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Studying Fossils

Hominoid Skull Comparison

Authors:Mari Knutson
Woodrow Wilson Biology Institute
1995

Target age or
ability group:
First year biology (9-12).
Class time
required:
Approximately 85 minutes.
Materials and equipment: Acrylic casts of primate skulls, rulers, data tables, measurement explanations, calipers. The calipers (see diagram below) can be made out of pressboard or even thick cardboard and a fastener. The skulls can be ordered from a supply house or perhaps borrowed from a university. I recommend the following skulls: Homo sapiens, Homo sapiens neanderthalensis, Australopithecus boisei, and Gorilla gorilla. Additional skulls such as Homo erectus and Pan troglodytes may be added. When ordering, I recommend female skulls of pongids since the overly large sagittal crest and canines of males can be confusing. From Ward's Earth Science catalog, the set of four skulls costs approximately $1200.
Rationale: This lab provides experience with evidence used to support evolutionary theory. As many lines of evidence necessarily are approached more abstractly, I appreciate the power of actually collecting data from physical evidence. In the previous lessons, we have covered comparative anatomy as a line of evidence for evolution by discussion, video, and as it relates to the study of fossils. I have also introduced classification by using primates as an example. I use transparencies and videodisk slides of primate anatomy to illustrate similarities and differences in various primates. As scientists assert that upright walking is the main difference between hominids and hominoid, the foramen magnum is discussed at length, as well as pelvic, leg, and spinal structure before this lab.
I have six skulls to work with and I want all students to collect data on each skull, so I split my class into four groups and rotate them through various related activities over four days. While six-eight students are working on the skulls, another group is making pencil and paper calculations of posture, while the third group works on a videodisk lesson, and the last group views a video such as NOVA's series with Don Johanson. Each station also has a relevant article to read and write about as homework. The end of the week sees a compilation of data where the students work in groups of three other than the group in which they collected data.
Closure: In cooperative groups of three, students compare data on the various skulls. They usually find that their data does not match exactly and this provides an opportunity to discuss the difficulty in obtaining consistent measurements. Many students come to the conclusion that "Lucy" truly is a link between humans and apes due to the weight of evidence from the foramen magnum position and tooth structure. This lab is valuable on its own but also allows me to concentrate on small data collection groups, incorporate even smaller cooperative groups to assess data, and illustrate how science works while giving my students hands-on access to a strong line of evidence for the scientific theory of evolution.
Suggested Readings "The Naked and the Bipedal" by Tim Folger (Discover, November 1993). For a contrasting hypothesis on bipedalism see "Standing Tall" by John Horgan (Scientific American, October 1994). Another article that is useful for illustrating the nature of science and hominid fossil interpretation is "One Less Missing Link" by Michael Lemonick (Time, October 3, 1994).

Calipers are overlapped and connected
with a nut and bolt if made out of
pressboard or a paper fastener if made
out of cardboard. (Enlarge so that one
side takes up an 8-1/2 by 11 sheet of paper.)

Acknowledgement: Adapted from a lesson presented by Dr. Martin Nickels, Illinois State University.

Hominoid Skull Comparison

Record your measurements on the following page. Characteristics to be measured are marked with *. All measurements should be made in millimeters (mm).

1. Use calipers and ruler to measure the maximum WIDTH of the braincase (cranium).

2. Use calipers and ruler to measure the maximum LENGTH of the braincase (from the bridge of the nose to the base of the cranium).

3. Use calipers and ruler to measure the constriction behind the eye orbits (sockets).

4. Does the skull have a bony ridge on top or sides?

5. Hold a ruler upright from the bridge of the nose. Does the frontal bone slope back flatly or does it rise more vertically?

6. Is the hole where the spine attaches directly underneath or angled to the back? Use your fingers or a ruler to determine the slope (direction).

7. Is the bone behind the ear well-developed (easy to see) or is it flat?

8. Does the skull have a bony ridge over the eyes (supraorbital)?

9.Distinguish between skulls if a brow ridge is present. Example: smallest, small, medium, large.

10.Is the nasal bone arched (peaked) or flat?

11.Does the face (below eye orbits) stick out in front of the forehead? Compare amounts between skulls.

12.Use calipers and ruler to measure from the bottom of the mandible to the top of the nasal opening.

13.Does the chin stick out or does it slope back?

14.Look at the mandible from the side. Is the third molar (wisdom tooth) visible or is it behind the jaw?

15.Is the shape of the mouth straight-sided (like a rectangle) or does it flare a bit in back (like a V)?

16.Count the number of incisors, canines, premolars, molars in one-half of the mandible.

17.Is there a shelf (indent) inside the mandible, at the front?

18.Do the incisors slant out beyond the other teeth or are they vertical?

19.Is there a gap between the upper incisors and canines to accommodate the lower canines?

20.Use a ruler to measure the length of a lower incisor.

21.Use a ruler to measure the length of an exposed upper canine tooth.

22.Use a ruler to measure the combined length x width of the chewing surface of the molars.

23.Note any features that seem to be unique to each skull.

EXAMPLES:
Is there a mandibular suture (a line or union running down the front of the lower jaw)?

Upper canine "size" (does this tooth project above the level of the other teeth?)

Dental comb (lower incisors and both canines extremely narrow and slant forward, used extensively in grooming).

Cusp pattern on first lower molar (Y-5 shaped groove or bilophodont).

Skull Data

Period

Name

Measurements to be done in millimeters (mm) are marked with an * Characteristics followed by a ? are to be answered yes or no.

A

B

C

D

E

F

G

Characteristic

Gorilla

Chimpanzee

A. boisei

H. erectus

Neanderthal

H. sapiens

1.

width of braincase*

2

length of braincase*

3

post-orbital indent*

4

sagittal crest?

5

forehead shape

6

foramen magnum location

7

mastoid process shape

8

brow ridge?

9

if ridge, compare size

10

nasal bone shape

11

facial prognathism (relative amount)

12

face height*

13

chin shape

14

lower 3rd molar

15

dental arcade shape

16

dental formula

17

simian shelf?

18

angle of incisors

19

canine diastema?

20

lower incisor length*

21

upper canine length*

22

molar surface area*

23

unique features

Use your data from the skull comparisons to answer the following.

1.List similarities between Homo sapiens and Australopithecus boisei.





2.Which traits distinguish Homo sapiens from Gorilla gorilla?





3.How is Neanderthalensis different from Australopithecus boisei?





4.Is Australopithecus boisei more closely related to humans or gorillas? ______

Evidence:






5.You have been on a dig at Olduvai Gorge and were lucky enough to find fragments of a skull that include the lower jaw. List any traits that would indicate the specimen is a hominid and explain why those traits would be indicative.

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