodytes . How would you describe the shape of the iliac blade in these two species? In what anatomical plane does the iliac blade lie in Homo sapiens and Pan troglodytes ? The pelvis in Homo sapiens are more bigger compared to the Pan troglodytes. The shape of the iliac blade is similar. They lie in sagittal and face more lateral. 2. Compare the size and orientation of the iliac blades in Australopithecus afarensis , Homo erectus, and Homo neanderthalensis to the pelvis of Homo sapiens and Pan troglodytes . How would you describe the shape of the ilium in the three extinct hominins? Are they more similar to humans or to chimps? Feature Chimp (Pan troglodytes) A. afarensis H. erectus H. neanderthalensis Human ( Homo sapiens ) Iliac blade orientation Coronally oriented Sagittally oriented Coronally oriented Sagitally oriented Sagittally oriented Iliac blade height and width Tall and narrow Big and narrow Short and narrow Short & Wide Short and wide 4

Pan troglodytes iliac blades are taller, narrow and oriented in the coronal plane. In all of the hominins, the iliac blades are shortened and rotated into the sagittal plane, as is the case for modern humans. 3. What can you infer about the role of the gluteal muscles as a balancing mechanism in the three fossil hominins (use information from lecture)? In chimpanzees, the gluteal muscles lie posterior to the hip joint and function as hip extensors. But in all three fossil hominins, the gluteal muscles lie lateral to the hip joint and function as hip stabilizers when the body's weight is supported on a single foot. The gluteal muscles on the balancing side fire to keep the torso from collapsing towards the unsupported foot 4. Does the pelvis of Australopithecus differ from that of Homo sapiens in any way? Describe any shape differences you observe. Yes, the pelvis of Australopithecus is smaller than Homo sapiens and the iliac blades are not pointed forward to the same degree 5. Now examine the pelvis of H. erectus . Which extant taxon does it most closely resemble? What does this tell you about the locomotion of this species? H. erectus most closely resembles H. sapiens. They therefore must have walked bipedally. Station 4 – The Foot Foot shape is also critical for locomotion. Non-bipedal primates have opposable big toes that angle away from the long axis of the foot as well as long and curved toes for grasping. In contrast, bipedal primates have a big toe that is line with the rest of the toes and tends to be larger than the big toe of non-bipedal primates; they also have arches running along the length and width of the foot. In each of the specimens below, describe the big toe position (either divergent or parallel). Note that several more fragmentary fossil specimens are provided, so you will have to reconstruct toe position by comparing all of the specimens to one another. You should also describe the 5

curvature of the toes/phalanges (curved or not curved), and identify whether the specimen has an arched foot (arch present or absent). *Ask your TA to help you orient the feet in the correct anatomical position.* 1. How is the big toe used during bipedal locomotion in Homo sapiens ? How does this differ from how the big toe is used in apes? It is used for balance and walking 2. Does the ape have an arched foot like a human? Hint: Be careful not to confuse toe/phalanx curvature with true arches of the foot. They do not have arched foot 3. What are some possible reasons for the arch in the human foot? Hint: Think about the different functions of an ape and human foot during locomotion It is to help people be able to walk 4. Compare the shape of the foot in Ardipithecus and Homo habilis to the morphologies you observe in chimps and humans. Which extant taxon do each of these specimens most closely resemble? What does this tell you about the locomotion of these species? (Make sure to support your answer with specific examples). The foot shape is more lager and wider compared to homo Habilis. This shows that these species have been walking a lot 5. Refer to the heatmap of the Laetoli footprints, which were left by Australopithecus 3.7 million years ago. Do the footprints more closely resemble modern human footprints or chimp footprints? Do the heatmaps provide evidence for the presence of arches? Feature Chimp ( Pan troglodytes ) Ardipithecus Homo habilis Human ( Homo sapiens ) Big toe position Divergent Divergent Parallel Parallel Toe/ phalanx curvature Curved Curved Straight Straight Presence of arches Absent Absent Present Present 6

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The footprints do not resemble human footprints. 7

Bipedalism Lab STUDENT 10.31.23 TU(1)

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