Human Evolution - Skull Analysis Gizmo Answer Key

Name: Britney Silva Date: 01-08-2022 Student Exploration: Human Evolution - Skull Analysis Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: bipedal, canine, cranial capacity, cranium, evolve, foramen magnum, hominid, hominin, index, maxilla, orbit, palate, skull Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Label one of the skulls below as human and the other as a chimpanzee skull. human chimpanzee 2. What features did you use to identify which skull was human and which was chimpanzee? The human skull has more room for the brain and has a less pronounced jawline than that of a chimpanzee. Gizmo Warm-up In 1924, a fossilized skull that looked very similar to a chimp skull was discovered. But the skull most definitely did not belong to a chimp. The location of the foramen magnum—a hole in the skull where the spinal cord exits—indicated that the individual was bipedal, or walked on two legs. This fossil was some of the earliest evidence of human evolution. Using the Human Evolution – Skull Analysis Gizmo, you will discover some of the ways that skulls can be used to learn about human evolution. Start by comparing two modern hominids: a human and a chimpanzee. 1. Examine the Front view of the Homo sapiens (modern human) skull. Then, use the Select skull menu to examine the same view of the Pan troglodytes (chimp) skull. How do the skulls compare? Human skull has a larger forehead, a smaller jaw, and fewer teeth than a chimpanzee's. Larger brow ridge and snout on chimpanzee skull 2. Now, examine the Bottom view of the two skulls. How do they compare? The mouth of the chimp is bigger, and the foramen magnum is closer to the front of the skull. Activity A: Foramen magnum Get the Gizmo ready: ● Select the Homo sapiens (modern human) skull. Introduction: Skulls, even from the same species, can have a wide variety of shapes and sizes. To compare skulls, scientists use measurements of certain features to calculate indexes. An index is a ratio of one measurement to another. An important index for measuring hominid skulls is the opisthion index. This index indicates the position of the foramen magnum in the base of the cranium. The opisthion index can indicate whether a hominid species was bipedal or not. Question: How does the location of the foramen magnum indicate if a species was bipedal? 1. Measure: Select the Bottom view. To determine the opisthion index for humans and chimps, follow the steps below and complete the table. ● Turn on Click to Measure Lengths. Measure the distance from the opisthocranion to the opisthion, as shown at top right. Record the opisthocranion-opisthion distance in the table below. ● Measure from the opisthocranion to the orale, as shown at bottom right. Record the opisthocranion-orale distance in the table. ● To calculate the opisthion index, divide your first measurement by your second measurement. Multiply this number by 100. Species Homo sapiens Pan troglodytes Opisthocranion-opisthi on distance (cm) 6.80 1.80 Opisthocranion-ora le distance (cm) 20.00 19.60 Opisthion index 34.0 9.18 2. Analyze: The opisthion index is an indicator of where the foramen magnum is situated. The greater the opisthion index, the closer the foramen magnum is to the center of the cranium. This position is usually found in species that stand upright. A low value for the opisthion index occurs when the foramen magnum is situated in the rear of the cranium. This may indicate that the species walked on its knuckles or on four legs. Using the index values you calculated, what can you conclude about humans and chimps? Humans are bipedal, and chimps are knuckle-walkers. 3. Gather data: Humans, chimpanzees, and the other great apes are hominids. Hominids evolved from a common ancestor that lived about 13 million years ago. Hominins are hominids that belong to the lineage that led to humans. Measure the opisthion index of the other hominids available in the Gizmo. (Note: the foramen magnum was not preserved in the Homo naledi skull.) Species A. afarensis A. africanus P. boisei H. habilis H. erectus H. heidelbergensis H. sapiens neanderthalensis H. floresiensis Opisthocranion-opisth ion distance (cm) 2.62 3.50 4.63 4.91 5.21 6.61 Opisthocranion-ora le distance (cm) 16.10 18.10 20.10 17.50 20.00 22.80 Opisthion index 16.3 19.3 22.9 28.1 26.1 29.0 6.93 24.70 28.1 4.10 16.70 24.6 4. Analyze: Hominins are characterized by bipedalism. A. Based on their opisthion indexes, which of the hominids in the Gizmo are hominins? All of them except from chimpanzees. B. Based on opisthion indexes, which hominin skulls are most similar to human skulls? All belong to the genus Homo (except florensinis) 4. Explain: Why do you think the foramen magnum is positioned near the rear of the cranium for knuckle-walking species and near the center of the cranium for bipedal species? I believe that it is situated in that location because of the angle that their head must be at in order for them to see clearly as they are moving around on all fours. Activity B: Get the Gizmo ready: Cranial capacity ● Select Side view. ● Turn off Ruler, and turn on Click to measure area. Introduction: The brain is housed inside the cranium. The internal volume of the cranium is called the cranial capacity. The larger an organism’s cranial capacity is, the larger its brain tends to be. Question: How does the cranial capacity compare amongst hominids? 