Bipedalism Lab Activity- KEY

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. Feature Ring-tail lemur ( Lemur catta ) Rhesus macaque ( Macaca mulatta ) Chimpanzee ( Pan troglodytes ) Gorilla ( Gorilla gorilla ) Foramen magnum position Posterior Posterior Intermediate Intermediate Feature Sahelanthropus Ardipithecus Paranthropus Human ( Homo sapiens ) Foramen magnum position ?Intermediate Anterior Anterior Anterior 1. What anatomical structure passes through the foramen magnum? The spinal cord passes through the foramen magnum 2. What is the relationship between foramen magnum position and locomotion? Posterior = Quadrupedalism; Anterior = Bipedalism; Intermediate = Knuckle Walking 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! The foramen magnum in Ardipithecus and Paranthropus is much more similar to humans in its placement, while the foramen magnum of Sahelanthropus appears somewhat more intermediately placed, though perhaps a bit more anterior than in chimpanzees. This suggests that Ardipithecus and Paranthropus had upright head postures, as would be involved in bipedalism. What the locomotion in Sahelanthropus would have been like is slightly less clear. (also note crushed state of Sahelanthropus skull).

5 In humans the big toe is used for balance and propulsion; in the apes the big toe is used for grasping 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. No. Apes don't have an arch. Humans have 3 arches, two longitudinal and one transverse 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 The arch in the human foot helps to evenly distribute weight and absorbs shock as the foot hits the ground during bipedal locomotion. 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 of Ardipithecus is much more similar to the chimp foot in that it has no arch, long curved toes, and a grasping big toe. This suggests that Ardipithecus was still using its foot for grasping and was not fully bipedal. The foot of Homo habilis is much more similar to humans (arches present, parallel big toe), indicating that this species would have been bipedal. 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. 1. How do the footprints compare to what you expect from humans and apes? In comparison to humans, the footprints are smaller and more closely spaced. The big toe appears to be parallel to the rest of the foot, which differs from the apes. 2. How do the footprints reflect the aspects of foot morphology you identified in Station 4? Use specific examples to justify your answer. 6