What do the Footprints Say???

• Reconstruct happenings from the geological past by analyzing a set of fossilized tracks

• Form defensible explanations of past events from limited evidence.

• As more evidence is available, modify or abandon your hypotheses.

Mission

Position #1• Can you tell anything about size or nature of

organisms?

• Were the tracks made at the same time?

• How many animals involved?

• Can you reconstruct a series of events represented by this set of fossil tracks?

• Suggest evidence to support your explanations!

Position #2• With new info,

revisit first explanation

• MODIFY your explanation and/or add new ones

Interpret What Happened

Questions to Consider...• In what directions did animals

move?• Did they change speed or

direction?• What might have changed the

footprint pattern?• Was the land level or

irregular?• Was the soil moist or dry?• In what kind of rocks were the

prints made?• Were sediments coarse or

fine?• Characteristics of track

environment?

Remember!• Any reasonable explanation must be based only

on those proposed explanations that still apply when all of the puzzle is projected

For Each Explanation...

• Be sure to indicate the evidence!

If you could VISIT the site, what evidence would you look for to support your hypothesis?

Adapted from a BSCS lab

LS Chapter 5-2 Notes

The Fossil Record

What is a Fossil?

• Fossil – preserved remains or traces of an organism that lived in the past.

• Most fossils form when organisms that die become buried in sediments.

What Do Fossils Reveal?

• Fossil record – millions of fossils that scientists have collected

• Extinct – if no member of that species are still alive.

• Most of what scientists know about extinct species is based on the fossil record.

• Fossil record also provides clues about how and when new groups of organisms evolved.

How Fast Does Evolution Occur?

Two Theories• Gradualism – tiny changes gradually add up to

major changes over very long period of time– Intermediate forms appear

• Punctuated Equilibria – evolution occurs during short periods of rapid change separated by long periods of little or no change.– No intermediate forms appear

Other Evidence for Evolution

• Appendix – appendicitis

• Scientists compare body structures, development before birth, and DNA sequences to determine the evolutionary relationships among organisms

Similarities in Body Structure

• Homologous structures – similar structures that related species have inherited from a common ancestor

Similarities in Early Development

• Early embryonic stage

• In early development, organism go through similar stages.

Similarities in DNA

• Method: Extracting DNA to compare.

• The more similar the sequences, the more closely related the species are.

• Question: Which animal are closer related?

• Rodent; Elephant Shrew; Elephant

Combining the Evidence

• Scientists combined evidence from– Fossils– Body structures– Early development– DNA and protein sequences

• In most cases, DNA and protein sequences have confirm conclusions based on earlier evidence.