Teacher’s Guide Introduction In this activity you will examine skull casts and other evidence to investigate and evaluate evolutionary relationships among living and extinct human relatives.
Materials per class: 1 skull cast of each of the following: Homo sapiens (modern human), Pan
Homo neanderthalensis Neanderthal), Homo erectus, Australopithecus
boisei, and Australopithecus afarensis
photographs and other visuals of modern humans, chimpanzees and gorillas
Materials per team: 1 metric ruler
Procedure: PART A – Comparison of Modern Apes and Humans
Using skull casts, photographs, and other visuals of humans, chimpanzees, and gorillas, your teacher will engage you in a discussion during which you compare these modern hominoids. During this discussion, you should make a list of the features these hominoids share and those features that make them differ. Use “Chart 1 - A Comparison of Modern Apes and Humans” to record your observations.
Procedure: PART B – Comparing Modern and Extinct Hominoid Skulls In this part of the activity you will make detailed observations and measurements of skull casts of seven modern and extinct hominoids. You will then use your data to determine if the extinct hominoids are more ape-like or more human-like in appearance. Your data will also provide a basis for drawing some conclusions about patterns of hominoid evolution.
1. Your team will move from station-to-station as you examine the skull casts. At each station you will find
a skull, metric ruler, protractor, and caliper. A few “rules” should be followed:
Do not make pencil or pen marks on the skulls.
Be careful with the skulls. They are expensive reproductions that are breakable.
Be sure to take turns in making the measurements.
Measure in millimeters (mm). Round off to whole numbers.
2. Complete the “Hominoid Skull Comparison Data Table” as you move from station-to-station. Refer to
the “Hominoid Comparison Checklist” for a description of each hominoid characteristic you observe.
Using observations and measurements from your completed Hominoid Skull Comparison Data Table, answer the following question in “Chart 2 -Analysis of Hominoid Skulls”: What evidence indicates the extinct hominids show a pattern of change in form that is consistent with the idea that modern humans evolved from ape-like ancestors?
Chart 1 – A COMPARISON OF MODERN APES AND HUMANS
Description in Modern Humans
Description in Modern Apes
Hands and feet
Arms and legs
Located side-by-side in front of skull providing excellent binocular vision. Excellent color vision. Development of visual organs seems to be at the expense of olfactory organs.
Grasping hands with opposable thumbs for precision grip. Big toe not used for grasping, in–line with other toes and smaller than in apes. Nails instead of claws and tactile pads on fingers and toes. Foot well-modified with double arch for extensive walking. Arms shorter than legs. Ability to brachiate. Knee and hip joints give ability to fully stand erect and move bipedally with smoothness and grace. S-curved Large brain case ~1,200 cc
Foramen magnum located beneath skull.
Absence of large bony ridges above eyes, sagital crest, and other bone ridges for attachment of massive neck muscles.
Face flat. Prominent lower chin. Snout does not protrude.
High forehead. Arrangement of teeth on the jaw is parabolic. Small canines. No gap between canie tooth and other teeth on jaw.
Broad, basin-shaped pelvis
NOTE: All primates share structural characteristics that reflect an ancestry that evolved adaptations for an arboreal way of life. Primates also share many other characteristics such as giving birth to a single offspring, a long period of infant dependency, and complex social interaction.
Same as in modern humans.
Grasping hands and feet with precision grip using opposable thumb not as refined as it is in humans. Big toe is large like a human thumb and not in-line with other toes. Nails instead of claws and tactile pads on fingers and toes.
Arms longer than legs. Ability to brachiate. Knee and hip joints do not permit standing erect as in humans. Walk and run using arms and hands. (knuckle walking). Arch-shaped Smaller brain case ~400 cc
Foramen magnum toward rear or skull.
Presence of large bony ridges above eyes, sagital crest, and bony ridges for attachment of large neck muscles.
Face sticks out. Receding chin. Protruding snout.
Forehead slopes back. Opposite rows of teeth on the jaw are parallel. Large canines. Gap between teeth allows large canine teeth on opposite jaws to “fit” when jaws are closed. Long, narrow pelvis
Chart 2 - ANALYSIS OF HOMINOID SKULLS
What evidence indicates the extinct hominids show a pattern of change in form that is consistent with the idea that modern humans evolved from ape-like ancestors?
The extinct hominid fossil skulls provide evidence of a transformation from ape-like to human-like characteristics. Many characteristics of the fossil hominid skulls when compared with modern humans and modern apes exhibit features that are intermediate in form between the two. Specifically, the fossils show a tendency in hominid evolution for a large cranium/brain, reduced brow ridge, loss of sagital crest, flat face, large chin, reduced snout, small canines, vertical incisors, parabolic dental arcade, foramen magnum positioned under the skull, and high forehead.
HOMINOID SKULL COMPARISON CHECKLIST 1. FOREHEAD: Does the forehead (frontal bone) look more vertical or does it slope backward?
2. CHIN: Does the chin stick out or does it recede back?
3. SAGITTAL CREST: A sagittal crest is a bony ridge that runs from front to rear on top of the cranium. Is it small, medium, large, or absent?
4. FACIAL PROGNATHISM: How much does the snout protrude when looking at the skull from the side? Is the protrusion large, medium, small or absent?
5. BROWRIDGE: The brow ridge is a heavy mass of bone directly over the eye orbits. Rate it large, small, medium.
6. DENTAL ARCADE: This refers to the shape of the arrangement of the teeth in the jaw when looking directly at the chewing surface of the teeth. Does the arrangement form a parabolic (rounded) shape with a relatively continuous outward curvature or is the arrangement rectangular with the premolars and molars in parallel rows?
7. CANINE TOOTH: What is the length in millimeters of the exposed part of the upper canine tooth?
8. DENTAL FORMULA: Record the number of incisors, canines, premolars and molars present in the upper jaw. (ICPM) 9. CANINE DIASTEMA: Is there a gap present on the upper jaw between the canines and incisors?
10. ANGLE OF INCISOR: Do the incisors rise vertically from the jaw or do they slant out?
11. FORAMEN MAGNUM: The foramen magnum is a large opening in the back or bottom of the skull through which the spinal cord enters the cranium. Determine if it is more to the rear or towards the bottom of the skull.
12. WIDTH OF CRANIUM: Use the caliper and ruler to determine the maximum width of the brain case. Measure from temple-to-temple and record your answer in millimeters.
13. LENGTH OF CRANIUM: Use the caliper and ruler to determine the maximum length of the brain case. Measure from the forehead to the back of the skull.
14. FACIAL SLOPE: Use the protractor to measure the angle make by the face and the upper jaw when viewed from the side.