1. Measure: To estimate the cranial capacity of each skull in the Gizmo, measure the area of the part of the cranium that houses the brain. This part of the cranium is roughly behind the red line in the diagram at right. You can also use the three skull images below as a guide for measuring the rest of the skulls in the Gizmo. After you measure the area of each cranium, multiply the result by 5. This will give you a very rough estimate of the species’ cranial capacity. Homo sapiens Pan troglodytes Species Area of cranium (cm2) Pan troglodytes A. afarensis A. africanus 87 78 91 Australopithecus afarensis Estimated cranial capacity (cm3) 435 390 455 P. boisei H. habilis H. erectus H. heidelbergensis H. s. neanderthalensis H. floresiensis H. naledi H. sapiens 109 117 155 198 228 125 204 204 545 585 775 990 1140 625 1020 1020 2. Analyze: Examine the estimated cranial capacities you calculated. A. Which species probably had the largest cranial capacities? The three human species - H. sapiens, H. sapiens neanderthalensis, and H. heidelbergensis—probably possessed the largest craniums. B. What do you think cranial capacity is a good indicator of? It is a reliable predictor of intellect and brain size, in my opinion. C. Did any hominids have a larger cranial capacity than humans? If so, which species? Yes, the cranium of neanderthalensis was larger than that of Homo sapiens. 3. Compare: Turn off the Area tool. Using the Front view, compare the size and shape of the forehead of a chimpanzee and the forehead of a modern human. How are they different? A. How are they different? Human skulls have foreheads that are substantially taller and wider than those of chimpanzee skulls. B. Why do you think humans have such large foreheads in comparison to chimps? The chimpanzees had to develop as their brains grew in size. It expanded upward rather than in the area of the throat, expanding the top of the skull outward. 5. Draw conclusions: Compare the data you collected in activity A with the data you collected in this activity. Which evolved first in hominins: bipedalism or large brains? Explain. Hominins were the first to develop bipedalism. The measurements demonstrate that the foramen magnum advanced toward the middle of the skull well before cranial capacity in order to accommodate a bipedal posture. In comparison to chimpanzees, older fossils also have lesser cranial capacities. Activity C: Get the Gizmo ready: Maxilla and mandible ● Select Side view. ● Turn on Click to measure angles. Introduction: Teeth and the bones around the mouth give a great deal of information about both a species’ diet and how it eats. Take a look at the skull features below. Question: How do the mouths of hominids compare? 1. Measure: As shown at right, place one of the protractor’s circles on the top of the zygomatic process. Place the vertex of the protractor at the top of the nasal opening (Hint: You may have to look at the Front view in order to see where the top of the nasal opening is in relation to the orbit). Place the other circle on the edge of the maxilla. The resulting angle is the maxillary angle. Complete the table. (Note: You will not be able to do this measurement on incomplete skulls.) Species Pan troglodytes Maxillary angle 109.52 Species Homo erectus Maxillary angle 59.52 Australopithecus afarensis 102.74 Homo heidelbergensis — Australopithecus africanus 116.83 Homo sapiens neanderthalensis — Paranthropus boisei 92.77 Homo floresiensis 59.04 Homo habilis — Homo sapiens 97.51 2. Observe: Select the Bottom view and look at the size and shape of each species’ palate. How does the maxillary angle and palate shape relate to the size of each species’ mouth? Depending on the maxillary angle, it reveals the size and shape of the mouth and teeth. 3. Compare: Compare the human’s and chimp’s teeth. A. How many teeth are found in each species’ maxilla? Pan troglodytes: 16 Homo sapiens: 16 B. How do the size and shape of human canines compare with chimp canines? Human canines are longer and skinnier than chimpanzee canines, which are more rounded and wide. 4. Form hypothesis: Chimps and humans eat similar foods. What do you think could explain the differences between the maxillary angle, teeth, and palate of these two species? Their posture causes the index to alter, which causes their spines to curve in opposite directions. It changes as the cranial capacity rises. 5. Infer: What is the relationship between the evolution of bipedalism, the increase in cranial capacity, and the decrease in tooth and mouth size of hominins? (Hint: As cranial capacity increased, the use of sophisticated stone tools became more common.) The majority of two-legged animals have a narrower maxillary angle, which expands cranial capacity and reduces mouth size. 6. Summarize: On a separate sheet of paper, record the age of each fossil. Then, look over all the data you collected. Summarize how hominins changed as they evolved. Hominins gradually grew more erect as their posture improved. The first bipedal hominins undoubtedly spent a lot of time in trees before slowly giving up on it and starting to move around on two feet. Their heads became bigger as they adopted a more upright position, which increased intelligence and tool use. Food processing increased as a result of this. The size of the mouth and teeth also grew as a result, giving us the flattened characteristics we have today. 7. Evaluate: Of the fossils presented in this Gizmo, Homo floresiensis is the youngest. In what ways does this species NOT follow the pattern of human evolution you described above? It is a prime example of a fully evolved human skull, hence it deviates from the course of human evolution.