Name: _______________________________________________  Period: _________


Activity:  Examining the Fossil Record



Fossils are traces of organisms that lived in the past.  When fossils are found, they are analyzed to determine the age of the fossil.  The absolute age of the fossil can be determined through radiometric dating and determining 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 (appearances) of fossils can be used to place fossils in sequences that often show patterns of changes that have occurred over time.  This relationship can be depicted in an evolutionary tree, also known as a phylogenetic tree.


There are two major hypotheses on how evolution takes place: gradualism and 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 and then stay the same for a large period of time.  This rapid change is attributed to a mutation in a few essential genes.  The sudden appearance of new structures could be explained by punctuated equilibrium. 





The fossil record cannot accurately determine when one species becomes another species.  However, two hypotheses regarding speciation also exist.  Phyletic speciation suggests that abrupt mutations in a few regulatory 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.  Phyletic speciation would also relate to the Punctuated Equilibrium hypothesis regarding evolution. Divergent speciation suggests that a gradual accumulation of small genetic changes results in subpopulation of a species that eventually accumulate so many changes that the subpopulations become different species.  This hypothesis would coincide with the gradualism model of evolution.  Most evolutionary biologists accept that a combination of the two models has affected the evolution of species over time.



Example 3:  Phyletic Speciation


Text Box: Species A
Text Box: Species B
Text Box: Species C









Example 4: Divergent Speciation


Text Box: Species B






Text Box: Species C


Text Box: Species B







1.      The diagram you are creating requires a large space.  To create your chart, cut along the dotted lines only for all 6 different pages.


2.      Tape the pages together (using very little tape) in the following order:

Page 1                         Page 4


Page 2                         Page 5


Page 3                         Page 6


3.      The chart should look as follows when it is put together:


Time Period


Years Ago

































4.       The group of “fossils” you will work with are fictitious animals.  Each fossil on your sheet is marked with a time period.  Cut out each fossil and make sure you include the time period marked below it.

5.      Arrange the fossils by age.  Remember that as sediment is deposited it will bury organisms.  Older fossils should be “lower” in the sediment.  On your data chart, place each fossil next to the period from which the fossil came from.  The term “upper” means more recent and should be placed towards the top and the term “lower” means an earlier time period and should be placed towards the bottom of the time period.

6.      You may have 3 specimens, one from the main time period, one from the upper and one from the lower.  Not all fossils are represented, illustrating the incompleteness of any fossil record.

7.      While keeping the fossils in the proper age order, arrange them by morphology (appearance).  To help you understand the morphology of the specimen, view the diagram below.  Arrange the fossils using the following steps:

a.        Center the oldest fossil at the bottom of the fossil column (toward the oldest layer).

b.      Throughout the chart, those fossils that appear to be the same (or close to the same) as the fossils preceding them should be placed in a vertical line.

c.       During a certain period, the fossils will split into two branches.  In other words, one fossil from that period will show one type of change, and another fossil will show a different change. When this happens, place the fossils side by side in the appropriate time period.  From this point on you will have two lineages. Place the light headed fossils on the left-hand side as you look at the chart.

d.      Number the fossils starting with the oldest fossil as #1. When the fossils branch into  each of the two lineages,  label one A4, A5 etc.. (light headed) and the other label B4, B5 etc... (dark headed)

8.       Once all the fossils have been placed correctly according to time and morphology, tape or glue the fossils in place.



1.       Give a brief description of the evolutionary changes that occurred in the organism from fossil #1 up to the top of both the “A” and “B” branches.    


a.        Head:






b.       Segments:






c.       Fin



2.      During which time period did the fossils differentiate into two branches forming two lineages?



3.       Punctuated equilibrium occurs when there is an abrupt mutation after a species has remained the same for a long period of time like from Fossil 3 to 4B when the head abruptly turns dark.  Give a different example of how the chart illustrates punctuated equilibrium. Use specific fossils from the chart to support your answer. 





4.      Gradualism occurs when there is a gradual accumulation of small genetic changes like from Fossil 4A (light head) to 5A to 6A to 7A with the fin just getting a little larger each time. Give a different example of how the chart illustrates gradualism.  Use specific fossils from the chart to support your answer. 







5.      Making the assumption that each fossil represents a separate species, explain how the chart illustrates divergent speciation.  Use specific fossils from the chart to support your answer.







6.       Define phyletic speciation. Which hypothesis (Gradualism or Punctuated Equilibrium) does phyletic speciation support?







7.      Define divergent speciation.  Which hypothesis (Gradualism or Punctuated Equilibrium) does divergent speciation support?





8.      Examine the fossil that was unearthed and brought to a museum.  Apparently the label and other information were lost. 

a.       Using your fossil record, determine the time period this fossil is likely from.


b.       Give two possible explanations for the lack of fossil evidence in the Californian and Idahodian.




9.       Of the two major species that arose from the parent species, which was more successful (Lineage A or Lineage B)?  How do you know?





10.   Provide a possible explanation for why one lineage was more successful than the other. Be specific!! (Give characteristics the organism has and why those characteristics might be advantageous.)







11.  Sometimes scientists do not have all the information in the fossil evidence either because the fossil did not form, it was only partially fossilized, or because it has not yet been discovered.  In order for scientists to piece together the information, they often have to infer and make predictions.  Look at the Oregonian time period.  For one of the lineages you should only have one specimen.  In your chart, draw in what you predict a species in this lineage would look like in the upper Oregonian.  Draw your predicted species in space below as well.









Lab Modified from the