Podcast
Questions and Answers
What characteristics define an index fossil?
What characteristics define an index fossil?
- Geographically restricted and long range
- Rare and slowly identified
- Common and easily identifiable (correct)
- Uncommon and widely dispersed
Which of the following is NOT a criteria for determining index fossils?
Which of the following is NOT a criteria for determining index fossils?
- Specific time span
- Wide geographic distribution
- Abundance in fossil record
- Long geologic range (correct)
Who first noted the unique sets of fossil taxa associated with rock?
Who first noted the unique sets of fossil taxa associated with rock?
- James Hutton
- Louis Agassiz
- William Smith (correct)
- Charles Lyell
What is the primary use of index fossils in geology?
What is the primary use of index fossils in geology?
Which of the following is an example of a Jurassic index fossil?
Which of the following is an example of a Jurassic index fossil?
Which group of fossils includes Venericardia planicosta?
Which group of fossils includes Venericardia planicosta?
What does the term 'geologic range' refer to in relation to index fossils?
What does the term 'geologic range' refer to in relation to index fossils?
Which of the following features identifies a crinoid?
Which of the following features identifies a crinoid?
Flashcards
Index Fossil
Index Fossil
A fossil that's common, widely distributed, and lived for a short period. Used to identify the age of rocks.
Geologic Range
Geologic Range
The time period a fossil existed on Earth. A short range is good for dating.
Fossil
Fossil
A preserved trace of past life or plant.
Fossil Example (Ammonite)
Fossil Example (Ammonite)
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Fossil Example (Gastropod)
Fossil Example (Gastropod)
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Fossil Example (Pelecypod)
Fossil Example (Pelecypod)
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Fossil Example (Brachiopod)
Fossil Example (Brachiopod)
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Fossil Example (Crinoid)
Fossil Example (Crinoid)
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Study Notes
Index Fossils
- Index fossils are widely distributed fossils with a limited timeframe.
- They are used to determine the age of rocks and correlate different rock layers.
- The word "fossil" means anything dug out of the earth.
- Fossils are remains of organisms or evidence of their existence.
- William Smith (1796) recognized unique fossil sets in rocks.
- Using fossils, rock layers can be correlated across vast distances.
- Specific fossil types are often confined to particular geologic time periods.
- These are called index fossils or guide fossils.
Characteristics of Index Fossils
- Lived for a limited time in Earth's history.
- Many fossils from the same organism must be found in rock layers.
- Fossils must be found across a wide area.
- The organism represented must be unique.
Animal Index Fossils
- Ammonites: Molluscs with coiled shells. Examples include Perisphinctes tiziani (Jurassic) and Trophites subbullatus (Triassic).
- Gastropods: Asymmetrical molluscs with spiraled shells. Example: Nerinea trinodosa (Jurassic).
- Pelecypods: Bivalve molluscs with a tongue-shaped foot. Example: Venericardia planicosta (Tertiary).
- Brachiopods: Bilaterally symmetrical animals with bivalve shells. Examples: Billingsella corrugata (Cambrian) and Dictyoclostus americanus (Carboniferous/Pennsylvanian)
- Crinoids: Marine invertebrates with cup-shaped bodies and feathery tentacles. Example: Cactocrinus multibrachiatus (Carboniferous/Mississippian).
- Trilobites: Extinct marine arthropods with divided bodies. Examples: Paradoxides pinus and Bathyurus extans (Cambrian and Ordovician respectively).
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