Gizmo-Human Skulls
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This skull is
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This skull is
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What characteristics did you use to distinguish the skulls?
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Introduction
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.

Examine the bottom view of the human and chimp skulls. How do they compare?
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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 answer the questions.
• Turn on Click to Measure Lengths. Measure the distance from the opisthocranion to the opisthion, as shown below. Record the opisthocranion-opisthion distance.
• Measure from the opisthocranion to the orale, as shown. Record the opisthocranion-orale distance.
• To calculate the opisthion index, divide your first measurement by your second measurement. Multiply this number by 100.

Homo sapiens - Opisthocranion-opisthion distance
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Homo sapiens - Opisthocranion-orale distance
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Homo sapiens - Opisthion index
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Pan troglodytes-Opisthocranion-opisthion distance
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Pan troglodytes-Opisthocranion-orale distance
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Pan troglodytes-Opisthion index
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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?
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Using the same methodology, calculate the Opisthion index for some of the other skulls.
Homo floresiensis-Opisthion index
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Homo neanderthalensis-Opisthion index
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Homo habilis-Opisthion index
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Australopithecus afarensis-Opisthion index
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Paranthropus boisei-Opisthion index
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Based on the Opisthion index, who, from the group you measured, was bipedal?
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Cranial Capacity
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?

Measure: To estimate the cranial capacity of each skull, 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. You can also use the other three skull images 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.

Estimated cranial capacity - Pan troglodytes
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Estimated cranial capacity - Homo sapiens
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Estimated cranial capacity - A. afarensis
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Estimated cranial capacity - H. erectus
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Estimated cranial capacity - H. neanderthalensis
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LONG ANSWER-Who had the largest cranial capacity and what do you think that implies?
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Mouths-Compare the number of each in the maxilla of humans and chimps. Compare the size and shape of the canines.
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