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Lecture 1

CHM110H5 Lecture Notes - Lecture 1: Foramen Magnum, Common Chimpanzee, Homo Habilis


Department
Chemistry
Course Code
CHM110H5
Professor
Judith C Poe
Lecture
1

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Name: Ruba Nizam Date: 4/3/2012
Student Exploration: Human Evolution - Skull Analysis
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.
__________________ ___________________
2. What features did you use to identify which skull was human and which was
chimpanzee?
The features that I used to determine which skull was human and which was chimpanzee
were the cranial capacity (humans have a larger capacity and a more rounder/pronounced
skull), facial prognathism (human faces don’t protrude beyond the top of the skull), and the
comparison between the teeth (humans have smaller teeth that are relatively regular in size
whereas the chimps have sharper teeth which differ in size)
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.
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.
1. How do the skulls compare?
Some of the similarities I found include the size and shape of the eye sockets, the
overall distinctive shape of the skull, the location of the mouth and nose, and the smooth
curve of the bottom part of the jaw and the opisthocranion. Some of the differences include
the size of the cranial capacity, the location of the eye sockets, the size of the teeth, higher
cheek bones in chimpanzees, larger hollow cheeks in chimps, a more pronounced/larger
nose and finally the fact that the chimps have a brow ridge whereas the humans don’t.
Human Chimpanzee

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2. Now, examine the Bottom view of the two skulls. How do they compare?
The only similarities I could find concerning the bottom view of the skulls are that they
have the same features; foramen magnum, opisthocranion (which are also rounded), the
jaw/teeth, the eye sockets, and the average width of the skull. Some of the differences I
found were the length of the skull and the teeth, and that chimps have large canines and
inconsistent size of the teeth whereas the humans have a consistent size of teeth with no
canines. Other differences include the location of the eye sockets and the distance
between them, the chimps jaw protrude outwards from the skull (humans doesn’t), the
location and size of the foramen magnum, and finally the size of the cranium capacity.
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 Opisthocranion-
opisthion distance (cm)
Opisthocranion-
orale distance (cm) Opisthion index
Homo sapiens 6.80 20.30 33.49753694
Pan troglodytes 2.10 20.60 10.19417475
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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?
Based on the opisthion index I can conclude that humans are bipedal and the chimps
are not. Therefore the humans walk on two legs while the chimps walk on their knuckles or
all four legs.
(Activity A continued on next page)
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