Unit 6: Evolution
Evidence for Evolution: Fossils
Name _______________________________________________
Date ________________ Period _______ Assignment 23
Notes
Fossils
1.
3.
5.
2.
4.
6.
Carbonization
 The soft body parts of the organism _______________________, leaving behind only the ___________________.
 The carbon leaves behind an _______________________ in the rock, sometimes with great detail.
Age Dating
 In horizontal layers of sedimentary rock, _____________________________________________________________ &
___________________________________________________________
Relative Dating uses _______________________ fossils to date sediment layers
Absolute Dating uses _____________________ to give the ____________________ of the fossil
Quick Check
Background
Fossils are traces of organisms that lived in the past. When fossils are found, they are analyzed to determine their age.
The absolute age of the fossil can be determined through radioactive dating and examining the layer of rock in which the
fossil was found. Older layers are found deeper within the earth than newer layers.
The age and morphologies or appearance of fossils can be used to place them in sequences that show patterns of
changes that have occurred over time. This relationship can be depicted in an evolutionary tree. There are 2 major
hypotheses on how evolution takes place, gradualism and punctuated equilibrium.
Gradualism
Punctuated Equilibrium
Gradualism suggests that organisms evolve through a process
of slow and constant change. For instance, an organism that
shows a fossil record of gradually increased size in small steps,
or an organism that shows a gradual loss of a structure.
Punctuated equilibrium suggests that species evolve very
rapidly then stay the same for a long period of time. This rapid
change is caused by a mutation in key genes. The sudden arrival
of new structures could show punctuated equilibrium.
The fossil record cannot accurately determine when one species becomes another species. However, 2 hypotheses
regarding speciation also exist, phyletic speciation and divergent speciation.
Divergent Speciation
Phyletic Speciation
Divergent speciation suggests that a gradual build-up of small
genetic changes results in subpopulation of a species that
eventually collect so many changes that the subpopulations
become 2 different species.
Phyletic speciation suggests that quick mutations in a few key
genes occur after a species has existed for a long period of time.
This mutation results in the entire species shifting to a new
species.
Procedure
1. Tape the pieces of your evolutionary tree together.
2. The fossils you will examine are based on fictitious animals. Each fossil is marked with a time period. Cut out each
fossil, including the time period below it.
3. Arrange the fossils by age on your chart by placing each fossil next to the period it came from. Upper means more
recent and lower means older. Each row may have up to 3 fossils, but not all fossils are present since fossil records
are often incomplete.
4. While keeping the fossils in the age order, arrange them by morphology or appearance using the following steps:
 Place the oldest fossil in the center at the top of the row.
 Place any fossils that appear to be the same or very similar to the fossils before
them in a vertical line.
 During a specific time period, the fossils will split into 2 branches - 1 fossil will show
1 type of change and another fossil will show a different change. When this happens,
place the fossils side by side. From this point on you will have 2 linear branches.
5. After all the fossils are placed correctly according to age and morphology, tape the fossils in place.
Analysis
1. Give a brief description of the evolutionary changes that occurred in the organism.
 In the oldest fossil I noticed its morphology or appearance to be:

But, as time went on, I noticed the changes in morphology or appearance such as:
2. During which time period did the fossils separate into two branches?
3. Explain how the chart illustrates both punctuated equilibrium and gradualism. Use specific fossils from the chart to
support your answer.
 According to the chart I saw punctuated equilibrium happening when:

And it looked like gradualism happened:
4. Examine the fossil that was unearthed and sent to the Milwaukee Public Museum. Using your fossil record, determine
the time period this fossil is likely from.
5. For each of the blanks in your fossil record make a sketch of what the organism might look like.
Time Period
Age
Wyomington
995,000 years ago
Fossils
Ohioian
745, 000 years ago
Nevadian
545,000 years ago
Texian
445,000 years ago
Oregonian
395,000 years ago
Coloradian
320,000 years ago
Montanian
170,000 years ago
Californian
80,000 years ago
Idahoan
30,000 years ago