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Studying Fossils

Authors: Don Pollock
Woodrow Wilson Biology Institute
1995

Target age or ability group: Grades 7-12
Class time required: 1-2 periods.
Materials and equipment: Scissors, envelopes, chart and/or model of human skeleton
Copies of pictures of the bones described
Summary of activity: Using a chart or model, students compare and contrast key skeletal differences between chimpanzees and humans: brain size, teeth, hand and thumb, trunk, pelvis, lower limb, foot and big toe. Students then sort and group a set of mixed "fossil bones" of chimpanzee or human. A set of Australopithecine bones is introduced and students apply their skeletal knowledge to the classification of these "mystery" bones. Early hominid evolution is "discovered" by students as they analyze bones that share characteristics of both apes and humans.
Prior knowledge,concepts or vocabulary necessary to complete activity: Students should have a basic knowledge of evolution. Concepts and vocabulary include: fossils, paleontology, skeletal system, DNA, phenotype.
Teacher instructions: Students should work in groups of two for the hands-on components of the activity and individually for the summary questions. The teacher should prepare two envelopes of bones for each group-envelope 1 contains chimp and human bones; envelope 2 contains Australopithecine bones. Students are not told the contents of the second envelope until they have derived the concept of an anatomically mixed organism from the activity. The activity should be followed by a fuller exploration of hominid evolution, including cranial measurements and phylogeny construction.

Digging For Fossils

Chimpanzees are our closest living relatives. Biologists have found that the DNA in the cells of humans and chimpanzees is about 99% the same. This close relationship exists also between horses and zebras, grizzly and polar bears. We would never mistake chimpanzees and humans because their external appearances (phenotypes) are distinct. By studying skeletal differences, paleontologists can determine if a fossil bone is from a human or a chimp.

Skeletal Differences

1. Brain Size

  • The modern human brain is more than three times larger than the chimpanzee. The cranial capacity is about 400 cc for the chimp and about 1400 cc for humans.
  • The foramen magnum ( an opening in the base of the skull) is where the spinal cord enters the skull. In the chimpanzee, this opening is located towards the back of the skull; in humans it is found closer to the middle of the skull base.

2. Canine Teeth

  • Human canine teeth, the third tooth from the center on each side, are considerably smaller than those of the chimpanzee.

3. Hand And Thumb

  • Chimps have longer and more curved fingers for climbing in trees and knuckle-walking. The human thumb is relatively straighter and longer than the chimp's.

4. Trunk And Rib Cage

  • Human and chimpanzee trunks are about the same size.
  • The chimp rib cage is triangular and narrow at the shoulder.
  • The clavicle or collar bone angles upward towards the shoulders in the chimpanzee, giving the appearance of having no neck.

5. Pelvis, Lower Limbs, Foot and Big Toe

  • The human pelvis is shorter than the chimp's.
  • The femur or thigh bone is longer in humans.
  • The chimpanzee footprint shows long, curved toes with the big toe divergent or pointing away from the other toes. This makes it more useful for grasping. The human footprint has a big toe that is convergent or pointing in the same direction as the other toes. This convergence allows the feet to better support the body's weight.

Activity: Digging for Fossils: Part One

In this activity your group will act as paleontologists at an African location where recent erosion has exposed many fossil bones. It appears that the fossils come from two different species but are mixed together. Your job is to carefully examine the fossil bones and properly classify them into either the human species (Homo sapiens) or the chimpanzee (Pan troglodytes).

Materials:Fossils envelope #1, identification sheet

Procedures: Empty the bones from envelope #1 and sort them into two columns on your desk- Chimpanzee or human. Leave plenty of space between the two columns. Then fill in the chart below with the proper catalog # of each fossil bone:

Species___________________

Species___________________

Catalog #

Fossil Type

Catalog #

 

 

Skull Side-view

 

 

 

Skull underneath view

 

 

 

Teeth

 

 

 

Jaw

 

 

 

Trunk-Rib Cage

 

 

 

Finger

 

 

 

Hand

 

 

 

Pelvis and Femur

 

 

 

Foot

 

Activity: Digging for Fossils: Part Two

Your team has just stumbled across another set of fossils which is neither human nor chimpanzee. Using your expert knowledge of humans and chimps you begin to analyze these new bones.

Materials:

Envelope #2

Procedure:

 

 

 

Open envelope #2 and compare each of the new fossils to the chimpanzee and the human. Rate each new bone as either:

  • chimpanzee
  • similar to chimpanzee
  • similar to both
  • human
  • similar to human

Analysis:

Describe the new fossil to the scientific community. Write a short essay about the signifigance of this fossil and what it might mean to the evolution of the hominids (the human family).

Suggest a name for the fossil. It was found in Southern Africa and seems to be related to both ape, and human. Be prepared to present your conclusions to the class!

On to Dinosaur Tracks:
From Stride to Leg Length to Speed

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