Conodont fossils are defined as a minute toothlike fossil composed of the mineral apatite (calcium phosphate) and are one of the most abundant fossils found on earth. Their origin was widely debated by paleontologists until a preserved specimen was found in Scotland in 1983. The fossils have been used by geologists to correlate, date, and heat map rock layers all over the world.

Why Watch This Video?

  1. Have you ever wondered how fossils could be used to improve modern-day society?
  2. Would you like to know how conodont fossils stumped paleontologists for over a century?
  3. Have you ever been confused by how fossils are used to define and identify geological periods?

Key Terms

Conodonts – Jawless fish that were widespread and abundant for around 300 million years starting in the Cambrian period to the Triassic period. They are now considered index fossils.

Index fossils – Fossilized remains that are used to define and identify geologic periods. The species must be abundant, widespread, distinctive, and around for a definitive amount of time.

Conodont alteration index – Chart that shows the color change of conodont fossils when heat is applied. It used by geologists to estimate the maximum temperature reached by sedimentary rock where the fossils were found.

Loose Ends

Why are conodont fossils so common?

Conodonts were abundant, widespread, and around for a long time. A large portion of their mouth and throat consisted of mineralized tissue that is resistant to weathering and changes in temperature.

Why did the conodont fossil found in Scotland in 1983 preserve its soft body tissue so well?

Soft tissue features were preserved by the formation of a calcium phosphate film from the softy body tissue onto an undisturbed bedding surface. However, it is likely that not all tissue was preserved.

Is the conodont alteration index still used by the petroleum industry?

It is still used by the petroleum industry today, but not as often as the previous decade. It is considered very accurate, but also time consuming.

5. Self-Test Questions

Scroll down for the answers.

1. When did conodonts go extinct?

  1. Ordovician–Silurian extinction events
  2. Late Devonian extinction
  3. Permian–Triassic extinction event
  4. Triassic–Jurassic extinction event

2. What caused the conodonts to go extinct?

  1. An ice age
  2. A sudden increase of carbon dioxide in the atmosphere
  3. An increase of predators
  4. A disappearance of prey

3. What kind of habitat did conodonts live in?

  1. Oceans
  2. Plains
  3. Rivers
  4. Marshes

4. What creature did conodonts most closely resemble?

  1. Starfish
  2. Eels
  3. Salmon
  4. Crabs

5. How are conodont fossils used by the petroleum industry?

  1. Determining radiation levels
  2. Determining the past porosity of the soil
  3. As geological thermometers
  4. They are sold for a profit


1. Triassic–Jurassic extinction event. Conodonts were impacted by all of extinction events listed above but were not eliminated until the Triassic–Jurassic extinction event.

2. A sudden increase of carbon dioxide in the atmosphere.  A rise of carbon dioxide in the atmosphere changed the salinity, acidity, and oxygen levels in the oceans and increased global temperatures making conditions unsuitable for their survival. Volcanoes are thought to be the catalyst of this event, but it has not been confirmed.

3. Oceans. Some conodont species lived in the open ocean and others stayed close to shore.

4. Eels. Conodonts are fish that mostly closely resemble eels with long tubular bodies, eyes, and mouth on one end, and tail fins on the other.

5. As geological thermometers. The conodont alteration index is used to determine whether sediments ever got hot enough for organic hydrocarbons to be converted into oil or gas.

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