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This page shows questions in the Calvert Cliffs public release module at MSDE. Life Science MISA
"Calvert Cliffs"

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Shark Tooth Fossils

Calvert Cliffs, located along the Chesapeake Bay in Maryland, contain sedimentary layers with fossils from the Miocene epoch that are 6 to 20 million years old. An epoch is a period of geologic time.

During the Miocene epoch, ancestors of Carcharodon carcharias (great white shark) inhabited the Chesapeake Bay, including Carcharodon hastalis, a shark that lived 20 to 3 million years ago, and Carcharodon megalodon, which lived 23 to 2.6 million years ago. As these organisms lived and died, their remains sank to the seafloor and were buried in sediment. A large amount of shark teeth fossils were found at Calvert Cliffs. Studies of teeth fossils show how sharks have evolved over time. Scientists compared teeth from great white sharks to teeth from the two shark ancestors, as shown.

These pictures show three shark teeth. The first picture is labeled C. carcharias. The picture shows a triangle-shaped tooth wider at the top and pointed at the lower end. A smooth band runs across the top wide end of the tooth. The two sides point downward and have jagged edges. The second picture is labeled C. hastalis. The picture shows a triangle-shaped tooth wider at the top and pointed at the lower end. A smooth band runs across the top wide end of the tooth. The two sides point downward and have jagged edges. The left side has a small curve halfway down the middle. The third picture is labeled C. megalodon. The picture shows a triangle-shaped tooth wider at the top and pointed at the lower end. A smooth band runs across the top wide end of the tooth but is V-shaped. The two sides point downward and have tiny, jagged edges.

Scientists also measured the shark teeth. They calculated the length-to-width ratios for the teeth from each species, as shown in the data table.

The table is titled Shark Tooth Sizes. The table has three columns and three rows. The first column heading is Species. The second column heading is Upper Jaw Teeth: Average Length-to-Width Ratio. The third column heading is Lower Jaw Teeth: Average Length-to-Width Ratio. The first row is C. carcharias, three point two four, two point one nine. The second row is C. hastalis, three point one one, two point four nine. The third row is C. megalodon, two point one eight, one point three eight.

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Molecular Data

Scientists use molecular data such as DNA sequences from fossils to study the evolutionary history of sharks. DNA from the mitochondria is highly conserved among individuals in the same species. They analyzed a mitochondrial DNA sequence for the protein cytochrome B in several species of sharks, including the following:

  • Isurus paucus and Isurus oxyrinchus (mako shark)
  • Lamna nasus (porbeagle shark)
  • Carcharodon carcharias (great white shark)

The scientists compared the DNA sequences in the shark species and recorded the number of differences among them. A sequence difference of 1% corresponds to approximately 6 million years. The percent of gene sequence that is different between two species was used to estimate, in millions of years ago (mya), when individual species of shark diverged from a common ancestor. The phylogenetic tree shows the results of these comparisons.

The title of the phylogenetic tree is Shark Phylogenetic Tree. There is a short line on the left side of this image. Above the line is the label forty-six to sixty-five million years ago. To the right, the line has two branches. The bottom branch is a horizontal line with the label Lamna nasus. The top branch is a horizontal line with the label forty-three to sixty million years ago. At the end of this horizontal line, the line branches again into a bottom line and a top line. The bottom branch is a horizontal line to the right with the label Carcharodon carcharias. The top branch is a short, horizontal line to the right with the label thirty-four to forty-eight million years ago. At the end of this horizontal line, the line branches again into a bottom line and a top line. The bottom branch is a horizontal line to the right with the label Isurus paucus. The top branch is a horizontal line to the right with the label Isurus oxyrinchus.

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The Miocene Epoch

During the Miocene epoch, temperatures on Earth increased. On land, forests disappeared while grasslands grew. Kelp forests formed in the oceans. The population of larger organisms increased on land and in the oceans.

Scientists study the climate of this period by analyzing sediments buried deep in the ocean bed, in ice caps, and in glaciers. The color, thickness, and chemical composition of these buried sediments provide scientists with clues about prehistoric climate.

The graph shows the changes in the climate on Earth from present to forty million years ago (mya).

The title of the graph is Climate Over Time. The x-axis is labeled Time in million years ago. The x-axis begins at zero and extends to the right to forty in intervals of ten. The y-axis shows an arrow pointing up and down. The top of the arrow is labeled Warmer and the bottom of the arrow is labeled Colder. The data line begins at an x-axis value of zero, and about halfway up on the y-axis. The line goes up and to the right until it reaches about three-fourths of the way up the y-axis and about sixteen on the x-axis, where it begins to fall. It continues to fall gradually to about two-thirds of the way up the y-axis at about twenty-three on the x-axis and then goes sharply up to just above three-fourths of the way up the y-axis at about twenty-five on the x-axis. It then drops sharply down to just below two-thirds of the way up the y-axis at twenty-six on the x-axis and stays at about that same level to about thirty-four on the x-axis. At thirty-five on the x-axis it rises sharply again back to about three-fourths of the way up the y-axis and then continues to rise until it ends at about four-fifths of the way up the y-axis and forty on the x-axis.

This is a question with 2 parts, including a multiple choice question that allows you to select only one option.

Changes during the Miocene epoch caused an increase in the number of shark fossils in the area of the Calvert Cliffs. Events that occurred during the Miocene epoch are listed, but they are not in the sequence that they occurred.

Event W: Dead organisms sink to the seafloor and get buried in sediments.
Event X: Sea levels rise and oceans expand.
Event Y: Marine animals inhabit the oceans covering Maryland.
Event Z: Climate warms.

Part A

Which of these were the first two in the sequence of events that led to the increase in shark fossils in the Calvert Cliffs?

  1. A.
    Event W, then Event Y
  2. B.
    Event Y, then Event W
  3. C.
    Event X, then Event Z
  4. D.
    Event Z, then Event X

Part B

Which of these were the last two in the sequence of events that led to the increase in shark fossils in the Calvert Cliffs?

  1. A.
    Event W, then Event Y
  2. B.
    Event Y, then Event W
  3. C.
    Event X, then Event Z
  4. D.
    Event Z, then Event Y

This is a multiple choice question that allows you to select only one option.

Changes in global climate during the Miocene epoch led to the formation of grasslands.

Which statement describes what most likely occurred as a result of these changes?

  1. A.
    The shape and structure of organisms changed as ecosystems changed.
  2. B.
    The predator population declined as the number of herbivores on the land increased.
  3. C.
    More fossils were buried in ice caps and in sediment beds as the animal population changed.
  4. D.
    More carbon dioxide was added to the atmosphere as the amount of vegetation on land increased.

This is a multiple choice question that allows you to select only one option.

Based on the Climate over Time graph, which of these changes most likely occurred between 21 million years ago and 14 million years ago?

  1. A.
    Melting ice caps led to increasing sea levels.
  2. B.
    Oceans cooled and polar ice sheets were formed.
  3. C.
    More sea-dwelling animals became land dwelling.
  4. D.
    Changing vegetation on land led to tectonic plate movements.

This is a multiple choice question that allows you to select only one option.

Based on the shark phylogenetic tree, the DNA of which two species is most closely related?

  1. A.
    L. nasus and I. oxyrinchus
  2. B.
    L. nasus and C. carcharias
  3. C.
    I. paucus and I. oxyrinchus
  4. D.
    I. paucus and C. carcharias

This is a test question that allows you to enter extended text in your response.

Identify and describe the evidence for common ancestry among different species of sharks.

Type your answer in the space provided.