Hominoid skull comparison



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HOMINOID SKULL COMPARISON

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

troglodytes (modern chimpanzee), (Gorilla gorilla (modern gorilla),

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

1 protractor


1 caliper




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.


Analysis

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





Structure

Description in Modern Humans

Description in Modern Apes


Eyes

Hands and feet


Arms and legs

Spine
Skull/cranium/brain/face

Teeth

Pelvic region


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?


hominoid teeth parabolic

hominoid teeth parallel




a = incisors

b = canines

c = premolars

d = molars




Parabolic Arcade

Parallel Arcade

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.

skull side view

Angle of facial slope

skull l&w

Width of cranium


Length of cranium

HOMINOID SKULL COMPARISON DATA TABLE


(Suggested Data – Interpretations May Vary)

FEATURES


A

Gorilla gorilla Gorilla

B

Pan

troglodytes Chimpanzee

C

Homo sapiens

Human

D

Homo Neander-

thalensis

Neanderthal

E

Homo

erectus

F

Australo-

pithecus boisei

G

Australo-

pithecus afarensis

Age of Specimen





Modern

Modern

Modern

30,000 YA

.4 -.5 MYA

1.8 MYA

2.9-3.6 MYA

Location and Date of Fossil Discovery











France

1908

China

1920’s

Tanzania 1959

Africa

1975

1.Forehead: more vertical or

slopes back




slopes

slopes

vertical

vertical

slopes

slopes

slopes

2.Chin: sticks out or

recedes back




recedes

recedes

sticks out

sticks out

recedes

recedes

recedes

3.Sagittal Crest: large, small

medium or absent




large

small

absent

absent

absent

medium

absent

4.Facial Prognathism: (snout

protrusion) large, small, medium, absent



large

large

absent

absent

medium

medium

medium

5.Browridge: large, small

medium



large

large

small

medium

medium

medium

medium

6.Dental Arcade: rows of molars parallel or parabolic


parallel

parallel

parabolic

parabolic

parallel

parallel

parallel

7.Canine Tooth: length of

exposed upper canine tooth

in mm


33 mm

22 mm

10 mm

---------

12 mm

9 mm

14 mm

8.Dental Formula: # of incisors-canine-premolars-molars in upper jaw (ICPM)

4-2-4-6

4-2-4-6

4-2-4-6

-------

4-2-4-6

4-2-4-6

4-2-4-6

9.Canine Diastema: gap

between upper incisors and

canines present or absent


present

present

absent

---------

absent

absent

absent

10.Angle of Incisor: vertical or slanted out


slanted

slanted

vertical

--------

vertical

vertical

vertical

11.Foramen Magnum: towards

rear or underneath



rear

rear

under

under

under

under

under

12.Width of Cranium: maximum width of brain case

in mm


103 mm

105 mm

142 mm

145 mm

130 mm

110 mm

100 mm

13.Length of Cranium: maximum length of brain case

in mm


~140 mm

~115 mm

165 mm

180 mm

160 mm

140 mm

130 mm

14. Facial Slope: the angle made by the face and the upper jaw viewed from side

50 deg

43 deg

76 deg

75 deg

72 deg

61 deg

57 deg





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