Bipedalism Lab STUDENT_updated June 2023

YOUR NAME: Isabella Sanchez LAB SECTION: 3 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 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. The Knee 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 Feature Baboon ( Papio hamadryas ) Chimp ( Pan troglodytes ) Siamang ( Symphalangus syndactylus ) Rhesus macaque ( Macaca mulatta ) Indri ( Indri indri ) Knee angle Straight Straight Straight Straight Straight Hominins Feature Australopithecus afarensis Homo erectus Human ( Homo sapiens ) Knee Angle Valgus Valgus Valgus 1

1. What patterns do you observe in the angulation (or lack of angulation) of the knee in non- human primates vs. hominins? All of the non-human primates have 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? The valgus angle’s position of knees under the body places them under the torso. 3. How does the knee joint of Homo erectus compare to the non-human primates and other hominins? The homo erectus has the valgus knee joint. 4. What can you infer about the locomotion of Homo erectus ? They had better locomotion efficiency because they were bigger 5. How does the knee joint of Australopithecus afarensis compare to the non-human primates and other hominins? It is more like the hominins. 6. What can you infer about the locomotion of Australopithecus afarensis ? That they travelled bipedally 2

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 ? Feature Chimp (Pan troglodytes) Australopithecus afarensis Homo erectus Homo neanderthalensis Human ( Homo sapiens ) Iliac blade orientation Sagittal Coronal Sagittal Coronal Sagittal Iliac blade height and width Tall/Narrow Short/Wide Shor/Narro w Tall/Wide Tall/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 pan toglodytes have a flat iliac blade and the homo sapiens have a flared and short blade. 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? The neanderthal Is wide and flared, homo had short and flat. 3. What can you infer about the role of the gluteal muscles as a balancing mechanism in the three fossil hominins? It is important for posture and stabilization. 4

4. Does the pelvis of Australopithecus differ from that of Homo sapiens in any way? Describe any shape differences you observe. Yes, the humans were tall and the Australopithecus is short. 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? It most closely resembles 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 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*** Feature Chimp ( Pan troglodytes ) Ardipithecus Homo habilis Human ( Homo sapiens ) Big toe position Divergent Divergent Parallel Parallel Toe/ phalanx curvature Curved Curve Straight Straight Presence of arches Arch No Arch No arch Arch 5

Station 5. Footprints At this station is a topographic* representation (and a 3D print) of fossil footprints from the site of Laetoli, Tanzania that have been dated to 3.6 million years ago. The trackways were made when a few Australopithecus individuals (one in the left trackway and two in the right trackway, producing the appearance of a larger footprint on the right) walked across an African plain recently covered by ash and rain from a volcanic eruption. The footprints were preserved when the wet ash hardened like cement and then was covered by more ash and sediments. Compare the shape of these fossil footprints to the pictures of chimp and human footprints at this station. Feel free to walk in these footprints and compare your stride to what would have been the stride of the Australopithecus individuals who created these footprints. *Topographic maps detail changes in elevation. Continuous lines on the map represent one elevation. This mapping style can be applied to footprints, teeth, and many other materials to analyze shape. 1. How do the footprints compare to what you expect from humans and apes? The humans push off toes. And the apes push off with a flat foot. 2. How do the footprints reflect the aspects of foot morphology you identified in Station 4? Use specific examples to justify your answer. Based on the curve of the foot 3. What do these footprints tell us about the way Australopithecus moved? Based off of what portion of the foot they used to push off of 7